2018 Volume 67 Issue 9 Pages 877-884
This study was conducted to investigate the properties of sulfate ion transfer and the effects of pore structure and surface potential on sulfate ion transfer in cementitious materials after 5mass% sulfate solution immersion. In this study, the sulfate ion effective diffusion coefficient, the oxygen gas diffusion coefficient, the porosity, the pore size distribution and the ion composition of the pore solution of cement paste specimens after 5mass% sodium sulfate and 5mass% magnesium sulfate solution immersion were measured. The tortuosity of sulfate ion diffusion and that of oxygen diffusion were calculated from each diffusion coefficient, and the ratio of two tortuosity which is indirectly expressing the effect of surface potential was calculated. Results shows that the tortuosity of sulfate ion transfer was greater than that of oxygen diffusion in most cases of sodium sulfate immersion. On the other hand, in almost half of magnesium sulfate immersion, the tortuosity of sulfate ion transfer was comparable with that of oxygen diffusion. Furthermore, the sulfate ion effective diffusion coefficients decreased with increasing of the ratios of tortuosity of sulfate ion diffusion and that of oxygen gas diffusion in the case of 5mass% sodium sulfate solution immersion. In the case of 5mass% magnesium sulfate solution immersion, the correlation was low as compared to sodium sulfate immersion. Therefore, it was suggested that the effect of surface potential was dominant in sulfate ion transfer in the case of 5mass% sodium sulfate solution and the effect of pore structure was acting more strongly in the case of 5mass% magnesium sulfate solution.
