Thermal responses of concrete slabs containing microencapsulated low-transition temperature phase change materials exposed to realistic climate conditions

This study examines the effect of microencapsulated low-transition temperature phase change material (PCM) additions on the thermal response of concrete slabs subjected to long-term realistic environmental exposure. To prevent direct contact of PCM with cement hydration products and possible leakage upon liquefaction, an inert PCM was encapsulated with a melamine-formaldehyde resin via an emulsification process before being added in concrete mixtures. Temperature monitoring was performed on three 500 x 500 x 150 mm large-scale concrete slabs with and without PCM for about 14 months encompassing two cold winter seasons. Results indicated that the addition of microencapsulated PCM effectively reduced excessive temperature drop and the number of freeze-thaw cycles concrete slabs experience during winter seasons, which may lead to service life extension by up to 5.2%-35.9% based on a freeze-thaw deterioration model. In particular, the effectiveness of PCM was found to be pronounced when the ambient temperature varied around the transition temperature (mild-cold seasons) while it became insignificant under prolonged exposure to extreme climate conditions such as cold winter and summer. The result of a visual condition survey was consistent with that of the model predictions, which verified the potential benefits of low-transition temperature PCM technology in concrete applications. This study also investigated the influence of microencapsulated PCM pellet embedment on the compressive and flexural strength characteristics.