Thermal conductivity of cementitious composites containing microencapsulated phase change materials

This paper investigates the effects of adding microencapsulated phase change materials (PCM) on the thermal conductivity of cement paste and cement mortar composites. Embedding cementitious composites with microencapsulated PCM has been considered a promising method for increasing the thermal mass of buildings to achieve greater energy efficiency and for reducing the risks of thermal cracking in pavements. Cement paste and cement mortar samples were synthesized with a constant water to cement ratio of 0.45. Both contained microencapsulated PCM with diameter ranging from 17-20 μm, volume fraction up to 30%, and a melting temperature around 24 °C. The cement mortar also contained quartz grains 150-600 μm in diameter such that the sum of the volume fractions of quartz and microencapsulated PCM was fixed at 55%. All samples were aged for more than 28 days. Their effective density and free moisture content were systematically measured. A guarded hot plate apparatus was designed, assembled, and validated according to the ASTM C177-13 to measure the effective thermal conductivity of the aged specimens of cement paste and cement mortar without and with microencapsulated PCM. Measurements were performed between 10 and 40 °C, encompassing the entire PCM phase change temperature window. The effective thermal conductivity of both the cement paste and the cement mortar composites was found to be nearly independent of temperature in the range considered. It also decreased as the volume fraction of microencapsulated PCM increased. Finally, excellent agreement was obtained between experimental data and the effective medium approximation derived by Felske (2004) for core-shell-matrix composites. These results can be used to design cementitious composite materials containing microencapsulated PCMs for energy efficient buildings and crack-resistant pavements.