Effects of Sequential Hydration on Restrained Shrinkage for Cement-Stabilized Unsaturated Soil Under Cycles of Wetting-Drying

Although cementitious stabilization offers advantages such as the beneficial use of in-situ marginal materials and industrial byproducts, it is often limited by shrinkage cracking, which hinders broader application. 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. Complementary analyses included optical microscopy with image processing and scanning electron microscopy (SEM) to assess microstructure. The results were compared with direct shear parameters and free drying shrinkage. Stabilized mixtures compacted at an optimum initial 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. Microstructural analysis revealed that shrinkage cracking is controlled by total porosity rather than porosity intensity. These results suggest that SH can significantly enhance performance in cement-stabilized slopes and other applications. Further research should optimize parameters and standardize SH implementation for broader adoption.