Molecular insights into enhancing bonding and erosion resistance in recycled aggregate concrete ITZ through carbonation

In engineering practice, using carbonation treatment technology can enhance the strength of recycled aggregate concrete (RAC). However, due to experimental constraints, the specific mechanism by which carbonation treatment improves the bonding and erosion resistance of RAC remains unclear. Therefore, this study employs molecular simulation methods to investigate in detail the mechanical behavior and microstructure of the interfacial transition zone (ITZ) in RAC before and after carbonation treatment, as well as the relationship between its microstructure and erosion resistance in corrosive environments. The results demonstrate that after carbonation treatment, the tensile strength of the ITZ at the nanoscale increases by more than 75 %, while the shear strength improves by over 298 %. Carbonation treatment significantly alters the bonding structure of the ITZ, increasing the number of ionic bonds and the coordination number at the interface by more than 870 % and 71 %, respectively, thereby markedly enhancing interfacial bonding performance. In erosive environments, the carbonated ITZ exhibits greater microstructural stability, with the erosion solution in nanopores unable to leach ions from the matrix (zero leaching), thus improving the erosion resistance of the ITZ. Additionally, these microstructural changes influence the distribution of ions in the nanopore solution, ensuring that the bonding performance of the ITZ remains unaffected by the erosive environment. This study elucidates the micro-mechanisms underlying the improvement of RAC performance through carbonation treatment, providing important theoretical foundations and data support for the broader engineering application of RAC.