Influence of alkaline activators on mechanical properties of environmentally friendly geopolymer concrete under different curing regimes

Previous studies highlighted the significance of tailoring alkaline activators (AA) to specific fly ash (FA) sources for optimal properties of geopolymer concrete (GPC). This study examines the influence of various AA's properties on mechanical properties and microstructures of local low-calcium FA-based GPC under varying curing conditions. A comprehensive investigation consists of several factors such as NaOH molarities (10 M, 12 M, 14 M, 16 M), ${\mathrm{Na}}_2{\mathrm{SiO}}_3/NaOH$ ratios (1.5, 2.0, 2.5) and $AA/FA$ ratios (0.5, 0.6). The results reveal a complex relationship, demonstrating that NaOH molarity positively influences compressive strength up to a threshold of 14 M, beyond which an adverse effect was observed while, the flexural strength was increased up to 16 M. Moreover, the study highlights the complex relationship between ${\mathrm{Na}}_2{\mathrm{SiO}}_3/NaOH$ ratios and mechanical strengths. Notably, these properties exhibited an increase as the ratio rose up to 2.0, but a subsequent decrease was observed when the ratio reached 2.5. Moreover, proposed regression equations predict the compressive and flexural strengths of both ambient-cured GPC and heat-cured GPC with marginal statistical errors. The optimal GPC mix exhibited 49% lower embodied ${\mathrm{CO}}_2$ emissions than the corresponding OPC concrete. GPC has higher cost, but it exhibited lower cost-to-strength ratio compared to OPC concrete.