Impact and Improvement of Crushed Tuff Sand on Sulfate Resistance of Cement Concrete at Low Temperature

Abstract

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 1±1°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%.