Shear deterioration characteristics of new-to-old concrete interface in a humid environment: An atomistic investigation

HP Huang and TF Wang and T Guo and MX Fang and B Jiang and YM Tu and YH Ji and C Wang and G Sas, STRUCTURES, 78, 109262 (2025).

DOI: 10.1016/j.istruc.2025.109262

The interface between new and old concrete is inherently a weak point in structures. Humidity can degrade its bonding, impacting structural durability. However, the nanoscale shear behavior of this interface and its deterioration in humid conditions remain unclear. In this study, two interfacial models were developed using hydrated calcium silicate (CSH) and silicon dioxide (SiO2) as the research substrates, including CSH-a (H2O/ Si=1.68)-to-CSH-b (H2O/Si=1.0) and CSH-a-to-SiO2 interfaces. The effects of different interfacial water layer thicknesses (0 & Aring;, 3 & Aring;, and 5 & Aring;) on the interfacial shear behavior were investigated through molecular dynamics simulation. It was discovered that the bonding properties of the CSH-a-to-CSH-b interface were superior to those of the CSH-a-to-SiO2 interface. When the thickness of the interfacial water layer is 0 & Aring;, all failure modes of the model occur within the CSH-a substrate, which has lower strength and unstable bonding energy. As the interfacial water layer thickness increases, the failure mode of the model shifts from shear failure inside the substrate to damage at the interface. Additionally, a humid environment has a negative impact on the shear strength of the interface. When the thickness of the interfacial water layer is increased from 0 & Aring; to 3 & Aring;, and then from 3 & Aring; to 5 & Aring;, the shear strength decreases by 23.7 % and 19.7 % for the CSH-a- to-CSH-b interface, and by 11.4 % and 23.1 % for the CSH-a-to-SiO2 interface, respectively. The findings of this study clarify the shear behavior of the new-to-old concrete interface at the nanoscale, particularly in terms of shear deterioration characteristics in humid conditions.

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