Sorptivity and the estimation of water penetration into unsaturated concrete

Uptake of water (and therefore ions) by unsaturated, hardened concrete may be characterised by the sorptivity. This is a simple parameter to determine and is increasingly being used as a measure of concrete resistance to expo sure in aggressive environments. The complete process is described by a non linear diffusion equation, with the hydraulic diffusivity a strongly nonlin ear function of the degree of saturation of the concrete. Accurate analytic al approximations to the solution of this equation, as well as numerical so lutions for general conditions, ex-ist when the diffusivity function is kno wn. Unfortunately it is not an easy function to determine, requiring accura te information on the water penetration profile. A simple alternative which estimates the diffusivity from sorptivity and porosity measurements is pre sented for an assumed exponential dependence of diffusivity on water satura tion. Predicted water penetration profiles corresponding to this estimated diffusivity are shown to be accurate by comparison with published experimen tal results.