Mix optimization for expansive soil stabilized with a novel waste material-based geopolymerization approach

Extensive areal distribution of expansive soil is a timely concern in engineering challenges. Geopolymers outperform conventional cement/lime treatment in expansive soil stabilization due to their superior mechanical and durability performance. However, the excessive cost and carbon footprint of commercial alkaline activators hinder geopolymer's widespread application. This study aims to derive a cost-effective, carbon-conscious mix to stabilize expansive soil using waste-based geopolymerization. Class F fly ash was activated via a novel solution of rice husk ash (RHA)-derived silicate and NaOH. Three factors (NaOH/RHA, NaOH molarity, mixing duration) were considered using the Taguchi method and utility concept for mix optimization, while further investigations were tailored to explore the effects of curing temperature (room temperature, 30 °C, and 40 °C) and the curing period (7, 14, and 28 days) on the strength development of treated soil. The results indicate that NaOH/RHA = 0.6, NaOH molarity = 3 mol/L, and a mixing duration of 40 min with curing temperatures of around 30 °C are ideal for maximizing the strength cost-effectively while significantly reducing the swell pressure (up to 28%). The shift from commercial Na2SiO3 to RHA-silicate is 89% cheaper and reduces the carbon footprint by 70%. The study benefits sustainable ground stabilization and efficient waste management.