Nanoscale research on interfacial shear behavior between concretes cast at different times

This study utilized molecular dynamics simulations to investigate the shear behaviour of the interface between new and old concrete. Two atomic models were developed to represent the new- to-old concrete interface, using hydrated calcium silicate (CSH) substrates with different water-to- silica ratios: CSH1 (H₂O/Si=1.0)-to-CSH3 (H₂O/Si=1.68) and CSH2 (H₂O/Si=1.5)-to-CSH3 interfaces. The results show that the primary bonding type in both interfaces is the Ca-O bond, and shear failure predominantly occurs within the CSH3 substrate with lower strength and unstable bond energy. Furthermore, the shear strength of the CSH1-to-CSH3 interface (0.93GPa) is 34.8% higher than that of the CSH2-to-CSH3 interface, indicating a correlation between shear property and bond energy stability and strength of the substrate. This study provides theoretical support for the design and optimization of new-to-old concrete interface.