Investigation on alkali-activated insulation mortar containing high-volume recycled concrete powder for energy-efficient buildings

Abstract

The influence of recycled concrete powder (RCP) on the thermal insulation of alkali-activated materials remains unclear. Hence, this study develops an innovative alkali-activated insulation mortar, serving RCP and blast furnace slag as the precursor and expanded polystyrene (EPS) beads as fine aggregate, together with air entrainer. Experimental results show that the mortar had satisfactory workability owing to the RCP substitution, supported by appearance and infrared thermal imaging tests. As the ratio increased, the density, compressive strength, and thermal conductivity of the mortar decreased, due to the increasing volume of porous paste and internal air voids. Subsequently, the material design of the mortar was optimized through the adjusted Box-Behnken design. The obtained mortar achieved a high-volume use (61.7 wt%) of RCP, and exhibited an extremely low conductivity (∼0.030 W/(m∙K)) among novel lightweight building materials. Energy simulation further indicates that the optimized mortar can surpass traditional insulation materials, including EPS, polyurethane, and rock wool panels, in reducing air conditioning energy consumption across all seasons and climate zones. This was particularly evident in colder cities such as Harbin and Lhasa. Given that increasing the thermal resistance of the envelope can effectively reduce building energy consumption, the development of such sustainable alkali-activated insulation mortar would undoubtedly contribute to the implementation of energy-efficient buildings.