The Swell-Shrink Behavior of Nanomaterial-Treated Expansive Soils

The swell-shrink behavior of expansive soil strongly affects the long-term stability of subgrades and other geotechnical infrastructures. This study investigated the effects of three nanomaterial additives, namely nano-lime, nano-calcined clay, and hydrophobic nano-silica, on expansive soil. A series of laboratory tests was performed to evaluate the swell-shrink behavior of nanomaterial-treated soils under varying initial water contents and curing durations. Additionally, microstructural analyses were conducted to reveal the underlying stabilization mechanisms. The results showed that all three nanomaterials reduced the swell-shrink potential of the expansive soil, but their improvement effects were strongly dependent on the initial water content. Nano-lime exhibited the strongest overall stabilization effect, especially under relatively high initial water contents, and its performance became more pronounced with curing. Nano-calcined clay provided a moderate but relatively stable improvement. In contrast, hydrophobic nano-silica performed better under relatively low initial water contents, indicating a distinct moisture-dependent behavior. Nano-lime and nano-calcined clay were more effective in refining the pore structure and promoting a denser soil fabric, whereas nano-silica mainly modified particle surface conditions and showed limited pore-refinement capacity under wet conditions. These findings highlight the novelty of the present study in terms of the moisture-dependent stabilization performance and comparative mechanisms of three representative nanomaterials under a unified low dosage, and they provide useful guidance for the improvement of expansive soil subgrades in engineering practice.