Mechanism of MgCl2-Regulated Hydration, Pore-Structure Evolution, and Strength Development in Cement-Stabilized Loess

To investigate the engineering performance and microstructural evolution of magnesium chloride–cement composite-stabilized loess, laboratory tests were conducted on loess treated with different cement contents and MgCl2 dosages. Compaction tests, unconfined compressive strength (UCS) tests after 7 and 28 days of curing, X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) analyses were performed to establish the relationship among hydration products, pore evolution, and strength development. The results showed that MgCl2 increased the maximum dry density and reduced the optimum moisture content, thereby improving the compactability of cement-stabilized loess. The UCS exhibited a non-monotonic response to increasing MgCl2 dosage, with an initial decrease followed by an increase and a subsequent decline. The optimal MgCl2 content was 1.7% for 8% cement and 1.8% for both 10% and 12% cement. Integrated XRD, SEM, and NMR analyses revealed that an appropriate MgCl2 dosage regulates the hydration and microstructural evolution of cement-stabilized loess through the formation of Mg-bearing reaction products, enhanced interparticle bonding, and refinement of the pore structure. The resulting reductions in total porosity and the proportion of medium and large pores were closely associated with the observed strength enhancement, establishing a clear hydration–pore structure–strength relationship. Although the 12% cement–1.8% MgCl2 mixture achieved the highest strength, the 10% cement–1.8% MgCl2 mixture provided a more favorable balance between mechanical performance and cement consumption. These findings provide mechanistic insight into MgCl2-regulated hydration and pore-structure evolution and support the optimized use of MgCl2 as an auxiliary modifier for cement-stabilized loess.