Low-Carbon Geopolymer Concrete with Recycled Fine Aggregates: Mechanical Performance and Eco-Efficiency Assessment

Abstract

The escalating environmental concerns associated with conventional Portland cement production, particularly its contribution to greenhouse gas emissions, necessitate the adoption of sustainable alternatives. Simultaneously, the underutilization of industrial by-products such as fly ash, and the overexploitation of natural river sand for fine aggregates, present significant ecological and resource challenges. In this context, geopolymer concrete (GPC), synthesized through alkali activation of fly ash, offers a promising low-carbon alternative to traditional cementitious systems. This study investigates the mechanical performance and eco-efficiency of GPC incorporating recycled fine aggregates (RFA) as a sustainable substitute for manufactured sand (M-sand). A geopolymer mix was developed using Class F fly ash as the sole binder and an 8M alkaline activator solution. The control mix used 100% M-sand, while subsequent mixes replaced M-sand with RFA at 25%, 50%, 75%, and 100% replacement levels. The influence of RFA on compressive strength, split tensile strength, and flexural strength was experimentally assessed. Results revealed that up to 50% replacement of M-sand with RFA enhanced mechanical performance, achieving strengths comparable to or exceeding the control mix. However, further increase beyond 50% led to marginal reductions in strength, attributed to the porous and angular nature of recycled aggregates. This study demonstrates that partial incorporation of RFA in GPC not only enhances its mechanical properties but also contributes to circular resource utilization and environmental conservation, making it a viable solution for sustainable construction.