Assessment of Durability and Resilient Strain Deformation of Expansive Subgrade Treated With Nano-Slag-Based Geopolymer

Abstract

Nano-geopolymer binders (NGB) of 5%, 10%, 15%, and 20% concentration were used to stabilize expansive subgrade soil against strain deformation, as well as to improve its durability. The composites were subjected to a series of zero-swelling, wetting (W-D) cycles, and dynamic resilient modulus tests to determine the subgrade resilient strength against 100,000 applied repetitive loads (ARL). The results revealed that the resilient moduli of the stabilized and unstabilized subgrade soils exhibited strain-hardening responses at low cyclic stress levels. Therefore, the rate of plastic strain deformation became microscopically negligible, and the tested subgrade was considered stable at this stage. Conversely, at high cyclic stresses, the nano-geopolymer-stabilized subgrade continued to exhibit strain hardening between 80,000 and 100,000 ARL. The unstabilized subgrades exhibited strain softening at an ARL of 20,000 owing to the poor adhesion between the NGB and soil particles, leading to excessive strain deformation. The results revealed that the W-D resistance of the treated subgrade was up to 96% compared to the unstabilized subgrade, which lost over 30% of its particle mass after the 6-number cycle. This study indicates that the NGB-treated subgrade possesses the potential to sustain medium-to-high ARL loads owing to improved stiffness through polymerization reactions.