Diffusion characteristic of sulfate anion in surface region of cement mortar at early stage

The SO₄ ^2- concentration distributions in surface region of cement mortar immersed in sulfate solution at early stage were measured by layered sampling method combined with chemical analysis, and the diffusion coefficients of SO₄ ^2- anions in surface region of mortar into internal area were calculated by means of instantaneous plane diffusion theory. The experimental results showed that the SO₄ ^2- concentration gradually reduced when the diffusion depth increased in the surface region of mortar. Diffusion coefficient (D) was relevant with the concentration and kind of environmental sulfate solution, which reduced with immersion time at the beginning, and then rose slowly after a period of time. The calculation of initial diffusion coefficient (D₀) and starting time of deterioration (t_∞) caused by sulfate attack was further attempted based on the data of diffusion coefficient, and it was found that D₀ and t∞ were all relevant with concentrations of sulfate and different kind of sulfate as well.