Effect of Microstructure Differences on the Thermal and Mechanical Behaviors of Porous Cementitious Composites Using Phase Change Materials

This study focuses on the effect of different microstructures on the thermal and mechanical behaviors of porous concrete impregnated with phase change materials (PCMs), referred to as PoroPCM. This study involved the preparation of a PCM embedded cement paste, which included a 20% volume replacement of paraffin-based melamine-formaldehyde-coated microencapsulated PCM. The prepared PCM embedded cement paste was mixed with approximately 20%, 40%, and 60% volume substitutions of the aerated foam to prepare the PoroPCM specimens. Two series of specimens were prepared by using two distinct mixing methods. One involved gentle mixing at a low energy, whereas the other used a high-speed mixer. X-ray computed tomography (CT) was used to visualize the three-dimensional (3D) microstructures of the PoroPCM specimens. The datasets extracted from the X-ray CT scans were reconstructed to quantify the spatial distribution of the pore network and analyze their effects on the thermal and mechanical behaviors, which were used to understand the governing parameters with different pore networks. The thermal behavior was measured in a temperature-controlled environmental chamber by placing a thermocouple at the center of the 100 mm cube specimens. The results indicated a significant enhancement in the thermal performance (delay in temperature increase) of the PoroPCM specimens owing to the phase transition and heat storage capacity of the PCM particles. In addition, the thermal behavior appeared to be influenced by the porosity, size distribution of the air voids, and internal moisture content, which were due to changes in the microstructure of the PoroPCM. Compressive strength tests revealed that the failure behavior of PoroPCM under a compressive load was ductile with a large deformation, and the failure was propagated by the disaggregation of a local collapse of the pore walls. Compressive strength is influenced by porosity, however, the influence of pore size is limited.