Effects of sequential hydration on restrained shrinkage for cement-stabilized unsaturated soil under cycles of wetting–drying

Although cementitious stabilization allows for beneficial use of in-situ marginal materials and industrial byproducts, its broader application is often limited by shrinkage cracking. Instead of one-time hydration (OH), this study proposes an innovative sequential hydration (SH) approach to mitigate shrinkage cracking in stabilized mixtures while sustaining high strength. Restrained drying shrinkage tests were conducted on three treatments—OH-100, SH-80, and SH-60—of a cement-stabilized soil. The samples underwent three cycles of drying and wetting. The investigation combined optical microscopy with image processing and scanning electron microscopy (SEM) to link microstructural evolution with macro-scale performance, which was also measured through direct shear tests and free drying shrinkage. Stabilized mixtures compacted at an optimum initial compaction moisture content (CMC) followed by SH exhibited lower shrinkage cracking potential and improved shear strength parameters compared to traditional OH mixes. After three cycles, OH-100 increased in drying shrinkage by ~ 200%, while SH-80 decreased by 72%. This difference is attributed to the progressive formation of hydrated products under SH versus the single-stage formation under OH. Restrained shrinkage tests revealed that tensile stress development and its spatial progression governed crack initiation and propagation. Locations of highest porosity and largest pore diameter shifted with cycles due to hydration kinetics and moisture redistribution. Ultimately, microstructural analysis identified total porosity, not porosity intensity, as the dominant factor controlling shrinkage cracking. These results position SH as a promising technique for enhancing performance in cement-stabilized slopes and other applications. To advance this technique, future work must focus on optimization and developing standard protocols for field implementation.