Effect of recycled concrete aggregate (RCA) on mortar's thermal conductivity susceptibility to variations of moisture content and ambient temperature

Abstract

Temperature and moisture are two factors that affect the thermal conductivity of building materials. Furthermore, the use of recycled concrete aggregate (RCA) in cementitious composites reduces their thermal conductivity due to increased porosity. However, this increase in porosity may affect the material's thermal conductivity susceptibility to changes in environmental conditions. No studies were found on the effect of RCA on thermal conductivity's susceptibility to moisture content and ambient temperature variations in cement mortars . To study these effects, a total of 135 thermal conductivity tests were performed on mortars with three levels replacement of natural aggregate by RCA, at different saturation degrees and temperatures within the range of expected service-life values. Compressive and flexural strength, permeable porosity, and bulk density were also evaluated. Remarkably, the use of RCA reduces the thermal conductivity's susceptibility to changes in ambient temperature. Besides, RCA increases the porosity, magnifying the susceptibility of thermal conductivity to moisture variations. These variations should be considered when thermal insulation is used as a factor for the environmental impact assessment of cement mortars. Finally, a combination of response surface method models was used to formulate a prediction equation that accurately estimates (error <5%) the thermal conductivity of cement mortars as a function of accessible porosity , saturation degree, and ambient temperature. This research contributes to a deeper understanding and more accurate prediction of RCA's effects on thermal conductivity of cementitious composites as a function of the environmental conditions, which is key to assessing RCA mortars' environmental impact during service life as part of a building component. • RCA reduced the thermal conductivity's susceptibility to ambient temperature changes. • Thermal conductivity's susceptibility to moisture content increases with RCA. • The increase on this susceptibility is related to the increase of porosity. • Thermal conductivity depends on porosity, moisture content and ambient temperature. • An equation that accurately estimates thermal conductivity of mortars is proposed.