Experimental tests were conducted to study the thaumasite formation of sulfate attack (TSA) erosion resistance of cement concrete made with crushed tuff sand. Different specimens made with either crushed tuff sand or river sand were soaked in a mixed solution of sodium sulfate and magnesium sulfate at the temperature of $10\pm 1°\mathrm{C}$ to simulate its working environment, and electrical pulses were used to accelerate corrosive medium migration. Afterward, the compressive strength and erosion products of before- and after-corrosion sample specimens were comparatively analyzed. The results showed that the strength of concrete made with crushed tuff sand was higher than that made with river sand before corrosion. However, the difference in their strengths diminished when the specimens were exposed to sulfate and a pulsed electric field for 2 months. This means that the specimens made with crushed tuff sand suffered a greater loss of strength compared with those made with river sand. The amount of thaumasite was higher than that of ettringite in the specimens made with crushed tuff sand; for specimens made with river sand, the situation was just the opposite. The reason that the crushed tuff sand reduced the sulfate erosion resistance ability of concrete at low temperatures is discussed on the basis of the mineral composition of tuff rock powder, the porous structure of concrete, and the interfacial transition zone (ITZ) microstructure of concrete. It was found that incorporating a certain amount of barium hydroxide can improve the anti-sulfate erosion ability, and the best dosage is around 4%.

The study on the hydration process of cement-based materials is of significance since it determines the development of the macro-properties. The hydration process of high-volume fly ash (FA)-cement based materials is quite special and needs systematic study. In this study, the hydration heat release of cement paste with high volume FA were measured with isothermal calorimetry at different temperatures. The full-width at half-maximum (FWHM) value of the exothermic peak and the cementitious index (CMI) of FA were used comprehensively to evaluate the influence of FA on cement hydration. It was found that increasing the FA content and water-binder ratio retarded the hydration process for paste but did not show obvious effects on the hydration of cement. The CMI values show that raising the temperature intensified the retarding effect of FA on cement hydration during the induction period, but promoted the subsequent hydration process. According to the normalized heat release to cement, and the change of CMI values with temperature, new evidence was found that FA may not act as nucleation sites during the hydration process of cement. The result can be better explained by the topochemical reaction mechanism.