Experimental investigation on the freeze-thaw durability of a phase change concrete in cold regions

In cold regions, freeze-thaw induced damage to concrete is among the most severe issues that affect structures, leading to shortened lifespans of concrete-related structures and causing substantial economic losses. Therefore, it is crucial to enhance the freeze-thaw durability in cold regions. To achieve this aim, we combined n-tetra-decane (C14) and expanded perlite (EP) to produce a composite phase change material (EPC14) with cement encapsulation. The essential material performances of the EPC14 were characterized through a series of physical and chemical tests. The measurement results show that the EPC14 possesses an appropriate phase change tem-perature, chemical stability, and mechanical reliability. Hence, it is an excellent candidate material for producing phase change concrete. In this study, we selected five volumetric replacement ratios of the EPC14 to fine ag-gregates (0%, 10%, 20%, 30%, and 40%) to prepare the phase change concretes (PCC-EPC14s). After these PCC-EPC14s samples were properly cured and then underwent 0, 50, 100, and 200 freeze-thaw cycles (FTCs), their physical and mechanical properties were systematically measured through nuclear magnetic resonance (NMR), resonance frequency tests, and uniaxial compression tests. The comprehensive measurement results demonstrate that at 0 FTCs, a higher content of the EPC14 results in larger porosity in the PCC-EPC14s, leading to lower compressive strength and relative dynamic modulus of elasticity. However, after 200 FTCs, the PCC-EPC14 (20%) exhibits the highest compressive strength and relative dynamic modulus of elasticity, whereas the PCC-EPC14 (0%) exhibits the lowest values for both of these properties. Furthermore, fractal theory was employed to analyze the mechanical properties of the PCC-EPC14s from a microscopic perspective. The results indicate that the PCC-EPC14 (20%) exhibits the largest NMR fractal dimension after 200 FTCs, signifying the least complexity and integration in its pore structure. In comparison to the PCC-EPC14s (0%, 10%, 30%, 40%), it is less prone to developing damage cracks under compression. In conclusion, we advise using the PCC-EPC14 (20%) in practical construction projects. The PCC-EPC14s prepared in this paper offer valuable insights for enhancing the freeze-thaw durability of concrete in cold regions.