A Cost-Effective and Low-Carbon Geopolymer Concrete Production by Mitigating Natural Sand Dependency

Abstract Geopolymer concrete, recognized for its reduced carbon footprint, presents an environmentally friendly alternative to conventional concrete. However, the limited availability of natural fine aggregates poses a significant challenge, even for geopolymer concrete. This study investigated the mechanical and microstructural properties of a novel geopolymer concrete that partially replaces natural fine aggregates with crushed steel furnace slag, a type of industrial waste. The mix design of the novel geopolymer concrete consisted of a 50 ∶ 50 mixture of fly ash and ground granulated blast furnace slag as binders, and varying proportions of crushed steel furnace slag as a partial replacement for natural fine aggregates, activated by a 12 M alkaline solution. In the first phase of the study, the workability and mechanical characteristics of the novel geopolymer concrete were investigated. The study’s second phase focused on the microstructural characteristics of the geopolymer concrete. The dependency of the strength parameters was also evaluated. Based on the mechanical and microstructural characteristics, an optimized quantity of crushed steel furnace slag was determined as a replacement for natural fine aggregates, without significantly affecting the properties of the geopolymer concrete. The proposed prediction models exhibited excellent agreement with the experimental results, as confirmed by high R -squared values, demonstrating a reliable forecast of the mechanical performance of CSFS-based geopolymer concrete, in line with existing literature and codal provisions of ACI 209R and Eurocode 2. Finally, a carbon dioxide emission and cost–benefit analysis was performed to determine the environmental and economic advantages of the optimized geopolymer concrete over conventional concrete. It was observed that geopolymer concrete made by replacing 50% of natural fine particles served as an optimum mix, providing an optimal balance of mechanical strength, cost reduction, and carbon dioxide emission reduction when compared to conventional concrete.