Influence of an Alkaline Activator and Mineral Admixture on the Properties of Alkali-Activated Recycled Concrete Powder-Foamed Concrete

Alkali-activated recycled concrete powder-foamed concrete (ARCP-FC) is a new type of insulation architectural material, which is prepared using recycled concrete powders (RCPs), slag powders, fly ash, and sodium silicate. In this study, the influence of the water-to-cement (W/C) ratio, the Na₂O content, and the mineral admixture content on the mechanical strength, physical properties, and thermal conductivity of ARCP-FC were investigated. The results showed that the compressive strength and dry apparent density of ARCP-FC decreased with the increase in the W/C ratio. In contrast, the water absorption rate increased as the W/C ratio increased. Fewer capillaries were formed due to the rapid setting property, and the optimal W/C ratio was 0.45. The compressive strength and dry apparent density first decreased and then increased with the increase in Na₂O content. Too high Na₂O addition was not conducive to the thermal insulation of ARCP-FC, and the optimal Na₂O content was 6%. The compressive strength and dry shrinkage gradually decreased, while the water absorption gradually increased as the fly ash content increased. Fly ash improved deformation, and the pore was closed to the sphere, reducing the shrinkage and thermal conductivity. The optimal mixture of ARCP-FC consisted of 60% recycled concrete powders, 20% slag, and 20% fly ash. The density, porosity, compressive strength, and thermal conductivity of ARCP-FC were 800 kg/m³, 59.1%, 4.1 MPa, and 0.1036 W/(m·K), respectively. ARCP-FC solved the contradiction between compressive strength and dry apparent density, making it a promising building material for external insulation boards and insulation layers.