Investigation on the pattern and effects of phase-change material loss under seepage pressure in PCM-clay core wall

Incorporating a paraffin-based phase-change material (PPCM) into core-wall clay (PCM-clay) enables the mixture to regulate the temperature during winter construction through latent-heat storage and release, offering a promising approach for mitigating freeze–thaw damage and extending the construction period of earth-rock dam core walls in cold regions. However, in practical applications, the potential loss of liquid PPCM under seepage pressure raises concerns regarding the impermeability and long-term integrity of the core walls. To address this critical issue, two seepage-loss test devices were developed in this study and systematic experiments were conducted to examine the characteristics, governing factors, and threshold of PPCM loss in clay. The results indicate that significant PPCM loss occurs only when the PPCM content exceeds the critical loss threshold. Following seepage, the remaining PPCM persists in two stable forms, adsorption/wrapping on soil particles and retention in pores via capillary forces, both of which resist further leakage. A higher PPCM content and greater clay density lead to a larger residual PPCM ratio, thereby helping to maintain the high impermeability of PPCM-mixed clay (PCM-clay). Specifically, approximately 5% and 6% PPCM remained after seepage at a gradient of 25 for soil with initial contents of 6% and 8%, respectively. These findings clarify the mechanism and critical control factors of PPCM seepage loss, providing essential guidance for the core-wall material application of PPCM-mixed clay in cold regions and ensuring the operational safety of the novel core-wall earth-rock dams. • Two customized test devices are developed to quantify PPCM seepage loss under hydraulic pressure. • A critical PPCM loss threshold is identified, above which liquid PPCM begins to leak. • Higher PPCM content and clay density increase the residual PPCM ratio, helping maintain high impermeability of PCM–clay