Evaluating long-term thermal and chemical stability and leaching potential of low-temperature phase change materials in concrete slabs exposed to outdoor environmental conditions

This study examined the potential of using phase change material (PCM)-integrated concrete slabs for long-term thermal-responsive applications in an outdoor environment condition. The objectives were to: (i) evaluate long-term thermal response, snow melting and freeze-thaw reduction efficiency of PCM integrated concrete slabs, (ii) characterize the chemical stability of PCM in cement matrix, and (ii) assess the possibility of PCM leaching into the cement matrix and subgrade soil of the slabs. The experimental program included: (i) outdoor experimentation using large-scale field concrete slabs, (ii) guarded calorimetric (LGCC) tests of cut-bar concrete specimens, (iii) Fourier transform infrared (FTIR) spectroscopic characterization of PCM in mortar and subgrade soil specimens, and (iv) low-temperature differential scanning calorimetric (LT-DSC) tests to assess and quantify the amount of PCM contamination in subgrade soil. Results presented varying degrees of effectiveness after three years of environmental exposure: Micro-encapsulated PCM (MPCM) concrete exhibited considerable success (i.e., similar to 50%) in snow melting while PCM infused in lightweight aggregates (PCM-LWA) concrete failed to provide substantial snow-melting; moreover, both PCM-LWA and MPCM slabs showed diminished resistance to freeze-thaw (F-T) cycles compared to the first-year winter cycle data. Factors contributing to efficiency loss are found to be shell degradation of microcapsules, potential leaching of PCM into subgrade soil (i.e., between 0.2 to 0.3% wt. concentration), and effects of warm temperatures influencing the degree of evaporation, as evidenced with LGCC, FTIR and LT-DSC results. Strategies to enhance efficiency and stability include improved encapsulation techniques, and vascularization methods.