Electrical characterization of freeze-thaw damage in saturated concrete and its interfacial transition zones

Determining the freeze-thaw (F-T) damage of the interfacial transition zone (ITZ) is crucial to understanding the mechanism of F-T in concrete and improving its frost resistance. In this paper, the F-T damage of saturated concrete/mortar and ITZ is characterized using AC impedance spectroscopy, and the micro-mechanisms of F-T damage in cement-based materials (CBMs) are summarized. Firstly, the damage factor was defined by the effective resistivity of the CBMs, and a correlation between the damage factor and the compressive strength loss was established. The F-T damage process was divided into a damage development stage and a damage stabilization stage based on the damage factor and fractal dimension. Then, the effective resistivity separation formula was proposed to calculate the ITZ effective resistivity, and the ITZ damage factor was calculated for non-destructive quantitative characterization of the F-T damage in the ITZ. Finally, the microscopic mechanism of F-T damage in CBMs and their ITZs was summarized based on damage factor, fractal dimension, super depth of field microscopy, and nanoindentation. The results showed a linear relationship between the damage factor and compressive strength loss (L_c = 0.176E_r+0.030); the ITZ had damage factors of 80 % and 70 %, which were 1.6 and 1.4 times higher than those of the matrix, respectively; F-T cycles produce micro-damage, part of which connects with the disconnected pores to form connected pores, the micro-damage extends and accumulates along the surface of the aggregates, leading to ITZ debonding from aggregate and deterioration of the mechanical properties.