The influence of volcanic ash (VA) on the mechanical properties and freeze-thaw durability of lime kiln dust (LKD)-stabilized kaolin clayey soil

Improving soft clay soil’s mechanical properties and durability has been the subject of intense research. In this context, traditional stabilizers such as cement and lime have been introduced as the most widely used materials. However, these materials face many challenges due to recent global concerns for reducing greenhouse gas emissions. Therefore, international research is shifting toward using environmentally friendly soil-stabilizing waste materials. This study, for the first time, evaluates the stabilization of kaolin clay soil using lime kiln dust (LKD) as a high CaO content waste pozzolan and volcanic ash (VA) as a natural pozzolan with high SiO 2 and Al 2 O 3 content. In general, it aims to demonstrate the effective performance of these two inexpensive and environmentally friendly additives in improving the mechanical features and durability of kaolin clay soil, thereby providing the necessary groundwork for the practical application of this method in stabilizing soft clay soil. This study included preparing samples with LKD at 3%, 5%, 7%, and 10% of the dry weight of clay and replacing VA with LKD at 0%, 25%, 75%, and 100%. The specimens were cured for 3, 7, and 28 days. After this curing period, the optimal sample was subjected to various freeze-thaw (F-T) cycles at 0, 1, 3, 7, and 10. The samples were examined by conducting compaction, scanning electron microscopy (SEM), unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), and X-ray diffraction (XRD) at different stages of adding stabilizers, as well as before and after introduction of F-T cycles. Adding LKD and VA further increased the UCS by accelerating pozzolanic and hydration reactions. Also, the mixture of LKD and VA in kaolin soil enhanced F-T durability and indicated less strength deterioration even after 10 cycles compared to the control sample. The optimal mixture of 5% LKD and 25% VA replacement improved 11 times in UCS and showed a slight reduction of only 7% after 10 F-T cycles compared to untreated kaolin clay. Overall, the combination of LKD and VA enhanced the mechanical features of kaolin clay soil and F-T durability, making it a low-cost, sustainable, and eco-friendly option for soil improvement. • Lime Kiln Dust (LKD) and Volcanic Ash (VA) were used for stabilizing kaolin soil • VA enhances the freeze-thaw (F-T) durability of the LKD-stabilized kaolin soil • Enhanced stiffness and toughness observed in kaolin stabilized with LKD and VA • Increased pozzolanic reactions with VA lead to more cementitious products • LKD and VA provide a sustainable solution for kaolin soil stabilization