Incorporation of phase change materials in an expanded clay containing mortar for indoor thermal regulation of buildings

Abstract

Improving traditional constructive solutions and finding new materials for more efficient building envelopes leads to significant opportunities to decrease the energy demand for heating and cooling, as well as to reduce global energy consumption and greenhouse gas emissions at the buildings’ level.The present work consists of the development and characterization of a new composite material incorporating microencapsulated phase change material (PCM) into a mortar composition, formulated with cement and lightweight expanded clay granules (LecaⓇ), for indoor thermal regulation of buildings. Despite the well-known problems in the traditional mortars with the incorporation of PCMs, such as workability and handling, two novel mortars were developed, using expanded clay granules of distinct sizes with and without PCM incorporation. The new mortars were tested to characterize the physical properties, shrinkage and capillarity, the mechanical behavior, compressive and flexural strength, and modulus of elasticity, as well as thermal properties, namely thermal conductivity, diffusivity, specific heat and thermal inertia. An additional analysis was carried out, comparing thermal properties of the mortar (with PCM), to quantify the influence of the mixing procedure on the PCM performance. Lastly, this new material was compared to a traditional mortar with PCM, produced and tested by another author ('L' formulation).The results show an increase of about 85% in shrinkage and 49% in capillarity in the formulations containing 25% of PCM. The compressive and flexural strength was reduced by 20%, and the modulus of elasticity was reduced by 52%. However, the thermal performance of the specimens has improved substantially. A reduction of 24% was attained, for the thermal conductivity, and the specific heat capacity was increased 17% with the PCM incorporation. The thermal diffusivity was reduced up to 82% and, finally, thermal inertia had a slight increase of 3%. 'L' formulation shows a similar behavior in terms of mechanical strength, when compared with mortars with PCM, but an increase of shrinkage and capillarity were observed (71 and 60%, respectively). Regarding thermal properties, this formulation proved to be the most conductive, with a 71% increase in the thermal conductivity value, and also the one with the highest specific heat, that increased 60%.The expanded clay mortar containing finer LecaⓇ particles was the formulation globally presenting the best results. As a conclusion, it was found that the mixing procedure of the mortars incorporating PCM into the aggregates could damage the PCM microcapsules, conditioning the mortar thermal performance.