Experimental and numerical study on the microstructure and chloride ion transport behavior of concrete-to-concrete interface

Concrete-to-concrete interfaces present both in new and existing construction, are commonly regarded as the weak link. Durability research of interfaces is a vital prerequisite for structural rehabilitation and strengthening applications under marine and coastal environments. Hence, to clarify the chloride ion transport behavior be-tween the new-old concrete composite system and its constituents, microstructural characteristics of the in-terfaces with various preparation methods were determined via field emission scanning electron microscopy. Then, the time-dependent diffusion chloride ion penetration together with its steady-state concentration distri-bution evaluated by using AgNO3 chromogenic, electron microprobe, and energy spectrum methods, as well as the numerical simulation based on the real interface roughness from the 3D laser scanning optical system. Results show that microcracks and a large amount of CaCO3 precipitations were formed in the concrete-to-concrete interface, where its porosity was higher compared to that of the matrix and interface transition zone around coarse aggregate; Therefore, the interface regions have higher tortuosity of water transport channel and strengthen the solution absorption rate, resulting in the internal chloride ions not only diffuse deeper perpen-dicular to the exposed surface but also ingress into the concrete on both sides as the concentration gradient simultaneously, leading to a diffusion peak formation. Furthermore, the effects of groove characteristics (such as orientations, clearance, width, and depth) on chloride transport were modeling evaluated in this study, in which the interfacial relationship could be optimized setting the reasonable groove and achieving the goal of durability equivalent to the cast-in-place structure.

Automated summary

This study determined the microstructural characteristics of concrete-to-concrete interfaces with various preparation methods. The results showed the formation of microcracks and CaCO3 precipitations in the interface, resulting in higher porosity compared to the matrix and interface transition zone. This higher tortuosity of water transport channel and increased solution absorption rate led to deeper diffusion of chloride ions and ingress into the concrete on both sides, causing a diffusion peak formation.