Alkali activation of ceramic solid wastes to incorporate in non-structural panels
Abstract
Este estudo foi motivado principalmente pela necessidade cada vez mais urgente de desenvolver ligantes alternativos ao conhecido Cimento Portland Ordinário (OPC). Assim, o desenvolvimento de novos cimentos alcalinos, utilizando diferentes resíduos industriais, muitos dos quais ainda em grande parte inexplorados, é uma solução promissora para a construção civil. Em todo o mundo, os materiais cerâmicos são amplamente utilizados na construção, no entanto, 30% da produção total de cerâmica é transformada em resíduo e 45% dos resíduos de construção e demolição resultam de materiais cerâmicos. Neste contexto, o principal objetivo deste trabalho foi investigar o potencial de dois resíduos industriais abundantes e menos comuns em cimentos alcalinos: resíduos cerâmicos (RC) ‒ principal precursor ‒ e escória de forno panela (LFS) ‒ para correção de composição. Silicato de sódio (SS) foi utilizado como o principal ativador em cimentos alcalinos para incorporação em painéis não estruturais. Para atingir este objetivo foi inicialmente realizada uma ampla campanha experimental para determinar a melhor formulação. A mistura selecionada (75% CW + 25% LFS) foi reforçada com diferentes teores (0%, 0,5 % e 1% em volume) de fibras de poliacrilonitrila (PAN). Foram testadas duas condições de cura: temperatura de 70°C e 20°C com 60% HR. Estas misturas foram avaliadas quanto às suas propriedades físicas, mecânicas, mineralógicas e microestruturais, aos 14, 28 e 90 dias de cura. Os resultados mostraram que a solução mais adequada para a finalidade específica, ou seja, a execução de painéis não estruturais, foi o cimento alcalino ativado (AAc) curado à temperatura ambiente, contendo 1% de fibra de PAN. Posteriormente, foram desenvolvidas duas soluções de painéis sanduíche, onde cada uma era composta por uma fina camada de AAc e uma camada isolante mais espessa de espuma de poliestireno extrudido ou aglomerado de cortiça expandida. Os resultados do comportamento mecânico indicaram a viabilidade do fabrico destes painéis, embora existam diferenças claras entre as duas soluções propostas foram observadas. Os resultados também demonstram que a tecnologia de ativação alcalina aumenta a condutibilidade térmica do AAc. A caracterização térmica dos painéis evidência desempenhos promissores após comparação com os materiais e soluções de construção correntes. Finalmente, a avaliação de sustentabilidade revelou que os dois painéis sanduíche propostos eram as alternativas mais sustentáveis em comparação com as três tecnologias convencionais selecionadas, uma vez que melhor combina os fatores ambientais, funcionais e económicos.
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Universidade do Minho Escola de Engenharia Norma Yolanda Gaibor Vaca Alkali activation of ceramic solid wastes to incorporate in nonstructural panels July 2022 Alkali activation of ceramic solid wastes to incorporate in non-structural panels UMinho | 2022 Norma Yolanda Gaibor Vaca
Norma Yolanda Gaibor Vaca Alkali activation of ceramic solid wastes to incorporate in non-structural panels Doctoral Thesis Doctoral Program in Solid Waste Management and Treatment Work performed under the supervision of Professor Doctor Dinis Leitão Professor Doctor Nuno Cristelo July 2022
ii DIREITOS DE AUTOR E CONDIÇÕES DE UTILIZAÇÃO DO TRABALHO POR TERCEIROS Este é um trabalho académico que pode ser utilizado por terceiros desde que respeitadas as regras e boas práticas internacionalmente aceites, no que concerne aos direitos de autor e direitos conexos. Assim, o presente trabalho pode ser utilizado nos termos previstos na licença abaixo indicada. Caso o utilizador necessite de permissão para poder fazer um uso do trabalho em condições não previstas no licenciamento indicado, deverá contactar o autor, através do RepositóriUM da Universidade do Minho. Licença concedida aos utilizadores deste trabalho Atribuição CC BY https://creativecommons.org/licenses/by/4.0
iii ACKNOWLEDGEMENTS I must assume that at this point in my life it is normal to have mixed feelings. After a period of almost five years invested in the research of this Doctoral Thesis, I am pleased to present this project to the scientific community. However, the completion of a Doctoral Thesis involves much more than the work reflected in this final document, since it represents a whole set of knowledge and experiences acquired of which I take with me the memorable ones, and after having overcome the undesirable ones (the covid-19 pandemic included), I also value them because they made me the woman I am today, more determined and at the same time humbler. Behind personal achievements, besides a considerable self-effort, a large number of contributions, support, suggestions, comments, or criticisms coming from many people usually are hidden. Their importance, in this case, is so valuable that, without them, it would certainly have been very difficult to get any noteworthy result. So that, it is a delight to express my deepest gratitude to all people who made this research work possible, to wit: A special mention goes to Professor Cândida Vilarinho, who at the time I started my studies was the director of the Ph.D. program "Solid Waste Management and Treatment". It is undeniable her total support from the first moment I arrived in Portugal, and it is through Prof. Candida that I came in contact with the wonderful task force that has accompanied me during this time, my supervisors. My heartfelt acknowledge to my direct advisors, Prof. Dinis Leitão and Prof. Nuno Cristelo, as well as to Prof. Vítor Cunha, Prof. Eduardo Pereira, Prof. Tiago Miranda, and Prof. Ana Briga-Sá. I would like to highlight their excellent professionalism and the highest human qualities. Thanks for your ethics, advice, guidance, patience, support, and great ability to listen in those not-so-good moments. Thank you for trusting in me and the opportunity to be part of the research group. I feel myself the luckiest person since I met you professors. It has been a great honor to learn from this outstanding work team. I would also like to recognize that this work was partially supported by the Secretary of Higher Education, Science, Technology, and Innovation, SENESCYT (Spanish acronym) from Ecuador, reference No. CZ03000052-2017. As well, it was supported in different stages by the research projects, namely, “GeoDesign” (NORTE-01-0247-FEDER-017501), “NextSea-Next generation monitoring of coastal systems in a scenario of global changes” (NORTE-01-0145-FEDER-000032), through funds from NORTE 2020 (Programa Operacional Regional do Norte) and FEDER (European Regional Development Fund), and
iv “CirMat - CIRcular Aggregates for SUStainable road and building MATerials” (UMINHO/BID/2021/22), financed by the Environment, Climate and Low carbon Economy Programme, between the Financial Mechanism Committee established by Iceland, Liechtenstein and Noway and Portugal. Thanks to the Department of Civil Engineering (DEC) of the University of Minho for providing the facilities and resources of the LMC and LEST laboratories for developing this research work. As well as the Chemical Department and Civil Engineering Department of the University of Trás-os-Montes e Alto Douro in Vila Real. My special gratitude to Prof. Pedro Tavares and Lisete Fernandes for their openness and collaboration on my project. All laboratory technicians and friends I met during my stay in each place, certainty, your scientific contribution, and support are significant in this work. I would also like to thank the companies “SGL Carbon Composites, S.A”, "Cerâmica Amaro Macedo", and the steel industry “Megasa” all of them located in Portugal for supplying the polyacrylonitrile fibers (PAN), ceramic wastes, and the ladle furnace slag (LFS), respectively. I will always be indebted to my parents, Rosaura Vaca and Carlos Gaibor for giving me the education, opportunities, and experiences that took me where I am now. Also, to my siblings, Edith, Juan Carlos, and Katty. They selflessly motivated me to look into new directions in life and seek my best way. My gratitude for their unfailing emotional support. It was their love that raised up to me again and again when I got weary. This journey would not have been possible if not for them. Thank you for showing how proud you have always been of me. Last but not least, I thank with loving my husband, Eduardo, for his special care and attention to me during this roller-coaster period of my life, especially in the most difficult moments. You were the one who helped me endure the frequent frustrations. Thank you for your unconditional trust, timely encouragement, and endless patience. I dedicate this achievement to my family and my husband.
v STATEMENT OF INTEGRITY I hereby declare having conducted this academic work with integrity. I confirm that I have not used plagiarism or any form of undue use of information or falsification of results along the process leading to its elaboration. I further declare that I have fully acknowledged the Code of Ethical Conduct of the University of Minho. University of Minho, July 2022 Full name: Norma Yolanda Gaibor Vaca _____________________________ Signature
vi Ativação alcalina de resíduos cerâmicos para incorporação em painéis não estruturais RESUMO Este estudo foi motivado principalmente pela necessidade cada vez mais urgente de desenvolver ligantes alternativos ao conhecido Cimento Portland Ordinário (OPC). Assim, o desenvolvimento de novos cimentos alcalinos, utilizando diferentes resíduos industriais, muitos dos quais ainda em grande parte inexplorados, é uma solução promissora para a construção civil. Em todo o mundo, os materiais cerâmicos são amplamente utilizados na construção, no entanto, 30% da produção total de cerâmica é transformada em resíduo e 45% dos resíduos de construção e demolição resultam de materiais cerâmicos. Neste contexto, o principal objetivo deste trabalho foi investigar o potencial de dois resíduos industriais abundantes e menos comuns em cimentos alcalinos: resíduos cerâmicos (RC) ‒ principal precursor ‒ e escória de forno panela (LFS) ‒ para correção de composição. Silicato de sódio (SS) foi utilizado como o principal ativador em cimentos alcalinos para incorporação em painéis não estruturais. Para atingir este objetivo foi inicialmente realizada uma ampla campanha experimental para determinar a melhor formulação. A mistura selecionada (75% CW + 25% LFS) foi reforçada com diferentes teores (0%, 0,5 % e 1% em volume) de fibras de poliacrilonitrila (PAN). Foram testadas duas condições de cura: temperatura de 70°C e 20°C com 60% HR. Estas misturas foram avaliadas quanto às suas propriedades físicas, mecânicas, mineralógicas e microestruturais, aos 14, 28 e 90 dias de cura. Os resultados mostraram que a solução mais adequada para a finalidade específica, ou seja, a execução de painéis não estruturais, foi o cimento alcalino ativado (AAc) curado à temperatura ambiente, contendo 1% de fibra de PAN. Posteriormente, foram desenvolvidas duas soluções de painéis sanduíche, onde cada uma era composta por uma fina camada de AAc e uma camada isolante mais espessa de espuma de poliestireno extrudido ou aglomerado de cortiça expandida. Os resultados do comportamento mecânico indicaram a viabilidade do fabrico destes painéis, embora existam diferenças claras entre as duas soluções propostas foram observadas. Os resultados também demonstram que a tecnologia de ativação alcalina aumenta a condutibilidade térmica do AAc. A caracterização térmica dos painéis evidência desempenhos promissores após comparação com os materiais e soluções de construção correntes. Finalmente, a avaliação de sustentabilidade revelou que os dois painéis sanduíche propostos eram as alternativas mais sustentáveis em comparação com as três tecnologias convencionais selecionadas, uma vez que melhor combina os fatores ambientais, funcionais e económicos. Palavras-chave: ativação alcalina, economia circular, painéis não estruturais, resíduos industriais, sustentabilidade.
vii Alkali activation of ceramic waste for incorporation in non-structural panels ABSTRACT This study was mostly motivated by the increasingly urgent need to develop alternative binders to the well-known Ordinary Portland Cement (OPC). In this way, the development of new alkali-activated materials, using different industrial by-products or wastes, many of which are still largely unexplored, is a promising solution for the construction industry. Worldwide, ceramic materials are extensively used in different types of construction, with a significant percentage ending up as a waste. Two significant numbers support this paradigm – approximately 30% of the total ceramic production is transformed in waste, and 45% of the construction and demolition waste result from ceramic materials. Thus, this study aimed to investigate the potential of two abundant and, at the same time, less common industrial wastes in alkaline cements: ceramic wastes (CW) ‒ as a main precursor, and ladle furnace slag (LFS) ‒ for composition correction. Sodium silicate (SS) was used as the main activator for the alkali activated cements that were incorporated in non-structural panels. To accomplish this objective, a comprehensive experimental campaign to determine the best blend composition was carried out, first. The selected mixture (75% CW + 25% LFS / SS-based) was reinforced using polyacrylonitrile (PAN) fibers with different content (0%, 0.5%, and 1% in volume). Moreover, two curing conditions were experimented, i.e., thermal curing under 70°C and 60% HR ± 5% and curing at ambient temperature (20°C and 60% HR ± 5%). Up to this point, all the mixtures were evaluated with respect to their physical, mechanical, mineralogical, and microstructure properties at 14, 28, and 90 curing days. Results showed that the most suitable solution for the specific purpose of its application, i.e., the manufacture of non-structural panels, was the alkali-activated cement (AAc) cured at ambient temperature containing 1% PAN fiber. Afterwards, two sandwich panel solutions were developed, each was composed of a thin layer of AAc and a thicker insulating layer of extruded polystyrene foam or expanded cork agglomerate. The results of the mechanical behavior indicated the feasibility of manufacturing these panels, although clear differences between the two proposed solutions were observed. Findings also suggested that the alkali-activation technology improves the thermal conductivity of the developed AAc. Thermal characterization of the two panels showed a promising performance when compared to currently available building materials. Furthermore, a Sustainability Assessment revealed that the two proposed half-sandwich panels were the most sustainable alternatives compared to the three selected conventional technologies since they combined the best the environmental, functional, and economic factors. Keywords: alkali activation, circular economy, industrial wastes, non-structural panels, sustainability
xiv Figure 3-7. SEM images of 75CR-25FA/SH or SS mixtures (M1 and M2) and 75CR-25LFS/SH or SS mixtures (M3 and M4) mixtures, after 90 days of curing time. ........................................................... 76 Figure 3-8. FTIR spectra of starting materials, the ladle furnace slag (LFS); ceramic residue (MCR) – milled for 32 hours; fly ash (FA), and 75CR-25FA/SH or SS mixtures (M1 and M2) and 75CR-25LFS/SH or SS mixtures (M3 and M4), after 90 days curing time. .................................................................... 78 Figure 4-1. Precursors used in the mixture: (a) ceramic waste (CW) before grinding; (b) CW after gridding; (c) ladle furnace slag (LFS) before sieving; and (d) after sieving ......................................................... 89 Figure 4-2. Particle size distribution (PSD) of precursors (ceramic waste (CW) after gridding and ladle furnace slag (LFS) after sieving) ........................................................................................................ 89 Figure 4-3. Test set-up for (a) the elasticity modulus; (b) the uniaxial compressive stress-strain .......... 92 Figure 4-4. Compressive stress-strain relationships of the M1 (0% fibers) alkali-activated mortar after: (a) 14, (b) 28, and (c) 90 days of curing ................................................................................................ 96 Figure 4-5. Compressive stress-strain relationships of the M2 (0.5% fibers) alkali-activated mortar after: (a)14; (b) 28; and (c) 90 days of curing ............................................................................................ 97 Figure 4-6. Compressive stress-strain relationships of the M3 (1% fibers) alkali-activated mortar after: (a)14; (b) 28; and (c) 90 days of curing ............................................................................................ 98 Figure 4-7. a) M1; b) M2; and c) M3 specimens after flexural strength test at 28 days curing ........... 100 Figure 4-8. Average curves of flexural strength of M1 (0% fiber) alkali-activated mortar after: (a)14; (b) 28; and (c) 90 days of curing ................................................................................................................ 102 Figure 4-9. Average curves of flexural strength of M2 (0.5% fiber) alkali-activated mortar after (a)14; (b) 28; and (c) 90 days of curing .......................................................................................................... 103 Figure 4-10. Average load-deflection curves for M3 (1% fiber) alkali-activated mortar after: (a)14; (b) 28; and (c) 90 days of curing ................................................................................................................ 104 Figure 4-11. Dependence of the mass increase on the suction surface Δmt / F, concerning the square root of time 𝑡 for samples of the alkali activated mortar after 28 days of curing ............................... 106 Figure 4-12. XRD patterns of starting materials (CW and LFS), and M2 (0.5% fiber) mortar at 14, 28 and 90 days curing time ........................................................................................................................ 108 Figure 4-13. SEM images of M2 (0.5% fiber content) after a) 14 days, b) 28 days, and c) 90 days curing time. Points 1 and 2) ceramic waste and ladle furnace slag particles, respectively; point 3) PAN fibers” ...................................................................................................................................................... 110 Figure 4-14. FTIR spectra of starting materials, the ladle furnace slag (LFS); ceramic waste (CW) – after milled, and M2 blend (0.5% fiber content) after 14-, 28-, and 90-days curing time. ........................... 112
xv Figure 5-1. Original materials in situ: (a) ceramic bricks waste (CBW); and (b) ladle furnace slag (LFS) ...................................................................................................................................................... 127 Figure 5-2. Dependence of the mass increase on the suction surface Δmt/F, about the square root of time √t for samples of the alkali-activated cement after 28 days of curing ........................................ 132 Figure 5-3. Uniaxial Compressive Strength (UCS) obtained for 0% (M1), 0,5% (M2) and 1% (M3) fibers contents after 14, 28 and 90 days curing ........................................................................................ 133 Figure 5-4. Young's modulus ( Ecm ) obtained for 0% (M1), 0,5% (M2) and 1% (M3) fibers contents after 14, 28 and 90 days curing.................................................................................................................... 134 Figure 5-5. Stress-strain curves for AAm control samples, M1_0% fibers, after (a) 14, (b) 28, and (c) 90 days curing..................................................................................................................................... 135 Figure 5-6. Stress-strain curves for AAM reinforced with 0.5% PAN fibers after a) 14, b) 28, and c) 90 days curing..................................................................................................................................... 136 Figure 5-7. Stress-strain curves for AAM reinforced with 0.5% PAN fibers after (a) 14, (b) 28, and (c) 90 days curing..................................................................................................................................... 137 Figure 5-8. Flexural strength and residual flexural tensile strengths for crack mouth opening displacements of 0.3 mm ( fR0.3mm )) and 0.5 mm ( fR0.5mm ) of the alkali-activated cement after 14, 28, and 90 days of curing ................................................................................................................................. 139 Figure 5-9. Load displacement curves under flexural loading for AAm control samples, M1_0% fibers, after a) 14, b) 28, and c) 90 days of curing ..................................................................................... 140 Figure 5-10. Load displacement curves under flexural loading for AAM reinforced with 0.5% PAN fibers, M2, after a) 14, b) 28, and c) 90 days of curing .............................................................................. 141 Figure 5-11. Load displacement curves under flexural loading for AAm reinforced with 1% PAN fibers, M3, after a) 14, b) 28, and c) 90 days of curing ..................................................................................... 142 Figure 5-12. X-ray diffractograms (XRDs) of the precursors (CBW and LFS) and the AAm reinforced with 1% of PAN fibers (M3), at 14, 28, and 90 days of curing time .......................................................... 145 Figure 5-13. SEM images of the AAm reinforced with 1% of PAN fibers (M3), after a) 14 days, b) 28 days, and c) 90 days curing time. Point 1) ceramic waste particles; Point 2) PAN fibers; Point *) C-A-S-H type gel.................................................................................................................................................. 147 Figure 5-14. FTIR spectra for precursors ceramic bricks waste (CBW), ladle furnace slag (LFS), and the studied cement. .............................................................................................................................. 148 Figure 6-1. Classification of the dominant insulating materials in the European Market, [31] ............ 162 Figure 6-2. (a) Flowability test, (f) Preparation of isolation materials for casting ................................ 166
xvi Figure 6-3. (a) Uniaxial Compressive Test performance; (b) Cubic specimens of 50 × 50 × 50mm3 after test execution. ................................................................................................................................ 167 Figure 6-4. (a) sample preparation; (b) bond of the metal disk to the samples' outer surface; (c) Pull-off tests set-up, real apparatus ............................................................................................................. 168 Figure 6-5. (a) Preparations samples before casting; (b) Set up for the direct shear test ................... 169 Figure 6-6. Set-up of the three-point bending test on half-sandwich AAc panels with different thermoinsulating materials: (a) extruded polystyrene (XPS) and (b) Insulation corkboard (ICB) .................... 170 Figure 6-7. Thermal Experimental Setup of the half-sandwich panels, AAc + extruded polystyrene (APXPS), AAc + Insulation corkboard (APICB), and the uninsulated panel (ACP): (a) sealed interior view; (b) sealed exterior view. .................................................................................................................................. 171 Figure 6-8. Utilized equipment for thermal performance analysis, Heat flux sensors, HF1 and HF2 , and inner surface temperature sensors, Tsi11, Tsi12, Ts21, and Tsi22 . .......................................................... 172 Figure 6-9. Force-displacement graph based on test results (a) APXPS and (b) APICB ............................. 176 Figure 6-10. Failure modes obtained on the pull-off tests (a) APXPS and (b) APICB ................................. 177 Figure 6-11. Mechanical shear behavior of panels with (a) XPS parallel groves (𝐴𝑃𝑋𝑃𝑆‖); (b) XPS perpendicular groves (𝐴𝑃𝑋𝑃𝑆 ⊥); and (a) ICB ............................................................................... 179 Figure 6-12. Specimens after direct shear tests (a) APXPS with XPS perpendicular groves (𝐴𝑃𝑋𝑃𝑆 ⊥); (b) APXPS with XPS parallel groves (𝐴𝑃𝑋𝑃𝑆‖); (c) APICB ........................................................................... 180 Figure 6-13. Vertical cross-section of semi-sandwich AAc panels with different thermo-insulating materials: (a) extruded polystyrene (APXPS) and (b) Insulation corkboard (APICB) .................................................. 182 Figure 6-14. Load displacement curves under flexural loading for (a) APXPS; (b) APICB, at 28 days of curing ...................................................................................................................................................... 182 Figure 6-15. Failure types in the panels (a) APXPS; (b) APICB ................................................................. 183 Figure 6-16. Indoor ( Tin ), outdoor ( Ten ) temperatures, and heat flux ( qi(n) ). ......................................... 185 Figure 6-17. Interior ( Ti(n )) and inner surface temperatures ( Tsi(n )) ...................................................... 186 Figure 6-18. Thermal transmission coefficients, U 1(ntotal) and U2 (ntotal) ...................................................... 189 Figure 7-1. Vertical cross-section of semi-sandwich AAc panels with different thermo-insulating materials: (a) extruded polystyrene (APXPS) and (b) Insulation corkboard (APICB). ................................................. 204 Figure 7-2. Life Cycle Assessment structure according to ISO 14040 ............................................... 205 Figure 7-3. Structure and assessment steps of the MARS-SC methodology, [21] .............................. 205 Figure 7-4. System boundaries of the study ..................................................................................... 206 Figure 7-5. Contribution analysis for (a) APXPS, and (b) APICB. .............................................................. 215
xvii Figure 7-6. Sensitivity Analysis ........................................................................................................ 220
xviii LIST OF TABLES Table 2-1. Waste generation projections for 2025 by region, [24] ...................................................... 14 Table 2-2. Waste generation rate of change, excluding major mineral wastes, EU-28, 2004-2018, [26] ........................................................................................................................................................ 17 Table 2-3. Design and development of construction material using industrial waste, [37]. .................. 21 Table 2-4. Circular Economy sources and definitions, adapted from [48] ........................................... 26 Table 2-5. Circular Economy-related basic principles ......................................................................... 26 Table 2-6. First articles on the life cycle assessment of geopolymers, [58] ......................................... 31 Table 2-7. Estimated emissions in the NaOH production process, (adapted from [4]) ........................ 39 Table 2-8. Physical and thermodynamic properties of anhydrous and hydrated sodium silicates, [88] 40 Table 2-9. Estimates of emissions arising due to sodium silicate manufacture, [86] ........................... 42 Table 2-10. Chronology of alkaline cement (adapted from [89]). ........................................................ 43 Table 2-11. Applications for alkaline cement, [89] . ............................................................................ 44 Table 2-12. Relationship between building construction methods, [92] .............................................. 46 Table 2-13. The unified classification system of offsite modern methods of construction, [92] ............ 47 Table 2-14. Classification of common PEWPS according to functional and constructional criteria, [92] 48 Table 3-1. Chemical composition of the CR, FA, and LFS (% wt) ......................................................... 67 Table 3-2. Minerals quantification in starting materials, ceramic residue (CR) – milled for 32 hours; Fly Ash (FA); ladle furnace slag (LFS), (% wt) ........................................................................................... 69 Table 3-3. Identification and characterization of the tested pastes ...................................................... 70 Table 3-4. Minerals quantification of the 75CR-25FA/SH or SS mixtures (M1 and M2) and 75CR25LFS/SH or SS mixtures (M3 and M4), after 90 days of curing time (% wt) ...................................... 75 Table 3-5. Chemical composition of mixtures at 90 days curing time, %Wt, (SD in parentheses) ......... 76 Table 4-1. Chemical composition of the ceramic waste (CW), and ladle furnace slag (LFS), % wt ........ 88 Table 4-2. Composition of the alkali-activated mortars ....................................................................... 90 Table 4-3. Uniaxial compressive strength (UCS), Elasticity modulus ( E ), and flexural strength ( f ) of the alkali-activated mortar after 14, 28, and 90 days of curing ................................................................ 95 Table 4-4. Open porosity of the alkali-activated mortar after 28 days of curing, (%) ........................... 105 Table 4-5. Mineral’s quantification in starting materials (CW and LFS), and M2 (0.5% fiber) mortar at 14- , 28 and 90 days curing time, (% wt) ............................................................................................... 108 Table 5-1. Identification and characterization of the tested cements ................................................. 128
xix Table 5-2. Open porosity of the alkali-activated cement after 28 days of curing, (%) .......................... 131 Table 5-3. Minerals´ quantification of the precursors (CBW and LFS) and the AAm reinforced with 1% of PAN fibers (M3), at 14, 28 and 90 days curing time, (% wt) ............................................................. 145 Table 6-1 Alkali-activated materials based on ceramic wastes (CW) and slag (S)............................... 160 Table 6-2. Technical specification according to supplier datasheet for extruded polystyrene (XPS) [46] foam and expanded cork agglomerate (ICB) [47]. ............................................................................ 164 Table 6-3. Non-structural panels based on alkali-activated cement with high ceramic waste, composition in kg/m3 ......................................................................................................................................... 164 Table 6-4. List of equations for the thermal performance assessment .............................................. 174 Table 6-5. Basic mechanical properties of the developed panels ...................................................... 176 Table 6-6. Experimental conditions and thermal parameters of ACP, APICB, and APXPS panels .............. 184 Table 6-7. Thermal conductivity (λ) of the ACP vs. traditional construction materials and thermal insulators [57]. ............................................................................................................................................... 188 Table 7-1. Half-sandwich panels composition, (wt.%) ....................................................................... 204 Table 7-2. Inventory of the materials and supplies inputs for each analyzed building solution ........... 208 Table 7-3. Indicators, units, and quantification methods .................................................................. 210 Table 7-4. Weight for each sustainability indicator, [21] ................................................................... 211 Table 7-5. List of equations for the sustainability comparative analysis of the interior partition solutions ...................................................................................................................................................... 211 Table 7-6. Quantification of Environmental, Functional, and Economic parameters for each studied partition walls technologies ............................................................................................................. 213 Table 7-7. Normalized values of the studied impact categories ........................................................ 216 Table 7-8. Sustainable performance results ..................................................................................... 218
xx LIST OF ACRONYMS AAc alkali-activated cement AAm alkali-activated mortars AAMs alkali activated materials ACP panel of alkali-activated cement based on ceramic wastes and slag only AP acidification Potential APICB Panel with insulation corkboard APXPS Panel with extruded polystyrene foam 𝐴𝑃𝑋𝑃𝑆 ‖ Parallel direction of the grooves of the XPS insulation material 𝐴𝑃𝑋𝑃𝑆 ⊥ Perpendicular direction of the grooves of the XPS insulation material C water absorption C-A-S-H calcium aluminum silicate hydrate CBW Ceramic bricks waste CC Construction Cost CDW construction and demolition wastes CE circular economy Cf fiber content CoV coefficient of variation CR ceramic residue C–S–H calcium-silicate hydrate CW ceramic waste e.g. for example Ecm elasticity modulus EDX X-ray Energy Dispersive Analyzer EE_T total embodied energy EE_NR non-renewable Embodied energy EP eutrophication potential EU European Union f ct f flexural strength fR 0.3mm flexural strength mouth opening displacements of 0.3 mm fR 0.5mm flexural strength mouth opening displacements of 0.5 mm
xxi FA fly ash FTIR Fourier Transform Infrared Spectroscopy GBFS ground blast furnace slag GHG greenhouse gas GP geopolymer GPa Gigapascals GWP Global Warming Potential HFn HFP01SC plate sensors HWR heavyweight reference masonry partition wall ICB insulation corkboard λ thermal conductivity LAC Latin America and the Caribbean LCA Life Cycle Assessment LCC Life Cycle Costing LC-CBA Life-Cycle Cost-Benefit Analysis LCI Life Cycle Inventory LCIR Life Cycle Interpretation of results LFS ladle furnace slag LVDTs linear variable differential transformers LWR lightweight reference plasterboard partition wall LWS lightweight sandwich solution MARS-SC multicriteria decision-making support method MDF medium-density fiberboard MMC Modern Methods of Construction MPa Megapascals MSW municipal solid waste N-A-S-H sodium aluminum silicate hydrate NDA environmental sustainability dimension NDE economic sustainability dimension NDF functional sustainability dimension NDj performance at the level of the dimension j NS sustainability score
xxii ODP ozone layer depletion OPC Ordinary Portland Cement P open porosity PAN polyacrylonitrile PE person Equivalent PERH Plano Estratégico de Resíduos Hospitalares; (Strategic Plan for Hospital Waste) PERSU Plano Estratégico para os Resíduos Sólidos 2020; (Strategic Plan for Solid Waste) PESGRI Plano Estratégico de Gestão dos Resíduos Industriais; (Strategic Plan for the Industrial Waste Management) PEWPS Prefabricated Enclosure Wall Panel Systems 𝑃 𝑖 normalized indicator PNAPRI Plano Nacional de Prevenção de Resíduos Indústrias; (National Plan for the Industrial Waste Prevention) PNGR National Waste Management Plan (Portuguese acronym) POCP Photochemical oxidation PSD particle size distribution PU polyurethane foam PVA Polyvinyl alcohol PVC polyvinyl chloride qn heat flux R thermal resistance Rse external superficial thermal resistances Rsi internal superficial thermal resistances SA sensitivity analysis SAB US Environmental Protection Agency's Science Advisory Board SDGs Sustainable Development Goals SEM Scanning electron microscope SH sodium hydroxide SI sustainability indicator SIPs structurally insulated panels SP superplasticizer SS sodium silicate
xxiii Te exterior temperature Ti interior temperature τs shear bond Tsin inner surface temperature sensors U thermal transmission coefficient UCS uniaxial compressive strength UN United Nations UTAD University of Trás-os-Montes and Alto Douro WBP waste red clay brick powder WCP waste ceramic powder 𝑤𝑖 weight of the ith indicators XPS extruded polystyrene XRD X-ray diffraction
7 Chapter II: State of Art 2. STATE OF ART 2.1. WASTE MANAGEMENT AND SUSTAINABILITY 2.1.1. Sustainable development: a global objective For stimulating sustainable development, the United Nations has elaborated “the 2030 Agenda", a plan of action for people, the planet, and prosperity. It includes 17 Sustainable Development Goals (SDGs) (Figure 2-1) and 169 targets. Heads of State and Government at a special UN conference implemented it on 25 September 2015. The 2030 Agenda is a commitment to eradicate poverty and achieve sustainable development by 2030 worldwide, ensuring that no one is left behind. The adoption of the 2030 Agenda was a landmark achievement, providing for a shared global vision toward sustainable development for all [5]. In the case of Portugal, it has founded a council for the sustainable development of companies (BCSD) that provides resources to its organization. BCSD's activity is supported by the global network of the WBCSD, the largest international business organization dedicated to sustainable development [6]. Figure 2-1. Sustainable Development Goals [7]
State of Art 8 Solid waste management and treatment are in some way linked with some of the goals in the 2030 Agenda, as is exhibited in Figure 2-2. Besides, it is strongly bonded with “Goal 12. Ensure sustainable consumption and production patterns”. Monitoring SDG 12 responsible consumption and production in an EU context focuses on the sub-themes of decoupling environmental impacts from economic growth, energy consumption, and waste generation and management. Goal 12 has 11 targets which are listed below: 1. Implement the 10-year framework of programs on sustainable consumption and production, all countries taking action, with developed countries taking the lead, considering the development and capabilities of developing countries; 2. By 2030, achieve the sustainable management and efficient use of the natural resource; 3. By 2030, halve per capita global food waste at the retail and consumer levels and reduce food losses along production and supply chains, including post-harvest losses; 4. By 2030, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle, in accordance with agreed international frameworks, and significantly reduce their release to air, water, and soil in order to minimize their adverse impacts on human health and the environment; 5. By 2030, substantially reduce waste generation through prevention, reduction, recycling, and reuse; 6. Encourage companies, especially large and transnational companies, to adopt sustainable practices and to integrate sustainability information into their reporting cycle; 7. Promote public procurement practices that are sustainable, and in accordance with national policies and priorities; 8. By 2030, ensure that people everywhere have the relevant information and awareness for sustainable development and lifestyles in harmony with nature; 9. Support developing countries to strengthen their scientific and technological capacity to move towards more sustainable patterns of consumption and production; 10. Develop and implement tools to monitor sustainable development impacts for sustainable tourism that creates jobs and promotes local culture and products; 11. Rationalize inefficient fossil-fuel subsidies that encourage wasteful consumption by removing market distortions, in accordance with national circumstances, including by restructuring taxation and phasing out those harmful subsidies, where they exist, to reflect their environmental impacts,
State of Art 9 taking fully into account the specific needs and conditions of developing countries and minimizing the possible adverse impacts on their development in a manner that protects the poor and the affected communities.” [5] Figure 2-2. Goals for sustainable development related to waste management. Being sustainable development, specifically, the management of solid waste a concern for different areas, government, producers, academics, etc., in terms of sustainable construction some studies had been done from different perspectives. It was established that concrete waste could be used to substitute up to 50% of the clay whereas ceramic wastes could only substitute a maximum of 30% of the clay [8]. Another study showed that in Europe policies are needed to stimulate high-quality recycling of construction and demolition waste (CDW). Life cycle assessment (LCA) shows that landfilling is the scenario having the highest environmental impacts in terms of person equivalent (PE), followed by downcycling and recycling (-36%) and recycling after selective demolition (−59%). The decrease in environmental impacts is mostly due to the avoided landfilling of CDW and the recovery of materials from selective demolition. Life cycle costing (LCC) results indicate that landfilling is the scenario bearing the highest total economic costs [9]. In the United States, in the way of incorporating
State of Art 10 construction sectors within the concept of sustainable building, which also concerns waste management, it was developed a study that sets a statistical paradigm with field-based values for typical construction projects to be followed as a guide, indicating how much cost can be saved, and how much landfill volume can be relieved when material waste is recycled [10]. In Singapore, there is a research report which undertook to review perceptions and awareness of sustainable construction methods and policies within the Singaporean construction industry. The main conclusion of the work is that government regulatory and incentive programs may be able to drive positive change effectively and efficiently, but this needs to happen alongside initiatives to support client awareness and adoption of sustainable practice [11]. 2.1.2. Solid waste management, the legal framework in EU and Portugal The waste management approach was the last environmental affair that was tackled in all the countries that have framed and implemented environmental policies. Water quality, sewage collection, reduction and control of gas emissions issues were addressed first. Even in the context of the European Union (EU), waste concerns were the object of particular legislation only in the 1970s. Moreover, in Portugal, waste management has deemed a priority until the 1990s [12]. So that, to manage and protect natural resources, environmental protection policies emerged to raise awareness of the importance of caring for the environment. In this scene, the EU consolidated its management policy in the documents Directive 2006/12/EC [13] and Directive 2008/98/EC [14], as amended Directive (EU) 2018/851 [15], which provides the “framework for the handling of waste in the Community”. It defines key concepts such as waste, recovery, and disposal and puts in place the essential requirements for the management of waste, notably an obligation, especially the responsibility for the waste management operators to have a permit/license or be registered, and an obligation for the Member States to draw up waste management plans. It also establishes major principles, such as an obligation to handle waste in a way that does not have a negative impact on the environment or human health [16]. Sustainable waste management has two main objectives, which are (i) the decrease in waste generation and (ii) the reduction of resource exploitation. These objectives are built-in the waste hierarchy (Figure 2-3), which has become a fully accepted guideline for waste management operations by the Directive 2008/98/EC [17]. It is in agreement with the polluter pays principle, which requires
State of Art 11 that the cost associated with the waste disposal must be borne by the current holder of the waste, by the previous holders, or by the producers of the waste. Figure 2-3. Waste hierarchy (Adapted from Decree-Law n. º 73/ June 17th, 2011) The European Union's (EU) environmental policies are transposed to its member states. Therefore, Portugal, one of them, must fulfill these objectives and create laws from a pre-conceived EU standard. Thus, with the document already generated by the EU, Portugal modified and created the Decree-Law (DL 73/2011), of June 17th, under which “the Government considers it a priority to reinforce the prevention of waste production and encourage its reuse and recycling with a view to prolonging their use in the economy before returning them in conditions suitable for the natural environment (...), considers it important to promote the full use of the new organized waste market as a way to consolidate the recovery of waste, with advantages for economic agents, as well as to promote the use of specific waste with high recovery potential", in transposition of Directive No. 2008/98/EC, of the European Parliament and of the Council, of 19 November, about waste" [18]. More specifically, in Decree-Law No. 73/2011 - Article 7, the recycling and re-use of waste are identified in the scope of the 2030 targets. Regarding waste recycling, the aim is to achieve a recycling rate of at least 50% of the value of the waste produced. Another target for 2030 is related to the reuse of these wastes so that such waste can be incorporated as a substitute for natural materials. Thus, Decree-Law No. 18/2008 of January 29, established the obligation to use at least 5% of the recycled material in public works construction, to prevent the extraction of natural materials and use other than the disposal of waste in landfills. Some other important solid waste management policies [19] are described below: ‒ Statement of Rectification No. 14/2021, rectifies the Law n. º 20/2021, of April 16, regards to the General Regime for waste management approved by Decree-Law No. 178/2006, of 5 September; Preventin and reduction Preparation for reuse Reclycle Valorization Disposal
State of Art 12 ‒ Decree-Law No. 102-D/2020: Approves the general regime for waste management, the legal regime for the disposal of waste in landfills and amends the regime for the management of specific waste flows, transposing Directives (EU) 2018/ 849, 2018/850, 2018/851 and 2018/852. ‒ Decree-Law No. 92/2020: Changes the general regime for waste management. ‒ Decree-Law No. 152-D/2017: Unifies the regime for the management of specific waste streams subject to the principle of extended producer responsibility, transposing Directives No. 2015/720/EU, 2016/774/EU, and 2017 /2096/EU. ‒ Ordinance No. 335/97 (Portaria nº 335/97): Establishes the rules to which waste transportation within the national territory is subject ‒ Decree-Law No. 210/2009: Establishes the constitution, management, and operation of the organized waste market. ‒ Decree-Law No. 152/2002: Establishes the legal regime to which the procedure for issuing a license, installation, operation, closure, and post-closure maintenance of landfills for waste disposal is subject and proceeds with the transposition to order national legal framework of Directive 1999/31/EC, of the Council, on the disposal of waste in landfills. ‒ Decree-Law No. 46/2008: Validates the construction and demolition waste management regime. ‒ Ordinance No. 28/2019: Amends Ordinance No. 145/2017, of April 26, which defines the applicable rules to road, rail, river, sea, and air transport of waste in national territory and creates electronic guides for monitoring of waste (e-GAR). It is noteworthy that in Portugal the strategies that guide waste planning and management are reflected in specific plans, as of Decree-Law No. 73/2011, to integrate the waste issue in the country, the National Waste Management Plan (PNGR – Portuguese acronym) was created by the National Waste Authority (NRA) to establish national strategic guidelines for waste prevention and management policy and the rules that ensure the consistency of the specific waste management instruments. The diagnostic elements of this plan were made available in public consultation at the end of 2020 to be updated and be called PNGR-2030, to allow interested parties to present technical contributions for its preparation. The elaboration of the PNGR 2030 was determined by Dispatch No. 4242/2020, of 7 April, of the Offices of the Minister of State, Economy and Digital Transition, the Ministers of Planning and Environment and Climate Action, the Minister of Agriculture, and the Minister of the Sea [20]. The PNGR 2030 is based on two objectives: to promote the efficiency of the natural resources used in the
State of Art 13 economy and prevent or reduce adverse impacts arising from the production and management of waste [21]. APA is the entity responsible for preparing, reviewing, and implementing the National Waste Management Plan, namely, Strategic Plan for Hospital Waste (PERH 1 ), Strategic Plan for the Industrial Waste Management (PESGRI1), National Plan for the Industrial Waste Prevention (PNAPRI1) and the Strategic Plan for Urban Solid Waste (PERSU1 2020+) approved by Portaria n.º 241-B/2019. PERSU1 2020+ helps to manage municipal waste and is a tool that provides strategies and targets, which are described in DL 73/2011. 2.1.3. Solid waste generation in the EU and Portugal Worldwide, increasing population density along with population migration from rural to urban areas and industrial expansion lead to great amounts of waste generation resulting in socio-economic and environmental issues. A report from The World Bank estimates that currently 1.3 billion tons of waste is generated per year all over the world, and by 2025 this amount will increase to 2.2 billion tons per year. These data show an urgent need for strategies to treat the increasing rate of generation around the planet [22]. Waste generation varies as a function of affluence, however, regional and country variations can be significant, as can generation rates within the same city. The global impacts of solid waste are growing fast. Solid waste is a large source of methane, a powerful greenhouse gas (GHG) that is particularly impactful in the short term. The recycling industry, with more than two million informal waste pickers, is now a global business with international markets and extensive supply and transportation networks. Table 2-1 presents the waste generation projections for 2025 by region in the world. According to World Bank Group, in 2018, most of the waste generated is from East Asia & the Pacific region, representing 23% of the total, followed by Europe & Central Asia with 20%, North America with 17%, Latin America with 14%, the Caribbean 11%, and the Middle East & North Africa region are the lowest generation rates with 9% [23], Figure 2-4. Moreover, Figure 2-5 shows the correlation between income levels and waste generation. High-income countries constitute 16% of the global population, however, they are in charge of over one-third of the world's waste. 1 Portuguese Acronym
State of Art 14 Table 2-1. Waste generation projections for 2025 by region, [24] Region Current Available Data Projections for 2025 Total Urban population (millions) Urban Waste Generation Projected population Projected Urban Waste Per Capita (kg/capita/day) Total (Tons/day) Total population (millions) Urban population (millions) Per Capita (kg/capita/day) Total (Tons/day) AFR 260 0.65 169,119 1,152 518 0.85 441,840 EAP 777 0.95 738,958 2,124 1,229 1.5 1,865,379 ECA 227 1.1 254,389 339 239 1.5 354,810 LCR 399 1.1 437,545 681 466 1.6 728,392 MENA 162 1.1 173,545 379 257 1.43 396,320 OECD 729 2.2 1,566,286 1,031 842 2.1 1,742,417 SAR 426 0.45 192,410 1,938 734 0.77 567,545 Total 2980 1.2 3,532,252 7,644 4,285 1.4 6,069,703 AFR: Africa; EAP: East Asia & Pacific; ECA: Eastern & Central Asia; LAC: Latin America & the Caribbean; MENA: the Middle East & North Africa; OECD: Organization for Economic Co-operation and Development; SAR: South Asia Figure 2-4. Waste generation by region of the world, [23]
State of Art 15 Figure 2-5. Waste generated by income level, [23] According to the last data available, in 2018, the total waste generated by all activities and households for the twenty-eight members of the European Union (EU-28) reached 2337 million tons (being the highest amount during the last 10 years reported) which translates into an average of 4931 kg per inhabitant of the EU. On the other hand, data from the same year shows that the EU-28 generated 812 million tons of waste excluding major mineral wastes, equivalent to 35 % of the total waste generated, Table 2-2. It means, on average, 1.8 tons per inhabitant of waste excluding major mineral wastes were produced [25]. Figure 2-6 shows the production of waste by economic activities and households in the EU. According to these data, it can be observed that the construction sector accounted for 34.7% of the total waste generated, and manufacturing represented 10.2%.
State of Art 16 Figure 2-6. Waste generation by economic activities and households, EU-28, 2018 (%), [26] Waste generation, excluding major mineral wastes, increased, on average, by 4.2% between 2004 and 2018, and when expressed about population size, the EU generated, on average, 1.8 tons per capita in 2018. Regarding each waste component (Table 2-2), it should be noticed that the construction waste increased by 20.1% during the 20042018 period, thus showing an opposite behavior compared with other sectors. In contrast, in the same period the manufacturing waste generation, decreased quite considerably, by 24.9%. However, there is no doubt that there is still a lot to do. Ceramic production and its corresponding waste generation are strongly related to both sectors. The numbers confirm the relevance of waste valorization to proposing new management and treatment alternatives. Regarding waste treatment, in 2018, around 2200 million tons of waste were treated in the EU. It excludes the exported waste but includes the treatment of waste imported into the EU. Thus, the registered data cannot be directly compared with those on waste generation. The recycled waste used for backfilling, i.e., the waste used in excavated areas for slope reclamation, safety, landscape engineering purposes, or incinerated with energy recovery rose by 33.9 % from 2004 to 2018. As a result, the share of such recovery in total waste treatment grew from 45.9% in 2004 to 54.6% in 2018, consequently, the waste final disposal diminished by 4.2%. The share of disposal in total waste treatment reduced from 54.1% in 2004 to 45.4% in 2018. 0,9% 0,5% 35,9% 26,6% 10,6% 9,8% 8,2% 4,2% 3,4% Agriculture, forestry and fishing Wholesale of waste and scrap Construction Mining and quarrying Manufacturing Waste/water Households Services (except wholesale of waste and scrap) Energy
State of Art 23 activated with alkali powder. It is highlighted that the key parameter that regulates most of the properties both in the fresh and hardened state of alkali-activated compounds is the activator/precursor ratio, influencing the mechanical performances, the rheological properties, and the shrinkage: the higher the activator dosage, the higher the consistency class and shrinkage. Furthermore, the elastic modulus of slag-based mortars is lower than that of OPC mortars in the same strength class. Alkali Activated Materials (AAMs) resemble to have promise for a sustainable future in construction since the Global Warming Potential (GWP) and Gross Energy Requirement (GER) are reduced by about 80% compared with traditional Portland cement mortars with the same compressive strength. Briga-Sá et al. [42], used different percentages (6.25%, 8.16%, and 8.75%) of textiles wastes (TW) to be incorporated into cement-based lightweight blocks (LWB). The study aimed to know the thermal performance of the developed LWB, where results showed their suitability for thermal insulation applications. Thermal resistance values of 0.34 m2°C/W, 0.61 m2°C/W, and 0.67 m2°C/W for the LWB1, LWB2, and LWB3 were estimated, respectively. Concluding that higher thermal stability is achieved when a higher percentage of TW is incorporated in the cementitious mixture composition. The comparison of the LWB with currently available building materials, such as simple masonry walls and insulating concrete forms, revealed promising results for the proposed textile waste-based materials. Bagarić et al. [43], presented a case study of dynamic hygrothermal performance of a developed building envelope system under real outdoor climate conditions and with real occupants living in the house for one year in 2017/2018, (Croatia). For this purpose, ventilated prefabricated sandwich walls, containing a high amount of construction and demolition waste (50%), were built. The impact of panels’ high massiveness on the energy performance of an exemplary building was assessed according to the new EN ISO 52016-1:2017 standard for different climates and different operating modes of technical systems. After experimental monitoring and transient numerical simulations, it was concluded that a heavyweight envelope constructed with ventilated prefabricated wall panels from CDW can perform satisfactorily, from both hygric and thermal aspects. Therefore, the presented envelope system could foster the large-scale deployment of buildings, however, the applicability for other climates and conditions of use should be verified first. Future work is needed especially related to the efficiency of ventilation for different conditions (climate and building use), monitoring of indoor comfort (in terms of temperature, relative humidity, CO2), and energy consumption in ground floor apartments.
State of Art 24 Benallel et al. [44], develop and characterized new thermal insulation materials from cardboard waste and plant fibers. Four different types of agricultural by-products plenty available in the South-East of Morocco (reed, alfa, fig branches, and olive leaves) with different mass fractions of cardboard waste (20%, 30%, 40%, 50%, and 60%) were used. Results showed that the increase in fiber content caused a slight increase in bulk density and thermal conductivity while the maximum rate of water absorption decreased significantly. The lowest thermal conductivity value was 0.072 W/m.K with a density of 176 kg/m3 and a maximum water absorption rate of 262%, which corresponded to the composite of 40% alfa fibers and 60% cardboard waste. It was concluded that the developed insulation panels exhibited good insulating properties compared to conventional insulation materials and several environmental and economic advantages were identified. Lazorenko et al. [45], studied the influence of shape and size of plastic waste on the fresh-state and hardened-state properties of geopolymer (GP) mortars. GP was made using fly ash and waste plastic bottle (PET) in form of shredded flakes, strips, and grinded particles of different sizes. Results showed that regardless of the shape of plastic aggregate, adding the waste PET to fresh geopolymer mortars reduced workability. However, the GP including PET particles had near workability and flexural strength to the control sample, the compressive strength and splitting tensile strength were lower due to poor interaction between PET particles and the matrix. Still, the PET grinded particles were the most effective form of aggregate. Future work is needed to enhance the adhesion at the interface of PET particles and GP mortars. 2.2. CIRCULAR ECONOMY Population in the world is growing and with it the demand for raw materials. However, the supply of pivotal raw materials is restricted. Moreover, extracting and using raw materials has a major impact on the environment. It also increases energy consumption and CO2 emissions. Nevertheless, smarter use of raw materials can lower CO2 emissions. The European Commission is convinced that the transition to this circular model, outlined in Figure 2-8, will contribute to the creation of more jobs and will encourage companies to invest in the innovation of their products and processes. At the same time, the protection of human beings and the environment will be safeguarded.
State of Art 25 Figure 2-8. Circular economy model,[46] The concept of the “circular economy” has gained significant traction since its introduction a halfcentury ago. Scholars, practitioners, governments, and non-governmental organizations have recognized the apparent appeal of closing material loops, reusing and recycling industrial “nutrients” to extract their maximum value with minimum waste. The intense activism by the Ellen Macarthur Foundation since its foundation in 2010 [47], and its international partners, which involves large organizations such as Google, Unilever, Philips, and Renault, shows the concern from the industries side. While from the scientific side the interest has significantly grown, where 75% of all CE publications have taken place in the last 5 years, as exhibited in Figure 2-9. Figure 2-9. Circular Economy publications (source: Scopus®), [48]
State of Art 26 Table 2-4 is presented a few CE concept definitions from different authors, while Table 2-5 shows the basic principles related to CE. It can be confirmed once more that waste management is one of the fundamental principles to consolidate a CE. Table 2-4. Circular Economy sources and definitions, adapted from [48] ID Author Citations Circular Economy Definition 1 Ghisellini, Patrizia 1495 “Circular economy (CE) as a new model of economic development promotes the maximum reuse/recycling of materials, goods, and components to decrease waste generation to the largest possible extent. It aims to innovate the entire chain of production, consumption, distribution, and recovery of materials and energy according to a cradle to cradle vision”, [49] 2 Geissdoerfer, Martin 1364 “A regenerative system in which resource input and waste, emission, and energy leakage are minimized by slowing, closing, and narrowing material and energy loops. This can be achieved through long-lasting design, maintenance, repair, reuse, remanufacturing, refurbishing, and recycling”, [50] 3 Bocken, Nancy M. P. 1137 “The circular approach contrasts with the traditional linear business model of production of take-make-usedispose and an industrial system largely reliant on fossil fuels, because the aim of the business shifts from generating profits from selling artifacts to generating profits from the flow of materials and products over time”, [51] “Circular business models thus can enable economically viable ways to continually reuse products and materials, using renewable resources where possible”, [51] 4 Korhonen, Jouni 867 “Circular economy is an economy constructed from societal productionconsumption systems that maximize the service produced from the linear naturesociety-nature material and energy throughput flow. This is done by using cyclical materials flows, renewable energy sources, and cascading1-type energy flows. A successful circular economy contributes to all three dimensions of sustainable development. Circular economy limits the throughput flow to a level that nature tolerates and utilizes ecosystem cycles in economic cycles by respecting their natural reproduction rates”, [52] 5 Ellen MacArthur Foundation N/A “A circular economy is based on the principles of designing out waste and pollution, keeping products and materials in use, and regenerating natural systems”, [47] Table 2-5. Circular Economy-related basic principles ID Principle Description 1 9R Framework A set of 9 strategies to be considered for a CE approach, in order of priority: Refuse, Rethink, Reduce, Reuse, Repair, Refurbish, Remanufacture, Repurpose, Recycle, Recover. 2 Waste Hierarchy A priority operations order in waste management: prevention, preparing for reuse, recycling, another recovery (including energy recovery), and disposal. 3 Clean and Renewable Energies The use of clean and renewable energy sources instead of fossil and polluting sources. 4 Upcycle Transforming waste materials, useless, or unwanted products into new materials or products with high perceived value. 5 Resource Efficiency The use of the planet's limited resources in a sustainable manner and minimizing environmental impacts, delivering greater value with less input. 6 CE Categories Re-principles, waste, efficiency, value retention, sustainability, resources, design, system perspective, energy, cycles.
State of Art 27 The CE is based on three essential principles: “(1) Designing waste and pollution, (2) keeping products and materials in use, and (3) regenerating natural systems”. Moreover, the CE is a complex system that links different markets, stakeholders, material, information, and energy flows. CE transition goes further than market changes and indeed impacts sustainability, so it is important to identify the high complexity emerging from the relationships between actors, strategies, energy, material flows, and the circular ecosystem. Assessing the sustainability impacts of circular systems is another significant challenge. Although the circularity action can be estimated by different methodologies, such as Life Cycle Assessment, Data Envelopment Analysis, Simulation, Material Flow Analysis, and others, a practical measuring method is not an easy task. The circularity complexity has been classified into five levels; the first one is shorttime and micro-scale, including single products or services. The complexity grows as the time lengthens and the unit of analysis extends to industries, industrial parks, regions, countries, and the whole planet. These levels of complexity drive to different CE execution levels (policy level, organizational level, and consumer level). There are several barriers to the implementation of CE despite its benefits linked to strategies to achieve sustainability and minimize the environmental impact of economic growth. It has been implemented guided by soft drivers, such as legislative policies, but at the same time, it has challenging barriers, such as lack of technical solutions and low financial investment. Some authors account for six limitations and challenges for a CE that is associated with (1) system boundaries, (2) physical scale of economy, (3) governance, (4) thermodynamic, (5) social, and (6) cultural context. Singularly, the mentioned thermodynamic limit is about the transformation in the system to close the loop. Nevertheless, new flows of resources are constituted with CE, causing more waste and emissions [53]. On the other hand, it is well known that industrial activities worldwide, annually produce massive quantities of waste that induce huge problems for their treatment and disposal, along with a financial loss and energy emission. Hence, creating novel sustainable materials and products, developing green manufacturing processes, and following a reliable life cycle management is the only feasible way to reverse the actual situation, to enhance the Circular Economy. In this way, the so-called geopolymers (GP) are a sustainable typology of hydraulic (alkali-activated) binders that are widely studied globally being a promising and valid substitution of the traditional cementitious materials, such as the OPC. Lately, the use and production of GP products have called the attention of more and more researchers for their superior mechanical properties that make them suited for different applications in
State of Art 28 construction. Concerning climate change and greenhouse gas emissions, GP could efficiently mitigate the CO2 emissions released by the cement plants and the related industries (i.e., aggregate, additive, etc.). Furthermore, GPs’ manufacture represents a relatively low energy consumption with low emissions of the pollutant. Also, GP technology offers the indisputable benefit of the great potential of incorporating vast typologies of wastes as raw materials improving the sustainability of processes and products. So far, different by-products and wastes have been studied, so, GP raises high expectations as a new binder material to be widely used in construction as, e.g., a substitute for OPC. Therefore, GPs enable the redirection of the current waste streams from landfills and the substitution of a carbonintensive product, in the perspective of the circular economy [54]. 2.2.1. Life cycle assessment (LCA) Life Cycle Assessment (LCA) is an efficient and methodical tool for measuring the potential environmental burdens related to a product, process, or activity by determining, quantifying, and evaluating the impact of the used energy, materials, and wastes discharged to the environment. LCA considers the possible environmental impacts along a product’s life cycle (i.e., cradle-to-grave) from raw material acquisition through production, use, and disposal [55]. LCA is an iterative process, as illustrated in Figure 2-10, that involves the ISO 14000 series in the development of its main stages: i) Goal and Scope Definition, and ii) Life Cycle Inventory (LCI); International Standard ISO 14041 iii) Life Cycle Impact Assessment (LCIA); International Standard ISO 14042 iv) Life Cycle Interpretation of results (LCIR); International Standard ISO 14043 The goal and scope definition of an LCA describe the product system in terms of the system boundaries and a functional unit. The functional unit is the essential basis that allows alternative goods, or services, to be compared and evaluated. The functional unit is defined as a quantitative description of the service performance (the needs fulfilled) of the investigated product system(s). LCI stage includes compiling data for each unit process regarding all relevant inputs and outputs of energy and mass flow, air emissions, and soil and water discharges caused by or otherwise attributable to a product's life cycle. This phase also includes calculating both, the material and energy input and output of a building system. The Life Cycle Impact Assessment (LCIA) is an evaluation of a product life cycle, on a functional unit basis, in terms of several impact categories by analyzing all
State of Art 29 environmental burdens obtained in the LCI. Finally, Life cycle interpretation ensues at every phase in an LCA. When two product options are compared and one of them shows higher consumption of each material and each resource, an interpretation purely based on the LCI can be irrefutable. However, it is possible to compare across impact categories, especially when there are trade-offs between product alternatives, or if it is worthwhile to prioritize areas of concern within a single life cycle study. Figure 2-10. Phases and applications of an LCA, (ISO 14040:2006) For the development of LCA, the use of the software is needed as the main tool, and depending on the potential users, there is dedicated software. In general, it can be classified into three types of software: • Generic LCA software is commonly designed for use by researchers, consultants, and other LCA specialists. • Specialized LCA-based software of different types for specific decision-makers, generally intended for use by designers in engineering or construction, the purchasing department, or environmental and waste managers. • Tailored LCA software systems to be used for clearly determining applications in specific IT environments (as interfaces to business management software). These are usually firm-specific adaptations of generic software or software packages programmed directly for the needs of the firm [56]. Regarding LCA, government, and policy, Governments play a key position in instituting the frameworks and conditions for the production and consumption patterns of goods and services in our societies.
State of Art 30 As a tool undertaking the environmental mainstay within the concept of sustainable development, LCA is relevant in developing and supporting linked strategies to help diminish wastes, emissions, and the resources consumption that are ascribed to the supply and consumption of goods and services. The EU policy seeks for developing a sustainable, climate-neutral, circular, and bio-based economy. Some of these policy initiatives have been conceived under the umbrella of the European Green Deal, which specifies the EC's priorities for the period 2019-24. Summing up, the policies aim to support the unlink of economic growth from resource use; allow the gradual implementation of the net-zero GHG emissions target by 2050, with transitional goals for 2030; and guarantee that people and regions are implicated and not outpace in this transition. In this way, each of the policy documents contributes by sketching specific targets and strategies for their specific field of action and related stakeholders. Figure 2-11 depicts five policy pursuits related to EU building stock development and building construction and operations: Figure 2-11. Mapping of the EU policy documents with defined policy objectives, highlighting their focus, [57] On the other hand, in LCA when a process generates more than one product, the environmental impact of this process needs to be assigned between the product and the by-product. If the by-product is considered waste, all impacts are allocated to the main product, but if this by-product is considered a co-product of the process, then environmental impacts must be shared between the main and coproducts. Allocation can be done by mass or any other physical characteristic (e.g., energy). When no physical characteristic is relevant, then allocation can be done by a non-physical one (e.g., economic value) [58].
State of Art 31 Partial analyses are useful for civil engineering materials like concrete or alkali-activated materials because they can be included in end-products having different life cycles. As it is known, 1 m3 of concrete can be used in a structure, a wall, a bridge, or a road. Therefore, it is of definite interest to have quantified environmental impacts by providing results for 1 m3 of concrete or any other materials. The use of these data for the construction sector when compared to other materials such as wood or bricks must be made with great attention as the material with the lowest environmental impact per unit of volume (or mass) is not necessarily the one that will have the lowest environmental impact once integrated into a structure over its service life [59]. There are several studies about the life cycle assessment of geopolymers to determine how significant are the environmental impact. Table 2-6 shows the main results of the first LCA articles found about geopolymers, where the conclusions are varied, and they highly depend on the studied product. Table 2-6. First articles on the life cycle assessment of geopolymers, [58] References Weil et al., 2009 Habert et al., 2011 McLellan et al., 2011 Turner and Collins, 2013 Yang et al., 2013 Functional unit 1m of compliant concrete 1m of Concrete with a mix design 1m concrete 1m concrete of 40 MPa 1m concrete of 24,40,70 MPa System boundaries Cradle to grate Cradle to grate Cradle to grate Cradle to construction Cradle to preconstruction Reference OPC Freeze-thaw resistant concrete according to DIN EN 206 1 DIN 1045 4 Equivalent mechanical strength 100% OPC (2) OPC and slag (2) OPC and FA (2) 1 OPC 100% OPC (3); OPC+ SCM (3) Number of geopolymers 1 hybrid slag fly/ash ratio 80:20 cured, room cure FA (8 refs, 48 mixes) GBFS (4 refs, 12 mixes) MK (4 refs, 17 mixes) FA (4) FA (1) AA GGBS (3), AA FA (3), AA MK (1) Data source Ecoinvent, literature, industry Ecoinvent, literature, industry Literature, calculation Industry and the Australian government Korea LCI Database Information Network, Japanese database Data quality Very good to adequate Good, but lack control for MK No, mass, economic Good, but lack control for MK Good Good
State of Art 32 Table 2.6. ( Continued ). First articles on the life cycle assessment of geopolymers, [58] Impact considered 3 indicators: ADP, GWP, CED 10 indicators Energy, greenhouse emissions, and cost Co2 footprint Co2 footprint Conclusion Improvement on GWP, but a similar impact on ADP and CED Higher impacts in other categories than global warming Results depend on the transport distance Small improvement when taking into account the process Favorable to geopolymers Note, OPC: Ordinary Portland cement; AA: alkali-activated; SCM: supplementary cementitious materials; FA: fly ash; GBFS: ground blast furnace slag; MK: metakaolin; ADP: abiotic depletion potential; GWP: global warming potential; CED: cumulative energy demand. More recently, different studies with different LCA approaches have been carried out, to mention, a study conducted in Italy that applied the LCA methodology to evaluate the environmental performance of the current regional management of CDW and to identify critical aspects and possible improving actions [60]. In Hong Kong, it was developed a Life-Cycle Cost-Benefit Analysis (LC-CBA) framework through the integration of the life-cycle assessment (LCA) and cost-benefit analysis (CBA) to guide decision-making in sustainable food waste management. The author suggests the LC-CBA developed in the study is widely applicable to inform decision-making on sustainable food waste management worldwide [61]. More recently studies of LCA related to the incorporation of different wastes, such as in road construction as a tool to quantify the potential impacts derived from the use of traditional and alternative materials [62] have been made. Salas et al. [63], conducted an LCA of a Geopolymer Concrete (GC) after scaling up the LCI from laboratory scale to industrial scale and concluded that sodium hydroxide production is the most relevant life cycle process regarding the environmental performance of GC, as it is also a main raw material in the production of sodium silicate. Other items such as concrete mixing facilities, curing process, and transport, affect a few impact categories each one. Bianco et al. [64], studied concrete of strength classes 35, 50, and 70 MPa and developed a silicate activator derived from waste glass (AABR). It was compared with the Ordinary Portland Cement concrete and alkali-activated concrete made with commercially available chemicals (AABC). Results showed that when waste glass-based activator is used, a significant reduction in every environmental category is evidenced in comparison to the use of commercially available chemicals. Besides, usage of alkali-activated concretes rather than of OPC concrete lets a significant decrease in environmental categories, such as global warming (≈64% for AABC and 70% for AABR), acidification potential (≈23% for AABC and 35% for AABR), and terrestrial eutrophication (≈53% for AABC and 60% for AABR).
State of Art 39 terms of greenhouse gas emissions (through electricity consumption) and in terms of emissions of other components, such as mercury which sometimes is used in this process. The main energy consumption in the sodium hydroxide production process occurs in the electrolytic cell, which has a high electrical power requirement despite being extremely efficient when the membrane cell is used. For example, from different audits related to the amount of energy consumption by Australian manufacturers of sodium hydroxide, its membrane cell produces 2,800 kW/h per ton of chlorine. These data were used to estimate the results of CO2 emissions per kg of NaOH produced, Table 2-7. From where a total emission of 1.95 kg of CO2 per kg of NaOH [66] was estimated. Table 2-7. Estimated emissions in the NaOH production process, (adapted from [4]) 2 Activity Emission Unit Electricity consumption in the cell per ton of NaOH 1.285 kW/h Emissions from the cell 1.581 kg CO2 Proportion of cell electricity consumption in the process 115.8 % Overall emissions from electricity 1.830 kg CO2 Percentage of cell electricity used in fuel 25.3 % Energy consumption on fuel 0.325 kW/h Overall emissions from fuel 0.086 Kg CO2 Total emissions 1.915 Kg CO2 2.3.2.3. Alkali silicates Sodium silicate is the generic name for a series of compounds with the formula Na2O·nSiO2. In theory, the number n can be any number. Sodium silicates with different values in the number n can have different properties with highly diversified industrial applications. Generally, sodium silicates usually have a ratio of 1.6 to 3.85. 2 The references cited in Table 2-7 are presented as in [4]
State of Art 40 The SiO44− anion is a key constituent in high-performance alkali-activated materials because it advantages the formation of a denser and stronger structure [70]. Sodium silicate in combination with sodium hydroxide provides an important reactive part of silica that is widely used to produce the activator. However, the main drawbacks of sodium silicate are, that it is the most expensive raw material to produce alkali-activated materials and the highest emitter of greenhouse gases among the basic materials [86]. The cost of sodium silicate can be around 20% to produce an alkali-activated materials concrete, depending on the dosage. Regarding the greenhouse gases, the authors found that emissions from the production of sodium silicate represent 50–70% of the total in an alkaliactivated materials concrete design [87]. It was mentioned that, commercially, liquid sodium silicates are usually produced with a mass SiO2/Na2O ratio that varies between 1.60 to 3.85, which means that there is no defined composition. This causes the structure and properties of these liquid vitreous silicates to vary. Table 2-8 is presented some physical and thermodynamic properties of anhydrous and hydrated sodium silicates. Table 2-8. Physical and thermodynamic properties of anhydrous and hydrated sodium silicates, [88] Formula Density (g/cm3) Melting point (°C) Heat Formation ΔH (Kcal/g·mol) Free Energy ΔG (Kcal/g·mol) Entropy (S) Na2O·SiO2 2.614 1089 -359.8 -338 29 Na2O·2SiO2 2.5 874 -576.1 -541.2 39.4 Na2O·nSiO2 - - 151.8 – 28.3n -142.6 - 195.6n 18 + 11n Na2O·SiO2·5H2O 1.75 72.2 -722 -631.5 77 Na2O·SiO2·6H2O 1.81 62.9 -792.6 -688.2 87 Na2O·SiO2·9H2O 1.65 47.9 -1005.1 -803.3 107 Two very important factors to consider when using this type of activator are: a) The concentration of silica, and b) The molar ratio SiO2/Me2O A solution with a low molar concentration (1/1) is composed mainly of monomers (SiO44-) and dimers (Si2O52-), while a solution with a high molar ratio (3.3/1) has a higher proportion of polymeric species. The pH value of the solution depends on its molar ratio SiO2/R2O. At pH values lower than 10, the solution starts to gel. To avoid this phenomenon, what is usually done is to control the SiO2/Na2O ratio
State of Art 41 and raise the pH value by the addition of alkalis, which is usually in the form of NaOH. The result is known as "waterglass" (xSiO3·YNa2O·nH2O) [4]. 2.3.2.4. Sodium silicate production Sodium silicates, also known as "waterglass", are inorganic chemical compounds produced from the combination, in different proportions, of high purity silica sands (SiO2) and sodium carbonate (Na2CO3). The fusion of these materials at temperatures above 1000 °C results in the sodium silicate in stone (Na2O·xSiO3) in the form of an amorphous crystal. This solid silicate is dissolved in water to obtain the soluble or liquid silicate, which is used in several industrial applications, such as detergents and soaps, paper and cardboard, civil engineering, water treatment, cement, adhesives, etc. Sodium silicates are synthesized through two possible production methods: the dry process and the wet process. The raw materials used in the dry process are soda ash and silicon oxide, while caustic soda and silica are the essential materials used in the wet process [4]. Like most industrial processes, sodium silicate production requires an important amount of energy, and it will be translated into CO2 emissions (Table 2-9). It is known that silicate solutions are the most used in the alkaline activation of aluminosilicates (slag, fly ash, and metakaolin). The availability of soluble silica is of importance in these systems, since it affects the workability, the adjustment, and the development of mechanical resistances, modifying both the composition of the gels and the microstructure of the material formed [4].
State of Art 42 Table 2-9. Estimates of emissions arising due to sodium silicate manufacture, [86] Emissions arising from the energy expended during manufacturing Energy flow (MJ/1000 kg) Emissions (kg CO2-e/kg) Electricity 3118 1.065 Coal 296 0.027 Oil (heavy) 9 0.001 Average/light 456 0.003 Diesel oil 144 0.01 Gas 1270 0.076 Others 78 0.009 Total 5371 1.222 Emissions caused by transport Air emissions (kg/1000 kg) Emissions (kg CO2-e/kg) Carbon dioxide (CO2) 288.7 0.289 Methane (CH4) 0.128 0.003 Total 0.292 Grand total (kg CO2-e/kg) 1.514 2.3.3. Applications of Alkali-activated materials The earliest endeavor to use alkalis in cement date back to 1930, when H. Kühl published research on the setting of slag mixed with dry potash solutions L. Chassevent and R. Feret afterward defined the need to investigate slag as a cement component. In 1940, A.O. Purdon published the outcomes of the first large-scale laboratory study on cement made with slag and live lime in the absence of Portland clinker. Later, in 1957, Victor Glukhovsky was the first to research the probability of formulating low-calcium or even calcium-free cementitious materials, which initially was called “soil cement”, using clays and alkaline metal solutions [89]. Table 2-10 presents a chronology summary of the highlights of the research on alkaline cement. The alkali activation of industrial waste materials has become an important area of research in many laboratories due to the probability to use these materials to synthesize low-cost and environmentally sound cementlike construction materials. During the last five decades, alkaline cement and concretes have aroused great interest among the scientific community and the construction industry. During the years 1999-2000, a group of scientists in Ukraine inspected several concrete structures built with alkali-activated slag cement, among which were different buildings such as silage ditches, railway
State of Art 43 embankments built-in 1982, residential buildings of up to fifteen plants built-in 1960, and buildings manufactured during the period 1999-2000, special concrete pavements for heavy-duty trucks (5060 tons) built-in 1984, etc. [4], [90], Figure 2-13. Table 2-10. Chronology of alkaline cement (adapted from [89]) 3 . Year Name Country Study/Impact 1930 Kühl Germany Slag setting in the presence of dry potash 1937 Chassevent Unknown Slag reactivity measurement using a dry potash and soda solution 1940 Purdon Belgium Clinker-free cement consisting of slag and caustic soda or slag and caustic alkalis synthesized with a base and an alkaline salt 1957 Glukhovsky USSR Binder synthesis using hydrous and anhydrous aluminosilicates (vitreous rocks, clays, steel mill slag) and alkalis; proposal for a Me2O-MeO-Me2O3SiO2-H2O cementitious system; coining of the term “soil cement” 1981 Davidovits France Alkalis mixed with a blend of burnt kaolinite, limestone, and dolomite, and trademarks such as Geopolymer, Pyrament, Geopolycem, Geopolymite 1986 Krivenko USSR Principles governing system Me2O-MeO-Me2O3-SiO2-Al2O3 properties; proposal for the generic name “alkaline cement” and the specific name “geocement” 1999 Palomo Spain Production of hardened cementitious materials from alkali-activated type F fly ashes 2006 Shi & Krivenko & Roy Ukraine - USA First book on alkali-activated cement 2014 Provis J., & van Deventer J.S. J UK & Australia Alkali activated Materials State of the art Report. RILEM TC 224-AAM Table 2-11 presents some examples of the applications that have been studied until 2010. While more updated advances on geopolymers developments in engineering applications have been reported by Nawaz et al. [91], who mentioned that due to the geopolymers' outstanding mechanical properties, better acid and thermal resistance, low carbon emissions, low energy requirements for processing, etc. make them propitious to use in civil engineering in contrast with traditional cementitious materials like cement and lime. More specific studies from different authors regarding the applications of geopolymers in soil stabilization, concrete and mortars, fire resistance, coastal or marine applications, self-cleaning concrete applications to inhibit microbial attack, building insulation, and manufacture of ceramic products were listed in Table 2-11. 3 The references cited in Table 2-10 are presented as in [89]
State of Art 44 a) Building constructed with alkaline activated slag concrete, Berezina Street 2, Lipetsk, Russia, 1994; b) Pipes for the sewerage system (1500 mm diameter) (Gourly and Johnson, 2005); c) Prestressed concrete sleepers produced by alkaline slag activation. Moscow-Saint Petersburg line (Russia) was built-in 1989. Figure 2-13. Applications with alkali-activated fly ash concrete (Pictures taken from [4] Doctoral Thesis Document). Table 2-11. Applications for alkaline cement, [89] . Year Civil engineering Non-civil engineering Hydraulic Roads Agricultural Industrial Residential Mining 2010 Corrosion-resistant concretes for marine engineering applications. Immobilization of liquid radioactive waste in alkali-activated cement 2000 Inorganic adhesives and glues, protective coatings for corrosive and high-temperature environments 1990 Acidresistant concrete articles and structures High-rise building with precast and cast-in-situ concrete Compounds for radioactive waste immobilization Precision tool housing 1985 Cast-in-situ concrete floors and landings Concrete blocks for buildings, garages, storage houses, etc. 1980 Heatresistant concrete articles and structures Floor slabs, foundation wall blocks, foundation blocks, piles Oil well mortars and grouts Linings of MDpumps for aluminum melts 1975 Strengthened soils for road bases a) b) c)
State of Art 45 Table 2-11 ( continued ) Applications for alkaline cement, [89] 1970 Tubing of anti-slide systems Cast-in-situ concrete pavements and precast reinforced concrete pavers Cast-in-situ and precast concrete pasture sites, fertilizer storage space, silo pits Foundation blocks, floor slabs, columns, beams, foundation wall blocs, elements of a cleaning-up system Reinforced pit props, sleepers 1960 Cast-in-situ and precast prestressed concrete sea break-waters, irrigation systems components Pavement slabs, kerbs, landing field slabs 2.4. CONSTRUCTION SYSTEMS IN PREFABRICATED PANELS Prefabricated Enclosure Wall Panel Systems (PEWPS) are often used for several reasons, such as allowing the construction process to be streamlined as it can be carried out in parallel with earlier phases of construction, fewer human resources are needed, there is a greater guarantee of the homogeneity and final quality of the construction elements, due to the higher control of the production parameters, optimization of resources and materials and, consequently, reduction of waste generation. This can translate into lower costs when the quantities of panels required for building work are high. In some cases, it may also have a specific aesthetic purpose. 2.4.1. Constructive methods The methods of building construction are the way how units and components are produced and assembled. The way of managing this process varies from region to region and is subjected to the size of the project, the level of technology, and the materials available. Thus, three different contemporary construction methods are distinguished, categorized by ascending technologic level and descending flexibility, as exhibited in Table 2-12. To understand the benefits and limitations of Prefabricated Enclosure Wall Panel Systems (PEWPS), for example, it is helpful to identify and analyze the different so-called Modern Methods of Construction (MMC) (also known as “system building methods”) that have fostered recently. Although the post-war boom of prefabricated construction in several countries has led to some partial perception that prefabricated buildings are unsightly or of lower quality, there
State of Art 46 is a restored and increasing interest in prefabricated building systems, as they mean savings in time and materials as well as higher standards of quality over more conventional methods of construction. Despite there are several innovative site-based modern methods of construction (such as stick-built timber/metal framing, in situ concrete tunnel-formwork, building blocks, etc.), the off-site MMC (also known as “Off-site manufacturing (OSM) methods”), i.e., prefabrication elements or parts of structures, constructed in the factory, then transported and assembled on-site have called the attention of the construction industry. Table 2-13 explains a unified classification of off-site MMC, where the spotlighted area defines the category of the constructional system focused on the present section. Table 2-12. Relationship between building construction methods, [92] Tradicional methods Post-traditional methods (on-site manufacturing) System building (off-site manufacturing) Decreasing flexibility and need for on-site skilled labor Increasing efficiency, accuracy, availability of materials and solutions Type of construction Small up to mid-scale dwellings guided by local style and traditional building trades and practice (e.g., carpentry, plastering, joinery). Small up to large-scale complex buildings with many individual architectural requirements. Small up to large-scale systematized buildings, based on principles such as prefabrication, pre-assembly, sub-assembly, etc. Materials, components, and availability Limited range of local traditional materials (e.g., traditional brick and stone masonry, wood, adobe, etc.). Vast range of both traditional and new materials and components (e.g., reinforced concrete, steel, blockwork, etc.) The increasing availability of new commercial systems, materials, and finishings (e.g., precast concrete frames, wall panels, etc.). Fabrication site The fabrication and assembly take place at the site (usually at the position where the completed structure is to be located). The amount of on-site fabrication has been reduced by the introduction of some prefabricated and standardized factory-produced components. Most of the building's components are factoryproduced and site assembled and are usually related to a specific building type. Equipment and labor Typically, only requires rudimentary equipment. Need for skilled craftsmanship, familiar with the operation in their trade Requires expensive machinery for many different operations. Still needs for labor-intensive operations (e.g., bricklaying and carpentry). May require lifting machinery. Specialized off-site manufacture and low-skilled labor on-site for fast assembly. Efficiency and flexibility Low efficiency and replicability. Maximum flexibility: each task can be tailored for each purpose. Need to organize the construction process efficiently during the design stage. Medium flexibility Efficient factory production of many similar building components. Relatively high inflexibility owing to the high level of accuracy required, making mistakes comprises the assembly process.
State of Art 47 Table 2-13. The unified classification system of offsite modern methods of construction, [92] 2.4.2. Classification of panels Table 2-14 illustrates a wide classification system for PEWPS following the different constructional and functional criteria. Even though there are innumerable commercial solutions available in the market, the following six most common PEWPS have been chosen for comparison purposes, ranked by decreasing order of weightiness: pre-cast concrete wall panels; structurally insulated panels (SIPs); self-supporting composite lightweight panels; curtain wall panels; light-frame wall panels, and rainscreen/cladding panels (ventilated façade). Level Category Subcategory Definition Examples Scheme Factory-made components (simpler elements) Door and window sets, furniture, etc. Sub-assemblies (major building elements) Pre-cast concrete assemblies (foundations, stairs, columns, beams, etc.), roof trusses, etc Wall cladding (nonloadbearing) Cladding panels Vertical panels (may be loadbearing) Enclosure walls and partitions Non-vertical panels (usually loadbearing) Structural floor and roof panels (cassettes) 3 Hybrid systems (or semi volumetric) Combination of volumetric and panelised methods of construction. The hybrid approach can be used to bring flexibility to the development and can also reduce uniformity of design. Highly serviced areas such as kitchens or bathrooms constructed as volumetric units, with the rest of the dwelling constructed with panelised systems Volumetric construction (“pods”) Pre-assembled smaller three dimensional units which create usable space and are usually fully factory finished internally and completed with plumbing and wiring, to be installed within, or onto an independent structural frame. Bathroom and kitchen pods Modular construction (whole building) Pre-assembled larger three dimensional units produced in a factory, fully fitted out before being transported to site and stacked onto prepared foundations to form the actual structure and fabric of the building. Outskirt units, hotels, prison blocks, medium rise residential, student accommodation. Increasing degree of prefabrication, size of prefabricated components and complexity of pre-assembly Non-volumetric systems (2D) Volumetric or modular systems 4 Decreasing degree of on-site construction labour, customization and flexibility Volumetric systems (3D) Components and sub assemblies These elements, although predominantly associated with traditional methods, are made in a factory to help improve the construction process on-site. These items are not full housing ‘systems’ and are usually factory made or, occasionally, site-assembled. 1 Panelised systems Two-dimensional units built in a factory and transported to site for assembly into a three-dimensional structure or to fit within an existing structure, creating or separating usable space. 2
State of Art 48 Table 2-14. Classification of common PEWPS according to functional and constructional criteria, [92] 2.4.2.1. Constructional criteria • Structural role Except for the structural role of any eventual pre-existent backing wall, from a constructional point of view, two fundamental types of PEWPS can be determined: i) Non-loadbearing wall panels do not strengthen the structure on which they are placed, nor support vertical loads other than their self-weight but can transfer lateral forces to the building structure. These panels are easier to demolish, dismantle or replace; Common PEWPS (organized by decreasing order of weightiness) Classification criteria Classification methods Classification results ● ● ● ● ○ ○ ● ● ● ● ● ● ○ ● ○ ● ● ● ● ● ● ● ○ ● ● ● ● ● ● ● ○ ● ● ○ ● ● ● ● ● ● ● ● ● ● ● ○ ● Construction in layers ● ● ● Multiple layers Layered (or composite) ○ ● Sandwich (or trilayer) ● ● ○ Cellular-core (or honeycomb-core) ○ ○ ○ Stud frame (or skeletal) ● ● ● ● ● ● With air cavity Stationary ○ ○ ○ Vented ○ Ventilated ● Pressure-moderated (or equalized) ● ○ Weathertightness Perfect barriers (barrier walls) Face-sealed ○ ○ ● ● ○ ○ Concealed barrier ○ Imperfect barriers Mass or storage systems ○ Screened and drained walls ● ● ○ ○ ● ○ ○ ● ○ ● ● ○ Light-frame wall panels Curtain wall panels Self-supporting composite lightweight panels Structurally insulated panels (SIPs) Pre-cast concrete wall panels Without air cavity None Yes, but not specific to the panel Yes, specific to the panel Rainscreen/cladding panels (ventilated façades) Panel-to-subframe assembly Cladding panels Single leaf Multiple leaves Single layer Stick-built wall panels Heavyweight Lightweight Panel-to-structure assembly Panel-to-panel assembly Non-loadbearing Loadbearing Infill walling panels Unitized wall panels Spandrel wall panels Ventilation Insulation layer/core Correspondence: ● usual (or binding) ○ possible (or optional) Structural role Size of the panels (and degree of prefabrication of the system) Weight Type of assembly Construction in leave Constructional Functional
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61 Chapter III: Alkali Activation of Recycled Ceramic Aggregates 3. ALKALI ACTIVATION OF RECYCLED CERAMIC AGGREGATES Alkali-activation of different types of industrial wastes has been extensively explored. However, scarce studies about ceramic wastes were found. Therefore, this part of the research focused on reusing the ceramic fraction from the CDW due to their availability and generation trend. The fundamental properties and the behavior in alkaline activated systems of this ceramic residue alone or in combination with other industrial wastes (fly ash or ladle furnace slag) were investigated. Materiales de Construcción Vol. 70, Issue 339, July-September 2020, e222 ISSN-L: 0465-2746 https://doi.org/10.3989/mc.2020.13619 Alkali activation of recycled ceramic aggregates from construction and demolition wastes N. Gaibor a , J. Coelho b, D. Leitão a, T. Miranda c, P. Tavares d, N. Cristelo e a. CTAC, Department of Civil Engineering, Azurém Campus, University of Minho, (Guimarães, Portugal) b. School of Engineering of the University of Minho, Azurém Campus, (Guimarães, Portugal) c. ISISE, Institute for Science and Innovation for Bio-Sustainability (IB-S), Department of Civil Engineering, University of Minho, (Guimarães, Portugal) d. CQ-VR, Centro de Química - Vila Real, Department of Chemistry, University of Trás-os-Montes e Alto Douro, (Vila Real, Portugal) e. CQ-VR, Centro de Química - Vila Real, Department of Engineering, University of Trás-os-Montes e Alto Douro, (Vila Real, Portugal) [email protected]
Alkali Activation of Recycled Ceramic Aggregates 62 Abstract Environmental concerns are becoming increasingly more significant worldwide, thus creating the urgent need for new sustainable alternatives in the industrial sector. The present study assesses the fundamental properties of ceramic residue (CR) originated by demolition operations, specifically, the floor and wall tiles and sanitaryware furniture, for further incorporation in the construction sector, namely in alkali-activated binders, mixed with other better-known precursors - fly ash (FA) and ladle furnace slag (LFS). Different CR/FA and CR/LFS weight ratios were considered and analyzed by mechanical behavior and microstructural analysis, which included uniaxial compression strength (UCS) tests, Scanning Electron Microscopy (SEM), X-ray Energy Dispersive Analyser (EDX), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Results obtained showed that the combination of CR and FA or LFS activated with sodium silicate, produced UCS values higher than 20 MPa and 59 MPa, respectively, after 90 days of curing. Keywords: Alkali activation; Ceramic; Physical properties; Mechanical properties; Waste treatment. Resumen Globalmente, las preocupaciones ambientales son cada vez más significativas, creando así la necesidad urgente de nuevas alternativas sostenibles en el sector industrial. El presente estudio evalúa las propiedades fundamentales de los residuos cerámicos (CR) provenientes de demolición, para ser reincorporados en el sector de la construcción, estos son, ligantes activados alcalinamente, mezclados con otros precursores más conocidos: cenizas volantes (FA) y escorias de horno de cuchara (LFS). Se consideraron diferentes relaciones de peso CR/FA y CR/LFS, se analizó el comportamiento mecánico y análisis microestructural, que incluye pruebas de resistencia a la compresión uniaxial (UCS), microscopía electrónica de barrido (SEM), análisis por energías dispersivas de rayos X (EDX), RayosX (XRD) y espectroscopía infrarroja por transformada de Fourier (FTIR). Los resultados obtenidos mostraron que, a 90 días de curado, la combinación de CR y FA o LFS activada con silicato de sodio produjo valores de UCS superiores a 20 MPa y 59 MPa, respectivamente. Palabras Clave: Cerámica; Cemento activado alcalinamente; Tratamiento de residuos; Propiedades mecánicas; Propiedades físicas.
Alkali Activation of Recycled Ceramic Aggregates 63 3.1. INTRODUCTION Worldwide environmental concerns are becoming increasingly more significant. The shortage of natural resources and the increasing levels of greenhouse gas emissions to the atmosphere frames a scenario that inevitably, forces mankind to create new sustainable alternatives for the industrial sector. The use of different kinds of industrial waste and residues as alternative materials in the construction industry can contribute in a very effective way to such sustainability. On the other hand, the generation of construction and demolition wastes (CDW) and, specifically, the generation of brick and ceramic waste fractions, is accelerating globally due to the increasing renovation and reconstruction of old buildings, which constitute about 45% of the total CDW [1]. In 2014, the total waste generated by all activities for the twenty-eight members of the European Union (EU-28), reached 2503 million tons (being the highest amount during the last 10 years reported). The generation of CDW increased by 57.2 % during the 2004-2014 period, thus showing an inversed trend, when compared with other sectors. For instance, the generation of manufacturing waste, in the same period, decreased by 32.2 %. The numbers confirm the relevance of reinforcing waste valorization in order to propose new management and treatment alternatives [2]. The ceramic industry is plentifully located in different parts of the world. China and Europe are the world leaders in ceramic production. It is also exported to other regions due to its durability and variety in design. In the European Union (EU), the ceramic industry represents approximately 25% of global production. The major producing countries in the EU are Italy, Germany, Spain, France, the United Kingdom, Portugal, and Austria [3]. Except for the ceramic industry's vast economic benefits, it causes adverse environmental impacts. Ceramic industries produce around one-third of the total ceramic production which is disposed of without any further treatment. This solid waste leads to severe environmental pollution and significant land location [4]. The search for sustainable solutions that take advantage to waste materials from the ceramic industry is currently a crucial challenge for this sector. The construction industry shows an increasing demand for new, bold, sustainable structural and nonstructural materials. Ceramic products represent a significant part of the construction industry and, therefore, the requirements in terms of raw materials are also raising. Natural resources are facing a decrease with time due to uncontrolled uses. It is worth noting that progress in the incorporation of
Alkali Activation of Recycled Ceramic Aggregates 64 alternative materials might be a useful way to diminish the use of natural resources by recycling the ceramic residue coming out from CDW [5]. However, recycling and using such wastes for newer construction purposes is not a fresh concept; it has been practiced since the Roman Empire when people reused stones obtained from former roads in the construction of new ones [6]. Still, the construction industry represents a very significant possibility to apply, using direct or indirect strategies, significant percentages of several types of by-products and/or wastes. Some common examples are fly ash, CDW, or blast furnace slags, which have been used as a cement or aggregate replacement, embankment fill, and road and railway pavement foundation, among others. It is thought that there is room for the further use of increased volumes of these residues and, also, to introduce of new types of industrial by-products in the production chain [7]. Some studies related to waste incorporation in civil construction are showing up next and along with the present document. Ceramic residues are hard, durable, extremely resistant to chemical, physical, and biological degradations, and highly thermally stable [4]. Ceramic producers and the construction sector are looking for valuable waste disposal ways due to an increase in the pile-up of them. There is important research work in the development of sustainable alkali-activated building materials using ceramic wastes, such as bricks manufacturing [8], [9], hybrid binder based on ceramic tile wastes [10], ceramic materials from ecofriendly geopolymer precursors [11], ceramic roof tiles [12], among others. As it can be evidenced, for the synthesis of geo-polymers, ceramics waste as an efficient alternative has been employed [13], Huseien et al. [14] stated the geopolymer industries can use the ceramic wastes safely without requiring any remarkable change in the production and application process. The author studied the performance of waste ceramic powder (WCP), at different content of 50%,60%, and 70%, as a binder on the mechanical and microstructure properties of alkali-activated mortars (AAms), mixed with ground blast furnace slag (GBFS) and fly ash (FA). The specimens were left for 24 hours at ambient temperature (27 ±1.5) °C and relative humidity of 75%, then tested at ages of 1, 3, 7, 28, 56, 90, 180, and 360 days. Results showed a compressive strength higher than 70 MPa at age of 28 days. While Hwang et al. [1] used waste red clay brick powder (WBP) and waste ceramic powder (WCP) as source materials to develop an alkali-activated paste. The ceramic waste was 60% of the total weight of the precursors, and the remaining 40% contained fly ash (FA) and ground granulated blast furnace slag (GGBFS). The alkali-activator solutions were Na2SiO3 and NaOH. Samples were cured at ambient temperature for 3, 7, 28, and 56 days. The alkali-activated paste with WBP presented higher compressive strength (36–70 MPa). It was due to the finer particle size and higher CaO content
Alkali Activation of Recycled Ceramic Aggregates 71 Fourier Transform Infrared Spectroscopy (FTIR). SEM analyses were developed on an FEI Quanta 400 scanning electron microscope, at 30 kV, in low vacuum mode, with partial pressure inside the chamber (1.3 mbar), avoiding the deposition of a conductive layer. An EDS analyzer, from EDAX, allowed a chemical analysis of the elements present in each sample, using the same spectrum acquisition time and a ZAF correction model. The FTIR spectra were acquired using a Thermo Scientific Nicolet iS50 FTIR spectrometer, resorting to an ATR (Attenuated Total Reflectance) accessory with a diamond crystal. The instrument was controlled by the Omnic software package, version 9.2.28, from Thermo Fisher Scientific Inc. A spectrum range of 4000 to 400 cm-1 was defined, with a resolution of 4 cm-1 and 64 scans by 90 seconds for each sample. 3.3. RESULTS AND DISCUSSION 3.3.1. Compressive strength The uniaxial compressive strength (UCS) results are presented in Figure 3-4, showing the data for the pastes prepared with CR and FA, and Figure 3-5, showing the data for the pastes with CR and LFS. the effectiveness of the CR, pastes with an increasing amount of FA and LFS (up to, and including, a 100% content for each case) are also presented, so that a threshold could be established, and direct comparison could easily be made. Curing periods of 1, 14, 28, and 90 days are presented, yet it is important to remember, at this stage, that the 1-day curing specimens were exclusively cured at 70ºC, while the remaining specimens were cured for 1 day, at 70ºC, while the remaining curing was developed at ambient temperature (20 - 23ºC). In general, curing time increased the UCS, regardless of the type of precursor (CR+FA or CR+LFS) or activator (SH or SS). Also evident are the higher strength values obtained with the SS-based pastes, comparatively to the SH-based specimens, irrespective of whether the precursor combination. Finally, the third and most relevant observation is the higher UCS achieved by the CR+LFS precursor combination, when compared with the CR+FA blend. For the CR+FA combination, activated with SH, the most effective solution was the 50% CR and 50% FA. When SS was used, the proportion of 75% CR and 25% FA achieved the highest UCS value after 90 days. However, it is significant, considering that the purpose of the present study is the disposal of the ceramic residue, that the 100% CR paste (which represents the highest possible volume of CR
Alkali Activation of Recycled Ceramic Aggregates 72 incorporated) showed the highest UCS for the CR+FA combination after 1, 14 and 28 days, and showed only a marginally lower UCS after 90 days. This suggests that the use of FA is not absolutely required, which would represent a significant gain in terms of economic and logistical efforts. Regarding the CR+LFS combination, the scenario was slightly different for the SH-based pastes, with the 75% CR + 25% LFS representing the higher UCS. Another significant difference was the extent of such strength increase, at the 90-day mark: the addition of 50% FA produced a UCS improvement of 1.9x, relatively to the 100% CR, while the addition of 25% LFS produced a UCS improvement of 4.6x, relatively to the same 100% CR paste. For the SS-based pastes, the CR+LFS scenario was similar to the one described for the CR+FA pastes, i.e., the addition of 25% of the alternative precursor represented the most performing combination for both cases. However, the 75%CR + 25%LFS paste now showed higher UCS values for all curing periods, and not just for 90 days. Not only that, but the difference, at the 90-day mark, between the 100%CR and the 75%CR + 25%LFS was clearly more significant (3.15x) than the difference between the 100%CR and the 75%CR + 25%FA (1.1x). Figure 3-4. UCS of the CR+FA pastes, prepared with SH (M1) or SS (M2), after 1, 14, 28, and 90 days of curing 100CR 75CR25FA 50CR50FA 25CR75FA 100FA 0 5 10 15 20 25 Compressive Strength (MPa) 1d 14d 28d 90d (M1) SH-based pastes 100CR 75CR25FA 50CR50FA 25CR75FA 100FA 0 5 10 15 20 25 (M2) SS-based pastes Compressive Strength (MPa) 1d 14d 28d 90d
Alkali Activation of Recycled Ceramic Aggregates 73 Figure 3-5. UCS of the CR+LFS pastes, prepared with SH (M3) or SS (M4), after 1, 14, 28, and 90 days of curing 3.3.2. Mineralogical and microstructural characterization The pastes with the highest strength values from each set (M1, M2, M3, and M4), corresponding in most cases to the composition 75% CR + 25% (FA or LFS), were selected for microstructural analyses, using XRD, SEM/EDS, and FTIR to characterize the cementitious materials developed during their respective reactions throughout the initial 90 days of curing. Figure 3-6 shows the XRD diffractograms of the different pastes, 75CR+25FA (SH or SS) (M1 and M2) and 75CR+25LFS (SH or SS) (M3 and M4). The products resulting from the activation reaction present similar peaks which were also found in the initial materials, suggesting that the equivalent phases are essentially inert to the alkaline activation process. In cases where a slight reduction of their intensity is detected, it is due to the material dilution (induced by the blend with the activator). The presence of mullite in M1 (25.1 ± 1.5) and M2 (23.2 ± 1.5) is somewhat higher in comparison to the other two mixtures (see Table 3-4), fundamentally influenced by the outset constituents, CR and FA with significant Si content (Table 3-1). Crystalline phases of Mu in the pastes were also displaced in range, from 28 – 30°(2θ) to 30 to 35°(2θ) in contrast to CR and FA XDR diffractograms (Figure 3-3). These 100CR 75CR25LFS 50CR50LFS 25CR75LFS 100LFS 0 10 20 30 40 50 60 70 Compressive Strength (MPa) (M3) SH-based pastes 1d 14d 28d 90d 100CR 75CR25LFS 50CR50LFS 25CR75LFS 100LFS 0 10 20 30 40 50 60 70 (M4) SH-based pastes Compressive Strength (MPa) 1d 14d 28d 90d
Alkali Activation of Recycled Ceramic Aggregates 74 variations are a consequence of the formation of amorphous phases in the aluminosilicate gel, which will partially crystalize, in time (zeolitic precursor) [22]–[24]. The anorthite (A) was identified in the four mixtures since the CR is the major component. However, higher A content was evidenced in M3 (16.5 ± 1.1) and M4 (15.0 ± 1.1) (Table 3-4) as a result of having a precursor (LFS) with high Ca content. In all blends, the main peak was registered at approximately 26º (2q), corresponding to quartz, which makes it the most relevant crystalline phase. It is also worth mentioning that for neither case the Na2CO3.H2O (thermonatrite) phase was found, denoting that the Na was retained in the gel, thus not migrating to the surface. Figure 3-6. XRD patterns of the 75CR-25FA/SH or SS mixtures (M1 and M2) and 75CR-25LFS/SH or SS mixtures (M3 and M4), after 90 days of curing time (O: Oligoclase; Q: Quartz; Mu: Mullite; A: Anorthite; Co: Calcio Olivina; Ca: Calcite; S: Sillimanite). 10 20 30 40 50 60 70 80 Mu Q Q Q Q S, Ca A, Co CoCo, Q Q O, A O AO, Mu Mu Mu Mu Q Mu Mu Mu Mu Q Q Q Q Q Q Q Q M4 M3 M2 2q M1 O, A O AO, Mu Mu Mu Mu Q Mu Mu Mu Q Q Q Q Q Q Q Q Q A A Co Mu Mu Mu Mu Co Mu Mu Mu Q Q Q Q Q Q AQ A, Co CoCo, Q A S AMu Mu Mu Mu Co Mu Mu, Mu Q Q Q Q Q Q Q S Q
Alkali Activation of Recycled Ceramic Aggregates 75 Table 3-4. Minerals quantification of the 75CR-25FA/SH or SS mixtures (M1 and M2) and 75CR25LFS/SH or SS mixtures (M3 and M4), after 90 days of curing time (% wt) Material O Q Mu A Co Ca S Rwp (%) M1 9.1 ± 0.9 55.9 ± 2.0 25.1 ± 1.5 9.9 ± 0.9 - - - 8.4 M2 13.8 ± 1.1 53.4 ± 2.0 23.2 ± 1.5 9.7 ± 0.9 - - - 8.4 M3 - 46.9 ±2.0 21.6 ± 1.5 16.5 ± 1.1 13.8 ± 1.1 1.2 ± 0.1 10.0 M4 - 48.6 ± 2.0 19.2 ± 1.5 15.0 ± 1.1 10.8 ± 1.0 2.3 ± 0.2 4.1 ± 0.4 9.9 O: Oligoclase; Q: Quartz; Mu: Mullite; A: Anorthite; Co: Calcio Olivina; Ca: Calcite; S: Sillimanite The same four pastes, cured at ambient temperature for 90 days, were analyzed with SEM. The chemical composition was also obtained, with 10 points per image. Figure 3-7 shows SEM images of selected samples, enabling an understanding of the morphology and general distribution of the different constituents in the mixtures. Based on all the images exhibited, it can be said that the resulting paste is generally compacted, homogeneous, and with low porosity. In M1(75CR-25FA/SH) is possible to observe several FA (points A) or CR (points C) unreacted particles covered with reaction products. However, in M2 (75CR-25FA/SS), even after 90 days, an unreacted particle without any signs of Na ‘attack’, can still be detected (points A). It was also observed a slightly higher Ca content in the M2 paste, compared with the M1, which might result from a higher dissolution degree. Regarding the type of gel developed, an N-A-S-H type was detected (point *) when using FA as a complementary precursor, regardless of the activator solution used (SH or SS). A similar situation can be seen for the 75CR-25FA/SH (M3) and 75CR-25LFS/SH (M4) pastes. Some small LFS (points B) and CR (points C) unreacted particles are distinguished. The most significant aspect of M4 was the Ca content varies throughout the sample, which can be due to the incidence of particles with an important presence of Ca. Concerning the type of gel developed, and when LFS in combination with CR was used, its calcium content naturally affected the composition of the gel, which can be classified as an N, C-A-S-H, if SH acted as an activator (M3), or C-A-S-H (points *) [25], [26], when the precursors were instead activated with SS (M4), Figure 3-7. The general chemical composition of the four studied mixtures is summarized in Table 3-5, where is presented the average value of the analyzed points and their standard deviation (SD).
Alkali Activation of Recycled Ceramic Aggregates 76 Figure 3-7. SEM images of 75CR-25FA/SH or SS mixtures (M1 and M2) and 75CR-25LFS/SH or SS mixtures (M3 and M4) mixtures, after 90 days of curing time. Table 3-5. Chemical composition of mixtures at 90 days curing time, %Wt, (SD in parentheses) M1 75CR-25FA/SH M2 75CR25FA/SS M3 75CR-25LFS/SH M4 75CR-25LFS/SS Na2O 6.66 (1.93) 15.06 (3.47) 10.49 (1.04) 5.24 (1.77) MgO 0.84 (0.26) 1.47 (0.82) 1.79 (0.91) 1.80 (1.61) Al2O3 19.53 (5.44) 14.58 (1.33) 16.65 (4.43) 12.26 (4.86) SiO2 63.35 (3.59) 57.92 (5.34) 52.12 (3.12) 59.09 (11.30) SO3 - - 2.22 (1.47) 2.55 (3.32) K2O 5.81(1.24) 2.61 (0.61) 2.44 (0.26) 2.03 (1.03) CaO 1.84 (1.03) 2.70 (0.59) 11.44 (3.07) 15.52 (11.73) TiO2 0.52 (0.32) 0.84 (0.33) 0.66 (0.23) 0.57 (0.29) MnO - - - 0.11 (0.26) Fe2O3 1.46 (0.50) 4.82 (4.67) 2.21 (2.15) 0.83 (0.42) CaO/SiO2 0.01 (0.00) 0.02 (0.01) 0.22 (0.06) 0.27 (0.36) NaO/Al2O3 0.36 (0.14) 1.05 (0.28) 0.67 (0.18) 0.48 (0.27) SiO2/Al2O3 3.44 (0.84) 3.97 (0.18) 3.31 (0.82) 5.41 (2.03) SiO2/Na2O 10.24 (2.86) 4.06 (1.18) 5.01 (0.59) 12.62 (4.74)
Alkali Activation of Recycled Ceramic Aggregates 77 Figure 3-8, shows the FTIR spectra for the starting materials (LFS, CR, and FA) as well as the M1 (75CR25FA), M2 (75CR25FA), M3 (75CR25FA), and M4 (75CR25FA) pastes activated with SH or SS, after 90 days of curing, which present a set of bands centered in the frequency range between [400 - 2000] cm-1. Different behavior in the spectra of each of the materials is observed, for LFS two main bands are detected at 840 cm-1 and 1040 cm-1, which are generally associated with deformation vibration of carbonates (CO32-), C-O, while the 560 cm-1 band is linked with the Al-O-Al bond and 490 cm-1 and 440 cm-1 are associated with O-Si-O connections. The fly ash (FA) evidences a wide main band at 1015 cm-1, this is associated with Si-O-Si or Si-O-Al bonds, while the 790 cm-1 and 420 cm-1 bands are related to Si-O bonds (quartz). In addition, the presence of another band that records at 550 cm-1 is associated with the octahedral aluminum (Al-O-Al bonds) of the mullite [27], previously distinguished in this material by XRD, (see Figure 3-3). The CR sample shows a deep and wide main band that appears around 1040 cm-1. This is typical of asymmetric tension vibration, related to Si-OSi or Si-O-Al, confirming some crystallinity of the material. The bands at 795 cm-1, 775 cm-1, and 420 cm-1 correspond to O-Si-O bonds (quartz). The FTIR spectra of the four different mixtures are also presented in Figure 3-8, where basically the characteristic vibration bands of the main components of the starting materials are shown. At the end of the 90 days of curing, the most significant change was the displacement of the main CR band (1040 cm-1), for shorter wavelengths, which is attributed to a structural reorganization caused by the formation of reaction products [28]. But, in mixtures of the studied proportions of M1 and M2, the displacement was between 995 cm-1 and 1010 cm-1, which is related to the formation of the typical NA-S-H gel, while M3 and M4 shifted around 960 cm-1, this translation is connected to the presence of LFS in the composition, promoting the formation of N, C-A-S-H type gel.
Alkali Activation of Recycled Ceramic Aggregates 78 Figure 3-8. FTIR spectra of starting materials, the ladle furnace slag (LFS); ceramic residue (MCR) – milled for 32 hours; fly ash (FA), and 75CR-25FA/SH or SS mixtures (M1 and M2) and 75CR25LFS/SH or SS mixtures (M3 and M4), after 90 days curing time. 3.4. CONCLUSIONS The fundamental properties of the ceramic residue from an operator with a Portuguese license and their performance in combination with fly ash (FA) or ladle furnace slag (LFS) as precursors of alkali activation were studied and tested four different mixture compositions, in accordance with the main aim of this study. The following are the main conclusions obtained: 1. Different CR/FA (M1 and M2) and CR/LFS (M3 and M4) ratios were prepared and tested for the purpose. The UCS test was performed for each specimen after 1, 14, 28, and 90 days to determine the efficiency of the blends. The highest compressive strength (59.95 MPa) was reached by the combination of 75CR-25 LFS/SS at 90 days of curing. It can be stated that this resulting material is stiffer compared to the CR-FA/SH or SS mixture, where the highest strength in the same conditions was 20.26 MPa; 2000 1800 1600 1400 1200 1000 800 600 400 LFS FA CR 550 995 1010 960 960 420 440 690 790 1040 1015 440 490 560 840 wavenumber (cm-1) 1400 775795 M1 M2 M3 M4
Alkali Activation of Recycled Ceramic Aggregates 79 2. M1-M2 and M3-M4 mixtures are calcium-poor or calcium-rich aluminosilicates, respectively, which are basically determined by the starting materials. Higher calcium content positively affects the strength of the mixture. As was evidenced throughout the UCS results; 3. The combination of the CR+FA precursors, regardless of the alkaline solution (SH or SS), enabled the formation of a cementitious gel-type, namely, N-A-S-H. On the other hand, NC-A-S-H or C-A-SH gels are identified, when CR+LFS is activated whether SH or SS, respectively. ACKNOWLEDGMENTS This work was supported by Portuguese funding through the Foundation for Science and Technology – FCT/MCTES (PIDDAC), within the framework of the R&D Project “JUSTREST – Development of Alkali Binders for Geotechnical Applications Made Exclusively from Industrial Waste”, reference PTDC/ECMGEO/0637/2014. The author would also like to acknowledge the support of the Secretary of Higher Education, Science, Technology, and Innovation, SENESCYT (Spanish acronym) from Ecuador, reference No. CZ03000052-2017. REFERENCES [1] C.-L. Hwang, M. Damtie Yehualaw, D.-H. Vo, and T.-P. Huynh, “Development of high-strength alkali-activated pastes containing high volumes of waste brick and ceramic powders,” Constr. Build. Mater. , vol. 218, pp. 519–529, Sep. 2019. [2] Eurostat, “Waste statistics - Statistics Explained,” 2018. [Online]. Available: http://ec.europa.eu/eurostat/statistics-explained/index.php/Waste_statistics. [Accessed: 03-May2018]. [3] Cerame-Unie, “Ceramic industry | Cerame-Unie - The European Ceramic Industry Association.” [Online]. Available: http://cerameunie.eu/ceramic-industry/. [Accessed: 08-May-2018]. [4] M. S. Khan, M. Sohail, N. S. Khattak, and M. Sayed, “Industrial ceramic waste in Pakistan, valuable material for possible applications,” J. Clean. Prod. , vol. 139, pp. 1520–1528, Dec. 2016. [5] H.-J. Chen, T. Yen, and K.-H. Chen, “Use of building rubbles as recycled aggregates,” Cem. Concr. Res. , vol. 33, no. 1, pp. 125–132, Jan. 2003. [6] A. Jindal and G. D. Ransinchung R.N., “Behavioural study of pavement quality concrete containing construction, industrial and agricultural wastes,” Int. J. Pavement Res. Technol. , Apr. 2018.
Alkali Activation of Recycled Ceramic Aggregates 80 [7] N. Cristelo, A. Fernández-Jiménez, T. Miranda, and Á. Palomo, “Sustainable alkali activated materials: Precursor and activator derived from industrial wastes,” J. Clean. Prod. , vol. 162, pp. 1200–1209, 2017. [8] H. R. Gavali, A. Bras, P. Faria, and R. V. Ralegaonkar, “Development of sustainable alkaliactivated bricks using industrial wastes,” Constr. Build. Mater. , vol. 215, pp. 180–191, Aug. 2019. [9] S. K. Amin, S. A. El-Sherbiny, A. A. M. A. El-Magd, A. Belal, and M. F. Abadir, “Fabrication of geopolymer bricks using ceramic dust waste,” Constr. Build. Mater. , vol. 157, pp. 610–620, Dec. 2017. [10] L. M. Murillo, S. Delvasto, and M. Gordillo, “A study of a hybrid binder based on alkali-activated ceramic tile wastes and portland cement,” in Sustainable and Nonconventional Construction Materials using Inorganic Bonded Fiber Composites , Elsevier Inc., 2017, pp. 291–311. [11] M. A. Villaquirán-Caicedo and R. M. de Gutiérrez, “Synthesis of ceramic materials from ecofriendly geopolymer precursors,” Mater. Lett. , vol. 230, pp. 300–304, Nov. 2018. [12] A. R. G. Azevedo, C. M. F. Vieira, W. M. Ferreira, K. C. P. Faria, L. G. Pedroti, and B. C. Mendes, “Potential use of ceramic waste as precursor in the geopolymerization reaction for the production of ceramic roof tiles,” J. Build. Eng. , vol. 29, May 2020. [13] Z. Sun et al. , “Synthesis and thermal behavior of geopolymer-type material from waste ceramic,” Constr. Build. Mater. , vol. 49, pp. 281–287, Dec. 2013. [14] G. F. Huseien, A. R. M. Sam, K. W. Shah, M. A. Asaad, M. M. Tahir, and J. Mirza, “Properties of ceramic tile waste based alkali-activated mortars incorporating GBFS and fly ash,” Constr. Build. Mater. , vol. 214, pp. 355–368, Jul. 2019. [15] L. Reig, M. A. Sanz, M. V. Borrachero, J. Monzó, L. Soriano, and J. Payá, “Compressive strength and microstructure of alkali-activated mortars with high ceramic waste content,” Ceram. Int. , vol. 43, no. 16, pp. 13622–13634, Nov. 2017. [16] N. R. Rakhimova and R. Z. Rakhimov, “Alkali-activated cements and mortars based on blast furnace slag and red clay brick waste,” Mater. Des. , vol. 85, pp. 324–331, Nov. 2015. [17] G. F. Huseien, A. R. M. Sam, K. W. Shah, J. Mirza, and M. M. Tahir, “Evaluation of alkaliactivated mortars containing high volume waste ceramic powder and fly ash replacing GBFS,” Constr. Build. Mater. , vol. 210, pp. 78–92, Jun. 2019. [18] G. F. Huseien et al. , “Waste ceramic powder incorporated alkali activated mortars exposed to elevated Temperatures: Performance evaluation,” Constr. Build. Mater. , vol. 187, pp. 307–317, Oct. 2018. [19] N. Cristelo, P. Tavares, E. Lucas, T. Miranda, and D. Oliveira, “Quantitative and qualitative assessment of the amorphous phase of a Class F fly ash dissolved during alkali activation reactions – Effect of mechanical activation, solution concentration and temperature,” Compos. Part B Eng. , vol. 103, pp. 1–14, Oct. 2016. [20] CCP14, “CCP14 Homepage - Tutorials and Examples - Powder Cell for Windows, Structure Visualisation/Manipulation, Powder Pattern Calculation and Profile Fitting by Werner Kraus and Gert Nolze.” [Online]. Available: http://www.ccp14.ac.uk/tutorial/powdcell/. [Accessed: 17-Jan-2020].
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 87 fibers, i.e. tows or monofilament; ii) discontinuous fibers, i.e. short fibers with a diameter of 3–5 μm; iii) whiskers, with diameter less than 1 μm or high aspect ratio; iv) particulates [27]. In general, several works have been conducted on studying the fiber reinforcement of alkali-activated materials with different fibers such as polypropylene [28], [29], [30], Polyvinyl alcohol (PVA) [31], basalt [32], carbon [32], among others. More related to CW use, the feasibility of using fiber-reinforced alkaliactivated blast furnace slag and ceramic binders was assessed by Abdollahnejad et al. [25]. Besides, one-part alkali-activated slag/fly ash binders containing ceramic aggregates to be reinforced with different fiber types (PVA, PP, basalt) and combinations (single and hybrid) [33] were also studied by this author. However, specifically regarding the use of ceramic wastes and polyacrylonitrile fiber reinforcement in alkali-activated materials systems, no information was found, which justifies the originality of this research. This study addresses the feasibility of developing an enhanced-strength ceramic-based mortar reinforced with polyacrylonitrile fibers (PAN) within the scope of novel composite mortars based on alkaline activation. Moreover, it aims to characterize ceramic waste’s (CW) fundamental properties and assess its potential in the development of Aam. For this purpose, a CW from a company that produces clay bricks and roof tiles was used as the primary precursor in combination with ladle furnace slag (LFS) as a complementary starting material in the presence of sodium silicate (SS). Furthermore, the influence of different fiber dosages, i.e., 0.5% and 1%, and the curing age (14, 28, and 90 days) on the main mechanical and physical properties were also assessed. Additionally, it was performed a microstructural analysis, including Scanning Electron Microscopy (SEM), X-ray Energy Dispersive Analysis (EDX), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). 4.2. MATERIALS AND METHODS 4.2.1. Materials The materials used in this study as precursors were ceramic waste (CW) rich in both silicon dioxide (54.9%) and aluminum oxide (26.3%), and ladle furnace slag (LFS) that is a calcium-rich aluminosilicate (64.2%), see Table 4-1. Sodium silicate (Na2SiO3) was used as an alkaline activator in the solution form. The CW was provided by a brick manufacturing company located near Braga, in the northwestern region of Portugal. The LFS from melting scrap in an electric arc furnace was supplied
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 88 by the Portuguese ironwork company Megasa , located in Maia. For the mortar’s reinforcement, discrete PAN fibers with an 8 mm length and an approximate diameter of 20 µm were used. The latter was adopted due to its availability and chemical (good in alkaline medium) and thermal resistance (good in short-term processing temperature up to 220°C), as can be corroborated in the corresponding technical sheet [34]. Table 4-1. Chemical composition of the ceramic waste (CW), and ladle furnace slag (LFS), % wt Precursor Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl2O K2O CaO TiO2 Cr2O3 MnO Fe2O3 ZnO CW 0.13 1.30 26.28 54.89 0.42 0.59 0.12 3.97 0.64 1.40 0.30 0.86 9.10 - LFS 0.31 3.54 4.86 19.68 - 4.69 - - 64.23 0.31 - 0.35 1.39 0.64 The CW (i.e., before and after grinding) and the LFS are presented in Figure 4-1. It can be observed that about 80% of the CW particles had a diameter within the 2 – 18 cm range. It is known that for alkali activation purposes, the particle size of precursors is important since the coarser particles are less involved in the geopolymerization process [35]. Therefore, CW was ground in a ball mill, using 12 steel balls of 0.41 kg each for 0.33 h at 50.50 rpm. The original LFS (i.e., as received in the laboratory) was sieved in a nominal mesh opening of 250 µm, and only the passing fraction was used. The particle size distribution (PSD) of both precursors (CW and LFS) was determined in two stages. For the coarse particles (granulometry above 63 µm, i.e., sieve no. 200) standardized ASTM sieves were used, arranged in a column with ½ phi intervals, according to the modified Wentworth scale and agitation intervals of 5 minutes. As for the finer particle sizes (i.e., < 63µm), the PSD was determined by X-ray on a Sedigraph analyzer to measure particles up to 0.15μm. Figure 4-2 shows the PSD curves of the final materials, where it can be seen that the milling of the CW produced a well-graded material, with a fine fraction of about 38%.
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 89 (a) (b) (c) (d) Figure 4-1. Precursors used in the mixture: (a) ceramic waste (CW) before grinding; (b) CW after gridding; (c) ladle furnace slag (LFS) before sieving; and (d) after sieving Figure 4-2. Particle size distribution (PSD) of precursors (ceramic waste (CW) after gridding and ladle furnace slag (LFS) after sieving) 0 20 40 60 80 100 0,001 0,010 0,100 Percentage passing (%) Particle size (mm) LFS CW
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 90 4.2.2. Alkali activated mortar compositions In a previous work [36], CW from CDW was studied in different CW/LFS ratios, namely, 75:25, 50:50, and 25:75, in weight (wt%), in which were alkali-activated either with sodium hydroxide (SH) or sodium silicate (SS). In total, ten different mix compositions were prepared and reviewed, including the reference samples (100 wt% for CW and LFS). Based on the results from this latter work, the composition 75 CW + 25 LFS, activated with SS, was used as the reference paste since it reached the highest compressive strength values. However, for the present study, the proportions of the precursors and activating solution were slightly modified, i.e., CW + LFS/SS equal to 0.72:0.28/ 0.48 for each formulation. Additionally, in the attempt to obtain better workability of the mortar, polycarboxylatebased superplasticizer (SP) [37] was also added (2% in wt) to the precursors, thus facilitating the incorporation of the fibers and their subsequent dispersion. This adjustment was necessary because the origin and type of the present waste are different from the waste used in the mentioned previous study [36]. Based on the results of preliminary tests related to the improvement workability of the developed mortars, as well as available literature (e.g., [30], [38]) where a fiber content in the range of 0.2%-2% for geopolymers is suggested, it was determined to use 0.5% and 1% fibers´ content. Table 4-2 shows the compositions of the alkali-activated mortars developed in the present work. Table 4-2. Composition of the alkali-activated mortars Paste ID Precursor (wt. ratio) Activator/ Precursor (wt. ratio) SP/ precursor (wt. ratio) PAN fiber (vol. fraction) CaO / SiO2 Na2O / Al2O3 SiO2 / Al2O3 SiO2 / Na2O CW LFS SS M1 72 28 0.48 0.02 0 0.32 0.32 2.84 8.96 M2 0.5 M3 1 Preparation of the blends occurred as follows; in the batching process, the CW, LFS, SS, and the SP were added to the mixer bucket, in this order, and mixed for 1-minute. The mixture procedure was executed in an industrial mixer at the minimum speed (i.e., 140 ±5 rpm). Subsequently, PAN fibers were incorporated and stirred again for 2 min to guarantee a homogeneous distribution. Promptly, after the mixing process (3 minutes total), the homogenized mortar was poured inside of stainlesssteel prisms molds and mechanically compacted for 1 minute on a shaking table. The flow properties of the fresh mortar were characterized by the slump-flow test [39]. During this test, for the three studied blends, the initial diameter was 100 mm, and after 15 strokes, the spread of the diameter
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 91 passed to 150 mm, 135mm, and 125mm, for mortars with 0%, 0.5%, and 1% of fiber content (C f ), respectively. There was no significant evidence of segregation. It can be ascribed to applying an adequate precursor/activator ratio, beyond using the superplasticizer, which originally acts as a microrollers and significantly reduces the paste's friction and flow resistance [40]. However, the influence of the superplasticizer in the mixture was not very significant since there are several compatibility issues as reported in the literature [41]. Afterward, the curing was performed in two phases; first, the mortar was subjected to a curing temperature of 70°C during the early 24 hours, then the specimens were demoulded and cured at ambient temperature (20-23 ºC) and humidity of around 60% HR ± 5% for the remaining of the 14-, 28-, and 90-days period. For each studied series with different fiber content (unreinforced – 0, 0.5, and 1%) and curing time (14, 28, and 90 days), five prismatic specimens were prepared to be conducted the compression test, and four specimens for each of the physical and other mechanical tests. 4.3. FABRICATION AND TESTING OF THE SPECIMENS 4.3.1. Mechanical properties After the corresponding curing period and before mechanical testing, each specimen was rectified, weighed, and each edge of the cubes was measured for further calculations. The main mechanical properties of the M1, M2, and M3 series were assessed through experimental tests. The Young’s modulus ( Ecm ) was determined according to the EN 12390-13 standard [42], and a customized procedure obtained the compressive stress-strain relationship and the uniaxial compressive strength (UCS) based on the adaptation of recommendations from [43]. Five specimens with a dimension of 50×50×100 mm3 were used for the abovementioned tests. The tests were performed on a servohydraulic testing rig with a load actuator of 300 kN. Tests were carried out under closed-loop displacement control at a rate of 0.002 mm/min. Figure 4-3 shows the adopted test set-up for obtaining the elasticity modulus and the compressive stress-strain relationships.
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 92 (a) (b) Figure 4-3. Test set-up for (a) the elasticity modulus; (b) the uniaxial compressive stress-strain The tensile behavior under flexure was assessed through three-point bending tests. The test set-up was adapted from the recommendations of the standards BS EN 1015-11:1999 [44] and EN 14651:2005 [45], respectively, for plain mortars and fiber-reinforced concretes. Each series comprised four notched prismatic specimens of 40х40 mm2 cross-section and 160 mm length with a span of 100 mm. An electromechanical universal testing rig, LLOYD LR50K, fitted with a 50 kN load cell, was used. The tests were performed under displacement control with a rate of 0.002 mm/min. 4.3.2. Physical properties The physical properties were obtained from the fractured halves of the flexural specimens (i.e., 40х40х80 mm3) after 28 days of curing; four specimens were used per test and series. The open porosity (P), which translates the absorption of water by immersion under vacuum, as well as the water absorption (C) due to capillary action, were determined according to the procedures prescribed by the standards LNEC E 395 [46] and BS EN1015-18:2002 [47], respectively. 4.3.3. Microstructural and chemical analysis The microstructural analysis was performed on both the original materials’ precursors and some selected samples of the developed alkali-activated mortars (i.e., mix M2, at 14-, 28-, and 90-days
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 93 curing). The Scanning Electron Microscopy (SEM) analyses were carried out on an FEI Quanta 400 scanning electron microscope, at 30 kV, in low vacuum mode, with partial pressure inside the chamber (1.3 mbar), avoiding the deposition of a conductive layer. An EDS analyzer from EDAX allowed a chemical analysis of the elements present in each sample, using the same spectrum acquisition time and a ZAF correction model. The XRD was assessed on a PANalytical X’Pert Pro diffractometer, fitted with an X'Celerator detector and a secondary monochromator, using CuK radiation at 40 kV and 30 mA. The scans were acquired with Bragg-Brentano geometry, covering a 2q range between 7 and 85º, with a nominal step size of 0.017 and 100 s/step. In the case of the CW, LFS, and resulting pastes, phase quantification was performed on diffraction patterns applying Rietveld [48], with the code Highscore Plus 4.8. Table 4-5 presents the values in weight percentage. The amorphous phase was simulated through the Le Bail model [49]. Volume percentages were converted into weight percentages using the respective density. Finally, the FTIR spectra were acquired using a Thermo Scientific Nicolet iS50 FTIR spectrometer, resorting to an ATR (Attenuated Total Reflectance) accessory with a diamond crystal. The instrument was controlled by the Omnic software package, version 9.2.28, from Thermo Fisher Scientific Inc. A spectrum range of 400 to 4000 cm-1 was defined, with 4 cm-1 and 64 scan resolution during 90 seconds for each sample. The material was previously milled with the aid of a laboratory mortar and pestle for 20 min. 4.4. RESULTS AND DISCUSSION 4.4.1. Mechanical behavior 4.4.1.1. Compressive behavior Table 4-3 presents the average uniaxial compressive strength (UCS) and the coefficient of variation of the alkali-activated mortars reinforced with distinct PAN fiber contents (i.e., 0, 0.5, and 1% in volume) after curing periods of 14, 28, and 90 days. In general, the curing age increased the compressive strength values, irrespective of the fiber ratio added, ranging from approximately 27 to 47 MPa, respectively, at 14 and 90 days. It is in agreement with the results of other studies where the waste ceramic brick was used as a precursor [23], [50], [51], since it presents a relatively lower reactivity in
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 94 comparison with other CW with different compositions, e.g., ceramic wastes from the floor and wall tiles and sanitaryware furniture [16], [36]. The series reinforced with PAN fibers exhibited higher UCS than the one unreinforced. The effects of moderate fiber content on the compressive strength can be either negative or positive. The compressive strength can decrease the UCS when fibers originate more air voids and a less compact matrix. In contrast, it may improve when fibers counteract micro-cracking propagation and delay its coalescence into macro-cracks [33]. In the present study, it was observed that fiber addition enhanced the compressive strength of the studied Aam (Table 4-3). In particular, it may be attributed to the fiber geometry used in the present study, namely small dimension and high aspect ratio (length/diameter) that favors the micro-cracking arrestment during the pre-peak stage under compression [52], and therefore the increase in the compressive strength. The post-peak behavior, i.e., after reaching the maximum load, at all curing ages and notwithstanding the fiber content, was not possible to obtain due to problems controlling the test because of the brittle nature of the material even when reinforced. This can be associated with the relatively high porosity of the alkali-activated matrix, later explained in section 4.4.2.1, and some problems with the closedloop displacement control of the servo-hydraulic equipment. The M2 series (0.5% fibers) registered an increase of approximately 17% in strength at 90 days of curing, Figure 4-5(c), compared to the reference series (M1_0% of fibers), Figure 4-4(c). However, a different behavior was observed on M3 (1% fibers) at 14and 90-days curing (see Figure 4-6(a) and 6(c), and the UCS values were slightly lower (nearby 5% and 12%, respectively) in comparison to M2 Figure 4-5(a) and 5(c). It can be attributed to the mixing process. As it is explained by Ranjbar [38], the order of fiber addition into the blend is important to obtain uniform fiber dispersion. For multifilament fibers, e.g., PAN fibers, the author recommends mixing with the alkali activator solution in advance to separate the fiber bunches and then mixing with dry aluminosilicates and other fillers. As was not the case, PAN fibers were not homogeneously distributed in the mortar, and they formed clumps or balls (see Figure 4-7, c), plus the relatively low workability of the fresh paste affected the mechanical properties of the whole matrix.
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 95 Table 4-3. Uniaxial compressive strength (UCS), Elasticity modulus ( E ), and flexural strength ( f ) of the alkali-activated mortar after 14, 28, and 90 days of curing M1 (0% Cf) M2 (0.5% Cf) M3 (1% Cf) 14d 28d 90d 14d 28d 90d 14d 28d 90d UCS (MPa) (CoV, %) 26.90 (10.1) 34.44 (9.7) 39.30 (8.2) 41.31 (5.1) 40.69 (0.8) 46.92 (3.6) 39.43 (5.2) 46.79 (11.8) 41.52 (6.1) Ecm (GPa) (CoV, %) 6.72 (5.2) 8.21 (8.3) 10.88 (1.3) 9.94 (6.7) 11.16 (4.2) 12.2 (2.8) 9.21 (5.6) 12.38 (13.9) 10.75 (2.3) 𝑓𝑐𝑡 𝑓 ( N/mm2) (CoV, %) 5.19 (9.1) 4.44 (8.0) 5.39 (8.3) 5.89 (7.1) 4.28 (15.7) 3.90 (24.1) 4.59 (7.4) 7.58 (2.1) 6.47 (6.8) fR0.3mm ( N/mm2) (CoV, %) - - - 1.73 (63.2) 0.87 (57.2) 0.33 (126.2) 2.38 (33.8) 4.10 (13.8) 5.63 (13.5) fR0.5mm ( N/mm2) (CoV, %) - - - 0.55 (83.3) 0.14 (200) 0.05 (173.2) 1.03 (46.8) 2.74 (36.7) 2.82 (12.8)
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 96 (a) (b) (c) Figure 4-4. Compressive stress-strain relationships of the M1 (0% fibers) alkali-activated mortar after: (a) 14, (b) 28, and (c) 90 days of curing 0,0 0,3 0,6 0,9 1,2 1,5 0 10 20 30 40 50 Stress (MPa) Strain (%) 14d_0f samples Average curve 0,0 0,3 0,6 0,9 1,2 1,5 0 10 20 30 40 50 Stress (MPa) Strain (%) 28d_0f samples average curve 0,0 0,3 0,6 0,9 1,2 1,5 0 10 20 30 40 50 Stress (MPa) Strain (%) 90d_0f samples average curve
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 103 (a) (b) (c) Figure 4-9. Average curves of flexural strength of M2 (0.5% fiber) alkali-activated mortar after (a)14; (b) 28; and (c) 90 days of curing 0,0 0,2 0,4 0,6 0,8 1,0 1,2 0 400 800 1200 1600 2000 Load (N) Deflection (mm) 14d_0.5f samples average curve 0,0 0,2 0,4 0,6 0,8 1,0 1,2 0 400 800 1200 1600 2000 Load (N) Deflection (mm) 28d_0.5f samples average curve 0,0 0,2 0,4 0,6 0,8 1,0 1,2 0 400 800 1200 1600 2000 Load (N) Deflection (mm) 90d_0.5f samples average curve
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 104 (a) (b) (c) Figure 4-10. Average load-deflection curves for M3 (1% fiber) alkali-activated mortar after: (a)14; (b) 28; and (c) 90 days of curing 0,0 0,2 0,4 0,6 0,8 1,0 1,2 0 400 800 1200 1600 2000 Load (N) Deflection (mm) 14d_1f samples average curve 0,0 0,2 0,4 0,6 0,8 1,0 1,2 0 400 800 1200 1600 2000 Load (N) Deflection (mm) 28d_1f samples % average curve 0,0 0,2 0,4 0,6 0,8 1,0 1,2 0 400 800 1200 1600 2000 Load (N) Deflection (mm) 90d_1f samples average curve
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 105 4.4.2. Physical properties 4.4.2.1. Open Porosity Generally, water absorption by capillarity ( C ) and immersion ( P ) could be affected by adding fibers [52]; therefore, the assessment of those parameters was carried out for all the series, and the results are reported in Table 4-4. According to the test results, tested specimens showed relatively high porosity values regardless of the fiber content, above 20%, for all compositions (i.e., M1, M2, and M3). Then, using PAN fibers did not lead to tortuosity or larger pores than the control sample (M1). Similar behavior was found in a study related to alkali-activated mortars for bricks with cellulose and basalt fibers, where it was reported porosity values of about 25% [65]. Pore formation, size, and distribution can be attributed to the high CaO content of the precursors due to the formation of calcium silicate hydrates [66], [67], in this case, ascribed to the presence of LFS (Table 4-1). Table 4-4. Open porosity of the alkali-activated mortar after 28 days of curing, (%) M1 (0% f) M2 (0.5% f) M3 (1% f) Porosity (%) (CoV) 23.26 (1.22) 23.51 (1.59) 21.71 (1.44) 4.4.2.2. Water absorption (Capillarity) Water absorption due to capillary action ( C ) is directly related to material porosity since more porous materials with open and interconnected pores lead to larger water absorption [68],[69]. Thus, C of the studied alkali-activated mortars was influenced by the pore structure of mortar specimens prepared with high CW content and LFS, where the capillary pores are a consequence of the chemical reactions and the remaining water in the system, which is evaporated due to the hardening of the matrix through the curing time [70]. The precursors' chemical composition also restricted the C-A-S-H gel formulation and exhibited higher porosity and permeability to water. In all series, the capillarity coefficients were nearby 0.0002 kg / (m². min0.5) (Figure 4-11), which is significantly lower than 0.53-0.62 kg/m2.min0.5 reported in [65] for cellulose and plain alkali-activated desulfurization slag-based mortars. The reported C coefficient also suggests that C was not governed by the addition of fibers, consistent with the open porosity results (section 4.4.2.1).
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 106 Figure 4-11. Dependence of the mass increase on the suction surface Δmt / F, concerning the square root of time √𝑡 for samples of the alkali activated mortar after 28 days of curing 4.4.3. Mineralogical and microstructural characterization To characterize the reaction products developed after 14, 28, and 90 days of curing and considering that the composition of the pastes was identical (only the fiber content was modified), samples from the M2 series were randomly selected. They were subjected to microstructural analyses, i.e., X-ray diffraction (XRD), Electron Microscopy (SEM), X-ray Energy Dispersive Analyzer (EDX), and Fourier Transform Infrared Spectroscopy (FTIR). 4.4.3.1. XRD Figure 4-12 plots the XRD diffractograms of the original precursors (i.e., LFS and CW) and the AAm (M2) paste. It can be observed that LFS presents a tenuous halo between 28 and 38°(2θ), characteristic of amorphous materials [71], as well as some crystalline phases, such as calcium olivine (highest content at 48.5%), cuspidine, mayenite, lime, and larnite. By contrast, the CW is fundamentally quartz (81.1%, Table 4-1), even though other phases were also identified, namely muscovite, hematite, and garronite. This precursor also shows a halo between 25 and 30°(2θ). The 2 4 6 8 10 0,0000 0,0005 0,0010 0,0015 0,0020 Water absorption due to capillarity (g/mm2) Time (√min.) M1 (0%f) M2 (0.5%f) M3 (1%f)
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 107 presence of these halos in the precursors indicates the existence of a vitreous phase, which is fundamental for the alkaline activation reactions [3], [36], [72]. After curing for 14, 28, and 90 days, these halos became less intense and shifted in range, translating into a formation of an amorphous gel. The ceramic waste evidently influenced the diffraction peaks and the developed crystallinity phases in the resulting paste. However, some peaks in the reaction products were also identified in the LFS, revealing that some phases are basically inert to the alkali activation process. An increase in crystallinity can either increase or decrease certain mechanical properties, depending on the space available in the paste to be filled with crystals. Besides, the transition of amorphous gels to ordered structures can originate from internal stresses due to inevitable microstructure variations [33],[73]. Although the resulting gel is mostly amorphous, some new semi-crystalline clusters were detected in the M2 paste, such as enstatite, illite, phengite, calcite, and feldspar. These observations are in line with findings in Huseien et al. [22], where it is shown that these semi-crystalline phases are observed in alkali-activated mortars containing ceramic wastes, GGBFS, and FA. The XDR patterns of the M2 mixtures throughout the curing time show a decrease of the characteristic quartz peaks (Table 4-5), accompanied by a slight increase of mullite (90 days), obtained from the Al2O3 in the CW. Moreover, the newly formed crystalline Mgand silicate-based phase, enstatite, which showed a significant content increase with curing time (reaching 30.3% after 90 days, Table 4-5), suggests that the phase composition of the studied samples may be affected by the available soluble SiO2 content provided by the alkali-activator solution. [74].
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 108 (Q: quartz; M: muscovite; C: calcium olivine; E: enstatite; I: Illite; P:Phengite; Ca: Calcite; F: Feldspar; Cu: Cuspidine; Ma: Mayenite; L: Lime; La: Larnite; H: Hematite; G: Garronite ) Figure 4-12. XRD patterns of starting materials (CW and LFS), and M2 (0.5% fiber) mortar at 14, 28 and 90 days curing time Table 4-5. Mineral’s quantification in starting materials (CW and LFS), and M2 (0.5% fiber) mortar at 14-, 28 and 90 days curing time, (% wt) Material Q H M G C Cu Ma L La E Ca P F I CW 81.1 4.4 13.8 0.6 - - - - - - - - - - LFS - - - - 48.5 18.5 6.7 2.1 24.2 - - - - - M2_14 days 44.1 2.5 12.1 - 10.1 - - - - 9.8 0.1 0 15.7 5.5 M2_28 days 26.1 1.7 4.4 - 7.7 - - - - 8.2 12.4 0 23.8 15.1 M2_90 days 12.4 0.4 12.7 - 13.2 - - - - 30.3 6.2 0.5 18.9 5.3 Q: Quartz; H: Hematite; M: Muscovite; G: Garronite; C: Calcio Olivine; Cu: Cuspidine; Ma: Mayenite; L: Lime; La: Larnite; E: enstatite; Ca: Calcite; P:Phengite; F: Feldspar; I: Illite 10 20 30 40 50 60 70 I,P,E Q QQ Q QQ Q M M Q HQ H MGG M Q M Cu CL C L La, C La L Ma C L C Cu C C Ma C FIC M Q Ca,C,E Q F I,MI MQ F C Ca Q IP Q C E FC I FQ M I,P,E E P F I FC MQQ Q Q E F I Ca FQ Q LFS CW 2q 14 days 28 days 90 days IP E QQ E QQ QE QQ
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 109 1. SEM micrographs The same samples from the M2 series were analyzed through SEM / EDX to perform a thorough qualitative analysis of the developed microstructure of the reaction products, which is illustrated in Figure 4-13. The effect of the curing time on the M2 AAm is evident; at 14 days, mostly unreacted particles (points 1 and 2 correspondings to CW and LFS, respectively) are still visible with some precipitated hydrates on their surface, this suggests the first signs of activation but a still small amount, Figure 4-13, (a). After 28 days of curing, hydration is not complete since CW and LFS particles are still detected. However, their surface is greater covered with reaction products, denoting a better extent of reaction, Figure 4-13, (b). After 90 days, most of the particles show an apparently higher reaction degree than in the previous curing stages, and the mass of aluminosilicate gel seams is more scattered in the structure of the paste. However, still, CW larger particles (Figure 4-13,c. point 1) were only partially reacted [50]. SEM micrographs also demonstrated the high-water absorption of this AAm. The observations were corroborated by previous findings [51], [75], where it was detected unreacted brick residue powder particles and pores in SEM images of alkaline activated mortar based on powdered brick waste. Regarding the type of gel produced, it can be classified as C-A-S-H due to the combination of the specific compositions of CW and LFS, with a significant content of calcium. This finding is in line with the results obtained by [76], [77]. As for the fiber reinforcement, the SEM images (Figure 4-13, points 3) show that hydrated particles are attached to the surface of PAN fibers, which evidence their good embeddedness in the matrix, thus enhancing the mechanical properties of the mortar, especially the flexural strength. The good adhesion of PAN fibers explains the increase in strength of M2 and M3, as fiber can act as a bridge when an external load is applied. Similar results concerning good adhesion in the case of PVA fibers in AAMs are reported in [25], [62].
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 110 a) b) c) Figure 4-13. SEM images of M2 (0.5% fiber content) after a) 14 days, b) 28 days, and c) 90 days curing time. Points 1 and 2) ceramic waste and ladle furnace slag particles, respectively; point 3) PAN fibers” 2. FTIR spectra of precursors and AAm Figure 4-14 displays the FTIR spectra of the initial materials (LFS and CW) and the M2 mixture after 14, 28, and 90 days of curing, which shows a set of bands positioned in the frequency range within [400 - 1800] cm-1. The LFS spectrum presents a wideband between 1550 and 1420 cm−1, centered at 1475 cm−1, associated with CO32− vibrations in different configurations [78], denoting the existence of carbonated compounds. The deep cupula perceptible between 1050 and 750 cm−1 is mainly assigned to silico-aluminate groups, among the main components of the slag structure (Table 4-1).
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 111 Finally, the 560 cm-1 band is associated with the Al-O-Al, while the bands at 490 cm-1 and 440 cm-1 are associated with the O-Si-O bonds. The CW exhibits an intense and broad main band around 1015 cm1. This band is characteristic of the asymmetric tension vibration related to Si-O-Si or Si-O-Al bonds [79], confirming the material's crystallinity. The bands at 420 and 440 cm-1 represent the O-Si-O bonds, mostly from the quartz. Some modifications in the microstructure of the M2 AAm paste can be detected, relatively to the original precursors. Such adjustments depend on several factors, including the composition of the precursor, the type of alkaline activator, and the curing conditions [78]. One of the most significant was the shift of the main band of the original CW to lower wavelengths (1000 cm−1), translating a structural reordination motivated by the precipitation of the reaction products, where the C-A-S-H type gel has been identified as the primary phase. This observation is in agreement with the findings reported by Hwang [72]. Comparing the three spectra of M2, it is possible to assume that the new band formed after 14 days, located at 1480 cm-1, is mainly attributed to the inclusion of soluble silicon (from the sodium silicate), suggesting that the 14-day period was not long enough to dissolve the precursor and start the nucleation process (when the silicon ions from the activator would be required). At 90 days, this band practically disappeared, as these additional ions are now combined with other species. This behavior confirms that the original quartz and mullite bands (690, 540, 440 cm−1) did not present any meaningful changes after 14 days, relatively to the original materials. In the 14-, 28-, and 90-day spectra are also visible the formation and growth of new bands, namely at 875 and 1410 cm−1, which are usually assigned with C-O functional groups [79], possibly result from the development of different types of carbonate minerals, like calcite. This agrees with the XRD results, which are illustrated in Figure 4-12.
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 112 Figure 4-14. FTIR spectra of starting materials, the ladle furnace slag (LFS); ceramic waste (CW) – after milled, and M2 blend (0.5% fiber content) after 14-, 28-, and 90-days curing time. 4.5. CONCLUSIONS The development of enhanced-strength alkali-activated mortars reinforced with different percentages of polyacrylonitrile (PAN) fibers was carried out in this research. Ceramic waste from a company that produced clay bricks and roof tiles was used as the main precursor in combination with ladle furnace slag (LFS) in the presence of sodium silicate (SS) as an activator. The main conclusions obtained in this work are: ‒ The efficiency of fiber addition, i.e., 0.5% and 1%, of the developed AAm was determined by the mechanical and physical properties. It exhibited an improvement of nearly 12% in elasticity modulus and about 20% in compressive and flexural strength with values up to 47 MPa and 7 N/mm2, respectively, at 90 curing days, compared to plain AAm; ‒ As expected, the main benefits of the fiber reinforcement were observed at the post-cracking stage of the flexural responses, with the toughness and residual strengths increased for increasing fiber content. Fiber rupture was predominant in the series with 0,5% of fiber, while fiber pullout 1800 1600 1400 1200 1000 800 600 400 1475 1000 440 420 875 1410 1480 690 540 1015 935 445 490 560 14 days 28 days wavenumber (cm-1) 90 days CW LFS 840
Effect of fiber reinforcement in alkali-activated ceramic/slag-based mortar under thermal curing 119 aggregate,” Cem. Concr. Compos. , vol. 103, pp. 11–21, Oct. 2019, doi: 10.1016/j.cemconcomp.2019.04.024. [72] C. L. Hwang, M. Damtie Yehualaw, D. H. Vo, and T. P. Huynh, “Development of high-strength alkali-activated pastes containing high volumes of waste brick and ceramic powders,” Constr. Build. Mater. , vol. 218, pp. 519–529, Sep. 2019, doi: 10.1016/j.conbuildmat.2019.05.143. [73] Z. Abdollahnejad, T. Luukkonen, M. Mastali, P. Kinnunen, and M. Illikainen, “Development of One-Part Alkali-Activated Ceramic/Slag Binders Containing Recycled Ceramic Aggregates,” J. Mater. Civ. Eng. , vol. 31, no. 2, p. 04018386, Feb. 2019, doi: 10.1061/(ASCE)MT.19435533.0002608. [74] T. Yang, Q. Wu, H. Zhu, and Z. Zhang, “Geopolymer with improved thermal stability by incorporating high-magnesium nickel slag,” Constr. Build. Mater. , vol. 155, pp. 475–484, Nov. 2017, doi: 10.1016/j.conbuildmat.2017.08.081. [75] F. Ameri, P. Shoaei, S. A. Zareei, and B. Behforouz, “Geopolymers vs. alkali-activated materials (AAMs): A comparative study on durability, microstructure, and resistance to elevated temperatures of lightweight mortars,” Constr. Build. Mater. , vol. 222, pp. 49–63, Oct. 2019, doi: 10.1016/j.conbuildmat.2019.06.079. [76] F. Pacheco-Torgal, J. Castro-Gomes, and S. Jalali, “Alkali-activated binders: A review. Part 2. About materials and binders manufacture,” Construction and Building Materials , vol. 22, no. 7. Elsevier, pp. 1315–1322, Jul. 01, 2008, doi: 10.1016/j.conbuildmat.2007.03.019. [77] F. Pacheco-Torgal, J. Castro-Gomes, and S. Jalali, “Alkali-activated binders: A review. Part 1. Historical background, terminology, reaction mechanisms and hydration products,” Construction and Building Materials , vol. 22, no. 7. Elsevier, pp. 1305–1314, Jul. 01, 2008, doi: 10.1016/j.conbuildmat.2007.10.015. [78] U. De Filippis, E. Prud’homme, and S. Meille, “Relation between activator ratio, hydration products and mechanical properties of alkali-activated slag,” Constr. Build. Mater. , vol. 266, p. 120940, Jan. 2021, doi: 10.1016/j.conbuildmat.2020.120940. [79] M. F. Zawrah, R. A. Gado, N. Feltin, S. Ducourtieux, and L. Devoille, “Recycling and utilization assessment of waste fired clay bricks (Grog) with granulated blast-furnace slag for geopolymer production,” Process Saf. Environ. Prot. , vol. 103, pp. 237–251, Sep. 2016, doi: 10.1016/j.psep.2016.08.001.
120 Chapter: V Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 5. EFFECT OF NON-THERMAL CURING ON ALKALI-ACTIVATED CERAMIC/SLAG-BASED CEMENT REINFORCED WITH FIBERS. Research regarding ceramic wastes/slag-based material for geopolymer production cured at ambient conditions is scarce. Even more so when it comes to the incorporation of fibers in this material. Here we focused on improving the workability of the developed alkali-activated cement presented in the previous chapter to improve both, the fiber distribution (maintaining the same PAN fiber content, i.e., 0%; 0.5%, and 1% in volume) and consequently their mechanical performance. Also, a more sustainable way to produce activated alkaline cement was considered, therefore, ambient curing (20°C and 60% HR ± 5%) was experienced. Journal of Materials in Civil Engineering Under review since 04-23-2022 Manuscript number: MTENG-14776, 2022 Fiber Reinforced Alkali Activated Cements from Ceramic Waste and Ladle Furnace Slag cured at ambient temperature Norma Gaibor a*; Dinis Leitão b; Tiago Miranda c; Nuno Cristelo d; Lisete Fernandes d; Eduardo N.B. Pereira c; Vítor M.C.F. Cunha c a. School of Engineering of the University of Minho, Azurem Campus, 4800-058, Guimarães, Portugal b. CTAC, Department of Civil Engineering, University of Minho, 4800-058, Guimarães, Portugal c. ISISE, Institute for Science and Innovation for Bio-Sustainability (IB-S), Department of Civil Engineering, University of Minho, 4800-058, Guimarães, Portugal d. CQ-VR, Centro de Química - Vila Real, Department of Engineering, University of Trás-os-Montes e Alto Douro, 5001-801, Vila Real, Portugal *Corresponding author: n[email protected]m
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 121 Abstract The development of new alkaline-activated materials, as an alternative to Portland cement and conventional concrete, using different industrial by-products or wastes is getting considerable attention from the scientific community. This study aims to investigate the potential of ceramic waste, specifically from brick and tile production, and ladle furnace slag (for composition correction) as precursors in alkaline activated cement reinforced with polyacrylonitrile fibers. Sodium silicate, in solution form, was used to activate the precursors, and three different fiber contents were tested, namely 0, 0.5, and 1%, by volume. The cements were cured at 20°C and tested after 14, 28, and 90 days. Physical and mechanical properties were assessed, such as capillarity, porosity, uniaxial compressive strength, flexural strength, and elasticity modulus. In addition, microstructural analysis was also carried out, namely, Scanning Electron Microscopy, X-ray Energy Dispersive Analyzer, X-ray diffraction, and Fourier Transform Infrared Spectroscopy. The results revealed that environmentally friendly alkali-activated binders were produced from wastes with very few industrial recycling possibilities, and the addition of 0.5% fibers was able to potentiate its performance, up to a flexural strength of 8.84 N/mm2 and compressive strength of 29 MPa. The mechanical performance presented by this material is relevant, especially when considering that two abundant and lesscommon wastes were used (avoiding more frequent precursors, like coal fly ash or ground blast furnace slag, which are becoming scarce in Europe) and, also, considering that no thermal curing was applied. Calcium aluminum silicate hydrate (C-A-S-H) was detected as the main reaction product. Keywords: Ambient curing; ceramic waste; alkali activation; polyacrylonitrile fiber; physical and mechanical properties.
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 122 5.1. INTRODUCTION The production of ordinary Portland cement (OPC) is associated with high amounts of greenhouse gas emissions, which is significantly contributing to serious environmental issues [1]. About one ton of CO2 is released per ton of OPC produced, which means that the Portland cement industry alone is responsible for approximately 8% of the total global CO2 emissions to the earth’s atmosphere [2], and it is predicted that this value will increase up to 10% in the short term. Moreover, the production of OPC is also responsible for 36% of the global energy consumption, especially due to the calcination step [3]. These environmental concerns about OPC have encouraged researchers to look for sustainable alternatives. Over the last few years, alkali-activated materials (AAM) have appeared as a promising alternative to OPC, mainly due to its substantially lower CO2 emissions [4], as well as to some of its specific characteristics, like the faster setting, the high early-age strength and the enhanced durability [5]. The use of inorganic industrial wastes or residual products in the production of concrete and/or mortar can contribute towards a more sustainable building design and a greener environment. AAMs are developed by the reaction between aluminosilicate-based powders, usually referred to as “precursors”, and an alkaline solution. Depending on the nature of the starting materials, namely its calcium content, the reaction products can be classified as a sodium aluminosilicate gel (N-A-S-H), or a calcium aluminosilicate gel (C-A-S-H), or under very specific conditions, as a combination of the above mentioned (N-C-A-S-H) [6]. The mechanical behavior and durability performance of the AAM is mainly reliant on the gel type and volume that the alkali-activated system is able to develop [7]. Various authors have studied different types of industrial wastes and by-products, in the way to create sustainable alkali-activated building materials, to later be incorporated into civil construction. This development in introducing an alternative to OPC has drawn the attention of professionals in the commercial and academic sectors [8]. However, so far, the spotlights have been set on coal fly ash and blast furnace slag [9], which are two wastes that are becoming scarcer in Europe, as more efficient and/or cleaner alternatives for the production of power or steel, respectively, are optimized and installed. Viable alternatives, like construction and demolition waste [10] or different types of ceramic waste have also been tested as precursors in alkaline activated systems [11], especially for nonstructural applications, such as embankments or fills, road, and railway pavement foundations, among others.
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 123 In 2017, the overall production of ceramic waste (CW) exceeded 25 million tons, assuming that 1 m2 of ceramic can produce 1.9 kg of waste [12]. Therefore, it has been estimated that approximately 30% of the production within the ceramic industry goes to waste [13], while ceramic materials represent around 45% of construction and demolition waste [14]. As CW is amassing every day, there is a concern in the ceramic industries to find out an alternative solution for its disposal. Despite the recycling and reusing of several kinds of CW, the total amount used in the construction sectors in general and concrete industries are still irrelevant, which represents a very significant possibility to apply, with direct or indirect strategies, substantial percentages of this waste [15]. Thereby, the use of these materials in the construction sector relieves various environmental problems, such as, reducing the total demand and consumption of natural resources and raw materials, saving energy, and costs concerning waste disposal in landfills [16]. It is worthy to note that ceramic wastes can be used safely without any significant processing and be properly recycled for the construction sector. Furthermore, CW usually has an important aluminosilicate content, constituting an appropriate supplement for cement materials, by enhancing their mechanical strength and durability performance [11]. Regarding the use of CW as a precursor, Keppert et al. [17] used two different red-clay ceramic powders, with both producing satisfactory mechanical properties. However, their rheological performance hindered its use in applications requiring pumping or spraying, because of their high viscosity. It was concluded that, when the Ca content is above a specific threshold, it induces a broader pore size distribution and an overall higher porosity on the geopolymer, due to the formation of calcium silicate hydrates. Reig et al. [11] also studied CW materials of different origins (red clay brick and porcelain stoneware) to analyze the properties and microstructure of alkali-activated pastes and mortars. The resulting mortars developed a compressive strength ranging between 22 and 41 MPa, after 7 days of curing at 65 °C, based on the sodium concentration in the solution and the water/binder ratio. Azevedo et al. [18] characterized clay bricks’ waste to be used as an alternative precursor to produce roof tiles for buildings. It was proved that the waste has high silica and alumina content, which are fundamental compounds for the geopolymers synthesis. It also has fine particles and high pozzolanic reactivity. Hence, this waste has excellent potential to be applied as a raw material for getting ceramic roof tiles through geopolymeric reactions. Sun et al. [19] worked with ceramic waste (CW) derived from municipal waste collection, i.e. a combination of tiles, pan forms, blocks, etc., activated by sodium/potassium hydroxide and/or silicate solutions. Maximum compressive
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 124 strength of 71.1 MPa, after 28 days, was obtained, while its thermal resilience was also enhanced, showing a compressive strength of 75.6 MPa after heat treatment up to 1000 °C. On the other hand, a specific type of slag is discharged from the production of steel, very common and abundant in most European countries, is the so-called “ladle furnace slag” (LFS), resulting from the metallurgical secondary and the steel refining process [20]. According to statistics, 30 - 60 Kg of LFS for each ton of molten steel is generated [21]. The chemical and mineralogical composition of LFS is largely different from those of ordinary steel slag and blast furnace slag. Even more, the components of the LFS differ owing to many factors in the refining process, even within the same plant [22]. Regarding the mineralogical composition, LFS is mainly characterized by the presence of phases with cementing or low/non-reactive activity, generally C12A7 with a fast hydration rate and a small portion of the C2S, which is one of the main crystal mineral phases keeping the later performance of hardened cement paste. Its chemical components are calcium and silicon oxide and alumina [23]. As it is known, AAMs with a high calcium content (CaO + SiO2 > 70%) will produce a calcium aluminum silicate hydrate (C-A-S-H) gel as the major reaction product promoting the enhancement of the mechanical properties of the matrix [24]. Therefore, LFS (rich in calcium sources) has been used in the present research as a complementary precursor. In general, several studies have proved that the mixture of a high-calcium-level precursor (e.g. slag) with another low-calcium-level precursor (e.g. fly ash, ceramic wastes) reduces shrinkage compared to alkali-activated binders containing slag only [25]. In contrast, the analysis of the particular combination of CW and LFS cured at ambient temperature, as an alternative cement, is less known, but it is expected that this blended system could reduce or mitigate the cracking proneness of AAM due to shrinkage. Furthermore, one possible effective technological solution and relatively simple way, compared to other methods, to reduce the cracks caused by shrinkage and other disadvantages previously mentioned, is the incorporation of reinforcement fibers into the mix. That said, the level of cement improvement depends on the nature and type, content, and mechanical properties of the fibers, bond properties at the interface of the fiber and the matrix, and properties of the cement itself [26]. Some works have observed the effects of using different fibers in alkali-activated materials such as carbon fibers [27], polypropylene and basalt [28], and Polyvinyl alcohol [29], among others. Few studies were found regarding the fiber-reinforced cement prepared with ceramic wastes and slag. Abdollahnejad et al. [30] developed an experimental and numerical investigation, observing that,
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 125 regardless of the fiber type and curing method, increasing the fiber content increased the compressive and flexural strengths. However, the enhancement level was determined by fiber type and curing conditions (sealing and water bath). Several works regarding the alkali activation of different materials at room temperature are available in the literature, such as different combinations of slag with fly ash [31], glass powder [32], and silica fume [33], among others. Nonetheless, research concerning ceramic wastes/slag-based material for geopolymer production cured at ambient conditions is scarcer. Hwang et al. [14] studied the alkali activation with curing at 25 °C of the waste brick powder and waste ceramic sand used as a precursor and fine aggregate, respectively, and also the blend of waste red clay brick powder and ceramic from construction and demolition waste together [34], in both cases combined with slag. Room temperature cured alkali-activated materials have demonstrated their advantages in field applications [35] while at the same time, providing a promising alternative to reduce energy consumption due to heat-curing [24]. Nevertheless, limited studies about the combined influence of the development of alkali-activated ceramic/slag cements with fiber addition are available in the literature. Therefore, having in mind the previous considerations, the present study aimed at the application of two abundant industrial wastes – ladle furnace slag and ceramic waste from a ceramic brick industry in Portugal – as a combined precursor to produce alkali-activated cement. The use of such materials, which are known to possess lower reactivity than other, more common precursors (namely coal fly ash and blast furnace slag), allowed ambient curing conditions (20ºC), with inevitable financial and environmental benefits. It should also be highlighted that these are two valuable examples of industrial wastes with a very significant and increasing production rate, especially in Europe, for which a sustainable solution needs to be developed, thus avoiding their landfilling. Sodium silicate solution was used as the activator and, for a broader application range, and to mitigate the lower reactivity of the precursors, polyacrylonitrile fibers (0, 0.5, and 1% contents) were also included in the cements. The final products were assessed in terms of axial stiffness and compressive and flexural strength, physical behavior (capillarity and porosity), and microstructural analyses, which included Scanning Electron Microscopy (SEM), X-ray Energy Dispersive Analysis (EDX), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR).
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 126 5.2. MATERIALS AND MIXTURES 5.2.1. Materials Wastes from a ceramic brick (CBW) manufacturing company located nearby the city of Braga (northwestern Portugal) were used to develop the alkali-activated cements in this study, Figure 5-1(a). The ladle furnace slag (LFS), which is the result of scrap melting in an electric arc furnace, was supplied by the ironwork company Megasa , located near the city of Maia (northwestern Portugal), Figure 5-1(b). Both were used as the main and secondary precursor materials, respectively. The general characterization of these starting materials, i.e., the particle size distribution and chemical composition were described in the work by Gaibor et al. [36]. In which, the gradation curve showed that the grinding process of CW generated a well-graded material with a fine fraction of around 60%. In addition, it was determined that CBW mainly consists of silica (54.89 wt.%) and alumina (26.28 wt.%), while the LFS was characterized by a significant percentage of CaO (64.23 wt.%) and silica content of 19.68 wt.%. The sodium silicate (Na2SiO3) was the alkaline activator solution employed in the reaction process. The developed cement was reinforced with polyacrylonitrile fibers (PANf) of 8 mm in length and ~20 µm in diameter. PANf was chosen due to its properties, specifically the chemical (good in alkaline medium) and thermal resistance (good in short-term processing temperature up to 220°C) as it is shown in the corresponding technical sheet [37]. (a)
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 127 (b) Figure 5-1. Original materials in situ: (a) ceramic bricks waste (CBW); and (b) ladle furnace slag (LFS) 5.2.2. Alkali-activated cement mixture and production The present experimental work is the continuation of previous work, namely, Gaibor et al. [38], which was selected from a set of ten different mix compositions, including the reference samples (100 wt.% for CBW and LFS), the mixture with the best mechanical performance. The criteria for this selection were compressive strength. The mix with 75% of ceramic waste plus 25% of ladle furnace slag alkaliactivated with sodium silicate (SS) leads to the highest compressive strength i.e., nearby 60 MPa. Secondly, having into consideration some issues regarding the workability of these alkali-activated cements [36], the referred blend composition [38] was modified by adding a polycarboxylate-based superplasticizer [39] with a specific density of 1.03 ± 0.05 and a pH of 7 ± 1 and a small amount of water, in order to make the AAm workable and homogeneous [40] and consequently to improve the incorporation and distribution of fibers in these mixtures. Also, based on the available literature [41] stating that a cement design can be optimized by using up to 2% fiber by volume, it was determined to carry out this experimental work with 0, 0.5, and 1% of volume ratio of PAN. Table 5-1 shows the characterization of the developed cements.
Effect of non-thermal curing on alkali-activated ceramic/slag-based cement reinforced with fibers 128 Table 5-1. Identification and characterization of the tested cements Cement ID Precursor (wt. ratio) Activator/ Precursor (wt. ratio) SP/ precursor (wt. ratio) Water/SS (wt. ratio) PAN fiber (vol. fraction) CaO / SiO2 Na2O / Al2O3 SiO2 / Al2O3 SiO2 / Na2O CBW LFS SS M1 75 25 0.45 0.02 0.05 0 0.29 0.29 2.76 9.59 M2 0.5 M3 1.0 For alkali activation purposes, the time and order of adding the precursors, alkali activator, and fibers are important [42]. The mixing process occurred in two stages, first, the homogenization of the solid phase and the activator solution for 1 minute in an industrial mixer at the minimum speed (i.e., 140±5 rpm). Afterward, the SP and water were added and mixed for two more minutes at maximum speed (i.e., 285±10 rpm). Finally, the fibers were slowly incorporated into the cement and mixed again for 3 minutes at maximum speed to guarantee uniform distribution of PANf. Thus, the blend was mixed for a total of 6 continuous minutes. The flowability of the cement blending was measured through the flow table test, following the specifications of BS EN 12350-8. During the fresh state, no segregation was observed, this can be attributed to the correct precursor/activator ratio. The slumpflow test, after 15 strokes, yielded a result of the opened out diameter of 165 mm, 145 mm, and 133 mm, for cements with 0%, 0.5, and 1% of PANf content, respectively. Even though the reasonably low workability, an improvement can be noticed when comparing with results obtained by Gaibor et al. [36]. It is worth mentioning that the superplasticizer utilization, which originally plays the role of microrollers [43], did not significantly affect the friction and the flow resistance of this alkali-activated cement. Further research is needed to find a more suitable plasticizer in these highly alkaline mediums. Immediately after the slump-flow test, the cement was placed inside stainless-steel prisms molds and vibrated for 2 minutes to remove air bubbles. Samples were cured in a climatic chamber (Fitoclima 28000 EDTU) with constant environmental conditions of 20°C (±0.5°C) and 60% (±5%) relative humidity (RH). After the first 24 hours, specimens were unmolded and left to cure in the same terms till the testing time, i.e., 14, 28, and 90 days. As one of the main aims of this work was not to use thermal curing conditions, this curing method was not employed. Each set of blends (M1, M2, and M3) had five samples for the uniaxial compressive test and four samples to perform the other mechanical and physical tests, respectively, elasticity modulus, flexural tests, porosity, and capillarity tests.
General conclusions and future works 231 alkali activator (sodium silicate) was ranked in second place. Usually, when the alkali-activated materials are studied separately, the highest environmental burden is related to the activator. Furthermore, from the Sustainability Assessment (LCA) it was possible to comprise that the best solution is the one that better merges the environmental, functional, and economic factors. So, findings showed that the two half-sandwich panels proposed were the most sustainable alternatives when compared to the two conventional technologies, namely, the heavyweight conventional partition wall (hollow brick wall), and the lightweight gypsum panels wall (plasterboard wall), also against the conceptual design of lightweight sandwich walls taken as references. This interpretation was supported by the sensitivity analysis. Finally, the strength classes for the developed alkaline-activated cement (AAc) according to the EN 206-1 standard have been defined as a reference. Therefore, the AAc under thermal curing (70°C and 60% HR ± 5%) would correspond to the C40/50 strength class and when curing at ambient temperature (20°C and 60% HR ± 5%) would be a C20/25 strength class. Hence, it can be stated that the developed alkali-activated cement has a great potential being a promising alternative to conventional Portland cement-based materials to be used in several applications, some out of the scope of this work such as structural applications, thus contributing to a circular economy and sustainability in the AEC sector. Therefore, the presented non-structural panels are just an alternative. 8.2. FUTURE RESEARCH DIRECTIONS This thesis has mainly been concerned with the development of an alkali-activated ceramic waste/slag cement (AAc) and its feasibility to be used in the construction of non-structural panels for partition walls. The research presented in this thesis has significantly advanced the understanding in this field, but much further research is still needed for the safe and reliable application of the AAc and the developed panels in the practical field of Architecture, Engineering, and Construction (AEC) sector. ▪ The durability of the alkali-activated cement should be investigated since research is scarce on this topic. It might include tests such as chloride penetration, sulfate resistance, the aggregate/alkali reaction, freeze-thaw resistance, and carbonation;
General conclusions and future works 232 ▪ Further analysis on design optimization is encouraged, such as the thickness of each layer of the panel, either the rigid face or the insulating material. It might allow for improving the functional and mechanical properties according to the intended use; ▪ Complementary mechanical and functional tests for panels are recommended. To complement the tests carried out in the present work, there are others that, due to time limitations, it was not possible to perform, to mention some: impact tests, fire resistant behavior, sound reduction index, sound absorption, hygrometric behavior, among others. It will allow a complete characterization of the panels; ▪ Real scale panel manufacturing is required in order to evaluate, through experimental studies, the assembly structure to be used for on-site installation.
233 Annexes ANNEXES ARTICLES I. Gaibor, Norma, Leitão, D., Miranda, T., Cristelo, N., Pereira, E. N. B., & Cunha, V. M. C. F. (2021). Effect of polyacrylonitrile fiber on the properties of alkali-activated ceramic/slag-based mortar. Journal of Building Engineering, 44, 103367. https://doi.org/10.1016/J.JOBE.2021.103367 II. Gaibor, Norma, Leitão, D., Miranda, T., Cunha, V., & Cristelo, N. (2021). Effect of curing conditions on compressive strength behavior on alkali-activated ceramic wastes. Polo Del Conocimiento, 6(3), 977–990. http://repositorium.sdum.uminho.pt/handle/1822/70790 III. Gaibor, N, Coelho, J., Leitão, D., Miranda, T., Tavares, P., & Cristelo, N. (2020). Alkali activation of recycled ceramic aggregates from construction and demolition wastes. Materiales de Construcción, 70(339), 222. https://doi.org/10.3989/mc.2020.13619 IV. N. Gaibor, D. Leitão, T. Miranda, and N. Cristelo, “Development of alkali-activated ceramic residue and fly ash blends,” in Wastes: Solutions, Treatments and Opportunities III, CRC Press, 2019, pp. 591–599. https://doi.org/10.1201/9780429289798-94 PARTICIPATION IN CONFERENCES I. Norma Gaibor; Dinis Leitão; Pedro Tavares; Nuno Cristelo; Eduardo N.B. Pereira; Vítor M.C.F. Cunha, “Effect of curing conditions on the mechanical behavior of fiber reinforced alkali activated ceramic/slag-based cements”, IMFAHE´s VIII International Conference, 30th May, Boston - Massachusetts, Oral Communication. II. Gaibor, Norma, Leitão, D., Miranda, T., Cristelo, N., Pereira, E. N. B., & Cunha, V. M. C. F., “Generation, Management and treatment of industrial ceramic wastes”, VIII International
Annexes 234 Congress of Industrial Processes, Hydrocarbons, and the Environment, 20 – 22 October 2021, ESPOCH Ecuador, Oral Communication. III. Gaibor Norma, Leitão, D., Miranda, T., Cunha, V., & Cristelo, N, “Effect of curing conditions on compressive strength behavior on alkali-activated ceramic wastes”, VII International Congress: Application, Transport and Fluid storage in industrial process, hydrocarbons, and environment, 21 – 23 October 2020, ESPOCH Ecuador, Oral Communication. IV. N. Gaibor, D. Leitão, T. Miranda, and N. Cristelo, “Development of alkali-activated ceramic residue and fly ash blends”, 5th International Conference WASTES: Solutions, Treatments, and Opportunities, 4 – 6 September 2019, Caparica, Portugal, Oral Communication.