Impact of sodium hydroxide molarity on mechanical properties of fly ash–slag-based geopolymer concrete

The requirement of heat curing besides the poor workability of geopolymer concrete (GPC) is the main hurdle in its practical implementation. This study investigates the impact of sodium hydroxide (NaOH) concentration on the behaviour of fly ash slag blended ambient-cured GPC. The sodium hydroxide concentration was varied within the range from 8 molar to 14 molar to investigate its impact on fresh and hardened mechanical properties. The increase in sodium hydroxide concentration from 8 molar to 16 molar resulted in a continuous decrease in the workability of GPC. The target slump of more than 150 mm was achieved even for high sodium hydroxide concentration due to the presence of high-range water-reducing admixture. However, the increase in sodium hydroxide concentration positively influences the strength development of fly ash–slag-based ambient-cured GPC. The optimum 28 days compressive strength and splitting tensile strength of 44.3 MPa and 4.01 MPa, respectively, were achieved for the GPC with a sodium hydroxide concentration of 12 molar. The comparison of life-cycle assessment indicated that GPC is a sustainable alternative that offers a 49% reduction in greenhouse gas emissions compared to ordinary Portland cement-based concrete.