Effects of Recycled Brick Powder on Thermal, Mechanical Properties, and Pore Structure of Alkali-Activated Foam Concrete

To utilize waste clay bricks and reduce carbon emissions, recycled brick powder (RBP) was prepared from waste brick-concrete structures and used to produce alkali-activated slag-recycled brick powder foam concrete (ASRFC). This paper evaluated the impact of RBP replacement rates and water-binder ratio on the physical and mechanical properties of foam concrete, including its thermal conductivity, strength, and pore structure. The results demonstrated that the addition of 10% RBP resulted in decreases in the apparent density and thermal conductivity of ASRFC, while flexural strength and the flexural-compressive strength ratio exhibited significant increases. These phenomena can all be attributed to a reduction in the fractal dimension of the pores and a more uniform pore size distribution. However, when the RBP replacement rate exceeded 20%, the enhancement of pore structure was diminished, the strength of ASRFC was reduced, while the water absorption rate and thermal conductivity exhibited a significant increase. As the water-to-binder ratio (W/B) increases, the compressive strength of ASRFC displays a slight improvement, while the flexural strength and flexural-to-compressive strength ratio exhibit a significant decrease. The parameters of pore fractal dimension, pore size distribution, and thermal conductivity demonstrate a tendency to initially decrease and subsequently increase, with the optimal W/B determined to be 0.45. A significant correlation has been identified between the pore fractal dimension and thermal conductivity/strength of alkali-activated foam concrete.