Performance Assessment of Self-Induced and Externally Induced Pozzolanic Reactions in Lime-Treated Expansive Soil

The improvement of engineering properties of expansive soil by lime stabilization is primarily governed by pozzolanic reactions that take place after the initial adsorption of calcium on clay surfaces. The clay minerals present in the soil inherently facilitate pozzolanic reactions with lime, a process referred to as self-induced pozzolanic reaction treatment. Similarly, the addition of external pozzolans with lime can accelerate these reactions, leading to externally induced pozzolanic reaction treatment. Hence, the present study aims to investigate the efficiency of pozzolanic reactions of the above two methods by evaluating calcium and hydroxyl ions consumption, strength improvement, retention of strength under moisture attack, and resistance to desiccation. The formation of pozzolanic compounds was further confirmed using a Field emissions scanning electron microscope and was also examined by Fourier transform infrared spectroscopy analysis. Highly expansive soil was treated with 2%, 4%, and 6% lime by dry weight under self-induced pozzolanic reaction treatment (lime alone) and with lime supplemented by rice husk ash under externally induced pozzolanic reaction treatment. Calcium and hydroxyl ions consumption were measured using batch tests at curing time of 1 h and subsequently at 1, 3, and 7 days. The results show that externally induced pozzolanic reaction treatment exhibited rapid calcium consumption and a sharp pH drop, indicating a greater pozzolanic compound formation than self-induced pozzolanic reaction treatment. Residual calcium and pH decreased slowly in lime alone method but showed a rapid decline within 1–3 days in externally induced pozzolanic reaction treatment. While initial strength gain was notable in lime alone method, the externally induced pozzolanic reaction treatment method retained strength of 63, 86, and 86% for respective lime addition after moisture attack, confirming more effective pozzolanic activity. Desiccation cracks appeared in all self-induced pozzolanic reaction treatment specimens, whereas externally induced pozzolanic reaction treated specimens remained largely crack-free except at 2% lime content, indicating improved desiccation resistance due to enhanced pozzolanic bonding. Field emissions scanning electron microscope and Fourier transform infrared spectroscopy analyses validated the higher formation of pozzolanic compounds in externally induced pozzolanic reaction treatment. Overall, this study underscores externally induced pozzolanic reaction treatment as a more effective and durable approach to lime stabilization of expansive soils.