Impact of Alkaline Concentration on the Mechanical Properties of Geopolymer Concrete Made up of Fly Ash and Sugarcane Bagasse Ash

Geopolymer concrete (GPC) is a novel and environmentally friendly type of concrete that eliminates the use of cement, resulting in a significant reduction in carbon emissions and a more sustainable construction material. Alkaline activators are used in GPC to achieve rapid strength development. The most popular alkaline activators are sodium/potassium silicate and sodium/potassium hydroxide, which are known contributors to carbon emissions, hence limiting the advantages of GPC; therefore, reducing the amount of these alkaline activators that contribute to carbon emissions is necessary for developing a more sustainable geopolymer concrete. In this study, the influence of the variation in sodium hydroxide molarities on the performance of fly ash/sugarcane bagasse ash-based-geopolymer concrete was investigated. The different molarities used were 10 M, 12 M, 14 M, and 16 M sodium hydroxide solutions. In addition, the effect of sugarcane bagasse ash content (0%, 5%, 10%, 15%, and 20%) on the fresh and hardened geopolymer concrete properties were examined. The slump test, compression test, split tensile test, and flexure test were conducted on the cast samples. The results of this study showed that raising the concentration of NaOH from 10 M to 16 M while maintaining a sodium silicate to sodium hydroxide ratio of 2.5 resulted in a 3.75–10.2% improvement in compressive strength after 28 days. It is worth noting that, even at a concentration of 10 M, the concrete still achieved high strength.