Thaumasite formation in a tunnel of Bapanxia Dam in Western China

A site investigation and sampling was carried out on a sulfate-attacked concrete structure in Bapanxia Hydraulic Power Plant in Western China. The concrete had been exposed to ground water containing substantial concentrations of salts (SO42−, CO32− and Cl−) for about 6 years and was analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), laser-Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. It is shown that a white mushy mixture consisting of thaumasite, ettringite, gypsum and calcite is present in the residual concrete. This paper reports the first instance of the thaumasite form of sulfate attack of concrete in China.