Sustainable Use of Sugarcane Bagasse Ash in Fly Ash-based Geopolymers: Implications for Compressive Strength and Shrinkage

Abstract

Geopolymers are synthesized through the reaction between alkaline activator solutions and aluminosilicate-rich precursors, offering an alternative to Portland cement for sustainable construction. Sugarcane bagasse ash (SCBA), an agricultural byproduct rich in SiO₂, presents potential for incorporation into fly ash (FA)-based geopolymer systems. While SCBA has been explored for environmental benefits, limited studies have evaluated the combined influence of SCBA and alkaline activator solutions on hardening behavior. This study investigated the effects of SCBA content (0%, 10%, 20%, 30% by mass), NaOH concentration (8M, 12M, 16M), and liquid-to-solid (L/S) ratio (0.2, 0.4, 0.6) using 36 geopolymer paste mixtures. SCBA was processed by drying, sieving to 149 µm, and calcining at 700 °C for 2 hours. Specimens were cured at 90°C for 24 hours, followed by ambient curing. Bulk density, apparent porosity, water absorption, compressive strength, and shrinkage were evaluated. Results showed that SCBA content and L/S ratio strongly affected compressive strength and shrinkage. The mixture containing 10% SCBA, NaOH 12M, and L/S = 0.4 achieved the highest compressive strength (47.65 MPa at 90 days), along with reduced porosity and water absorption. In contrast, SCBA replacement above 20% resulted in decreased strength and increased shrinkage. The results indicate the potential of SCBA as a partial FA replacement to promote sustainable construction materials.