Properties and mechanisms of brick-concrete recycled aggregate strengthened by compound modification treatment

Abstract This study aims to enhance the physical and mechanical properties of brick-concrete recycled aggregate (BCRA) using pozzolan slurry combined with sodium silicate and silicon-based additives. To investigate the modification mechanism, the particle shape characteristics, pore structure, and microstructure of BCRA were studied before and after the compound modification treatment. The research results showed that the apparent density of BCRA after compound modification treatment can be increased by 2.6%, and the water absorption and crushing index can be reduced by 42.4% and 28.5%, respectively. Specifically, the modification treatment of pozzolan slurry combined with sodium silicate has advantages in improving the apparent density and mechanical strength of BCRA, while the modification treatment of pozzolan slurry combined with silicon-based additives is more effective in reducing the water absorption of BCRA. Macro, meso, and microstructure changes were observed in the treated BCRA, where surface homogeneity, low porosity, and increased compactability were observed. The dynamic water absorption characteristics were also tested to evaluate the hydrophilic and hydrophobic behaviors of the untreated and treated BCRAs. Finally, a compound modification mechanism model for the BCRA was established.