Gradient erosion mechanism of ultra-low water binder ratio cement-based materials (ULWC) at low temperature: From molecular structure to macroscopic pore structure

The study of damage mechanisms is crucial for enhancing the service performance of low- temperature concrete. This study reveals the gradient erosion mechanism of ULWC behavior under low-temperature. The study employs in-situ detection techniques to analyze the effects of low-temperature on the C-S-H and crystal structures, including internal stress and chemical composition. It also uses 1 H NMR and CT to compare the frost heave of gradient pores with the matrix contraction. The results indicate that low-temperatures lead to irreversible degradation of crystal structures and collapse of C-S-H, resulting in spontaneous shrinkage. Furthermore, in the gradient pore structure, the frost heave of gel pores opposes the shrinkage of the matrix, ultimately leading to the reorganization of C-S-H grain stack structure and the refinement of micropores and degradation of macropores. Therefore, the gradient erosion mechanism suggests that although low temperature may disrupt the chemical structure of ULWC, it will refine the pores in the microstructure.