Valorization of industrial wastes for stabilizing highly expansive clays: Mechanical, microstructural and durability improvements

The utilization of wastes as amendments for stabilizing problematic clayey soils in pavement subgrades has garnered substantial interest due to their economic efficiency and contribution to the recycling process. In this study, two industrial waste materials, namely Carbide Lime (CL) and Water Treatment Sludge (WTS), are utilized for the treatment of highly expansive clay as the subgrade of pavement structures. By performing a comprehensive set of Ultrasonic Pulse Velocity (UPV), Unconfined Compressive Strength (UCS), pH assessment, and Electrical Conductivity (EC) tests, it is observed that incorporating 25 % CL into the highly expansive clay, followed by the 10 % WTS replacement for CL, yields the highest enhancement in the soil’s mechanical characteristics. The combined addition of 25 % CL and 10 % WTS significantly enhances soil densification, achieving a UCS of 7700 kPa and a UPV of 2200 m/s, surpassing the performance of samples without WTS. Furthermore, the swelling potential (S_P) is completely eliminated at 10 % CL, even within 7 days of curing. The stabilized samples also demonstrate excellent durability, retaining their strength and swelling control under consecutive Freeze-Thaw Cycles (FTCs). From a micromechanical perspective, the pozzolanic reactions induced by the addition of CL and WTS are shown to produce Calcium-Silicate-Hydrate (C-S-H) and Calcium-Aluminate-Silicate-Hydrate (C-A-S-H) binding gels, which fill soil pores and mitigate microcracks caused by freezing and thawing, ensuring long-term structural integrity of the highly expansive clayey subgrades. These findings demonstrate that the combination of CL and WTS not only improves initial mechanical and swelling properties but also ensures durability and stability under harsh climatic conditions, making it a robust solution for expansive soil stabilization.