Chloride penetration in concrete subject to wet-dry cycling: influence of pore structure

The objective of the work is to investigate the effect on the distribution of chloride at different depths of some factors concerning concrete pore structure, namely water/cementitious material ratio, cement type and percentage ground granulated blast furnace slag (GGBS). Concrete cubes are subjected to repeated wetting and drying cycles with various concentrations of sodium chloride solution, during which their mass is monitored. The effective porosity, weight and distance sorptivity and chloride solution penetration depths are calculated. Samples are extracted from the cubes at a range of depths and analysed for chloride content. The results show that the most significant effect of sorptivity on long-term chloride ingress to concrete is its effect on surface chloride content. The value of this parameter is a way of taking account of absorption when modelling chloride ingress under cyclic wetting and drying conditions. The values of cover depth recommended in BS8500-1 that are needed to ensure a time to corrosion of 100 year are calculated assuming the surface chloride content is 0.14% for GGBS and pulverised fuel ash (PFA) concretes. Our cyclic wetting and drying experiments produce higher surface chloride contents (0.29-0.62%) that would lower the time to corrosion using the cover depths recommended in the code.