Comparison of the thermal and mechanical properties of concrete incorporating microencapsulated and macro-encapsulated phase change materials

The incorporation of phase change material (PCM) into concrete represents a promising approach to regulating internal temperatures and delaying the freezing process in cold regions. Currently, there are two primary methodologies for incorporating PCM into concrete: macro-encapsulated phase change aggregates (MPCAs), which are fabricated by incorporating PCM into porous carriers via vacuum adsorption, and microencapsulated phase change materials (MPCMs), which utilize a physical or chemical shell to enclose the PCM core. However, comparative studies evaluating the comprehensive performance of phase change concrete (PCC) integrated via these two encapsulation routes remain scarce. This study employed two types of MPCAs and two types of MPCMs to prepare PCCs, and evaluated the encapsulation performance of the aggregates for PCM as well as their thermal energy storage properties. Furthermore, the thermal regulation capacity and mechanical performance of the resulting PCCs were tested, alongside a systematic assessment of their transient thermal responses during cooling-heating cycles. Experimental results demonstrate that all prepared PCCs significantly delay temperature fluctuations, with a maximum delay freezing time of 3.41 h in pore water and a temperature reduction of 3.57 °C compared to ordinary concrete, effectively buffering severe internal temperature drops. Regarding the comparison of the two methodologies, although MPCMs exhibit superior encapsulation efficiency and thermal properties, their inherent mechanical fragility limits the 28d compressive strength of PCCs to only 12.3 and 8.8 MPa, failing to meet the requirements for load-bearing structures in cold regions. In contrast, MPCA-based PCCs achieve a balance between thermal regulation and structural performance, maintaining robust 28d compressive strengths of 31.3 and 28.5 MPa. This ensures the basic functional integrity of the PCC while demonstrating promising thermal regulation potential.