Freeze-thaw (F-T) cycles cause significant frost heaving and thaw weakening in roadway subgrade soils. Frost heaving and thaw weakening occur only when there is available water, frost susceptible soil and temperature fluctuations around the freezing temperature of water. The goal of this study is to use Phase Change Materials (PCMs) to lower freezing temperature of soils and minimize the temperature fluctuations during F-T cycles. PCMs absorb and/or release high latent heat when they undergo a phase change. PCMs with the appropriate phase change temperature have the potential to reduce temperature fluctuations around the freezing/thawing point of soil, thereby helping reduce the damage inflicted by freeze-thaw cycles. In this study, three different types of PCMs were mixed with Glacial Till (GT) and Sandy Soil (SS). The PCM types were inorganic PCM (PCM-A), organic PCM (PCM-B), and PCM-B in powder form (pPCM-B). The characterization of PCM and soil-PCM mixture was determined by Atterberg limits, Harvard miniature compaction test, differential scanning calorimetry (DSC), scanning electron microscope (SEM) imaging, freezing point depression and PCM evaporation tests. DSC tests confirmed that the selected PCMs have high latent heat. Freezing point depression tests showed that PCM-B and pPCM-B freeze above the freezing point of water in soil, suggesting they would delay the freezing of soil. SEM images showed no change on the surface of soil-PCM mixtures compared to the control specimens, indicating no chemical reaction between soil and PCMs occured. PCM-B did not evaporate from the surface of soils for a 2-hour period at various environmental conditions. Based on characterization tests, PCM-B was selected as the best-performing PCM, and it was tested for further performance tests such as resilient modulus (MR), frost heave-thaw settlement tests. PCM-B did not cause an adverse effect on the MR of GT at different number of freeze-thaw cycles. PCM-B showed a good thermoregulation effect and slowed down the water migration in the frozen region of soil by reducing the permeability of the soils. Furthermore, after 2 F-T cycles, all soils with PCM-B achieved significantly lower heave rate, maximum heave and moisture content than control specimens. The results suggest that PCMs can be highly effective at mitigating freeze-thaw damage in subgrade soil.
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