Impact of leaching and chlorides on sulfate attack for cement paste

The effect of leaching and chlorides on the sulfate ingress and cracking damage is investigated for cement paste. Disk specimens with one-dimensional diffusion were exposed to solutions of 10g/L Na2SO4 + pH of 13, 10g/L Na2SO4 + pH of 7, and 10g/L Na2SO4 + 19g/L NaCl + pH of 7. The sulfate ingress, surface cracks and mineral phase distribution were characterized through ICP, optical microscope, BSE and XRD. Further analysis is performed on the gypsum formation and crystallization. The experimental results and the analysis show that: (1) the leaching accelerates the sulfate ingress and induces the cracking damage with a spalling pattern; (2) the chlorides mitigate the sulfate ingress and the crack propagation, and the sulfates in turn reduce the chloride binding; (3) the gypsum detected in leaching case results from cracking and its crystallization in crack space is not likely to contribute to the crack propagation.