The rapid growth of the construction industry has led to increased consumption of Ordinary Portland Cement (OPC), which contributes significantly to global carbon dioxide emissions. Geopolymer technology has emerged as a sustainable alternative binder utilizing industrial and agricultural waste materials. Rice Husk Ash (RHA), an agricultural by-product rich in silica, has potential as a geopolymer precursor; however, its low calcium content limits early strength development. This study investigates the influence of Ground Granulated Blast Furnace Slag (GGBS) on the fresh and mechanical properties of RHA-based geopolymer paste. Geopolymer paste specimens were prepared by partially replacing RHA with slag at different proportions. Sodium hydroxide and sodium silicate solutions were used as alkaline activators, and specimens were cured under ambient conditions. Fresh properties such as workability and setting time were evaluated, while compressive strength tests were conducted to determine mechanical performance. Experimental results indicate that the incorporation of slag significantly improves workability, reduces setting time, and enhances compressive strength. The improved performance is attributed to the formation of N-A-S-H and C-A-S-H gel structures that produce a denser geopolymer matrix. The study demonstrates that RHA–slag geopolymer paste can serve as a sustainable and low-carbon alternative to conventional cement-based materials.

Keywords Geopolymer, Rice Husk Ash (RHA), Sustainable Construction, Compressive Strength, Alkaline Activation.