Durability performance of geopolymer stabilised expansive soil incorporating novel rice husk ash-based waste derived alkaline activator

Abstract

Despite strong mechanical and durability properties, conventional geopolymers in expansive soil stabilisation often face environmental and cost challenges. Consequently, alternative sustainable binders are increasingly pursued, though durability studies of such novel geopolymerisation methods remain limited. This study assesses the durability of a novel waste-derived geopolymer binder that utilises fly ash (FA) and slag as aluminosilicates and rice husk ash (RHA)-based silicate, replacing commercial silicate for geopolymer-soil stabilisation. Optimised mix ratios were used for specimen preparation: 0.6 NaOH/RHA, 3 M NaOH, and a 40-min mixing duration for RHA-based silicate preparation, and 16% FA and 4% slag with 12 M NaOH as the precursor and hydroxide component of the activator, respectively. The results demonstrate that the stabilised specimen successfully endures all 12 cycles, exhibiting a mass loss of only 10.5%. Consequently, strength, chemical, and microstructural examinations were conducted on stabilised specimens cured for 28 days at 40 °C. The binder increased the raw soil strength by 1150%, meeting good–very good CBR subgrade criteria. Incorporating geopolymers elevated the soil pH, electrical conductivity (EC), and cation exchange capacity (CEC), facilitating improved geopolymerisation while maintaining heavy metal leaching thresholds. Microstructural analyses validated the laboratory results, providing crucial insights into sustainable ground stabilisation using reclaimed waste materials.