Abstract
Sulfate attack is grouped into two general categories. One is transformation of hydration products, and another is sulfate ion transfer. There are a lot of studies on transformation of hydration products. However, there are few studies on sulfate ion transfer. Considering sulfate ion transfer is absolutely imperative to predict the deterioration rates of concrete. In addition, ettringite that is the principal hydration products of sulfate attack has a large specific surface area, therefore, ettringite has a potential impact on the microstructure of concrete if a large amount of ettringite is generated in concrete. Thus, the experimental evaluation of sulfate ion transfer and the clarification of effects of ettringite on the microstructure are needed for investigate.
In this study, sulfate ion effective diffusion coefficient, porosity, and the amounts of hydration products of hardened cementitious paste after sodium sulfate solution immersion were measured. Tortuosity of sulfate ion, which was an index expressing sulfate ion migration path length affected by the microstructure, was calculated.
From the experimental results, sulfate ion effective diffusion coefficient was decreased by using 70％ blast furnace slag-cement with 10％ anhydrite and 10％ limestone powder. The sulfate ion effective diffusion coefficient was correlated with the sulfate ion tortuosity. The sulfate ion tortuosity could not be estimated using the amount of C-S-H, empty pore volume and the specific surface area of C-S-H. In contrast, it could be estimated using the amount of ettringite and the specific surface area of ettringite, in addition to C-S-H. Hence, it was suggested that ettringite has a potential impact on the microstructure of concrete causing sulfate attack.
