Mechanical properties of geopolymer concrete with partial replacement of fly ash by agricultural waste ashes

Abstract

Abstract Concrete, primarily composed of cement, contributes substantially to environmental degradation due to high CO₂ emissions. With cement production increasing by approximately 7% annually, geopolymer concrete (GPC) offers a sustainable alternative. By using industrial waste ashes as a primary binder instead of cement, GPC reduces energy consumption, mitigates waste disposal issues, and significantly lowers carbon emissions. This study assessed the effects of Rice Husk Ash (RHA), Cassava Peel Ash (CPA), and Sugarcane Bagasse Ash (SCBA) as partial replacements for Fly Ash (FA) in GPC, focusing on compressive and split tensile strengths. The mix preparation involved an alkaline solution prepared in advance, combined with FA, RHA, SCBA, CPA, sharp sand, and granite in a 1:1 liquid-to-solid ratio. The mix was cast, oven-cured for 4 h, and tested at 7, 14, and 28 days. The 100% Fly Ash (FA) mix achieved the highest compressive strength of 2.3 N/mm 2 at 28 days due to its low SiO₂/Al₂O₃ ratio (0.28) and high alumina content, which promote efficient geopolymerization. In terms of tensile strength, the 50% FA + 50% CPA mix exhibited the highest value of 0.65 N/mm 2 at 28 days, surpassing the 100% FA mix (0.30 N/mm 2 ) and the 50% FA + 50% SCBA mix (0.60 N/mm 2 ). The relatively low strength values are attributed to the short 4-h curing period, which limited full geopolymerization. This study demonstrates that using agricultural waste ashes in geopolymer concrete promotes sustainability and highlights how SiO₂/Al₂O₃ ratios influence compressive and tensile strength, guiding optimized mix designs.