The properties of chloride ion diffusion of concrete under high temperature conditions, with implications for the storage of spent nuclear fuel in concrete casks

This paper discusses the properties of chloride ion diffusion of saturated concrete subjected to salt attack under high temperature conditions. Immersion tests were conducted for various concrete specimens of plain and fly-ash concrete with three values of waterbinder ratio (W/B=40, 50, 60%) in 3.5% NaCl solution, which were controlled at four levels of temperature, i.e. 20, 40, 65, and 90°C. The depth of chloride ion penetration and the chloride profiles of concrete were investigated by using the potentiometric titration method (AgNO₃), and the apparent diffusion coefficient was predicted from the measured chloride profiles. The influence of temperature on the diffusion coefficient of chloride ion was discussed, by using the Arrhenius equation. Test results indicated that the apparent diffusion coefficient of chloride ion of concrete increases remarkably along with temperature rise, and there was a linear relation between the natural logarithm values of the diffusion coefficients and the reciprocal of the temperature from the Arrhenius plots. Concrete with lower water-binder ratio has a tendency towards having higher temperature dependency, and the activation energy of fly-ash concrete was higher than that of plain concrete under a temperature of up to 90°C.