Properties of modified metakaolin-based geopolymer concrete with two types of waste aggregate

The widespread use of cement in construction contributes significantly to carbon dioxide (CO2) emissions, creating an urgent need for environmentally friendly alternatives. Geopolymer concrete (GPC), which contains no cement, offers a sustainable solution. The focus is on developing a modified metakaolin-based GPC that incorporates recycled materials to improve sustainability while assessing its mechanical and durability properties. The research involved enhancing the binder by replacing 5% of metakaolin with calcium oxide and silica fume by weight. Additionally, to reduce environmental impact, 10% of the natural coarse aggregate volume was substituted with crumb rubber and shredded plastic waste. A detailed mix design was conducted using specific proportions of materials, including metakaolin, coarse aggregates, fine aggregate, sodium hydroxide, sodium silicate, water, and superplasticizer in particular proportions (372, 910, 603, 83, 192, 7, and 56 kg/m³, respectively). The study evaluated mechanical properties, including compressive strength, splitting tensile strength, and modulus of elasticity, alongside durability metrics such as water absorption, permeability, abrasion resistance, and shrinkage. The incorporation of recycled materials, including 10% crumbed rubber and plastic waste aggregate, resulted in performance reductions, with compressive strength decreasing by 25 and 34%, tensile strength by 17 and 41%, and modulus of elasticity by 10 and 33%, respectively. Despite some declines in performance, the modified geopolymer concrete demonstrated improved permeability, abrasion resistance, and shrinkage while remaining within acceptable limits. Microstructural analyses confirmed the beneficial effects of recycled materials on matrix integrity. The findings support the use of geopolymer concrete as a sustainable, low-carbon construction material.