Influence of dry-wet cycles on compressive strength of silty soil stabilized with calcium carbide slag - plant ash and micro-mechanism

Disposal of silty soil near rivers and lakes can lead to environmental pollution and occupation of land resources. However, stabilized silty soil can be utilized as a subgrade filler. To promote waste recycling and mitigate pollution, calcium carbide slag (CCR) and plant ash (PA) were used as composite stabilizers to solidify silty soil for subgrade applications. However, subgrade structures are susceptible to dry-wet cycles due to rainfall and fluctuations in water levels, leading to a deterioration in mechanical performance. To investigate the resulting strength and microstructural changes, CCR-PA stabilized silty clay samples (cured for 7, 14, and 28 days) were subjected to 0-6 dry-wet cycles. Subsequently, unconfined compressive strength (UCS), pH, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) analyses were conducted. Results indicate that as the CCR: PA ratio increases, the UCS initially increases and then decreases. When the curing age is 28 days and the CCR: PA ratio is 4:6, the UCS reaches the maximum of 529.89 kPa. Although dry-wet cycles degrade the overall strength, the CCR-PA composite significantly mitigates this effect. The stabilized soil maintained a UCS 1.57 to 1.63 times higher than that of soil stabilized with CCR alone. Microscopic analyses (XRD, NMR, and SEM) reveal that repeated dry-wet cycles physically damage the internal structure by expanding pores and developing micro-cracks, which reduces macroscopic strength. However, this physical deterioration is effectively counteracted by chemical stabilization mechanisms. Specifically, pH, XRD, and SEM results confirm that CCR creates an alkaline environment that promotes secondary hydration with the active SiO₂ in PA. This reaction generates abundant gel-like substances that fill pores and bind soil particles. Ultimately, this study elucidates how the synergy between physical structure refinement and chemical gelation enhances the durability of stabilized soil against dry-wet cycles. These findings present a resilient, cost-effective, and environmentally sustainable engineering strategy for utilizing industrial and agricultural by-products in soft soil subgrades across moisture-fluctuating regions.