Mix design for recycled aggregate thermal insulation concrete with mineral admixtures

Abstract

The objective of this study was to prepare a type of recycled aggregate thermal insulation concrete (RATIC), in which thermal insulation particles (TIPs) were used as solid sealed ‘holes' instead of air holes to allow the thermal conductivity coefficient of the concrete to be reduced. This paper presents the results of a laboratory study on the performance of natural and recycled aggregate concrete, which was prepared by the incorporation of TIPs and different mineral admixtures including ultrafine slag (UFS), nanosilica (NS) and nanocalcium carbonate (NCC). The compressive strength, thermal conductivity coefficient and dry density of the concrete mixtures were determined. The experimental results demonstrate that glazed hollow beads, at the optimal level of 130%, significantly reduced the thermal conductivity property of the recycled aggregate concrete. The properties of the concrete were improved by the addition of UFS and NS, while NCC produced a negative impact. As far as compressive strength was concerned, the replacement of cement by 10% UFS or 1% NS improved the mechanical performance, while the replacement of cement by 1·5% NCC and the addition of TIPs decreased the compressive strength of the recycled aggregate concretes. The effects of the UFS and NS mineral admixtures produced greater performance improvements in the concrete than the recycled coarse aggregate. Finally, the optimal mix proportion was determined. For this mix, the thermal conductivity coefficient and compressive strength of the concrete were 0·305 W/(m.K) and 46·7 MPa respectively.