Influence of recycled concrete powder and CO2 curing on the properties of thermal insulation mortars

Recycled concrete powder (RCP) is a promising supplementary cementitious material, its application in thermal insulation materials is however very limited. In this study, the influence of RCP substitution on the properties of insulation mortars was investigated. The results showed that as the RCP content increased, the compressive strength and thermal conductivity of insulation mortars decreased by 39.8% and 16.8%, owing to the increasing volumes of porous paste and internal air voids. Note that the mortar containing a high content (50 wt%) of RCP struggled to meet the strength requirements of the specification. Therefore, CO2 curing was further employed here to alleviate the strength loss and successfully increased the compressive strength by 11%similar to 38%. It was found that since the CaCO3 particles formed and densified the microstructure (confirmed by the porosity test), the strength reduction derived from the RCP substitution was compensated for. Consequently, insulation mortars incorporating 50% RCP after CO2 curing for 7 days exhibited satisfactory compressive strength (similar to 0.22 MPa) and relatively low thermal conductivity (similar to 0.048 W/(m center dot K)). The mortars showed improved aesthetic appearance and excellent thermal insulation capacity in both hot and cold environments. This study proposed a successful approach to combining reutilization of RCP and CO2 curing in insulation mortar generation, which effectively improved the sustainability of materials.