Corrosion damage of concrete in presence of SO₄^2- and CO₃^2-

A site survey with corresponding sampling was carried out for an attacked concrete exposed to ground water, which contains substantial salts. The degraded concrete component at 6 years old was taken from a hydraulic structure in the western China. Samples selected from the site were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis of X-ray (EDAX), and laser Raman spectroscopy methods. The results show that a white mushy mixture consisting of thaumasite, ettringite, gypsum, and calcite occurs in the residual concrete due to a long-term exposure to SO₄^2- and CO₃^2- in the ground water. It is validated that the thaumasite form of sulfate attack (TSA) occurs in the field concrete, which has been undergoing at a low temperature, an adequate humidity, as well as a sulfate and carbonate attack.