Alternating current method to determine chloride diffusion coefficient of hardened paste and concrete

Abstract

A slice sample is cut and saturated with 10% concentration sodium chloride solution. The saturated slice sample and 10% concentration sodium chloride solution are then connected in a continuous ring mould as a secondary coil in a non-contact electrical resistivity apparatus. The chloride diffusion coefficient DCl of hardened paste and concrete is calculated from the measured electrical resistivity of the slice sample based on the Nernst–Einstein equation. There is a bilinear relationship between the chloride diffusion coefficient and the reciprocal of time logarithm for different hydration periods of the samples. The slope is higher before 72 h than after 72 h. Parameter KD is obtained to describe connectivity for migration of ions. There is a good linear correlation of the chloride diffusion coefficient between concrete with an aggregate volume fraction 65% and paste with the same water–cement ratio, showing that the chloride diffusion coefficient of a concrete is a function of the chloride diffusion coefficient of a paste with the same water–cement ratio and the paste matrix volume fraction (1 − Va) inside the concrete.