Utilizing Lime Sludge as a Co-Additive to Cement Stabilized Expansive Soils under Cyclic Environmental Stressors

Transportation infrastructure is susceptible to moisture intrusion and temperature fluctuations, which negatively impact subgrade soil stability. Calcium-based stabilizers like cement and lime are commonly used to enhance soil properties. However, to reduce material consumption and promote long-term efficiency, researchers and engineers are exploring alternative materials or co-additives that offer sustainable and cost-effective stabilization solutions. In this study, lime sludge, a waste material from water treatment plants, was utilized as a co-additive to ordinary Portland cement for stabilizing high-plasticity clay. Laboratory experiments including unconfined compressive strength (UCS), mass loss, volumetric change, plasticity index, linear shrinkage, and free swell strain were conducted on untreated specimens and on those treated with cement alone or cement-lime sludge combinations to evaluate their performance before and after exposure to environmental stressors such as freeze-thaw-wet-dry (FTWD) and wet-dry-freeze-thaw (WDFT). The results showed that treated specimens had significantly enhanced engineering strength and reduced swell-shrink potential compared to untreated specimens. The inclusion of lime sludge further increased the strength of cement-treated specimens. In addition, specimens subjected to FTWD cycles demonstrated slightly better performance than those under WDFT cycles. Among the treatments, a combination of 8% cement and 4% lime sludge was able to withstand environmental stressors, with a residual strength of about 1,200 kPa (180 psi) after the eighth cycle. These findings provide preliminary evidence that lime sludge can be used as a sustainable co-additive to cement for stabilizing expansive soils, while also aiding in more efficient lime sludge waste management.