Marginal Lateritic Soil Stabilized with Calcium Carbide Residue and Fly Ash Geopolymers as a Sustainable Pavement Base Material

Two waste by-products, fly ash (FA) and calcium carbide residue (CCR), are used to develop geopolymer binders for stabilizing marginal lateritic soil as a sustainable pavement base. The liquid alkaline activator is a mixture of sodium silicate solution (Na2SiO3) and sodium hydroxide (NaOH) at a concentration of 10 molars. Unconfined compressive strength (UCS) and scanning electron microscopy (SEM) images of lateritic soil-FA geopolymers at different influential factors (curing times, Na2SiO3:NaOH ratios, and CCR replacement ratios) are measured. The soaked 7-day UCS of lateritic soil-FA geopolymers meets the strength requirement for both light and heavy traffic pavement specified by the local national authorities. The early 7-day UCS and cementitious products increase with increasing CCR replacement ratio, and the cementitious products are clearly observed at CCR = 30% (the highest CCR replacement ratio tested). However, the CCR replacement ratio providing the maximum 90-day strength is found at 20%. FA particles in lateritic soil-FA geopolymer at excessive CCR replacement ratio of 30% are evidently spongy and cracked because of early aluminosilicate gel precipitation and generated heat, hence the subsequent reduced strength. The CCR replacement is recommended for low NaOH geopolymer binder (Na2SiO3:NaOHratios90:10) at 20%. This research seeks to enable CCR traditionally destined for landfill to be used as a promoter in geopolymer binder, which is significant in addressing the sustainable usage of CCR from engineering, economical, and environmental perspectives.