Performance Evaluation of Geopolymer Concrete with Waste Glass Powder and Alkaline Activator

486 Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 p ISSN: 2635-3342; e ISSN: 2635-3350 Original Research Article Performance Evaluation of Geopolymer Concrete with Waste Glass Powder and Alkaline Activator *1Afolabi, O.E., 1Dahunsi, B.I.O., 1Labiran, J.O., 2Hassan, D.E. and 3Sanni, A. 1,2,3Department of Civil Engineering, Faculty of Technology, University of Ibadan, Oyo State, Nigeria. 2Department of Civil Engineering, Faculty of Technology, Ajayi Crowther University, Oyo, Oyo State, Nigeria. 3Department of Civil Engineering, Universidade Federal do Para, Belem, Brazil. *afolabi.o[email protected] http://doi.org/10.5281/zenodo.18061617 ARTICLE INFORMATION ABSTRACT Article history: Received 09 Oct. 2025 Revised 06 Nov. 2025 Accepted 09 Nov. 2025 Available online 30 Dec. 2025 In this study, the performance of geopolymer concrete incorporating waste glass powder (WGP) as a supplementary cementitious material and an alkaline activator was evaluated. Geopolymer concrete, known for its eco-friendliness and ability to utilize industrial by-products, was assessed for its mechanical properties, durability, and sustainability aspects. The study explored the impact of varying sodium hydroxide (NaOH) molarities (10M, 12M, and 14M) on the strength properties of WGP geopolymer concrete, alongside different curing periods (7, 14, and 28 days). A notable trend was observed in the slump values, which decreased from 67 mm for the 10M NaOH solution to 0 mm for the 14M solution. This reduction indicates lower workability and increased stiffness as molarity increases, likely due to accelerated setting and reduced fluidity. Among the mixes, the 12M NaOH mixture showed the most promising compressive strength, with values of 10.50 MPa, 13.60 MPa, and 17.07 MPa at 7, 14, and 28 days, respectively. This demonstrates the potential for the 12M mixture to achieve higher strength with extended curing, highlighting its applicability in sustainable construction. © 2025 RJEES. All rights reserved. Keywords: Waste glass powder Alkaline activator Geopolymer concrete Compressive strength Molarity 1. INTRODUCTION Addressing concerns related to environmental impact and resource management necessitates sustainable measures aimed at reducing the volume of this waste within the municipal solid waste stream. Managing the considerable annual production of global waste glass presents a substantial challenge. The proper management of waste glass, considering its type and quality, entails the options of recycling or landfill disposal. Despite the apparent recyclability of all waste glass for reuse in glass factories, a significant issue arises due to variations in the quality and color of the collected glass. The presence of mixed glasses with different colors and origins leads to an unpredictable color and 487 O.E. Afolabi et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 properties in the new glass, rendering it non-recyclable and requiring disposal in landfills (Vafaei & Allahverdi, 2017). Nevertheless, the favorable chemical composition and pozzolanic properties found in waste glass offer promising potential for its utilization in the cement and concrete industries. This not only presents an environmentally friendly solution but also addresses sustainability concerns within both the glass and cement sectors (Jani & Hogland, 2014). Concrete stands as one of the most extensively employed construction materials globally. Yet, the production of traditional Portland cement, the primary binding agent in concrete, contributes significantly to carbon dioxide emissions. (Mehrab & Vahid, 2021). Hence, there's an increasing focus on formulating alternative binders to mitigate the environmental impact associated with concrete production. Geopolymer concrete has emerged as a promising substitute for Portland cement concrete. Formulated by activating aluminosilicate materials with an alkaline solution, geopolymer concrete boasts various advantages over its Portland cement counterpart, such as increased strength, reduced permeability, and enhanced resistance to fire and chemicals. (Jair de Jesús et al., 2020). Glass, a material with 72% silica content (SiO2), exhibits unique properties when finely ground to a 600-micron powder. This finely ground glass reacts with the alkali in cement through the Pozzolana reaction, generating cementitious products that provide abrasion resistance to strength development (Veena & Rao, 2016). Renowned for its aesthetic appeal, transparency, malleability, remarkable durability, and resistance to abrasion, glass is a commonly utilized material in various applications (Topçu & Canbaz, 2003). In its intrinsic nature, glass is inorganic, non-metallic, hydrophobic, incombustible, and brittle, yet remarkably ductile at high temperatures (Mehta & Ashish, 2020). Classified into 24 types, major categories include soda-lime, fused silica, lead, vitreous silica, borosilicate, alkali silicate, aluminosilicate, germanium oxide, and barium glasses (Liew, Sojobi, & Zhang, 2017), (Hajimohammadi, Ngo, & Kashani, 2018 ). Glass can take various forms, from flat sheets to shaped objects like bottles, cathode ray tubes, or lamp glasses, depending on its production and intended use (Hama, Mahmoud, & Yassen, 2019). When waste glass is processed into fine particles, it meets the physical, mechanical, and chemical characteristics required for Class F and Class C pozzolanic materials, as outlined in ASTM C 618 standards (Aliabdo, Abd Elmoaty, & Aboshama, 2016). The global scale of glass production, reaching approximately 130 million tons, results in the annual generation of over 100 million tons of waste glass (WG). This substantial volume accounts for roughly 5% of the total solid waste produced worldwide each year, as reported by The World Bank and various studies (Ferdous et al., 2021; Siddika et al., 2021; Guo, Bao, & Meng, 2021). Despite efforts to recycle a portion of waste glass from containers and packaging to create new glass products, the recycling process for WG, particularly when dealing with specific colors and physical characteristics, poses significant economic challenges. The energy-intensive nature of this recycling process adds to the complexity (Andiç-Çakır et al., 2016). It's worth noting that various types of glasses, such as window panes, tempered glass, laminated glass, Pyrex, borosilicate glass, light bulbs, mirrors, and glassware, are not used as raw materials for new glass production and are considered contaminants in the recycling process (Arabi et al., 2019). Glass powder proves to be a versatile material with effective applications in geopolymer production. It can serve as a valuable source of silica and be employed as a precursor or activator solution in geopolymer production. Additionally, waste glass (WG) powder finds utility as precursors, aggregates, or in the development of activator solutions for geopolymer concrete. The incorporation of WG powder notably accelerates the geopolymerization process, leading to enhanced strength in the final geopolymer concrete (Hajimohammadi, Ngo, & Kashani, 2018). Therefore, the aim of this study was to investigate the development of sustainable geopolymer concrete by incorporating waste glass powder and an alkaline activator for geopolymerization. 488 O.E. Afolabi et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 2. MATERIALS AND METHODS 2.1. Material Collection and Preparation of Samples Flat sheet glass was used as the source of waste glass powder (WGP). The glass waste was locally obtained from a glass vendor in Ibadan, Oyo State, Nigeria, and was cleaned, dried, crushed, and milled into a fine powder suitable for use as a supplementary material. The alkaline activator consisted of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃). The NaOH pellets, with a purity of 99%, were dissolved in water according to the required molarity and mixed with sodium silicate solution at a ratio of 2.5. Both chemicals were sourced locally from chemical stores in the Ogunpa market, Ibadan. Natural river sand obtained from a river site in Ibadan was used as the fine aggregate, with particle sizes ranging from 150 µm to 4.75 mm in accordance with ASTM C33/C33M (2018). The sand was washed and screened to remove impurities. Crushed granite with a nominal size of 12.5 mm, procured from a quarry plant in Ibadan, served as the coarse aggregate and conformed to ASTM C33/C33M (2018) specifications. Distilled water used for sample preparations was purchased from a vendor in the Yemetu area of Ibadan. 2.2. Experimental Procedure for the Production of Geopolymer Concrete 2.2.1. Design mix and procedures As per (Davidovits J., 2002), Table 1 outlines the recommended material ratios for geopolymer concrete mixes. The suggested alkaline liquid to binder ratio falls within 0.3–0.45, while the sodium silicate to sodium hydroxide solution ratio is advised to be in the range of 2.0–2.5. The total content of aggregate in the mass of geopolymer concrete is specified as 65–85%, with the fine aggregate content in the total aggregate volume set at 30%. The acceptable range for super plasticizer is designated as 1.5–4% by the mass of the binder content. If additional water is required, it can be incorporated within the range of 0.02–0.06% by the mass of the cementitious material as shown in the table. Table 1: Specifications for materials employed in geopolymer concrete mixes. Materials Range of values Alkaline liquids/Binder 0.3–0.45 Sodium silicate/sodium hydroxide 2.0–2.5 Water/Binder 0.16–0.24 Total aggregate in mass of concrete 65–85% Fine aggregate content in total aggregate 30% Added water content 0.02%–0.06% of mass of cementitious material Super Plasticizers 1.5%–4% of mass of cementitious material For this project, the concrete mix proportions were designed based on the unit weight of plain concrete, taken as 2400 kg/m³. Coarse aggregate accounted for 70% of the total aggregate volume, while fine aggregate constituted 30%. The ratio of alkaline liquid to cementitious (geopolymer) materials was maintained at 0.35, and the ratio of sodium silicate (Na₂SiO₃) to sodium hydroxide (NaOH) solution was fixed at 2.5. Table 2 presents the mix design parameters, including the quantities of geopolymer source material, alkaline activator, water-to-binder ratio, solid content in the alkaline solution, total water content, and corresponding water corrections. The base mix was prepared using a sodium hydroxide concentration of 10 M, while similar mixes were developed for higher molarities of 12 M and 14 M. 2.2.2. Preparation of molar solution of NaOH To prepare a one-molar (1 M) sodium hydroxide (NaOH) solution, 40 g of NaOH flakes (molecular weight = 40) were dissolved in one liter of distilled water. The solution was prepared 24 hours prior to concrete casting to minimize the risk of contamination during the mixing of geopolymer concrete constituents. It was observed that the temperature of the solution increased during preparation due to the exothermic nature of the dissolution process. For the preparation of a 10 M sodium hydroxide solution, 400 g of NaOH flakes were gradually dissolved in approximately 750 mL of distilled water while stirring continuously. After complete dissolution, the solution was allowed to cool to room temperature before adding the remaining quantity of water to make up a total volume of one liter. Owing to the exothermic nature of the reaction, 489 O.E. Afolabi et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 appropriate safety measures were observed to avoid direct contact of the solution with the skin and eyes. The calculation is done using equation 1. 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑁𝑎𝑂𝐻 𝑡𝑜 𝑏𝑒 𝑑𝑖𝑠𝑠𝑜𝑙𝑣𝑒𝑑 = 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 × 𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑁𝑎𝑂𝐻 (1) Molecular weight of NaOH = 40; Molarity M = 10 M From Equation 1, the weight of NaOH to be dissolved = 400g. This is also adopted for Molarity M12 and M14, which are 480g and 560g, respectively. Table 2: Design mix of materials Materials used Quantity Unit weight of Concrete 2400 kg/m3 Percentage of aggregate in total mass of concrete 70% Aggregate content in total mass of concrete 1680 kg/m3 Percentage of fine aggregate in total mass of aggregate 30% Fine aggregate in total mass of aggregate 504 kg/m3 Coarse aggregate in total mass of aggregate 1176 kg/m3 Cementitious materials Ratio of alkaline liquid to cementitious material 0.45 Mass of Cementitious material and alkaline liquid 720 kg/m3 Mass of Cementitious material 533 kg/m3 Mass of alkaline liquid 187 kg/m3 Alkaline liquids required Ratio of sodium silicate and sodium hydroxide 2.5 Mass of sodium hydroxide 53 kg/m3 Mass of sodium silicates 134 kg/m3 Water in Sodium silicate Na2O 15.30% SiO2 33.69% H2O 51.01% Water content in sodium silicate 69 kg/m3 Solids content in sodium silicate 65 kg/m3 Water in sodium hydroxide Molarity ratio 10 Mass of NaOH solids 400 gm NaOH 40% H2O 60% Solid content in sodium hydroxide 21 kg/m3 Water content in sodium hydroxide 32 kg/m3 Total water content 101 kg/m3 Water to cementitious material ratio 0.19 2.2.3. Concreting: batching, mixing and casting into molds The constituent materials were weighed out and batched according to the mix design specified in Table 3. Manual hand mixing was adopted for the sake of this research. The preparation of Geopolymer concrete is similar to that of the OPC, all constituent was poured into the mixing container and mixed together for about 5 to 10 minutes to establish homogeneity. Following mixing, the fresh concrete was poured into a mould measuring 100mm x 100mm x 100mm in three layers. Each layer was compacted using 25 blows from a tamping rod. In total, 3 batches were mixed, with 9 cubes cast in each batch. Consequently, a grand total of 27 cubes were cast. These specimens were subsequently utilized for the compressive strength test. 2.2.4. Test on fresh concrete The fresh mix's workability was assessed through the slump test, following the guidelines outlined in BS 1881-102, 1983. This involved utilizing a standard device shaped like a truncated cone, with dimensions of 490 O.E. Afolabi et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 100mm upper diameter, 200mm lower diameter, and 300mm height. The mold was positioned on a smooth, flat, vibration-free, and non-absorbent surface. Concrete was poured into the mold in three equal layers, each compacted by 25 rams with a standard rod. Afterward, the mold was gently raised, and the slump of the concrete was measured using a meter rule. The experimental setup is shown in Plate 1. Table 3: Experimental mix design proportion for the concrete specimen Materials M1 (10M) M2 (12M) M3 (14M) Coarse aggregate 10.584 10.584 10.584 Fine aggregate 4.536 4.536 4.536 WGP 4.03 4.03 4.03 Alkaline solution 2.3 2.3 2.3 Water required 1.15 1.15 1.15 Plate 1: Slump test 2.2.5. Curing Once cast, all wrapped molds were left undisturbed inside a 60°C oven for a period of 12 hours. Prior to demolding, the molds were left in the oven to naturally cool down to ambient temperature before being removed from the oven. Following this, the specimens were carefully packed, demolded, and carefully stored at ambient temperature for different curing ages, which are 7,14, and 28 days, and were used for destructive tests. This setup is shown in Plate 2. Plate 2: Curing in oven 2.2.6. Test on hardened concrete The compressive strength tests were conducted using a Universal Compression Loading machine with a capacity of 100KN, following the guidelines outlined in BS 1881-116, 1983. cubic specimens were weighed and positioned in the machine, with plates placed on the top and bottom of the sample to ensure even 491 O.E. Afolabi et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 distribution of the load as shown in Plate 3. Readings were recorded when there was no further progressive reading on the digital load and strength display screen gauge. The compressive strength can be calculated using Equation 2. 𝑓𝑐𝑐 =F 𝐴 (2) Where, fcc is the compressive crushing strength, in N/mm2, F is the crushing load, in N, and A is the net area of the specimen, in mm2 Plate 3: Compressive testing 3. RESULTS AND DISCUSSION 3.1. Particle Size Distribution The sieve analysis result presented in Figure 1 shows that the fine aggregate is well-graded with a fineness modulus of 3.3, classifying it as coarse sand in accordance with ASTM international standard (2018). This gradation indicates a good distribution of particle sizes, which enhances packing density and reduces voids in the mix. Consequently, the coarse and well-graded nature of the sand contributes to improved strength and durability of the geopolymer concrete, although it may slightly reduce workability. Figure 1: Particle size distribution 3.2. Specific Gravity The average specific gravity for sand and granite was calculated as 2.68 and 2.61, respectively. According to (Popovics, 1992), aggregates with a specific gravity below 2.4 are categorized as lightweight, while those with a specific gravity up to 2.75 are considered normal weight. It is noteworthy that all the obtained values 0 20 40 60 80 100 0.01 0.1 1 10 Percentage Finer (%) Particle size (mm) 492 O.E. Afolabi et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 fall within the acceptable range of 2.4 to 2.75 for both fine and coarse aggregates as specified by (BS 8122, 1995). 3.3. Plastic State of Concrete The workability results of the fresh concrete mix with varying molarities of NaOH is shown in Figure 2 indicates that higher concentrations of Sodium hydroxide in the mix correspond to reduced workability. Notably, the 12M concentration necessitated additional water during casting to enhance workability further. All slumps shape gives a true slump. Figure 2: Effect of molarity of NaOH on slump value 3.4. Hardened State of Concrete The compressive strength results for the waste glass powder (WGP) geopolymer concrete are presented in Figure 3. The results show that the compressive strength increases with curing age for all mixes, indicating continued geopolymerization over time. Among the three molarities studied, the mix prepared with 12 M NaOH exhibited the highest compressive strength at all curing ages, increasing from 10.50 N/mm² at 7 days to 17.07 N/mm² at 28 days. This suggests that 12 M NaOH provided an optimal balance of alkalinity to effectively dissolve silica and alumina from the glass powder, enhancing the formation of geopolymeric gel and improving matrix densification. Figure 3: Effect of NaOH molarity on compressive strength of WGP geopolymer concrete 4. CONCLUSION The performance evaluation of sustainable geopolymer concrete with waste glass powder and alkaline activator was investigated and the following conclusive remarks were drawn from the analyzed result and discussions: 0 10 20 30 40 50 60 70 10M 12M 14M Slump Value Molarity 0 5 10 15 20 10M 12M 14M Compressive strength Molarity 7 days 14 days 28 days 493 O.E. Afolabi et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 486-493 i. Geopolymer concrete with 12M sodium hydroxide and added water (0.15% of binder) shows the best workability and retains the highest strength at 28 days. ii. Testing geopolymer concrete with WGP at 10M, 12M, and 14M molarities indicates that 12M consistently performs best. Its compressive strength increases significantly over time, reaching 17.07 MPa at 28 days. Lower strengths are observed with 10M and 14M, with 14M unexpectedly decreasing at 28 days. 5. 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