Air lime renders with microencapsulated phase change materials: Assessment of microstructural and thermal properties

Microencapsulated phase change materials (PCMs) have been successfully integrated into air lime-based rendering mortars to enhance thermal properties, aiming to boost the thermal efficiency of the buildings in which are applied. Two microencapsulated PCMs, with melting points at 18 degrees C and 24 degrees C, were seamlessly introduced into fresh rendering mortars in varying proportions (5%, 10%, and 20% by weight of lime), in formulations that include different chemical additives, such as a superplasticizer (polycarboxylate ether) and an adhesion enhancer (starch-based additive). In some mixes, metakaolin (MK) was also added as a mineral admixture. Starch addition was seen to promote the formation of aragonite and vaterite (calcium carbonate polymorphs), facilitating the smooth integration of microcapsules within the lime matrix. Hotbox simulations with tested materials containing as low as 0.01-0.04 g of PCM per gram of dry mortar, yielded outstanding energy efficiency values (822.4 and 732.8 kJ/m2, respectively, for PCMs with melting points at 18 degrees C and 24 degrees C). Temperature attenuations of up to 6.1 degrees C during the heating stage and up to 3.9 degrees C during the cooling stages were observed. This outcome not only emphasizes the potential for enhancing thermal efficiency through PCM incorporation into air lime renders but also hints at a remarkable future for energy-efficient construction materials.