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In cold climatic areas, bridge expansion joint concrete is susceptible to damage from freeze-thaw (F-T) cycles and chloride-salt erosion. This paper investigates the differences between the surface layer of concrete (C-S) and the interior of concrete (C-I) under various curing conditions, focusing on pore structure characteristics. The salt freeze-thaw (sF-T) resistance of the C-S and C-I was analyzed using the surface scaling, mass growth rate, and apparent chloride diffusion coefficient after one-sided sF-T cycles (Dapp′). The results indicate that the pore structure of the C-S was more intricate than that of the C-I. However, the paste structure of the C-I was denser. The fractal dimension (DF) of the C-I was lower than that of the C-S under different curing conditions, with a reduction of approximately 10 %. Additionally, it was observed that the C-I exhibited significantly higher sF-T resistance than the C-S. To obtain a more precise evaluation of the concrete's sF-T resistance, it is recommended to remove 2 mm from the edges of the specimen. Furthermore, the Dapp′ is a more reliable indicator of concrete's sF-T resistance when the F-T medium is a chloride-salt solution. The Dapp′ of the C-I decreased by 26.8 %, 33.2 %, and 49.9 % under the curing conditions of 20℃-95 %RH, 5℃-70 %RH, and 0℃-50 %RH, respectively, when using concrete specimens with 2 mm of edges removed, compared to the C-S. The study results can serve as a fundamental basis for designing and constructing of concrete for bridge expansion joints in cold climatic areas.
Zhao et al. (Tue,) studied this question.