Development of Self-Heating Concrete Using Low-Temperature Phase Change Materials: Multiscale and In Situ Real-Time Evaluation of Snow-Melting and Freeze–Thaw Performance.

This work examined the performance of self-heating concrete under laboratory thermal conditions and outdoor real-time conditions during the fall and winter seasons. Snow-melting and freeze–thaw performance of low-temperature phase change materials (PCM) incorporated self-heating concrete slabs in various scales were evaluated. PCM exhibited high enthalpy of fusion (ΔHf≈170–180 J/g), long-term thermal stability, and desirable supercooling. The experimental program included (1) optimization of concrete mix designs for maximum PCM incorporation, (2) characterization of thermal properties of PCM-mortar specimens using longitudinal guarded comparative calorimetry (LGCC), and (3) large-scale PCM concrete slabs in outdoor conditions to evaluate the real-time thermal performance against freeze–thaw events and snow-melting efficiency. Two different approaches were used to incorporate PCM in concrete: (1) submersion of liquid PCM in porous lightweight aggregates (PCM-LWA); and (2) microencapsulated PCM (MPCM). Both PCM-LWA and MPCM concrete not only exhibited promising snow-melting capabilities but also lowered the number of freeze–thaw cycles during cold seasons. PCM-LWA concrete performed better in decreasing the number of freeze–thaw (F-T) cycles due to the undercooling phenomenon created by the LWA pore network confinement pressure, allowing gradual latent heat release; the undercooling phenomenon in PCM-LWA results in phase transformation in a wider low-temperature range (i.e., 3.94°C to −13.04°C). Therefore, the PCM-LWA concrete was effective in melting snow within a wider range of low temperatures. MPCM concrete was found to provide a rapid melting capability during a snowfall event due to its "one-shot" heat release phenomenon. Both LWA-PCM and MPCM concrete slabs demonstrated promising heat response and snow-melting capability. Snowfall and freeze–thaw cycles occur frequently during winter seasons in North American regions with cold climate, resulting in snow accumulation on concrete roads and flatworks as well as concrete freeze–thaw damage. In this paper, a "self-heating" concrete was developed via incorporation of low-temperature phase change material (PCM), and its promising snow removal and freeze–thaw improvements were validated. The self-heating concrete can be used to construct pavements, driveways, bridge decks, and any other types of flatworks. When the ambient temperature falls to ∼0°C , PCM will release desirable amounts of heat energy (ΔHf=170–180 J per g of PCM added) by changing its phase from liquid to solid. As a result, the accumulated snow and ice melts at a gradual pace. In addition, heat release from the incorporated PCM lowers the number of freeze–thaw cycles, improving freeze–thaw performance of concrete made elements in cold regions, which in turn improves concrete durability and service life by minimizing the susceptibility to freeze–thaw scaling and spalling. [ABSTRACT FROM AUTHOR]