Abstract
TSA (thaumasite form of sulfate attack) is known as one of the forms of sulfate attack that can occur in a cold environment, weakening the hard tissue of concrete. Practically, thaumasite is generated with ettringite in concrete upon penetration of sulfate ion, which is a component of both. Therefore, an investigation of TSA requires detection of thaumasite distinctly from ettringite. Thaumasite being a member of the ettringite group and thus showing diffraction lines under X-ray diffraction (XRD) quite similar to those of ettringite, distinguishing thaumasite from ettringite is rather difficult. In this study, changing of XRD patterns of thaumasite and ettringite by heat treatment and vacuum treatment was examined, focusing on their crystal water. Although the crystal water of ettringite was easily lost under vacuum treatment, the crystal water of thaumasite remained stable as attested by the observed X-ray diffraction lines. The applicability of this method was examined by using thaumasite produced using cement materials and concrete specimens exposed to a low-temperature, sulfate-rich environment.
