The performance study of lithium slag in improving silty clay and its engineering application as subgrade soil

Silty clay is highly susceptible to structural damage, limiting its application in high-grade highway construction. Lithium slag, a byproduct of the rapidly expanding new energy industry, exhibits notable pozzolanic activity and offers potential for soil improvement. This study investigates the effectiveness of lithium slag in enhancing the compaction, mechanical properties, water stability, and durability of silty clay, while supporting environmentally friendly road construction. A series of tests were conducted to evaluate the environmental safety, physical–mechanical behavior, and field performance of lithium-slag-modified silty clay. The results indicate that a 40% lithium slag content yields the most significant improvement, markedly increasing strength and water stability. XRD analysis shows that, in an alkaline environment, SiO₂ and Al₂O₃ in lithium slag dissolve and react with Ca²⁺ and OH⁻ generated during hydration to form C–S–H and small amounts of C–A–S–H gels. These hydration products fill soil pores and enhance structural compactness and durability. Field application further confirms the feasibility of the proposed filling scheme and construction process for a lithium-slag subgrade. This study provides a promising approach for the resource utilization of waste lithium slag in road engineering.