Impact of Curing Age and Capillary Action on Microstructural and Stress–Strain Response of a Geopolymer-Stabilized Sandy Soil

This study investigated the improvement in a type of sand using a geopolymer made of recycled glass powder (RGP) as the base material and sodium hydroxide (NaOH) as the alkaline activator. Using maximum uniaxial compressive strength (UCS), the impact of alkaline activator concentration and the RGP content were investigated to determine the optimum mix design. Groundwater level increments were simulated through a laboratory procedure to study the effect of curing age and capillary action on the behavior of stabilized soil. The UCS of samples at different ages (14, 28, 45, and 60 days) and different degrees of saturation (Sr=0%, 20%, 50%, 80%, and 100%) were determined and their stress–strain diagrams were drawn. Using the stress–strain relationships, UCS, modulus of elasticity (Es), shear modulus (G), and resilient modulus (Mr) of the stabilized soil were estimated. The results showed that fully saturated stabilized samples did not disintegrate and exhibited a considerable UCS of up to 1.88 MPa at the age of 60 days. The greatest observed reduction in the UCS through saturation was between Sr=0 to 20%. To further investigate and validate the mechanical results, chemical and microstructural studies including X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FTIR) were carried out. The results showed that during the curing period, the silicon/aluminum (Si/Al) ratio increased from 2.98 in untreated soil to 4 in stabilized samples, indicating active geopolymerization, which enhanced UCS and reduced the potential for disintegration. Additionally, the crystal size decreased from 53 to 24 nm for the 45-day stabilized samples when the degree of saturation changed from 0% to 100%. This finding suggests that if RGP-based geopolymer-stabilized soil contacts water after fully drying, geopolymerization reactions will resume that involve the dissolution of both crystalline and amorphous phases.