Experimental studies on the chloride ion permeability of concrete considering the effect of freeze–thaw damage

Abstract

A series of laboratory experiments were conducted to investigate the effect of freeze–thaw (FT) cycles on mechanical properties and chloride permeability of concrete with the strength class of C30 in this paper. The mechanical property tests were performed on the specimens subjected to 0, 5, 15, 30, 50, 75 and 100 standard FT cycles to determine the compressive strength, normalized dynamic elastic modulus (NDEM) and mass loss. Also, the chloride natural diffusion tests of concrete specimens, after 0, 5, 15, 30 and 50 FT cycles, were conducted in a self-design tidal cycling simulation device to investigate the chloride ingress into concrete in marine environment of tidal zone. Based on the Fick’s second law, a time-dependent model was developed to predict the chloride profiles of frost-damaged concrete. Additional FT cycling tests at different minimum temperatures of freezing process (−4 and −11 °C) and the chloride natural diffusion tests were conducted to study the effect of minimum temperature on the chloride diffusion in concrete. The experimental results revealed the significant influence of FT action on the mass loss, compressive strength and NDEM. After 50 FT cycles, the mean of NDEM dropped to 60%, indicating that the specimen was destroyed by FT action. With the decrease of minimum freezing temperature, the loss of NDEM increased apparently, performing a good linear relation. A substantial effect of FT damage on the chloride profiles was observed: compared to the counterparts of the control groups without being exposed to FT attack, chloride concentration was larger for the frost-damaged concrete, and this difference increased with the extension of exposure duration. A linear relation between the apparent chloride diffusion coefficient and the loss of NDEM was also obtained regardless of the exposure time. Moreover, it was found that the proposed model was applicable for the prediction of chloride profiles in concrete subjected to FT cycles at different minimum freezing temperatures. In other words, the proposed model can be used to describe the chloride ingress into frost-damaged concrete, regardless of the cause of the damage (due to the number of FT cycles or the minimum freezing temperature).