Thermal and mechanical variations of cementitious composites with phase change materials using a contactless ultrasonic method

Abstract

Recently, research on reducing building energy by applying phase change materials (PCMs), such as n-octadecane, to cementitious materials, is being actively conducted. PCMs were modified as a type of lightweight aggregate (LWA) to prevent leakage in concrete. In this study, a fully contactless ultrasonic system was applied to monitor thermal and mechanical variations of concrete plates including PCM-LWAs subjected to temperatures up to 48 °C. Because surface preparation and direct coupling processes were not required, this method collected reliable information without thermal interference. The measurements were conducted during the melting and free cooling process of PCM-LWAs, where the methods monitored the variation of leaky Rayleigh waves for dynamic modulus changes of the solid material. The experimental results illustrated that the contactless ultrasonic system enabled a 5.5 % reduction in dynamic modulus for a concrete plate mixed with 160 kg/m3 PCM-LWAs, and showed the time lag effect of heat transfer and surface temperature reduction through heat storage performance. Further comparison studies of the dynamic modulus variation among different mix proportions of PCM-LWA concrete plates were conducted using temperature cycles. Based on the experimental study, the unique thermal and mechanical behaviors of PCM-LWA mixed concrete plates were discussed.