Impact of the phase change material (PCM) integration on the mortar’s thermal inertia: The role of the aggregates and PCM types

Integrating phase change materials (PCMs) into building materials has gained attention for enhancing thermal performance and energy efficiency. However, the impact of different PCM types on cementitious materials' thermal and mechanical properties requires further study. This work addresses this gap by incorporating two bio-based esters and a paraffin-based PCM into natural aggregate mortar (NAM), recycled concrete aggregate mortar (RCAM), and lightweight aggregate mortar (LWAM). Thermal and mechanical properties were evaluated using the transient plane source method, heating and cooling cyclic tests, and standard mechanical tests. PCM impregnation was influenced by both PCM viscosity and mortar porosity. High-viscosity PCMs (paraffin) achieved greater absorption in more porous mortars like LWAM, while the incorporation of low-viscosity PCMs (esters) was higher in less porous matrices. LWAM absorbed the highest PCM mass (12.55 g), while NAM and RCAM had higher percentages of filled pores (up to 23.85 % and 28.92 %, respectively). PCM incorporation improved thermal inertia across all mortars, but there was a tradeoff between the rise in conductivity and thermal inertia. LWAM demonstrated the best overall performance, with the lowest thermal conductivity (1.04–1.15 W/m·K) and highest specific heat (921.92–1243.10 J/kg·K). PCM addition also increased the compressive and flexural strength of LWAM by up to 15 %, with less significant improvements observed in NAM and RCAM. This study's novelty is its fundamental understanding of the combined effects of PCM viscosity, mortar porosity, and PCM type on thermal and mechanical properties, contributing to the deployment of energy-efficient construction materials. • PCM viscosity and mortar porosity condition PCM incorporation in different mortars. • PCM incorporation is maximized for high-viscosity PCM and high-porosity mortars. • LWAM with paraffin minimizes the conductivity-effusivity increase tradeoff. • Novel analysis of thermal response and hysteresis in PCM-enhanced mortars. • PCM significantly enhanced compressive strength in LWAM by up to 15 %.