Ambient-Cured Foamed Geopolymer Blocks: Mix Optimization and Microstructural Performance

This study aims to develop sustainable, ambient-cured lightweight foamed geopolymer blocks utilizing fly ash (FA) and sugarcane bagasse ash (SCBA) to reduce energy consumption in masonry unit production. A comprehensive parametric investigation was conducted on six key mix variables: ordinary Portland cement (OPC) addition, SCBA replacement, foam dosage, liquid-to-binder ratio, alkaline activator ratio, and sand-to-binder ratio. The engineering properties, specifically 7-day compressive strength and bulk density, were evaluated and supported by microstructural characterization using XRD and SEM. The experimental results revealed that the optimum mix comprising a binder of 90% FA and 10% OPC, 10% SCBA replacement, 3% pre-formed foam, a liquid-to-binder ratio of 0.7, a sodium silicate-to-sodium hydroxide ratio of 1.0, and a sand-to-binder ratio of 2.25 was formulated and achieved a lightweight classification (≤ 1,800 kg/m³) with a compressive strength of 9.05 MPa. The significance of this study lies in establishing an optimum mix design that enables the utilization of multiple agro-industrial wastes in structural blocks without the need for energy-intensive thermal curing, thereby offering a viable and eco-friendly alternative for the construction industry.