Effect of Alkali Activators on Mechanical and Durability Properties of Fly Ash based Geopolymer Concrete
Abstract
The production of ordinary Portland cement (OPC) is one of the major sources of carbon dioxide emissions in the construction industry, creating a need for more sustainable building materials. Fly ash-based geopolymer concrete (GPC) has emerged as a promising alternative because it can reduce environmental impact while providing good engineering performance. This study examines how different proportions of sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) affect the strength and durability of GPC compared with conventional OPC concrete. Initial trials using NaOH:Na₂SiO₃ ratios of 1:0.5 and 0.5:1 were conducted to identify a suitable curing condition. The main investigation was then carried out using geopolymer mixes with activator ratios of 1:1 and 0.5:1, all oven-cured at 80°C, with OPC concrete used as the control mix. Compressive, split tensile, flexural, shear, and pull-out strengths were evaluated using Indian Standard methods, while durability was assessed through water penetration and X-ray diffraction (XRD) tests. The results showed that heat curing significantly improved early-age strength, especially for the 0.5:1 mix. Although OPC concrete achieved slightly higher 28-day strength, the geopolymer mixes showed comparable mechanical performance, lower water penetration, and clear evidence of successful geopolymerization.