Technical and Environmental Feasibility of Recycled Plastic Fibres From Food Packaging Wastes as Reinforcement in Concrete

   Doctoral Thesis  Interuniversity Doctoral program in Agrarian, Food, Forestry and Rural Development Engineering   TECHNICAL AND ENVIRONMENTAL FEASIBILITY OF RECYCLED PLASTIC FIBRES FROM FOOD PACKAGING WASTES AS REINFORCEMENT IN CONCRETE PIETRO ANTONIO VACCARO Sevilla, 2022    I   Doctoral Thesis Programa de Doctorado en Ingeniería Agraria, Alimentaria, Forestal y del Desarrollo Rural Sostenible por la Universidad de Córdoba y la Universidad de Sevilla     TECHNICAL AND ENVIRONMENTAL FEASIBILITY OF RECYCLED PLASTIC FIBRES FROM FOOD PACKAGING WASTES AS REINFORCEMENT IN CONCRETE PIETRO ANTONIO VACCARO Sevilla, 2022   Thesis directors: Dra. Adela Pérez Galvín Dr. Jesús Ayuso Muñoz Dr. Antonio López Uceda    II   III  Doctoral Thesis Programa de Doctorado en Ingeniería Agraria, Alimentaria, Forestal y del Desarrollo Rural Sostenible por la Universidad de Córdoba y la Universidad de Sevilla  TECHNICAL AND ENVIRONMENTAL FEASIBILITY OF RECYCLED PLASTIC FIBRES FROM FOOD PACKAGING WASTES AS REINFORCEMENT IN CONCRETE Memoria de tesis presentada por Pietro Antonio Vaccaro para optar al Título de Doctor por la Universidad de Sevilla y la Univeridad de Córdoba Sevilla, Febrero 2022 VºBº del Director VºBº del Director VºBº del Director Fdo. Adela Pérez Galvín Fdo. Jesús Ayuso Muñoz Fdo. Antonio López Uceda Doctorando: Fdo. Pietro Antonio Vaccaro   IV  V A mi familia To my family “Fatti non foste a viver come bruti ma per seguir virtute e canoscenza” ― Dante Aleghieri. “Longum iter est per praecepta, breve et efficax per exempla” ― Lucio Anneo Séneca.  XII manufactured concrete in monolithic state. Following the processing, analysis and comparison of the results obtained from the tests, the following conclusions could be drawn: 1) mechanical: • The physical properties studied were not significantly affected by the addition of recycled plastic fibres; • The addition of RPF produced a certain decrease in compressive and flexural strength, but an improvement in the post-cracking properties of the concrete was achieved; • The increase in toughness index with an increase in the percentage of recycled plastic fibres confirmed their stitching action inside the cement matrix; • The toughness index presented by the concrete with commercial fibres was greater than that with the same dosage of RPF, due to its rougher surface and greater adherence to the cementitious matrix. Furthermore, it should be noted that the toughness index relative to the mixture with 6 kg of recycled plastic fibres per cubic meter of concrete was comparable to that with commercial plastic fibre (PFRC-REF). This suggests that manufacturing RPF with a rougher surface could lead to a reduction in the amount needed to achieve similar toughness index levels to PFRC-REF; 2) environmental: • Waste plastic food packaging, used for the preparation of plastic sheets to be used as fibre reinforcement in concrete, showed low release levels of the elements determined by the Council Decision 2003/33/EC and they were under the inert limits, except for antimony. Hence, they were classified as non-hazardous material; • The low release levels in concrete with RPF confirms that its incorporation into concrete reduced the concentrations in leachates to a minimum. The concentrations of the elements with higher mobility, in the long-term, were much lower than the limits imposed by regulations for “shaped” construction materials, such as Soil Quality Degree (from The Netherlands); • The study carried out to identify the transport and chemical mechanisms, indicated that the release patterns were: wash-off for Sb, Zn (although Zn also presented depletion in the final steps) and Cr in concrete samples with RPF; dissolution for Ba, except for FRC-REF samples; and diffusion for Cr in FRC-REF and C-REF samples; • This type of material did not present any possible environmental impact and could be a viable alternative that would help increase the valorisation of such types of plastic waste, which is considered as being one of the biggest concerns worldwide. XIII INDEX 1. Introduction ........................................................................................................................................................ 1 1.1 Background.........................................................................................................................................1 1.1.1 A brief history of plastic ...................................................................................................................... 1 1.1.2 Classification and application of plastics ........................................................................................... 4 1.1.3. Plastic materials used in food packaging industry ........................................................................... 7 1.2 Problems of plastic waste..................................................................................................................9 1.2.1 Legislative framework and standards related to the management of plastic waste ..................... 9 1.2.2 End-of plastic waste from food packaging ..................................................................................... 16 1.3 Use of reinforcing fibres in concrete..............................................................................................20 1.3.1 Types of fibres used in reinforced concrete .................................................................................... 20 1.3.2. Physical and mechanical properties of concrete with plastic macro fibres ............................... 23 1.4 Environmental impact assessment by leaching behaviour as an indicator of sustainability in concrete .......................................................................................................................................................... 25 1.4.1 Background of environmental assessment through leaching tests .............................................. 25 1.4.2 Leaching tests applied to characterisation of pollutant potential of reinforced concret with macro plastic fibres ...................................................................................................................................... 28 1.4.3 Factors that affect the contaminating potential of a material and release mechanisms ........... 29 1.4.4 Environmental legislation applied in this Doctoral Thesis ........................................................... 31 References .............................................................................................................................................................. 34 2. Objectives, Methodology and Structure of the Doctoral Thesis ............................................................... 43 2.1 Objectives ................................................................................................................................................ 43 2.2. Methodology .......................................................................................................................................... 44 2.3. Structure ................................................................................................................................................. 44 3. Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres (Publication II) ...................................................................................................................................................... 47 3.1. Introduction ........................................................................................................................................... 47 3.2. Materials and Methods ......................................................................................................................... 49 3.2.1. Recycled Plastic Fibres (RPFs) from Food Packaging Waste (FPW) ........................................ 49 3.2.2. Fibre-Reinforced Concrete (FRC) Specimens Made with RPF .................................................. 50 3.3 Experimental Methods .......................................................................................................................... 51 3.3.1. Physical Properties ............................................................................................................................. 51 3.3.2. Compressive Strength ....................................................................................................................... 51 3.3.3. Elastic Modulus .................................................................................................................................. 51 3.3.4. Flexural Strength ................................................................................................................................ 51  XIV 3.3.5. CMOD and Toughness ..................................................................................................................... 51 3.4. Results and Discussion ......................................................................................................................... 51 3.4.1. Physical Properties ............................................................................................................................. 51 3.4.2. Compressive Strength ....................................................................................................................... 52 3.4.3. Elastic Modulus .................................................................................................................................. 53 3.4.3. Flexural strength ................................................................................................................................ 54 3.4.5. Toughness ........................................................................................................................................... 55 3.5. Conclusions ............................................................................................................................................ 57 References ...................................................................................................................................................... 58 4. Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste (Publication III) ......................................................................................................................................... 63 4.1. Introduction ........................................................................................................................................... 63 4.2. Materials .................................................................................................................................................. 66 4.2.1. Recycled Plastic Fibres (RPF) from Food Packaging Waste (FPW) ......................................... 66 4.2.2. Fibre Reinforced Concrete Specimens (FRC) Made with RPF .................................................. 67 4.3. Experimental Methods for Environmental Assessment ................................................................ 68 4.3.1. Compliance Test for RPF UNE-EN 12457-4:2003 ..................................................................... 69 4.3.2. Determination of the Availability Threshold of FRC ................................................................. 69 4.3.3. Determination of the Leaching Behaviour of Monolithic Specimens ...................................... 69 4.4. Results and Discussion ....................................................................................................................... 71 4.4.1. Release Levels on Leachates from RPF by UNE-EN 12457-4:2003 ...................................... 71 4.4.2. Determination of Maximum Leachability for Heavy Metals by NEN 7371 ............................ 72 4.4.3. Diffusion Leaching Tests in FRC Specimens Made with RPF ................................................. 74 4.5. Conclusions ............................................................................................................................................ 78 References ...................................................................................................................................................... 79 5. Main results and general discussion ............................................................................................................... 83 6. Conclusions ....................................................................................................................................................... 87 6.1. General conclusions .............................................................................................................................. 87 6.2. Future lines of research proposed ...................................................................................................... 87   XV LIST OF TABLES Table 1.1. Abbreviated terms, name and the main uses of the plastics used in the civil construction sector ................................................................................................................................................................................... 6 Table 1.2.Main physical and mechanical characteristics of the plastics used in the civil engineering ........ 6 Table 1.3. Geometric characteristics of the micro and macro plastic fibres most used in the civil construction sector ............................................................................................................................................... 21 Table 3.1. Technical data of recycled plastic fibres (RPFs) and commercial polypropylene fibre (CPF). Abbreviated terms, name and the main uses of the plastics used in the civil construction sector ........... 50 Table 3.2. Results of the test methods conducted on concrete samples, related to their physical properties ................................................................................................................................................................................. 52 Table 4.1. Technical data of plastic sheets PET + ALU + OPA STE + PP G .......................................... 67 Table 4.2. Leachate concentrations (mg/kg m.s.) from RPF by UNE-EN 12457-4:2003 ........................ 71 Table 4.3. Leachate concentrations (mg/m2) from concrete specimens according to the diffusion leaching test ........................................................................................................................................................................... 74 Table 4.4. Cumulative emission (ε64), diffusion coefficient (De) and pDe ...................................................75 Table 4.5. Limits for diffusion release levels from shaped construction materials (in mg/m2). Slope of linear regression and correlation coefficient .................................................................................................... 77 LIST OF FIGURES Figure 1.1. The Parkesine factory at Hackney Wick, London (a) and the replica of the Bronze medal awarded to Alexander Parkes at the International Exhibition in 1862 in London (b) ................................ 1 Figure 1.2. Objects made with Bakelite: Siemens telephone (a) ; pocket camera (b) ; radio with valves (c) ................................................................................................................................................................................... 2 Figure 1.3. Polypropylene objects: fitting for plumbing systems (a); objects of wide daily use (b) ;seats of a stadium (c) ............................................................................................................................................................ 2 Figure 1.4. Containers in Polyethylene Terephthalate: plastic bottles for liquid packaging (a) ................... 3 Figure 1.5. The change in the relative importance of materials used in engineering over time ................. 3 Figure 1.6. Some objects made with Technopolymers: plastic engine (a); gears for food machineries (b) drone (c) New Jersey Road Separators (d) waste container lids (e) ................................................................. 4 Figure 1.7. The distribution and fields of use of plastics produced in Europe ............................................ 5 Figure 1.8. The demand for plastics in Europe, divided by sectors ............................................................... 5 Figure 1.9. The milestones in packaging history ............................................................................................... 7 Figure 1.10. Types of multilayer food packaging material structure: with six layers and three materials (Tetra Pak courtesy) (a), with four layers and four materials (SP Group courtesy)(b) ................................ 8 Figure 1.11.The EU waste hierarchy .................................................................................................................. 9 Figure 1.12. The main legislation regarding packaging and packaging waste: European (a) and Spanish (b) ................................................................................................................................................................................. 15 Figure 1.13. The 17 Sustainable Development Goals (SDGs) adopted by all United Nations Member XVI States ....................................................................................................................................................................... 15 Figure 1.14. Phases of mechanical recycling of plastic .................................................................................... 17 Figure 1.15. Scheme of the recycling methods of multilayer plastic packaging .......................................... 19 Figure 1.16. Examples of commercial microfibres used as concrete reinforcement in the civil construction sector ...................................................................................................................................................................... 21 Figure 1.17. Examples of commercial macrofibres used as concrete reinforcement in the civil construction sector ............................................................................................................................................... 22 Figure 1.18. Schematic flow of contaminants in the field and extrapolation to a laboratory test ........... 25 Figure 1.19. Characterisation and compliance leaching tests in different stages of the building cycle ... 26 Figure 1.20. Different study phases developed during the environmental assessment of the reinforced concrete made from plastic residues .................................................................................................................. 27 Figure 1.21. Material-specific and external factors (chemical and physical), influencing the release of contaminants from monolithic and granular material such as used in a road base .................................... 28 Figure 1.22. General leaching behaviour of three groups of constituents as a function of pH ............... 30 Figure 2.1. Methodology ...................................................................................................................................... 44 Figure 3.1. Plastic fibres: plastic waste rolls from food packaging (a); the prepared fibres (b); commercial polypropylene fibre (c) ......................................................................................................................................... 50 Figure 3.2. Compressive strength values for each mixture, along with the standard deviation bands: at 7 and 28 days (fck,cube) (a); at 28 days (fck,cyl) (b) ..................................................................................................... 53 Figure 3.3. Elastic modulus (Ecm) values for all mixtures at 28 days, along with the standard deviation bands ................................................................................................................................................................................. 54 Figure 3.4. Flexural strength values for all mixtures, along with the standard deviation bands ............... 55 Figure 3.5. Average load–CMOD curves of three specimens of each concrete type ................................. 55 Figure 3.6. Load–deflection curves of each concrete type (a); detailed view of the initial section of the curve (b). ........................................................................................................................................................................... 56 Figure 3.7. Values of toughness (a) and toughness index (b) ......................................................................... 57 Figure 4.1. Plastic sheets from food packaging: front and back sides (a) and the prepared fibres (b) ..... 66 Figure 4.2. Concrete specimens of FRC with RPF: FRC2, FRC4 and FRC6 ............................................. 67 Figure 4.3. Phases of the experimental procedure for leaching assessment of FRC made with RPF ............ 68 Figure 4.4. Comparison of two pH regimes in the availability test (pH 7 and pH 4) for heavy metals in samples: (a) control C-REF; (b) control FRC-REF; (c) FRC2 specimen; (d) FRC4 specimen; and (e) FRC6 specimen................................................................................................................................................................. 73 Figure 4.5. Graphical representation of diffusion-controlled leaching (mg/m2) vs. time (days) in samples: (a) control C-REF; (b) control FRC-REF; (c) FRC2 specimen; (d) FRC4 specimen; and (e) FRC6 specimen................................................................................................................................................................. 77 XVII ABBREVATIONS   CEN/TC CEN Technical Committee CEN-TS 15862:2012 European Committee for Standardization - Technical Specification CMOD Crack mouth opening displacement CPF Commercial polypropylene fibre C-REF Concrete without reinforcement EEA European Environment Agency ENAC Entidad Nacional de Acreditación EPS Sintered expanded polystyrene FPW Food packaging waste FRC Fibre reinforced concrete FRC2-REF Fibre reinforced concrete made with commercial fibre dosage of 2 kg/m3 FRC-REF Fibre reinforced concrete for reference FRP Fibre reinforced plastic HDPE Highdensity polyethylene ICP-MS Inductively Coupled Plasma Mass Spectrometry LDPE Low-density polyethylene LLDPE Linear Low-Density Polyethylene LVDTs Linear variable displacement transducers MDPE Medium-density polyethylene MLP Multilayer plastic NEN 7371 Dutch standard extraction test OPA STE Biaxially oriented polyamide PA Polyamide PAN Polyacrylonitrile PC Polycarbonate PE Polyethylene PE-HD/PE-MD Polyethylene, high and medium density PE-LD/PE-LLD Polyethylene, low and liear density PET Polyethylene terephthalate PF Plastic fibres PF Polypropylene fibres  XVIII PFRC Plastic fibre reinforced concrete PMMA Polymethylmethacrylate PP Polypropylene PFRC-REF Concrete made with commercial polypropylene fibres PS Polystyrene PUR Polyurethane PVC Polyvinyl chloride PVDC Polyvinylidene Chloride RPF Recycled Plastic Fibres RPFs Concrete reinforced with macro plastic fibres SA Strategic activities SDG Sustainable Development Goals SQD Soil Quality Decree ULDPE Ultra Low-Density Polyethylene   Chapter 1 1 1. Introduction 1.1 Background 1.1.1 A brief history of plastic The origin of plastic, understood as a natural polymer, dates back to ancient times, when Human began to use natural products such as amber, tortoise shell, horn [1], bones for his own purposes of animals, silk, wool [2], plant cellulose or starches [3]. The first semi-synthetic plastic material, Parkesine (also called synthetic ivory) was patented by the English chemist Alexander Parkes in the second half of the 19th century, following the development of studies on cellulose nitrate [3]. In Figure 1.1(a) we see the outside of the factory where Alexander Parkes produced the first plastic in the world [4] while Figure 1.1 (b) shows the Bronze medal that was given to the English chemist on the occasion of the International Exhibition in London in 1862 [5]. (a) (b) Figure 1.1 The Parkesine factory at Hackney Wick, London (a) [4] and the replica of the Bronze medal awarded to Alexander Parkes at the International Exhibition in 1862 in London (b) [5]. In 1869, the English Daniel Spill, former partner of Alexander Parkes, founded a company for the production of Xylonite, a plastic material that took the place of Parkesine [1]. Subsequently, in 1870, the American Hyatt brothers patented the celluloid formula [3,6], the aim was to replace the expensive and increasingly rare ivory used to build billiard balls with a cheaper material [1]. Celluloid will later be used in many other sectors: production of cinematographic films, material for use by dentists for making dental impressions [6], waterproofing of the wings and fuselages of the first aircrafts [7]. Nevertheless, it is from the early years of the twentieth century that plastic obtains its greatest successes. Starting from 1909, with the Bakelite patent by the Belgian chemist Leo Baekeland, indispensable objects for the nascent automotive industry were produced such as electrical parts [2,6,12], brake pads and pistons [8], as well as to everyday objects such as microwave pans, handles, bottle caps, linings [10,11,12]. The success of bakelite was essentially due to its remarkable resistance to electricity, heat and chemical action [12]. In Figure 1.2, it can be observed some objects made with a Bakelite casing: in Figure 1.2 (a) a Siemens telephone from 1929 [9] is depicted, in Figure 1.2 (b) a pocket camera produced in the mid- 1930s [10] while in Figure 1.2 (c) is shown one radio with valves of the 1950s [11]. Introduction 2 (a) (b) (c) Figure 1.2 Objects made with Bakelite: Siemens telephone (a) [9]; pocket camera (b) [10]; radio with valves (c) [11]. In the following years, many other synthetic plastics were produced: Polyvinyl Chloride (PVC), in 1912, by the German chemist Fritz Klatte [13]; Cellophane, in 1913, invented by the Swiss Jacques Edwin Brandenberger. Additionally, it was precisely when, from this last material produced in very thin and flexible transparent sheets, the development of packaging began [14,15]. At the beginning of the 1930s, with the emergence of the new raw material, oil, the development of synthetic materials derived from the petrochemical industry began. In 1935, the American chemist Wallace Carothers synthesized Nylon, a new synthetic fibre, that will be used mainly by the American and British textile industry in order to make up for the import of silk and for the production of parachutes, women's socks and ropes [1,16]. British chemists Rex Whinfield and James Tennant Dickson, in 1941, patented the first polyester fibre, Polyethylene Terephthalate (PET) [17], a material that, both for toughness and resilience, was superior to nylon [18]. Its use proved to be very useful in the military field, as a substitute for metals and natural materials [19]. In the early 1950s, the Italian chemical engineer Giulio Natta, together with the German chemist Karl Ziegler, developed a thermoplastic polymer, Isotactic Polypropylene (PP), which due to its dimensional stability, resistance to chemical products and a considerable duration at high temperatures, it will find various applications [20]. In Figure 1.3 you can see some examples of objects currently made with PP: weldable polypropylene fittings, designed for the construction of hot and cold sanitary water distribution systems [21], other everyday objects [22,23].  (a) (b) (c) Figure 1.3 Polypropylene objects: fitting for plumbing systems (a) [21]; objects of wide daily use (b) [22]; seats of a stadium (c) [23]. In 1973, the American engineer Nathaniel Wyeth created a variant of PET capable of withstanding the pressure of carbonated liquids: thus, the era of food packaging and the PET bottle, light, impact resistant and transparent, was born [24]. Figure 1.4 shows the variety of shapes, sizes, colours and uses of the containers that can be made using PET [25,26]. Chapter 1 3   (a) (b) Figure 1.4 Containers in Polyethylene Terephthalate: plastic bottles for liquid packaging (a) [25]; products specially designed for pharmacies and healthcare professionals (b) [26]. Starting from the 1960s and up to modern times, thanks to the development of new technologies, technopolymers (called engineering polymers) established themselves [27]. Figure 1.5 shows the relative importance of the materials used in engineering over time, divided by type (metals, polymers and elastomers, composites, ceramics, glass). In this diagram, the abscissa axis is time, in a non-linear scale, and on the ordinate axis is the relative importance of the materials, a magnitude assessed on the basis of the historical period: for the period that includes the Stone and Bronze Ages its value was established by archaeologists; in 1960 is based on the teaching hours of the study of materials carried out at the universities of the United Kingdom and the United States; in 2020 on the forecasts of the use of materials in cars by manufacturers. It is highlighted that starting from prehistory and up to the end of the 1950s, there has been a continuous decline in their relative importance and that instead, after the Second World War, following the post-war industrial recovery, the trend has reversed [88]. Figure 1.5 The change in the relative importance of materials used in engineering over time [88]. These plastics, due to their high physical-mechanical characteristics (stiffness, toughness, ductility, workability, resistance to high temperatures, static and dynamic loads or aging) allow to be used in place of metals [27], in many cases. They are used in almost all fields of human activities, from the manufacture Introduction 10    EUROPEAN STANDARDS 2004 Directive 2004/12/EC of February 11, 2004 [ 99 ] Subject: AMENDING DIRECTIVE 94/62/EC ON PACKAGING AND PACKAGING WASTE Main objectives of the Directive: Timescale for the transposition of directive Directive 94/62/EC into national law and set targets for the next five years; Clarification on the definition of “packaging” and illustrative examples; Encouraging the development of innovative, environmentally sound and viable recycling processes; Introducing cost-benefit analysis, which have indicated clear differences both in the costs and in the benefits of recycling the various packaging materials; Recovery and recycling of packaging waste should be further increased to reduce its environmental impact; The operators in the packaging chain as a whole should shoulder their shared responsibility to ensure that the environmental impact of packaging and packaging waste throughout its life c y cle is reduced as far as p ossible. 2015 Directive 2015/720 (EU, 2015) of April 29, 2015 [ 101 ] Subject: LIGHTWEIGHT PLASTIC CARRIER BAGS Main objectives of the Directive: Urging Member States to 'take measures to achieve a sustained reduction in the consumption of lightweight plastic carrier bags on their territory'; Ensuring an annual consumption of a maximum of 90 lightweight plastic carrier bags per person by 31 December 2019 and 40 per person by 31 December 2025, and/or the levying of charges on lightweight plastic carrier bags at the point of sale of goods or products before 2019; Establishing reporting obligations on the annual consumption of lightweight plastic carrier bags. 2008 Directive 2008/98/EC of November 19, 2008 [100] Subject: WASTE AND REPEALING CERTAIN DIRECTIVES Main objectives of the Directive: Waste Hierarchy; Protection of human health and the environment; Principles of proximity and self-sufficiency; Waste Management Plans. Chapter 1 11                           2018 Directive (EU) 2018/851 of May 30, 2018 [102] Directive (EU) 2018/852 of May 30, 2018 [103] Subject: WASTE FRAMEWORK Main objectives of the Directive:  Importance of waste prevention according to the so called waste hierarchy;  Flexibility regarding the nature of waste prevention implementation;  Countries waste prevention programmes and requires that objectives and qualitative or quantitative benchmarks are set;  Publish periodic reports on waste prevention, every 2 years. These reports will contain a review of the progress. Subject: AMENDING DIRECTIVE 94/62/EC ON PACKAGING AND PACKAGING WASTE Main objectives of the Directive:  The amendment requires Member States to take appropriate measures to encourage an increase in the share of reusable packaging placed on the market and the reuse of packaging;  Minimum targets by weight for recycling will be met for specific materials in packaging waste: no later than 31st December 2025, 50% of plastic; no later than 31st December 2030, 55% of p lastic. EUROPEAN STANDARDS 2019 Directive (EU) 2019/904 of June 5, 2019 [104] Subject: REDUCTION OF THE IMPACT OF CERTAIN PLASTIC PRODUCTS ON THE ENVIRONMENT Main objectives of the Directive:  Preventing and reducing the impact on the environment of certain plastic products;  Promoting a transition to a circular economy by introducing a mix of measures tailored to the products covered by the directive, including an EU-wide ban on single-use plastic products whenever alternatives are available;  Market restrictions (bans): the plastic products to be banned under the directive include: cutlery (forks, knives, spoons, chopsticks), plates, straws, cotton bud sticks, beverage stirrers, sticks to be attached to and to support balloons, food containers made of expanded polystyrene, products made from oxo-degradable plastic;  Consumption reductions: EU countries are required to: take measures to reduce the consumption of certain single-use plastics for which there is no alternative (drinking cups including covers and lids, and containers of prepared food for immediate consumption), monitor consumption of these single-use products as well as the measures taken and report the progress made to the European Commission. The directive requires an ambitious and sustained quantitative reduction in consumption of these products by 2026 (compared to a 2022 baseline);  Separating collection and designing requirements for plastic bottles: the directive sets a collection target of 90% recycling for plastic bottles by 2029 (with an interim target of 77% by 2025); these bottles should contain at least 25% recycled plastic in their manufacture by 2025 (for PET bottles), and 30% by 2030 (for all bottles); Introduction 12 a)                       SPANISH STANDARDS 1997 Ley 11/1997 of April 24, 1997 [105] Subject: PACKAGING AND PACKAGING WASTE Main objectives of the Law: Incorporating the substantive rules of Directive 94/62/EC; Promoting prevention and reuse of packaging; Establishing the recycling and recovery targets provided for in the aforementioned Directive; Requirements for packaging; Information to be provided to the Autonomous Communities, programming and economic tools; The sanctioning regime. Ley 66/1997 of December 30, 1997 [106] Subject: AMENDMENT OF THE LEY 11/1997 OF APRIL 24 Main objectives of the Law: The obligations established in Chapter IV of the Law 11/1997, of April 24, on Packaging and Packaging Waste, on the "System of deposit, refund and return and integrated systems for the management of used packaging and packaging waste", will be required from May 1, 1998 and not from January 1, 1998.  Compulsory marking: certain disposable plastic products placed on the market must carry a visible, clearly legible and indelible marking affixed to its packaging or to the product itself: sanitary items, wet wipes, tobacco products with filters, drinking cups; these labels should inform consumers about appropriate waste management options for the product or what type of waste disposal should be avoided for the product; and the presence of plastics in the product as well as the negative environmental impact of littering;  Extended producer responsibility: the directive incorporates the ‘polluter pays’ principle.  Awareness raising: EU countries must also take measures to inform consumers and to encourage responsible consumer behavior in order to reduce litter from such products, make consumers aware of reusable alternative products and the impact of inappropriate disposal of single-use plastic waste on the sewage system. Chapter 1 13                                   2000 Ley 14/2000 of December 29, 2000 [109] Subject: AMENDMENT OF THE LEY 11/1997 OF APRIL 24 ON PACKAGING AND PACKAGING WASTE Main objectives of the Law: Exceptions to the application of the obligations established in Law 11/1997 in article 6 (Deposit, return and return system and integrated management systems for used packaging and packaging waste. Obligations) or, where appropriate, in the section 2nd of chapter IV (Integrated management systems for packaging waste and used packaging). SPANISH STANDARDS 1998 Real Decreto 782/1998, of April 30, 1998 [107] Subject: APPROVAL OF THE REGULATION FOR THE DEVELOPMENT AND EXECUTION OF LEY 11/1997, OF APRIL 24, ON PACKAGING AND PACKAGING WASTE Main objectives of the Royal Decree: Definitions of packaging, composting or composting, biomethanization, economic agents responsible for packaged products, packer, first placing on the market, distance selling and automatic sale; penalty regime for packers ; Preparing business plans for the prevention of packaging waste; Recycling reduction and recovery; Obligations derived from the placing on the market of packaged products; Delivery of packaging waste and used packaging; Packaging requirements; Marking and identification of packaging; Information to Public Administrations. Ley 50/1998 of December 30, 1998 [108] Subject: AMENDMENT OF THE LEY 11/1997 OF APRIL 24 ON PACKAGING AND PACKAGING WASTE Main objectives of the Law:  Tax obligations for packers (se añade un apartado 4 al artículo 10 de la Ley 11/1997);  Penalty regime for packers (a letter h) is added to paragraph 2 of article 19);  The data on the application of the amendment will start from April 1, 1999. Introduction 14                                   2006 Real Decreto 252/2006, of March 3, 2006 [ 110 ] Subject: REVIEW OF THE RECYCLING AND RECOVERY OBJECTIVES ESTABLISHED IN LEY 11/1997, OF APRIL 24, ON PACKAGING AND PACKAGING WASTE, AND BY WHICH THE REGULATION FOR ITS EXECUTION, APPROVED BY REAL DECRETO 782/1998, OF APRIL 30TH. Main objectives of the Law: Modification of the recycling and recovery targets established in Law 11/1997, of April 24, on Packaging and Packaging Waste; Modification of the Regulation for the execution of Law 11/1997, of April 24, on Packaging and Packaging Waste, approved by Royal Decree 782/1998, of April 30; Voluntary agreements and collaboration agreements between the competent public administrations and the economic agents responsible for placing packaging and packed products on the market; Establishing models related to database systems on packaging and packaging waste; Definitions in the preparation of information on packaging and packaging waste; Determination of the data; Disposal on valorization; Presentation of the data. SPANISH STANDARDS 2011 Ley 22/2011 of July 28, 2011 [ 111 ] Subject: WASTE AND CONTAMINATED SOILS. Main objectives of the Law: The object, the definitions, as well as the reference to the classification and the European list of waste; Establish the legal regime for the production and management of waste, as well as the provision of measures to prevent its generation and to avoid or reduce adverse impacts on human health and the environment associated with their generation and management; Specific articles dedicated to the concepts of "by-product" and of "end of waste status" are introduced, and the conditions that a waste must meet to be considered a by-product or to lose its status as a waste are established; The principles of the waste policy: the protection of human health and the environment; A new waste hierarchy is formulated that specifies the order of priority in actions in the waste policy: prevention (in the generation of waste), preparation for reuse, recycling, other types of recovery (including energy) and, by finally, the elimination of waste; Chapter 1 15          (b) Figure 1.12 The main legislation regarding packaging and packaging waste: European (a) and Spanish (b) The reuse of waste, whatever its nature or origin, must be the goal to grant it a second life cycle. Even more so in engineering and construction sectors which accounted for 36% of final energy use and 39% of energy and process-related carbon dioxide (CO2) emissions [146]. In this framework, decarbonisation and resilience of the construction sector is necessary (responsible for almost 40% of energy and processrelated emissions). It is critical to achieve the challenge adopted on 25th September 2015 by United Nations General Assembly in Resolution 70/1: Transforming our World: the 2030 Agenda for Sustainable Development. The document lays out the 17 Sustainable Development Goals (SDG) illustrated in Figure 1.13 to end poverty and hunger, protect human rights and to protect the planet from degradation. Figure 1.13 The 17 Sustainable Development Goals (SDGs) adopted by all United Nations Member States. As it has been mentioned above, nowadays the massive use of plastic packaging characterized as singleuse or disposable is a matter of global concern and it is one of the aspects that the 2030 Agenda develops. The relationship between the SDGs and the need to curb plastic pollution is clear. The Plastic Soup Foundation, a UN Environment Programme-accredited non-governmental organization based in the Netherlands and founded in 2011, has highlighted the relationship among several SDGs: The administrative powers of each of the public administrations involved in waste management are defined; Waste management planning at national, regional and local level; The obligations of those are involved in the chain production and waste management; The transferal of waste, understood as the transport destined to elimination and valorisation The producres of elemnts that become waste are involved in the prevention and management planning of them, re-use, recycling and valorisation are encourged.; The regulation of containated soils; Responsibility, vigilance, inspection and control and sanction rules. Introduction 16  SDG 3: Good health and well-being.  SDG 6: Clean water and sanitation.  SDG 11: Sustainable cities and communities.  SDG 12: Responsible consumption and production.  SDG 13: Climate action.  SDG 14: Life below water (protection of the seas and oceans).  SDG 15: Life on land (restore ecosystems and preserve diversity). The reason of the massive use in packaging food sector is the excellent qualities it possesses high chemical inertness, impermeability to liquids and gases, lightness and non-toxicity. In that sense the present Doctoral Thesis is addressing an issue identified as key in the 2030 Agenda Action plan and the breakthroughs of the project advance to contribute to solve this environmental problem, not only because of the fossil resources needed to produce plastic-based films, but also because the final management mostly relies on landfill and incineration. The present Thesis will contribute to increase the recyclability rate of the plastic waste produced as it can be incorporated as reinforcement fibres for concrete mixtures in precast sector, aligning to achieve compliance with the 2030 Agenda. At national level, the National Integrated Energy and Climate Plan 2021-2030 (PEICTI 2021-23) has identified six strategic activities:  SA1: Health  SA2: Culture, creativity and inclusive society  SA3: Security for society  SA4: Digital world, industry, space and defense  SA5: Climate, energy and mobility  SA6: Food, bioeconomy, natural and environmental resources The present Doctoral Thesis is focused on achieving the SA5 strategic activity “CLIMATE, ENERGY AND MOBILITY”. This challenge is defined by the National Plan for achieving a more efficient economy and society in the use of resources and water, and resistant to climate change, the protection and sustainable management of natural resources and ecosystems and a sustainable supply and use of raw materials, to meet the needs of a growing world population within the sustainable limits of the planet's natural resources and ecosystems. 1.2.2 End-of plastic waste from food packaging The plastics market in Europe is largely oriented to packaging (39.6%), as can be seen in Figure 1.8, and, particularly, to the food market where the following polymers mainly predominate: PP (19.4%), PE - LD/PE-LLD (17.4%), PE-HD/PE-MD (12.4%), PET (7.9%) and PS + EPS (6.2%) [46]. Given the significant amount of plastic produced through the use of these polymers, which together make up 63.3 % of the plastic used in Europe in 2019 [46], the problem of the end-of-life of these products has been raised for some decades. There are three possible alternatives: recycling, energy recovery and landfilling. European statistics say that, in 2018, 42 % of the plastics used for packaging was recycled, while the rest was taken to energy recovery plants (39.5 %) and landfills (18.5 %) [46]. The objective of the European Union, according to Directive (EU) 2019/852 on Packaging and Packaging Waste, is to reach 50% in 2025 and 55% in 2030. In 2018, the Czech Republic, Germany, Spain and the Netherlands reached the goal of 50%, ahead of the time compared to the target set [46]. Chapter 1 17 Recycling plastic wastes for production of secondary raw materials such as pellets, aims to give plastic a new life. It is implemented through the following phases: collection, first sorting, shredding, washing, second sorting and control and extrusion (Figure 1.14) [46]. The first phase consists in the collection of end-of- life plastic products from separate and mix waste streams. The second is the separation of waste by type of material (plastics, aluminum, tinplate, cardboard, paper, etc.). Plastic packaging is in turn divided according to the type of polymer and by type of single or multilayer polymer [110], which will be treated. The third phase is where the plastic are ground into smaller pieces and in the fourth phase the shredded plastics are washed to remove dust and dirt. In the fifth phase, the plastics are sorted again and controlled before sent to extrusion which represents the last phase of the process during which, the plastic flakes, after being heated, are finally converted into homogenous pellets ready to use in the manufacture of new products. Figure 1.14 Phases of mechanical recycling of plastic (graph adapted from [46]) Another alternative to mechanical recycling is represented by chemical recycling, depolymerization, a treatment used mainly with complex plastic waste streams, like films or laminates. It consists of the chemical reversion of a polymer to its monomer or to a polymer of lower relative molecular mass and allows to obtain recycled plastics that have the same properties as the virgin ones and which therefore can also be used in applications in which there are both contact with food, as for food packaging. The conversion process is carried out through various methods: 1. thermochemical decomposition of plastic at high temperature and in the absence of oxygen. 2. pyrolysis technology, which turns plastic waste into a secondary raw material called pyrolysis oil gasification, i.e., the creation of syngas (synthetic gas) produced by the carbon residues of the pyrolysis process, using extremely high temperatures and minimal oxygen. COLLECTION FIRSTSORTING SHREDDING WASHING SECOND SORTINGAND CONTROL EXTRUSION END‐OF‐LIFEPRODUCTS RECYCLEDPOLYMERS Introduction 18 3. hydrogenation, the creation of syncrude (liquid and gaseous) through the application of hydrogen in a high temperature and pressure environment. Another option for material recovery consists of biological or organic recycling with which biodegradable plastics waste is treated microbiologically under aerobic or anaerobic conditions to produce energy in the form of heat, carbon dioxide and water vapor [115]. In addition to mechanical recycling and chemical recycling, the other option for plastics recovery technologies is energy recovery (waste-to-energy). Given the high calorific value, plastic packaging waste adapts very well to the waste-to-energy process with energy recovery and the use of this methodology would result in a significant reduction in the volume of waste going to landfills. Instead of using the primary resources of fossil fuels, energy is produced in this way in the form of generating heat, steam or electricity using plastic waste [111]. The process takes place through the incineration of the plastic and then with the total combustion of the plastic material with consequent emission of gaseous substances such as CO2, H2O, O2, N2. With modern systems and technologies, the containment of these gaseous emissions into the atmosphere is guaranteed and the combustion of plastics does not increase the emissions of harmful substances. For this purpose, the waste combustion plant is divided into five main sections: waste preparation and feeding, waste combustion, heat recovery, control of atmospheric emissions, stabilization and disposal of waste. ash and solid residues. Despite this, according to some researchers, there is evidence showing that incineration is not the terminator of plastic waste and ash and solid residues are potential sources of release of microplastics into the environment [113][114]. Incineration is the process that is mainly used for the waste-to-energy process of plastic waste that has a poor chance of being recycled otherwise, such as multilayer plastics for food packaging [116]. For these types of plastics, consisting of two or more thin layers of different materials, the recycling methods, in addition to incineration and landfill, are mainly two: the first is to separate the different components and then recycle them individually, the second is to mix all the components together in one compatibilization step (without separating into different components). Figure 1.15 shows the scheme of the recycling methods of multilayer plastic packaging materials [117]. Chapter 1 19 Figure 1.15 Scheme of the recycling methods of multilayer plastic packaging [117]. Helping to increase the quantity of multilayer plastic packaging waste that falls within the economic circle through its reuse is precisely the purpose of this study which, through the experimentation of innovative materials such as concrete made with the addition of macro plastic fibres obtained from industrial waste of multilayer films for food packaging, aims to present an alternative to the other recycling processes described above, which present some drawbacks regarding the environmental and energy costs. MultilayerRecycling Separationofthedifferent components Recyclingofatargetpolymerby disolutionandreprecipitation Separtionofthedifferent components Mechanicaldelamination Chemicaldelamination ofthedifferentlayers Chemicaldelaminationby decompositionofaninterlayer Delamiinationcausedby reactionsattheinterface Physicaldelamination Combinedprocessingofthe differentcomponents Introduction 26 Leaching tests can easily and quickly simulate the process by which constituents in a solid material (contaminated soil, sludge, sediment, compost, waste or a construction material) are released into the environment through contact with water. [139]. Understanding the rate and extent to which constituents (potential pollutant elements) of interest may be released to the leachate is central to defining the following: 1. potential environmental impacts through water-borne mechanisms including soil, groundwater and surface water contamination 2. human health and ecological risks from beneficial use and disposal of commercial materials and wastes 3. effectiveness of certain treatment processes for materials 4. designs and acceptance criteria for waste management facilities 5. degradation of structural performance of certain materials in the environment. Another important aspect to the environmental evaluation of construction materials made from recycled products is to evaluate the parameters which affects to release levels of potential pollutant elements as: 1. chemical and physical properties of the tested material 2. chemistry of the constituents evaluated 3. characteristics of the local environment in which the material is placed, including chemical properties (e.g., pH, oxidation-reduction potential, presence of reacting constituents such as carbon dioxide) and the nature of water interaction (e.g., frequency, amount, interfacial contact area). The present Doctoral Thesis includes the environmental behaviour of the studied material focused on leaching tests due to leaching processes allow us deep on study and research on material testing, and development of mathematical models to estimate long-term behaviour of recycled construction materials. Numerous leaching tests are available to assess the release from these materials under a variety of conditions. In general, the most commonly used methods are percolation tests for granular materials (unbound aggregates) and diffusion tests for monolithic products (cement-treated materials as mortars or concrete) [119]. In Figure 1.19 the material flow during the environmental assessment and different leaching methodologies of a construction material, is observed: Figure 1.19 Characterisation and compliance leaching tests in different stages of the building cycle [140]. Chapter 1 27 The starting point of the process observed in Figure 1.18 for construction materials made from recycled products as is the case of the material studied by the present Doctoral Thesis, is the material classification according to the pollutant potential performed according to the compliance test. The compliance test allows the classification of the waste according to its hazardous level, which conclude with the classification of this residue as inert, non-hazardous or hazardous material. If the residue complies with the legal values to be classified as inert or non-hazardous material, the following step can be achieved, and the incorporation of this waste to the dosage of the construction material (mortar or concrete) is possible. In that phase, the diffusion tank leaching tests performed to the monolithic. The different phases developed during the environmental assessment of the reinforced concrete studied are represented in Figure 1.20 following the exposed methodology: Figure 1.20 Different study phases developed during the environmental assessment of the reinforced concrete made from plastic residues. While monolithic materials often show diffusion-controlled release, granular materials usually show percolation dominated release. Examples of monolithic products are all cementitious products (e.g., concrete, bricks, coated materials). The release of both categories (see Figure 1.21) is influenced by material specific factors as well as environmental factors. Introduction 28 Figure 1.21 Material-specific and external factors (chemical and physical), influencing the release of contaminants from monolithic and granular material such as used in a road base [119]. Therefore, researchers focused on leaching tests as environmental tool of analysis use a common set of leaching tests that define and quantify the underlying mechanisms of contaminant release under a wide range of environmental conditions and that help us to verify that using a waste that is harmless to the environment is possible, and that it is therefore feasible, to manufacture a construction material with this by-product incorporated into the concrete dosage. 1.4.2 Leaching tests applied to characterisation of pollutant potential of reinforced concrete with macro plastic fibres Currently the framework for leaching tests on construction products is based on a limited number of test methods suited to meet the needs of regulators and manufacturers and related to a wide range of construction materials and a wide range of application scenarios. According to that, three types of tests can be distinguished: 1. Characterization tests are procedures used as a first step of analysis. These tests characterise the release behavior of the tested material allowing a basic characterisation and reducing the number of samples that require the laboratory characterization. 2. Compliance tests allow the checking of complying with regulations in environmental matter. These tests verify whether a material complies with the behavior of a reference material. Then, after the basic characterisation, the compliance test allows to check whether the material still complies with a proper behaviour. 3. On-site verification are a type of quality control leaching tests with the aim to determine easily and quickly if a material complies with the expected behaviour for a real application (on site works for testing). The experimental procedure in leaching tests establishes that the first step is the conformity test and to more complex and detailed characterization, the characterisation tests. In order to evaluate the environmental risk derived from the release and migration of hazardous elements that can be released using recycled materials, the release basic mechanisms must be identified. The basic mechanisms for contaminant release of (for a wide range of environmental conditions) are:  NEN 7371 [122,123] (maximum availability) The Dutch standard extraction test (NEN 7371, 2004) determines the maximum leachability of an element due to the aggressive conditions imposed by this procedure (which simulates a worst-case scenario) [124, 125]. Chapter 1 29 As a result, the test provides an upper limit of the leaching potential once the material is exposed in the field [126]. Thus, pH during the test is altered at very low a level which provokes a higher release of certain metals [127, 128, 121]. The Dutch leaching test NEN 7371, 2004 uses deionised water. Particles of recycled aggregate are crushed until they pass through a 125-lm sieve. The protocol consists of extracting the leachates in two steps with a liquid to solid ratio (L/S) of 50 l/kg each at pH of 7 (first extraction) and pH of 4 (second extraction). pH is kept constant by feed-back control and the addition of HNO3. The contact time in each step is 3 h. The Dutch procedure detects the maximum leachability of contaminants from the recycled aggregate due to the restrictive conditions imposed. The test is often regarded as the worst-case scenario compared to the real situation in which a recycled material is applied in road construction.  UNE 12457-4 [129] (compliance test) The UNE-EN 12457 standard is a compliance test with the purpose to analyse whether the granular recycled material complies with regulations. By comparing the obtained concentrations with the legal limits indicated by the European Landfill Directive (Council Decision DC, 2003/33/EC of 19, December 2002) [130]), a material can be classified according to their pollutant potential, and the most limiting elements can be detected. The European Standard UNE-EN 12457-3, 2002 [131] is the proposed batch test for leaching of granular waste materials and sludges at Compliance Level. The extractions are obtained in two successive stages at L/S of 2 l/kg and at L/S of 10 l/kg. The contact time with deionised water is 6 ± 0.5 and 18 ± 0.5 h respectively. In both stages, the solution is left to decant and pH, conductivity and temperature are measured. In this study, the solution was filtered through a 0.45-lm membrane filter, and subsamples of leachates from each material were collected. The samples were refrigerated until the analysis.  UNE-EN 15863:2015 [133] (diffusion leaching tank test with periodic leachant renewal) According to international experts, the leaching of compounds environmentally relevant from concrete samples is mainly controlled by diffusion mechanism [134, 119, 135, 136]. Consequently, the most suitable procedure for laboratory simulation of on-site behaviour of hardened concrete is a tank leaching test.  CEN-TS 15862:2012 [137] (the single stage batch leaching test) In the CEN-TS 15862:2012 standard, monoliths samples were contained in deionised water for 24 h with a L/A ratio of 12 cm3/cm2. 1.4.3 Factors that affect the contaminating potential of a material and release mechanisms The release of potentially contaminating substances, due to the contact of construction materials with water and their subsequent migration, again through water, into the environment, could jeopardize the quality of both deep and surface waters and soil and ultimately harm human health. For this reason it is very important to evaluate what are the factors that underlie the release and transport mechanisms of potential contaminants that may be present in building materials, both in the initial phase of their use, and in the phase of their recycling and in the phase of final disposal.  For monolithic materials (e.g., concrete, bricks, coated materials, blocks) the factors that cause the release of constituents from the materials to the aqueous phase are both of a chemical nature (pH, buffer capacity, chemical form, soluble salts, salt strength) and of a physical nature (permeability, size and shape, tortuosity, porosity).  For granular materials (e.g., sand, sinters, gravel, steel slag) the release processes are both chemical (pH, buffer capacity, chemical form, soluble salts, organic matter, salt strength) and physical (permeability, particle size, porosity). Introduction 30 Two overall processes cause the release of constituents from materials to the water phase: (1) Chemical processes (dissolution of minerals, adsorption, availability); (2) Physical transport processes (advection, surface wash-off, and diffusion). In practice, generally a combination of (1) and (2) cause the release to the water phase. The basic chemical mechanisms that control the release of contaminants have been previously defined by Van der Sloot and Dijkstra, [119]: 1- dissolution of a mineral (solubility control); 2- adsorption processes (sorption control); 3- or its availability (or total content) in the product. Some contaminants show affinity for adsorption to reactive surfaces. Positively charged heavy metal cations (e.g., Cu+2) that are not controlled by the dissolution of a mineral, are often controlled by adsorption to (negatively charged) surfaces present in the product such as organic material or oxide surfaces (sorption control). A number of inorganic constituents are not very reactive and show neither solubility control nor sorption control. Upon contact with water they will dissolve instantaneously and quantitatively. Those elements are availability controlled, as the total available concentration can be released from the product. About the factors which affect to release, the pH of the material and that of the environment in which the material itself is located are of fundamental importance in causing the release of many constituents [119]. The pH value of the surrounding fluid determines the maximum water phase concentration at that pH value, and each material has its own pH-dependent release curve (see Figure 1.22). As it has been exposed by previous researchers, the release curves are similar and systematic for different groups of elements, only the absolute level may differ between different materials which implies that the solubility controlling phases are the same and only the relative importance of the influencing factors may differ from one material to another. Figure 1.22 General leaching behaviour of three groups of constituents as a function of pH [119]. Aside from the chemical processes, physical transport processes determine the transfer of constituents from the material to the water phase. Three basic transport mechanisms can be distinguished: 1) advection is the process of transport of constituents taken along with the water (simulation of rain) percolating through the material. Percolation (only possible for porous materials such as granular materials) is the mechanism by which water, coming from precipitations, percolates along the tested material. Due to the further distribution of the constituent, advection plays an important role in leaching release); 2) diffusion is the transport of chemical elements solely due to the molecule’s movement in absence Chapter 1 31 of flow. For that, diffusion is crucial for monolithic and compacted materials with a very low permeability and porosity. The diffusion rate is dependent on the gradient of the elements between the material and the contacting water phase. 3) surface wash-off is a process similar to advection and is a concept used to define the initial process of wash-off of soluble materials on the external surface of monolithic products. But it is important to clarify that diffusion is the major transport mechanism in monolithic materials after this initial wash-off, . As mentioned before, it is important to distinguish granular (recycled aggregates) and monolithic products (concrete or mortars) because of the different transport regimes for these two categories. As aforementioned, the release behaviour due to contact with water is percolation dominated for granular materials and diffusion dominated for monolithic materials. As it has been stated by previous researchers [119], the amount of exposed surface area of the material increases the quantity of an element leaching from this material and diffusion proceeds faster. 1.4.4 Environmental legislation applied in this Doctoral Thesis The considerable types of waste that are produced every year in Europe, including plastics, made it necessary to introduce specific regulations, environmental regulation, in order to preserve the quality of the environment and prevent further irreversible damage to the whole planet (to improve environmental quality). Specific environmental regulations have been issued for each of these waste categories. Those that have interested the topic of this research have mainly referred to the recycling of waste derived from plastics. The regulatory pillars referred to are basically three: the European legislation Landfill Directive 2003/33/EC [130], establishing criteria and procedures for the acceptance of waste at landfills, the Spanish legislation, the Real Decreto 646/2020, of July 7, which regulates the disposal of waste at landfills [141] and the Dutch legislation, the SQD (Soil Quality Decree) [142] containing rules with respect to the quality of soil. The Landfill Directive 2003/33/EC [130] consists of eight articles which establish the criteria and procedures that the member states of the European Union must apply in accepting waste in landfills. The main points of the directive concern: 1. The procedure for determining the acceptability of waste in landfills. Each type of waste must be accompanied with a series of information necessary for it to be disposed of in landfills safely and for a long duration (type and origin, composition, consistency, leachability) also in order to understand its behaviour once delivered to the landfill (basic characterization). Subsequently, the waste must be subjected to compliance testing which will be carried out on sampling of waste according to the procedures established by the specific regulations, using the list of tests listed in the directive itself. Finally, the waste must be visually examined both before and after its delivery to the landfill (onsite verification), together with the related accompanying documents, in order to verify that the deposited product is the same as that which has been characterized and tested in the phases previous. Each Member State must provide for the testing requirements for on-site verification, including where appropriate rapid test methods and repeat them periodically for at least one month from the moment of acceptance of the waste in landfill. 2. The limit values and the test methods to be used for determining the acceptability of waste at landfills. Introduction 32 Regarding inert waste, the directive indicates a list of materials for which it is not necessary to carry out tests for their acceptance in landfills. The refusals not belonging to the indicated list must instead be subject to testing both for their acceptance and for the leaching limit values. The directive establishes the leaching limit values and the limit values for total content of organic parameters apply for waste acceptable at landfills for inert waste and granular wastes. For monolithic waste, Member States can establish acceptance criteria such as to provide the same levels of environmental protection envisaged by the limit values relating to granular wastes. Leaching limit values are also set for non-hazardous waste, granular hazardous waste acceptable at landfills for nonhazardous waste, waste acceptable at landfills for hazardous waste. Each Member State decides which test methods to use and corresponding limit values. Finally, criteria are established for underground storage, for inert waste, non-hazardous waste and hazardous waste. The Spanish legislation, with the Real Decreto 646/2020, of July 7 [141], represents a rule that transposes the EU directives on the landfill and environmental protection and at the same time harmonizes with the Spanish national legislation. Its objective is to legally and technically regulate the activities of conferring waste to landfills through actions that lead to a gradual reduction of their percentage as well as to prevent, reduce and prevent harmful effects on the environment and human health from being produced. Landfills are classified according to the type of residue that is delivered to them, namely: landfills for hazardous waste, landfills for non-hazardous waste and landfills for inert waste. The waste that cannot be landfilled is also listed: those of a liquid nature, explosive, oxidizing, flammable or corrosive, infected waste, tires and all those waste that do not meet the acceptability criteria established by the decree. As regards waste that can be reused, recycled or valorised and therefore must not be taken to landfill, a specific ministerial commission will have to draw up an administrative report which will be approved by January 1, 2023 and applied starting from January 1, 2024. The decree also establishes a whole series of rules that allow waste to be accepted in landfills only under certain conditions: having undergone preventive treatment in order to reduce the quantity deposited and the danger that these can produce for the environment and human health, control of the documentation of the residues delivered, the characterization of the waste and the related tests have been carried out for the purpose of acceptance in the landfill, the visual inspection of the residue both entering the landfill and at the point of discharge, when necessary, keep for at least three months the results of the analysis of the representative samples of the waste and the samples themselves, measure the weight of the waste. Both in the exploitation phase and in the post-closure period of the landfill, the standard establishes that inspections must be carried out by the competent authorities, in order to ensure that the general requirements for acceptance of waste in landfill are met, all are correctly applied, the procedures and criteria for the admission of waste, the state of the landfill infrastructures and installations is assessed and that the disposal operations are free from risks for human health and the environment. Part of the decree also deals with the management of waste associated with COVID-19 and establishes that the recommendations established by the health authorities must be followed for them. As regards the general requirements of each type of landfill, rules are established relating to their location, water control and leachate management, soil and water protection, control of gaseous emissions, harassment and risks, the stability of the soil on which the landfill will be built and its installations and infrastructures, the safety devices that must prevent free access to the landfill site. Chapter 1 33 For the purposes of accepting waste in landfills, the decree establishes admission criteria which consist of setting limit values for leaching and limit values for the total content of organic parameters, these values contained in the tables annexed to the decree. The aforementioned limits are diversified according to whether it is a non-dangerous or dangerous residue and of a granular or monolithic type. In addition, criteria and requirements are introduced to be able to deposit waste underground. In the decree, a separate chapter deals with regulating the methods of sampling and testing on waste. These tests will be carried out in laboratories accredited according to the UNE-EN ISO / IEC 17025 [143] standard by the Entidad Nacional de Acreditación (ENAC), or other accreditation entities of any other member state of the European Union. The sampling, for the purposes of the basic characterization of the waste, the conformity tests and on-site verifications, will be done on the basis of the criteria established by the UNE-EN 14899: 2007 standard (Characterization of waste - Sampling of waste materials - Framework for the preparation and application of a sampling plan) [144] taking into account the technical information of the UNE-CEN / TR 15310 series [145]. The test methods on the samples, which are used to determine the general properties of the waste, the leaching tests and the analyzes, must comply with a series of rules that are listed in the decree itself. The SQD (Soil Quality Decree), [142], is a decree, issued in 2007, by the Dutch Minister for Housing, Spatial Planning and the Environment and the State Secretary for Transport, Public Works and Water Management sustainable soil management in order to achieve a balance between the environment and man and to reconcile land use compatible with a healthy living environment. It was used in Chapter 3 of this doctoral thesis, as a reference regarding the criteria and limits of the leaching behavior of "shaped materials", including concrete with plastic macrofibres used in this research. The decree is divided into five chapters. The first, in addition to unambiguously defining the meaning of the fundamental terms recurring in the decree itself, establishes who owns the competences, responsibilities and coordination regarding the use of construction materials, excavated soil and dredged material. The second chapter deals with the issue of quality in the execution of a job. It is pursued by introducing prohibitions, obligations and sanctions for subjects, persons or institutions, which have been previously authorized by the competent Ministries, to carry out works concerning the use of building materials and the soil. The third chapter deals with building materials. It defines the rules concerning the composition and emission values of the substances contained in the construction material and that these values do not exceed the maximum values established and prescribed by the Ministerial authorities. The fourth chapter deals with excavated land and dredged materials used in building constructions, in road constructions, in raising land in hydraulic engineering constructions, in the redevelopment and stabilization of former quarries and mines, for the temporary storage. The uses of excavated and dredged materials containing dangerous substances are prohibited. The standard identifies three hazard ranking systems, one concerning the specific areas of the territory where the municipal council establish local soil use values for the use of excavated soil or dredged material, one concerning standards of general use and the last concerning the works taking place on a large scale. In the last chapter, the revocations, confirmations and amendments of previous regulations are established. Introduction 34 References 1. Gilbert, M. Plastics Materials: Introduction and Historical Development. Brydson's Plastics Materials. 2017, 1, 1-18. 2. Sperling, L. H. Introduction to Physical Polymer Science. 2005, 1, 1. 3. Young, R.J. and Lovell, P.A. Introduction to Polymers. 2011, 1, 3. 4. Young, G. 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Stagnoli Thermoplastic Gears. https://www.stagnoligears.com/en/technopolymer-parts/gearsfor-food-machineries/ (accessed October 05, 2021) 41. UNE EN ISO 1043-1:2012/A1:2016 Plastics - Symbols and abbreviated terms - Part 1: Basic polymers and their special characteristics- Amendment 1: New symbol ST for syndiotactic (ISO 1043-1:2011/Amd 1:2016). 42. Bustillo Revuelta M. Plastics. Construction Materials. 2021, 477-502 43. Siddique, R.; Khatib, J.; Kaur, I. Use of recycled plastic in concrete: A review. Waste Management. 2008, 28 (10), 1835-1852. 44. Lei Gu, Togay Ozbakkaloglu Use of recycled plastics in concrete: A critical review. Waste Management. 2016, 51, 19-42. 45. Plastics – the Facts 2020 An analysis of European plastics production, demand and waste data. PlasticsEurope. https://plasticseurope.org/wp-content/uploads/2021/09/Plastics_the_facts- WEB-2020_versionJun21_final.pdf (accessed October 9, 2021) Introduction 42 162. Ruiz-Herrero J.L., Nieto D.V., Lopez-Gil A., Arranz A., Fernandez A., Lorenzana A., Meriono S., De Saja J.A., Rodriguez M.A. Mechanical and thermal performance of concrete and mortar cellular materials containing plastic waste. Constr. Build. Mater. 2016, 104, 298–310. Chapter 2 43 2. Objectives, Methodology and Structure of the Doctoral Thesis 2.1 Objectives The objective of this doctoral thesis is to evaluate the potential of recycled plastic from food packaging waste as macro fibres in concrete in terms of mechanical performance and leaching behaviour. The multilayer composition of this plastic waste stream makes difficult its valorisation, as aforementioned in chapter one. The present doctoral thesis proposes the recycling of this waste as fibre reinforcement, preparing this material through cutting. This encourages the circular economy in construction and plastic sectors, to achieve the goals of the 2030 AGENDA. Hence, this study aims to incorporate this waste as reinforcement of concrete, adding post-cracking resistance to a brittle material such as concrete. Additionally, a leaching study is required since a waste has been incorporated into a construction material. To achieve these targets, different amount of recycled plastic fibres (2 kg/m3, 4 kg/m3 and 6 kg/m3) from food packaging waste were used for concrete production, as well as concrete with commercial plastic fibres and without fibres. Thus, the following points were addresses: 1. To carry out a literary review about the use of recycled plastic fibres as reinforcement in concrete with the purpose of knowing the benefits and drawbacks as well as their technical an environmental feasibility. In terms of mechanical behaviour, to compare these fibres with the commercial ones, and regarding the pollutant release, to check the different methodologies based in leaching test. 2. To evaluate the influence of the different amounts of recycled fibres used in the performance of the concretes produced, specifically in terms of: physical properties (density, open porosity and capillarity); post-cracking resistance; and toughness and toughness index 3. To analyse the leaching performance of the new concretes produced. With this goal, some experimental methods should be carried out: Compliance test for basic characterization of recycled plastic waste and its classification according to the pollutant potential. Availability test for determining the maximum release level of the concrete produced. Diffusion leaching tests on the new concrete produced as monoliths for, at short-term, measuring the release levels, and at long-term, pollutant behaviour of elements and identify their different release mechanisms. Objectives, Methodology and Structure of the Doctoral Thesis 44 2.2. Methodology In order to achieve the aforementioned objectives, the following steps were carried out drawn in Figure 2.1. This figure highlights the relevant activities and their sequency, along with their relationship with the publications presented in this Doctoral thesis by compendium of publications. Figure 2.1 Methodology 2.3. Structure This doctoral thesis is presented as a compendium of articles and has been structured in five chapters. Chapter 1 corresponds to the introduction. Section 1.3.2 named as “Physical and mechanical properties of concrete with plastic macro fibres” corresponds to the first publication named “A state-of-the-art review on use of macro plastic fibres in concrete” (Objective 1). The authors were: Pietro A. Vaccaro, Adela P. Galvín, Antonio López-Uceda & Jesús Ayuso. Published in NEW TRENDS IN GREEN CONSTRUCTION 53. ISBN 978-84-9927-554-3, in 2020. The objectives, methodology and structure of the thesis are collected in chapter 2. The following two chapters (3 and 4), correspond to the two articles published in indexed international journals. These articles, in chapters 3 and 4, are published in journals belonging to the second quartile of the Journal Citation Reports. The third chapter corresponds to the article " Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres”, the authors were: Pietro A. Vaccaro, Adela P. Galvín, Jesús Ayuso, Auxi Barbudo & Antonio López-Uceda. Published in Applied Sciences, in 2021, volume 11, number 21, page 9862. IF: 2.679 (Q2). In this study, concretes with different addition of recycled plastic fibre were produced (2 kg/m3, 4 kg/m3 and 6 kg/m3); and two more with commercial plastic fibre and one without any addition. It was studied the influence of the recycled plastic fibre on the physical Chapter 2 45 properties conducted such as density, open, porosity; and on the mechanical ones such as compressive and flexural strength, and toughness (Objective 2). The fourth chapter corresponds to the article called " Pollutant potential of reinforced concrete made with recycled plastic fibres from food packaging waste" the authors were: Pietro A. Vaccaro, Adela P. Galvín, Jesús Ayuso, A. Lozano-Lunar & Antonio López-Uceda. Published in Applied Sciences, in 2021, volume 11, number 17, page 8102. IF: 2.679 (Q2). In this article, firstly, the recycled plastic fibre was tested by leaching and classified according to its potential pollutant, and secondly, at short-term and at long-term leaching tests were carried out on the concretes produced; based on the results of the second one, pollutant behaviour of elements and release mechanisms were obtained (Objective 3). The last chapter presents the most relevant conclusions and future lines of research motivated by this doctoral thesis. Objectives, Methodology and Structure of the Doctoral Thesis 46 Chapter 3 47 3. Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres (Publication II) Article Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres Pietro A. Vaccaro 1, Adela P. Galvín 2, Jesús Ayuso 2, Auxi Barbudo 2,* and Antonio López-Uceda 3,* 1 International Doctoral School, Universidad de Sevilla, 41004 Sevilla, Spain; pietro[email protected]m 2 Construction Engineering Area, Universidad de Córdoba, 14014 Córdoba, Spain; [email protected] (A.P.G.); [email protected] (J.A.) 3 Mechanics Department, Universidad de Córdoba, 14014 Córdoba, Spain * Correspondence: [email protected] (A.B.); p6[email protected] (A.L.-U.)  Abstract For many decades, researchers have been working on finding innovative and sustainable solutions to address the enormous quantities of plastic waste that are produced every year which, after being collected, are transformed into energy, recycled, or sent to landfills. Giving a second life to plastic waste as a material to be incorporated, in the form of macro-fibres, into concrete, could be one such solution. The purpose of this study was to analyse the mechanical and physical behaviour of the hardened concrete reinforced with macro plastic fibres (RPFs) obtained from food packaging waste (FPW) discarded during the packaging phase. By varying the quantity of macro-fibres used, physical and mechanical properties such as compressive strength, modulus of elasticity, flexural strength, and toughness were evaluated. It was observed that, although the presence of macro plastic fibres reduced the mechanical resistance capacity compared to that of traditional concrete, their contribution proved to be of some importance in terms of toughness, bringing an improvement in the post-crack resistance of the composite material. This innovative mixture provides a further impulse to the circular economy. Keywords: circular economy; recycled macro plastic fibres; physical properties; mechanical properties; toughness  3.1. Introduction Concrete is a widely used construction material worldwide due to its great availability of raw materials and low cost [1]. Although concrete has good compressive behaviour, it does not respond adequately under high tensile stresses. To alleviate this, steel reinforcements have usually been used to improve its tensile and flexural strengths [2–4]. However, in recent years, natural (mainly vegetable), steel, glass, and synthetic fibres have also been used [1]. Synthetic fibres help to prevent plastic shrinkage cracks in fresh concrete [5], and improve concrete performance after cracking [6]. Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres 48 In recent years, the EU and its member states have endowed themselves with harmonized European standards regarding the production, classification, and use of FRC (fibre-reinforced concrete) (EN 14889-1 for steel fibres, and EN 14889-2 for polymer fibres). The current trend of international legislation, therefore, is to produce a fibre-reinforced concrete (FRC) that can be classified on the basis of its guaranteed performance, and not just the volumetric percentage of fibres contained within it (EN 206:2013 + A1:2016). Plastic fibres are synthetic fibres that are known to help improve the ductility, crack resistance, and impact resistance of conventional concrete. However, the contribution of the addition of these fibres was found to be less significant with respect to compressive strength and flexural strength [1]. Kazmi et al. [7], for their part, after investigating the fracture behaviour, mechanical characteristics, and microstructure of recycled aggregate concrete, observed an increase in mechanical properties—particularly, split tensile strength and residual flexural tensile strength—with the increase in dosage of these synthetic fibres. Plastic fibres can be in the form of micro plastic fibres or macro plastic fibres [1]. Micro plastic fibres refer to plastic fibres with diameters ranging from 5 to 100 µm and lengths ranging from 5 to 30 mm [8]; they are used to control plastic shrinkage cracking [9], which is caused by the shrinkage of fresh concrete during the first 24 h after placement due to excessive evaporation of bleed water [10]. Macro plastic fibres, which were used in this study, normally have a length of 30–60 mm and a cross-section of 0.6–1 mm2 [11]; these are used not only to control plastic shrinkage [12], but also to control drying shrinkage [6]. Another significant benefit is the post-cracking performance provided by the addition of macro plastic fibres [13,14]. On the other hand, world plastic production reached almost 368 million tons in 2019, of which approximately 58 million tons was generated in the EU (European Union). Of all the plastic produced in the EU in the year 2019, more than 20% was used in the building and construction sector, while almost 40% was used in packaging [15]. In the EU, in 2018, 24.9% of collected plastic waste was landfilled, 42.6% was transformed into energy (by incineration [16]), and the remaining 32.5% was intended for recycling [15]. According to a recent report [16], the target set by the new EU Directive 2019/852 provides for the achievement of a recycling percentage of plastic for packaging of 50% by 2025, and 55% by 2030. Hence, plastic wastes are universally considered to be a threat to the environment [17]. Among the various types of recycling management approaches, the reuse of waste and recycled plastic material in the construction industry is considered an ideal method for disposing of plastic waste [18]. A review has been published recently about current trends in plastic waste composites as construction materials [19], reporting diverse uses of the most common plastics, such as polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET), after proper recycling treatment—for instance, in bricks, as aggregate or filler in concrete, or as reinforcement in concrete in paving tiles or slabs. Benefits and drawbacks are weighed, highlighting as benefits the fact that its use increases its value, so recycling is encouraged, and raw material consumption is reduced; meanwhile, as drawbacks, sorting and selection, and the lack of study of recycled plastic waste in construction materials, are cited. Other studies, such as the one carried out by Platon et al. [20], dealt with other uses, such as the production of composite materials for sound insulation purposes produced by thermocompacting mixed plastic waste, from the production process of sanitary wares, and thermoplastic polymers. The use of recycled aggregates from plastic waste to replace natural aggregates has been previously studied. Mohammadinia et al. [21] showed the feasibility of substituting up to 50% of natural aggregates Chapter 3 49 for a combination of recycled plastic and glass aggregates in the construction of concrete footpaths. Corbu et al. [22] found that a combination of recycled aggregates from waste plastic and waste glass can totally replace natural aggregates in precast concrete pieces. Thorneycroft et al. [23] proved the feasibility of substituting up to 10% by volume of sand for recycled plastics in the manufacture of concrete. Elsewhere, Merlo et al. [24] detected a lack of adhesion between recycled plastic and cementitious matrix, explaining the loss of mechanical properties as ratio incorporation increased. In addition, authors such as Foti went even further, studying the use of PET plastic waste in strips of large size [25] or in grids of macro-strips [26] as reinforcements in concrete, suggesting the possibility of being considered for the reinforcement of concrete in place of steel. Within this sector, recycled plastic fibres can be used in FRC, which allows improvement of the concrete properties, in addition to the environmental benefits that this entails [4,18,27,28]. The global value of the packaging industry is around EUR 345 million, of which the EU accounts for one-third, and of which 50% is related to food packaging. Forecasts indicate that the sector will continue to grow both in size and in importance [29]. In terms of structure, monolayer and multilayer can be distinguished: monolayer films consist of a thermoplastic polymer sheet made mostly of PE, PP, or PET, with a range from 20 to 200 μm of thickness, while multilayer films are made up of a different number of sheets that can be polymeric (thermoplastics) or non-polymeric materials (paper or aluminium foils) [30]. Multilayer plastic waste used in food packaging does not enter the waste recycling stream due to the wide variety of materials, its multilayer composition [31], and the colours that make up the food packaging; hence, a call for a circular economy is proposed [32]. Currently, the technical feasibility of recycling this waste at low cost is not close to being achieved [31,33]. Indeed, due to the fact that it is not always managed properly, the recycling process is quite complex and, with the great environmental concern attached, the plastic sector is encouraged to participate in projects to deal with this issue [34,35]. This confirms the need to address studies such as the present work, which are essential in finding solutions that transform plastic waste from packaging into new resources, enabling not only contribution to the circular economy, but also the production of innovative materials for civil construction. In particular, this study deals with the analysis of the mechanical behaviour of concrete with the addition of macro-fibres obtained by cutting plastic sheets; specifically, measurements such as crack mouth opening displacement (CMOD) and toughness were obtained. Three different levels of fibre addition were used in the production of concrete (2 kg/m3, 4 kg/m3, and 6 kg/m3), and two reference concretes were produced (one without fibre, and another with a commercial fibre). The main novelty of this research consists of having used not commercial plastic fibres, but waste material derived from the processing of plastic for food packaging. These multilayer plastic wastes are difficult to recycle due to their heterogeneous composition. Hence, this work aims to valorise this waste, contributing to a circular economy. 3.2. Materials and Methods 3.2.1. Recycled Plastic Fibres (RPFs) from Food Packaging Waste (FPW) The recycled plastic waste (RPW) consisted of macro plastic fibres obtained from the waste derived from the production and processing of plastic, supplied in waste rolls by a local company that deals with the production of multilayer plastic for packaging. The plastic sheet was made of four overlapping layers of different materials: polyester, aluminium, biaxially oriented polyamide, and polypropylene (PET + ALU + OPA STE + PP G). The fibres used in the experimentation were obtained in the laboratory by cutting Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres 50 plastic sheets (Figure 3.1a,b). A commercial polypropylene fibre (CPF) was also used as a comparison (Figure 3.1.c). The fibres were in compliance with the EN 14889-2:2006 standard. The dimensions and main properties of the plastic fibres used are summarised in Table 3.1.  (a) (b) (c) Figure 3.1. Plastic fibres: plastic waste rolls from food packaging (a); the prepared fibres (b); commercial polypropylene fibre (c). Table 3.1. Technical data of recycled plastic fibres (RPFs) and commercial polypropylene fibre (CPF). Technical Data Unit RPF CPF Thickness mm 0.125 - Width mm 4 - Length mm 50 50 Diameter mm - 0.682 Aspect ratio - 63.00 73.53 Density g/cm3 1.13 0.91 Tensile strength MPa 500 530 Modulus of elasticity GPa 9.0 7.4 3.2.2. Fibre-Reinforced Concrete (FRC) Specimens Made with RPF Specimens of PFRC were prepared by adding recycled plastic fibres (RPFs) to the concrete mix at 2, 4, and 6 kg per m 3 of concrete. The prepared mixtures were assigned the following codes: PFRC-2, PFRC- 4, and PFRC-6, respectively. Two control specimens were also prepared: a control specimen of concrete without reinforcement (C-REF), and fibre-reinforced concrete made with a commercial polypropylene fibre (PFRC-REF; dosage of 2 kg per m 3 of concrete). The aggregates used for manufacturing the concrete mixes in the laboratory were coarse gravel (7–25 mm) at 960 kg per m 3 and sand (0–7 mm) at 970 kg per m 3 , both with a siliceous nature. A total of 280 kg of CEM II 42.5 AV-R cement per m 3 of concrete produced was used, reaching a water-to-cement ratio of 0.54. In order to improve the workability and avoid segregation of the mixture, along with having an S3 slump class according to UNE-EN 206:2013 + A1:2018, two different types of additives were used: the plasticizer Complast MR260 at 5 mL per kg of cement, and the superplasticizer Structuro 357 at 7.7 mL per kg of cement. The slump ranged between 15 cm for C-REF and 10 cm for PFRC-6 mix. Slump values decreased as macro-fibre content increased, in agreement with the findings of other authors [18]. The concrete produced for each single mixture was casted, resulting in nine cubic specimens with a length of 100 mm, three prismatic beams measuring 100 mm × 100 mm × 400 mm, and six cylindrical specimens with a diameter of 150 mm and a height of 300 mm, which were then cured in a climatic chamber (at 20 °C and 95% ± 5% relative humidity) and subjected to testing at various ages. Chapter 3 51 3.3 Experimental Methods 3.3.1. Physical Properties The dry density and the open porosity of the concrete specimens were obtained following the standard UNE 83980:2014. The performance of the mix concrete in terms of capillarity was determined using the Fagerlund method, following the standard UNE 83982:2008. Both tests were carried out on three cubic specimens with a length of 100 mm. 3.3.2. Compressive Strength The compressive strength test was performed in accordance with the UNE-EN 12350-2:2009 standard; it was carried out on three cubic specimens with a length of 100 mm after 7 and 28 days of curing, as well as on three cylindrical specimens with a height of 300 mm and a diameter of 150 mm after 28 days of curing. 3.3.3. Elastic Modulus The elastic modulus was determined, in accordance with UNE-EN 12390-13:2014, after 28 days of curing on three cylindrical specimens (Ø150 × 300 mm). 3.3.4. Flexural Strength The flexural strength was determined using three prismatic specimens (400 × 100 × 100 mm3 by length × width × height) after 28 days of curing. The tests were carried out using a four-point bending tensile testing machine, with notch-opening control, complying with the UNE 83509:2004 standard. 3.3.5. CMOD and Toughness The toughness index and CMOD were determined for each mixture by subjecting three prismatic specimens (equal to the flexural strength ones), notched (5 mm in width and 20 mm in height) in the central part, to a four-point bending tensile test, after 28 days of curing, in accordance with the UNE 83510:2004 standard. The measurement of the crack opening at the mouth of the notch of the specimen (CMOD) was performed using two linear variable displacement transducers (LVDTs) attached to the bottom of the concrete specimen. At the end of the test, the fissure was unique and corresponded to the notch. During the test, the applied loads and the corresponding opening of the notch made along the centre of the specimen were detected and recorded, thus obtaining, for each mix design, the load–CMOD curve. From the load–CMOD curve, the load and the relative resistance at the point of first cracking of the specimen were determined. The values of toughness T (N·m) were obtained by calculating the area under the load– deflection curve, from the point where the linear section of the diagram began, and up to the point where the arrow reached the value of 1/150 of the span between the supports of the specimen. The toughness index, I30, was obtained as the ratio between the area under the curve from the origin of the curve to the point where the deflection reached the value of 15.5 times the deflection corresponding to the formation of the first crack, and the area under the curve between the origin of the curve and the deflection related to the first crack. 3.4. Results and Discussion 3.4.1. Physical Properties The results of the dry density and water absorption in concrete samples are depicted in Table 3.2. The dry density values ranged between 2.21 g/cm3 and 2.25 g/cm3 for mixtures with recycled fibres, and Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres 58 A.B; project administration, J.A. and A.P.G.; funding acquisition, J.A. and A.P.G. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: The authors would like to express their gratitude to the SP-Group CENTRAL CÓRDOBA—Plastienvase SL for their efficient service, professionalism, and support to the present study. The authors also thank the Votorantim Group for freely providing the cement used in this research. Conflicts of Interest: The authors declare no conflict of interest. References 1. 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Properties of polypropylene fiber reinforced silica fume expansive-cement concrete. Constr. Build. Mater. 1999, 13, 171–177, doi:10.1016/S0950-061800027-6. 55. Wang, Y.; Zureick, A.H.; Cho, B.S.; Scott, D. E Properties of fibre reinforced concrete using recycled fibres from carpet industrial waste. J. Mater. Sci. 1994, 29,4191–4199, doi:10.1007/BF00414198. 56. Nibudey, R.N.; Nagarnaik, P.B.; Parbat, D.K.; Pande, A.M. Strength and fracture properties of post consumed waste plastic fiber reinforced concrete. Int. J. Civ. Struct. Environ. Infrastruct. Eng. Res. Dev. 2013, 3, 9–16. 57. Yin, S.; Tuladhar, R.; Collister, T.; Combe, M.; Sivakugan, N.; Deng, Z. Post-cracking performance of recycled polypropylene fibre in concrete. Constr. Build. Mater. 2015, 101, 1069–1077, doi:10.1016/j.conbuildmat.2015.10.056. 58. Foti, D. Preliminary analysis of concrete reinforced with waste bottles PET fibers. Constr. Build. Mater. 2011, 25, 1906–1915, doi:10.1016/j.conbuildmat.2010.11.066. 59. Signorini, C.; Volpini, V. Mechanical Performance of Fiber Reinforced Cement Composites Including Fully-Recycled Plastic Fibers. Fibers 2021, 9, 16, doi:10.3390/fib9030016.  Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres 62  Chapter 4 63 4. Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste (Publication III) Article Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste Pietro Vaccaro 1, Adela P. Galvín 2,*, Jesús Ayuso 2 , Angélica Lozano-Lunar 2and Antonio López-Uceda 3* 1 International Doctoral School, Universidad de Sevilla, 41004 Sevilla, Spain; [email protected]m 2 Department of Civil Engineering, University of Córdoba, 14014 Córdoba, Spain; [email protected] (J.A.); a ng e lic a . lo za n o@ u c o. e s ( A. L.- L .) 3 Department of Mechanics, University of Córdoba, 14014 Córdoba, Spain * Correspondence: [email protected] (A.P.G.); [email protected] (A.L.-U.); Tel.: +34-957-212-168 (A.P.G.)  Abstract In our modern, fast-paced life, plastic is a versatile material essential to our economy; daily life is unthinkable without it. However, there are serious downsides for the environment and health, which are becoming more and more stark in our society, and the recycling of plastic offers a partial solution to these widespread problems. The present work delves into the environmental assessment of fibrereinforced concrete specimens, made with recycled plastic fibres from food packaging waste. Leaching tank tests for the evaluation of the long-term release of pollutant elements, identification of leaching mechanisms, and the diffusion process of contaminants into the environment were conducted on fibre reinforced concrete. The results showed that the incorporation of the recycled plastic fibres, classified as non-hazardous, did not release relevant levels of any potential harmful element incorporated in concrete. Moreover, low mobility was detected in the studied elements and different release mechanisms were identified through long-term diffusion leaching tests. Hence, the environmental feasibility of the incorporation of recycled plastic fibre in concrete was proven. This study strengthens the objectives set out by the Circular Economy Action Plan, which includes the European Strategy for Plastics and aims to, among other things, boost the market for recycled plastics. Keywords: sustainable construction; leaching tests; recycled plastic; reinforced concrete; circular economy 4.1. Introduction Currently, facing the challenge of reducing the environmental impact resulting from our economic and social activities is a priority at all levels. The waste that is generated daily across the world is known. This waste has been studied in depth and new alternatives for recycling have granted some of its parts a second life cycle, e.g., recycled aggregates from construction and demolition waste, bottom ash from biomass combustion, or ash from solid urban waste. All of these examples refer to recycled materials that can be applied to engineering infrastructure. In addition, another example could be the utilisation Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste 64 of waste products for the manufacturing of recycled concrete: waste products, such as discarded tires, glass, steel, burnt foundry sand, and coal combustion by-products, have provided specific effects on the properties of fresh and hardened concrete [1]. However, there are numerous types of waste that are being generated in high quantities but, from an environmental point of view, they are not reused at acceptable rates. This is the case for plastic wastes coming from plastic food packaging, which is the subject of the present study. Plastic packaging is widely used in the food sector due to several properties: it is flexible and adaptable in form, hygienic, light, cost-effective, high versatility, and does not easily degrade [2]. Increasing its recycling potential is a priority. In recent years, the circular economy of plastic has been increasing year by year and, in the specific case of plastic recycling, for the first time in Spain (in 2017), the number of tons of recycled plastic exceeded that of plastic deposited into landfills. These data demonstrate the increase in society’s awareness, as well as the efforts and improvements of the collection systems, the modernisation of recycling processes, and the innovation of the plastics industry, which is incorporating more recycled material into new products. The plastics recycling sector in Spain is one of the most mature and powerful in Europe, with more than 120 companies and between 3500 and 4000 direct jobs, currently. The recycling of plastics will continue to grow, and it is estimated that, in 2030, with the recycling of 55% of plastic containers in Europe, savings of 14.8 million tons of CO 2 emissions will be achieved [ 3 ]. On the other hand, the construction sector is continuously evolving and reinforced concrete is an example of an innovative solution. Compared to other building materials, such as metal and polymers, concrete is significantly more brittle and exhibits poor tensile strength [4]. To overcome this deficiency, fibres have been added to concrete in recent decades [5,6], increasing the productivity and adapting more rational production techniques [7]. Fibre reinforced concrete (FRC) is composite material containing fibres in a cement matrix, either in an orderly manner or a randomly-distributed manner. Its properties are largely dependent on the type of fibre, fibre geometry, fibre content, orientation and distribution of the fibres, mixing and compaction techniques of the concrete, and size and shape of the aggregate [4]. The most common applications are pavements (slabs, industrial floors, or roadways), precast elements, and structural reinforcements. Different types of fibres have been used extensively in FRC (steel, polypropylene, glass, asbestos, polyester, etc.) [8], although steel and polypropylene are the most commonly used ones [9–12]. Polypropylene fibres (PF) are generally used in FRC structures to enhance shrinkage cracking resistance, impact strength, spalling resistance, splitting tensile strength, and other properties [8,12–15]. Alhozaimy et al. [16] observed that an additive amount of 0.1% PF in concrete had a 44% increase in its flexural toughness. Mindness and Vondran [17] reported that compressive strength increased by about 25% at 0.5% volume fraction of PF in the concrete mixture design. Hughes and Fattuhi [18] suggested that compressive strength decreases but flexural properties are improved with increasing fibre content. According to Kakooei et al. [8], polypropylene fibres have hydrophobic levels, which protect them against wetting with cement paste, although their hydrophobic nature has no effect on the amount of water needed for concrete. The studies demonstrated that concrete made from macro plastic fibres is a composite material that could replace a part of the steel reinforcement in upstream concrete. Therefore, the exploration of the possibilities of reusing different types of plastic waste in concrete manufacturing would lead to unbeatable results while plastics are consumed daily, worldwide and the production of this waste has increased immensely during the past 50 years. Chapter 4 65 Nowadays, industrial by-products are widely used due to their ability to be recycled and valorised as secondary materials, which allows for the simultaneous saving of natural resources and energy [ 19 ]. Industries are finding new ways to use materials that would otherwise be discarded. Researchers have already used different recycled fibres to improve the behaviour of ordinary concrete. Ahmadi et al. [ 20 ] concluded that adding recycled steel fibres into concrete is feasible and recycled aggregates can be used in the production of structural concrete with a 50% replacement of aggregates. Gu and Ozbakkaloglu [ 21 ] evaluated the use of recycled plastic materials in conventional cement mortar; this concrete has been researched extensively. Plastics have been used in fibre-reinforced concrete in two forms: plastic aggregates (PA) and plastic fibres (PF). The use of recycled fibres in concrete can lead to improved concrete properties, in addition to increased recycling rates. Apart from PET, most types of common plastic (e.g., PP, PVC) are stable for decades, even for centuries, inside concrete. Review findings indicate that the use of recycled plastic materials in concrete can contribute significantly to a more sustainable construction industry, but future studies on environmental aspects, such as the long-term behaviour of plastic materials in concrete and the environmental consequences of recycling of concrete containing plastics, is recommended. This is the focus of the present work. The incorporation of alternative materials in the production of concrete is liable to increase the quantity of pollutant elements in the product [ 22 ]. This fact could provoke an environmental risk due to the continued exposure of contaminated concrete to its surroundings [ 23 – 25 ]. Cement is a building material that has been extensively tested, with a long history of use under different environmental conditions; advantageous solidification results in a monolithic, watertight final product [ 26 ]. So, the use of potentially polluting materials in the manufacture of concrete would reduce the release of these in the case of contact with water; however, it could induce a loss of durability in the concrete [ 27 ]. Leaching tests have proved to be a useful tool for the environmental assessment of construction materials. Leaching is a diffusion–reaction phenomenon, which takes place when concrete is exposed to poorly mineralised or acid water [ 22 , 28 ]. Degradation consists of dissolution of calcium and hydroxide ions out of the matrix, which causes an increase in porosity and transport properties of surface concrete. Leaching and external sulphate attack on concrete leads to the dissolution of hydration products, mainly portlandite, and in cases of ingress of sulphate ions, to the formation of expansive products, such as gypsum and ettringite [ 27 ]. This emphasises the need to consider leaching behaviour in the design of concrete structures. Previous researchers in this area focused on the assessment of the underlying mechanisms of contaminant release and the chemical and physical factors that control leaching behaviour from construction materials under a wide range of environmental conditions [ 25 , 29 , 30 ]. Comparison with generally accepted norms, such as the European Council Decision 2003/33/EC [ 31 ], permits the assessment of whether application of a recycled product will be innocuous to the environment, although the release of substances from a material depends on their solubility, which is influenced by numerous factors including material composition, pH, permeability, contact time, and water/solid ratio [ 32 – 34 ]. With this framework, the present study aims to make a practical contribution to environmental sustainability and the circular economy, as it is focused on concrete made with non-commercial plastic fibres for reinforcement. Specimens of reinforced concrete were prepared using the plastic sheets used for food packaging at different weights per m 3 of concrete and two control specimens were used. In a preliminary laboratory phase, the mechanical performance of concrete made with the addition of recycled macro plastic fibres was evaluated and it was demonstrated that a certain Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste 66 improvement in the post-cracking properties of the concrete was achieved. The presence of plastic fibres inside the matrix increases both the ability of the concrete to resist the advancement of cracks and the ability to deform plastically before breaking, giving a certain residual tensile strength to the concrete matrix during the post-cracking phase. Once the mechanical assessment of using recycled plastic fibre as reinforcement in concrete was evaluated, the present study was implemented for the environmental assessment of RFC by means of leaching tank tests for the evaluation of the long-term identification of leaching mechanisms and the diffusion processes of contaminants into the environment. The following tests were performed: (1) compliance leaching test of recycled plastic fibres from food packaging waste for their pollutant potential classification, according to the EU Landfill Directive; (2) diffusion leaching test in tank for basic characterisation of pollutant release from concrete made with plastic fibres; and (3) dynamic diffusion leaching test for long term characterisation of pollutant release from concrete made with plastic fibres. All of these tests focused on the use of recycled materials coming from the processing of waste plastic used for packaging which, as highlighted by the Plastics Europe report, accounts for 45.4% of the packaging destined for recycling in Spain. 4.2. Materials 4.2.1. Recycled Plastic Fibres (RPF) from Food Packaging Waste (FPW) The FPW consisted of macro plastic fibres obtained from the waste products and processing of plastic, supplied in waste rolls by a local company that deals with the production of plastic for packaging. The fibres used in the experiments were obtained in the laboratory by cutting them from plastic sheets. The average dimensions of the fibres were 50 mm long, 4 mm wide, and 0.125 mm thick (Figure 4.1). Figure 4.1. Plastic sheets from food packaging: front and back sides (a) and the prepared fibres (b). The tested plastic sheets were made of four overlapping layers of different materials: polyester, aluminium, bi-axially oriented polyamide that is resistant to thermal sterilisation treatment (121 ◦C for 30 min), and polypropylene (PET + ALU + OPA STE + PP G). This is one of the most resistant multilayer complexes used in food packaging in terms of aluminium barriers. It is used for standing or flat bag formation, and also as tray lids. Aluminium makes it easily deformable; however, it does not lose the barrier effect. This composite material presents a high barrier to oxygen, humidity, aroma, and light, being rigid and opaque, sterilisable, and pasteurisable. The main properties and methods presented by the plastic sheet are summarised in Table 4.1. Chapter 4 67 Table 4.1. Technical data of plastic sheets PET + ALU + OPA STE + PP G. Technical Data Value Unit Method Thickness 125.00 ± 10% µm ASTM E 252 Density 1.13 ± 10% g/cm3 ASTM D 1505 Tensile strength 500 MPa ASTM D 882 Modulus of elasticity 9 GPa ASTM D 882 Unit weight 140.90 ± 10% g/m2 ASTM D 252 Oxygen permeability <0.5 cm3/m2/24 h ASTM D 3985 Water vapor permeability <0.5 g/m2/24 h ASTM F 1249 Permeability to carbon dioxide <0.5 cm3/m2/24 h ASTM D 3985 Permeability to nitrogen <0.5 cm3/m2/24 h ASTM D 3985 Departure sealing temperature 150-160 °C - Temperature for use -18-121 °C - Footnote: ASTM: American Society for Testing and Materials. 4.2.2. Fibre Reinforced Concrete Specimens (FRC) Made with RPF Specimens of FRC were prepared using the plastic sheets used for food packaging by the packaging company (Figure 4.2). This food packaging waste (FPW) was used at 2, 4, and 6 kg per m 3 of concrete, and the prepared mixtures were named using the codes: FRC2, FRC4 and FRC6. Two control specimens were also prepared: a control specimen of concrete without reinforcement (C-REF) and a fibrereinforced concrete made with commercial fibres of polypropylene at a dosage of 2 kg of fibre per m 3 of concrete (FRC2-REF). Figure 4.2. Concrete specimens of FRC with RPF: FRC2, FRC4 and FRC6. The aggregates used for manufacturing the concrete mixes in the laboratory were coarse gravel (6–20 mm) and sand (0–4 mm), both of a siliceous nature. The cement used was CEM II 42.5 AV-R at 280 kg per m 3 of concrete produced, reaching a water to cement ratio of 0.54. To improve the workability and to avoid the segregation of the mixture, two different types of additives were used: the plasticiser Complast MR260 at 5 mL/kg of cement and the superplasticiser Structuro 357 at 7.7 mL/kg of cement. Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste 74 region (i.e., pH ~ 1–2), the leached contents for all elements are at their maxima and represent the available contents (maximum leachability) as the paste was degraded. 4.4.3. Diffusion Leaching Tests in FRC Specimens Made with RPF 4.4.3.1. Basic Characterisation: 24 h Tank Leaching Test by CEN/TS 15862: 2012 Leaching of monolithic materials is essentially governed by diffusion phenomena. Thus, for a previously basic characterisation, the diffusion leaching tank test was performed according to the CEN/TS 15862:2012 standard. This is a fast test (24 h) that allows the measurement of concentrations of the legally regulated elements, as shown in Table 4.3. Anions (sulphate, chloride, and fluoride) and heavy metals (Hg, Pb, Cd, Mo, As, Ni, and Se) are not represented because they are under the detection limits. Table 4.3. Leachate concentrations (mg/m2) from concrete specimens according to the diffusion leaching test. Leachate Concentrations from Concrete (mg/m2) Elements C-REF FRC2-REF FRC2 FRC4 FRC6 pH values 10.2 10.1 10.4 10.3 10.2 Cr 0.0042 0.0072 0.0030 0.0027 0.0032 Zn 0.0568 0.0495 0.0508 0.0576 0.0545 Sb 0.0149 0.0033 0.0105 0.0076 0.0059 Ba 0.0159 0.0058 0.0100 0.0061 0.0080 The 24-h dynamic tank test was carried out and it provided a basic and quick characterisation of the levels released by the concrete specimens. The heavy metals listed in Table 4.3 were released at low rates for all specimens and non-relevant differences are observed between the control specimen without fibre (C-REF) and specimens prepared with fibre reinforced concrete. The low release levels detected on the concrete specimens are justified, since solidification and stabilisation (S/S) using cement as a binder is most often applied (worldwide) for controlling the environmental impact of residues; it involves a conversion of the residues into a monolithic or granular material, ensuring easy handling and transportation to landfill sites. It also immobilises toxic pollutants by physical encapsulation, chemical incorporation and/or adsorption [41,42]. The data showed that the level of the heavy metals presented in Table 4.3 were similar to the RPF except to the antimony ones, which were lower than in RPF and inert limit, classifying them as inert material [43]. 4. 4.3.2. Long Term Behaviour: Dynamic Tank Leaching Test by UNE-EN 15863: 2015 For a complete characterisation of the leaching behaviour of specimens in the long term, the dynamic tank leaching test was performed according to UNE-EN 15863:2015, to obtain different eluates over time (“i” fractions). To continue with the study of long-term leaching behaviour, the anions were not included due to their despicable release levels observed in previous sections. In the present section, the regulatory limits indicated by the Soil Quality Decree (SQD) [44] are used as a reference because this regulation specifies criteria for the (re)use of mineral materials in construction applications: “shaped materials”, and the limits are most accurate to apply to FRC specimens (it prescribes the rules for the use of “shaped” construction materials). Table 4.4 shows the pDe-values (negative logarithm of effective diffusion coefficient) for the elements which showed the highest mobility levels on concrete samples: Cr, Zn, Sb and Ba, along with cumulative emission (ε64) and the pH at the start and the end of the test. The pH of the eluates collected did not vary significantly over the course of the test, presenting values corresponding to a medium Chapter 4 75 alkaline, as expected. Only the elements Cr, Zn, Sb and Ba are represented because they present the higher mobilities. The cumulative emission for the elements in Table 4 did not present any substantial differences between the samples. The results obtained were consistent with the data obtained by previous researchers, in terms of cumulative emission at 64 days [28,45] and diffusion coefficient [46] in concrete. Table 4.4. Cumulative emission (ε64), diffusion coefficient (De) and pDe. Parameters C-REF FRC2- FRC2 FRC4 FRC6 Initial p H 10.2 10.4 10.3 10.2 10.4 Final pH 10.1 10.2 10.2 10.1 10.2 Cr Cumulative emission. ε64 (mg/m2) 0.125 0.189 0.135 0.185 0.168 Diffusion coefficient. De (m2/s) 1.500·10−14 8.270·10−14 1.580·10−14 2.800·10−14 1240·10−14 pDe 13.820 13.080 13.800 13.550 13.910 Zn Cumulative emission. ε64 (mg/m2) 2.271 2.778 2.504 2.020 2.207 Diffusion coefficient. De (m2/s) 3.770·10−14 1.380·10−14 3.410·10−14 1.660·10−14 2.480·10−14 pDe 13.420 13.860 13.470 13.780 14.610 Sb Cumulative emission. ε64 (mg/m2) 0.717 0.643 0.861 0.342 0.729 Diffusion coefficient. De (m2/s) 4.580·10−14 6.940·10−14 7.010·10−14 1.600·10−14 3.970·10−14 pDe 13.340 13.150 13.150 13.800 13.400 Ba Cumulative emission. ε64 (mg/m2) 4.261 3.965 3.992 3.277 3.403 Diffusion coefficient. De (m2/s) 8.130·10−14 5.480·10−15 5.100·10−15 4.530·10−15 1.710·10−15 pDe 14.090 14.260 14.290 14.340 14.770 The higher pDe value implies the lower speed of leaching of the component concerned with constant availability Uavailability. The pDe value determines the concentration gradient, which is the driving force for diffusion of the pollutant elements studied: pDe > 12.5: component with low mobility; 11.0 < pDe < 12.5: component with average mobility; pDe < 11.0: component with high mobility, according to the NEN 7343. Of all the represented elements: Cr, Zn, Se and Ba showed a pDe value higher than 12.5 because they are components with low mobility. The determination of the leaching mechanisms occurring in the diffusion test is possible, based on the leaching of components previously measured and establishing whether the matrix of the test piece is dissolving during the conduct of the test. It is possible to determine whether leaching is diffusion controlled or whether other leaching mechanisms also contribute, for all individual components. Despite the usefulness of shortterm tests, they do not provide information about the behaviour of contaminants in the medium or long-term. On the contrary, dynamic tests are usually employed for elucidating the dominant leaching mechanism from a stabilised/solidified (S/S) waste [47,48]. As a matter of fact, the main release mechanisms are: (i) solubility; (ii) diffusion from the internal porosity of the matrix to the surface; and (iii) surface wash-off (where substances concentrated at the surface of the monoliths may be released at the first contact with water) [49]. Figure 4.5 illustrates the graphical representation of diffusion-controlled leaching (mg/m2) vs. time (days) for the identification of leaching mechanisms of the four heavy metals studied. The Uavailability value obtained by the availability test is included to observe the maximum release level obtained for each heavy metal and each specimen is plotted in Figure 4.5, along with the obtained data from the diffusion test of cumulative leaching measurements (expressed in mg/m2) and its linear regression. Regarding the leaching behaviour of monolithic samples, there are three main basic transport and chemical mechanisms that usually control the leaching processes: surface wash off, where way the most soluble phases on the surface of the monolith are released quickly, diffusion transport of the solubilised species in the aqueous phase inside the monolith, and the surface dissolution of the monolith in contact with the aqueous phase that surrounds it (chemical mechanism control) [32,48]. Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste 76 For determining the main leaching mechanism, the linear regression that fits the experimental points of cumulative fraction released versus time, or the logarithmic representation of cumulative flux versus time, can be used [50–53]. According to Torras et al. [48], if the slope of the straight line fitting the experimental data is greater than 0.65, then surface dissolution is the dominant leaching mechanism; if the slope is close to 0.50 (0.35 < slope ≤ 0.65) diffusion transport is the leaching mechanism and if the slope is near 0 (slope ≤ 0.35) a phenomenon of initial wash-off or depletion (if it happened in the middle or at the end of the test) is occurring. According to the data obtained, all element concentrations in the leachates are below the permissible limits prescribed by the SQD and used as a reference for shaped construction materials, such as concrete. The limits for heavy metals are shown in Table 4.5. Chapter 4 77 Figure 4.5. Graphical representation of diffusion-controlled leaching (mg/m 2 ) vs. time (days) in samples: (a) control C-REF; (b) control FRC-REF; (c) FRC2 specimen; (d) FRC4 specimen; and (e) FRC6 specimen. Table 4.5. Limits for diffusion release levels from shaped construction materials (in mg/m2). Slope of linear regression and correlation coefficient. Parameters C-REF FRC2-REF FRC2 FRC4 FRC6 Cr SQD limit for shaped materials emission limits ε 64 (mg/m2) 120.0 Slope of the linear regression 0.522 0.566 0.299 0.197 0.299 Correlation coefficient, R2 0.907 0.739 0.992 0.951 0.989 Standard deviation 0.146 0.294 0.023 0.039 0.027 Zn SQD limit for shaped materials emission limits ε 64 (mg/m2) 800.0 Slope of the linear regression 0.369 0.343 0.326 0.293 0.327 Correlation coefficient, R2 0.944 0.946 0.936 0.960 0.963 Standard deviation 0.078 0.072 0.075 0.052 0.056 Sb SQD limit for shaped materials emission limits ε 64 (mg/m2) 8.7 Slope of the linear regression 0.317 0.255 0.287 0.378 0.272 Correlation coefficient, R2 0.951 0.911 0.936 0.997 0.977 Standard deviation 0.063 0.070 0.075 0.017 0.036 Ba SQD limit for shaped materials emission limits ε 64 (mg/m2) 1500.0 Slope of the linear regression 0.716 0.530 0.763 0.777 0.764 Correlation coefficient, R2 0.989 0.962 0.986 0.983 0.984 Standard deviation 0.065 0.091 0.079 0.090 0.086 According to the data in Table 4.5, Zn and Sb showed linear regression slopes that lead to the idea that Pollutant Potential of Reinforced Concrete Made with Recycled Plastic Fibres from Food Packaging Waste 78 the wash off mechanism occurred. A flat Zn curve appeared in the last steps of the diffusion test, indicating that the element has been depleted in dissolution. Ba presented a tendency towards a dissolution mechanism, except in the FRC-REF sample. In Figure 4.5, the cumulative leaching points follow the slope and the release levels increase along the steps. The element Cr presented lower values for the samples with RPF, corresponding to the wash off mechanism, whereas diffusion was detected for control specimens as has been observed in previous works: contaminants may be in the oxidised or reduced form (e.g., Chromium may be present as CrO4−2 or Cr+3). Heavy metals tend to be complex and strongly associated with the natural, humic substances present in natural waters or soils and these complex forms of heavy metals are generally highly soluble, being released more rapidly than simple forms [32]. Thus, comparing Cr and Ba patterns, it is clearly observed that the slope is more horizontal for Cr (diffusion) than for Ba (dissolution), and the difference in the release pattern is clearly observed for these elements with the differentiated mechanisms. 4.5. Conclusions Waste plastic food packaging, used for the preparation of plastic sheets to be used as fibre reinforcement in concrete, showed low release levels of the elements determined by the Council Decision 2003/33/EC and they were under the inert limits, except for antimony. Hence, they are classified as non-hazardous material. The environmental feasibility of RPF was proven when added to the manufacturing of reinforced concrete with macro recycled plastic fibres at different amounts (2, 4 and 6 kg per m3). The low release levels in concrete with RPF confirms that the process of stabilisation/solidification (S/S) of the waste in the cement matrix of the concrete, reduces the concentrations in leachatesto a minimum. The concentrations of the elements with higher mobility, in the long-term, were much lower than the limits imposed by regulations for “shaped” construction materials, such as SQD. The study carried out to identify the transport and chemical mechanisms, indicated that the release patterns were: wash-off for Sb, Zn (although Zn also presented depletion in the final steps) and Cr in concrete samples with RPF; dissolution for Ba, except for FRC-REF samples; and diffusion for Cr in FRC-REF and C-REF samples. These were identified in the curves of the cumulative leaching vs. time graphs, obtained by conducting the dynamic tank leaching test. Therefore, the present study contributes to the recycling of wastes, such as plastic packaging with a thickness of 0.125 mm and layers of different polymers, as reinforcement in concrete. This type of material does not present any possible environmental impact and could be a viable alternative that would help increase the valorisation of such types of plastic residue, which is considered as being one of the biggest concerns worldwide. Author Contributions: Conceptualization, J.A. and A.P.G.; methodology, A.P.G.; Software, A.L.-U.; Validation, J.A. and A.P.G. formal analysis, P.V. and A.L.-L.; investigation, P.V. and A.L.-U.; resources, J.A.; data curation, P.V. and A.L.-U.; writing—original draft preparation, P.V., A.L.-U. and A.P.G.; writing—review and editing, A.L.-L. and J.A.; visualization, P.V.; supervision, A.L.-U., J.A. and A.P.G.; project administration, J.A. and A.P.G.; funding acquisition, J.A. and A.P.G. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Acknowledgments: The authors would like to express their gratitude to the SP-Group CENTRAL Chapter 4 79 CÓRDOBA-Plastienvase SL for the efficient service, professionalism, and support to the present study. The authors would like to thank to the staff at the Inductively Coupled Plasma Mass Spectrometry (ICPMS) of the Central Research Support Service (SCAI) of the University of Cordoba for technical assistance. Conflicts of Interest: The authors declare no conflict of interest. References 1. Siddique, R.; Khatib, J.; Kaur, I. Use of recycled plastic in concrete: A review. Waste Manag. 2008, 28, 1835–1852, doi:10.1016/j.wasman.2007.09.011. 2. WRAP. Evidence Review: Plastic Packaging and Fresh Produce. 2018. Available on: https://archive.wrap.org.uk/sites/files/wrap/Evidence%20Review%20Plastic%20Packaging%20and%20 Fresh%20Pro- duce%20171218.pdf (accessed on 23 November 2020). 3. ANARPLA. Economía Circular del Plástico. 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Main results and general discussion This chapter presents the main results obtained in this Doctoral Thesis focused on finding a second life to wastes from multilayer food plastic packaging and at the same time to experiment with the use of innovative construction materials in the engineering and construction sector. Previous researchers have been working on finding innovative and sustainable solutions to address the enormous quantities of plastic waste that are produced every year which, after being collected, are transformed into energy, recycled, or sent to landfills. Providing the possibility of recycling to plastic waste as a material to be incorporated, in the form of macro-fibres, into concrete, could be one such solution. In recent years, the circular economy in the framework of 2030 Agenda has been applied to plastic wastes. Research works, which focused on reducing the production of this type of waste, has been increased last years. The plastics recycling sector in Spain is one of the most mature and powerful in Europe, and it is estimated that, in 2030, thanks to the recycling of most than a half of plastic containers in Europe, million tons of CO2 emissions will be achieved. For many decades, researchers have been working on finding innovative and sustainable solutions to address the enormous quantities of plastic waste that are produced every year. In that sense, the incorporation of plastic wastes as recycled fibres (in the form of macro-fibres) into concrete, could be one such solution as it is demonstrated in the present Doctoral Thesis. These plastic fibres are synthetic fibres that are known to help improve the ductility, crack resistance, and toughness of conventional concrete. This thesis has contributed to prove the mechanical feasibility of using recycled plastic fibres in concrete in terms of toughness, bringing an improvement in the post-crack resistance of the composite material. On the other hand, it was proven that the incorporation of the recycled plastic fibres was viable from an environmental point of view based on leaching tests. The experimental methodology performed was based on laboratory test for testing the physical and mechanical properties as: dry density and the open porosity, Compressive Strength, Elastic Modulus, Flexural Strength, CMOD and Toughness (Chapter 3). For the environmental evaluation, different leaching procedures were followed with the aim of reaching different levels of analysis: Compliance leaching Test for basic characterisation; the availability test to determine the maximum pollutant release and leaching tank test to study the release levels at long-term (Chapter 4). Mechanical Performance of Concrete Made with the Addition of Recycled Macro Plastic Fibres (Publication II) The aim of the research was to investigate the physical and mechanical characteristics of a concrete reinforced by adding, in the mixing phase, plastic macro fibres obtained from the multilayer plastic food packaging industry waste . For this purpose, different batches of concrete specimens were produced in the laboratory of cubic (100 mm length), cylindrical (300 mm height, 150 mm diameter) and prismatic (400 mm length, 100 mm width, 100 mmheight): (1) specimens without the addition of fibres (C-REF) and (2) specimens made with the addition of commercial macro plastic fibres (PFRC-REF), with a fibre dosage of 2 kg/m3, used as reference mixes; and (3) specimens with recycled plastic macro fibres with increasing dosage of 2 kg/m3 (PFRC-2), 4 kg/m3 (PFRC-4) and 6 kg/m3 (PFRC-6). The recycled plastic macro fibres (RPF) were mechanically obtained directly from multilayer films from a Spanish plastic food packaging manufacturing company. The dimensions of the fibres obtained were 50 mm in length, 4 mm in width