Experimental study on engineering and microstructural behavior of lime sludge stabilized expansive soils under cyclic environmental stressors

Moisture- and temperature-induced changes in microstructure and stabilization products remain a concern, requiring further study to clarify their effects on the engineering behavior of stabilized soils. Thus, this study aims to evaluate the engineering response of stabilized high-plasticity clay to moisture- and temperature-driven environmental conditioning, using hydrated lime (L) and lime sludge (S) under four sequences: freezing-thawing (FT), wetting-drying (WD), freezing-thawing-wetting-drying (FTWD), and wetting-drying-freezing-thawing (WDFT). Expansive soils were treated with a total dosage of 8% of L and S mixtures (4L4S and 6L2S) and evaluated through UCS and repeated load triaxial tests, further supported by microstructural and mineralogical analyses. Both 4L4S- and 6L2S-treated specimens exhibited improved engineering performance compared to the untreated soil due to short-term strength gains and long-term pozzolanic reactions. Importantly, the addition of lime sludge, a calcite-rich material, did not hinder the stabilization process, as 4L4S specimens achieved UCS values comparable to those of specimens treated with 5% hydrated lime. Both the treated specimens retained their integrity throughout the environmental conditioning phases, whereas the untreated specimens collapsed during the early stages. Among these durability studies, FT caused the most severe deterioration, due to substantial soil swelling during freezing. In contrast, coupled durability conditions caused relatively less damage, due to limited ice lens formation post drying phase, resulting in better engineering properties. Microstructural and mineralogical analyses were performed, which revealed the formation of cementitious gels, binding soil particles and enhancing the structural stability and durability of the treated specimens. Also, key variations in the mineral content, and related microstructure of the stabilized soils through thermogravimetric analysis were observed after different environmental conditionings. This explains the influence of the mineral contents and microstructure of stabilized soils on the long-term performance. • The effectiveness of lime sludge as partial replacement to hydrated lime for stabilizing expansive clays is established. • Different impacts of the coupled and uncoupled environmental durability cycles are investigated. • Microstructural and mineralogical investigations revealed the influence of environmental stressors on the long-term performance. • Need for the appropriate choice of durability protocols is recommended.