The thaumasite sulphate attack (TSA)

In the last few years the techniciances and experts could meet with a new sort of corrosion of concretes, so-called thaumasitesulphate corrosion or thaumasite sulphate attack (TSA). The reason of this manifestation and phenomenon is the transmutation of calcium-hydrosilicates (C-S-H) of the solidified concretes into pulpy and pasty thaumasite (CaSiO(3 center dot)CaCO(3 center dot)CaSO(4 center dot)15H(2)O). At present the thaumasite is well-known as a mineral too. Inspite of this unfortunately, by X-ray diffraction it is very difficult to distinguish thaumasites (TSA) from ettringits because of their similar morphology and crystal-structures. In their article the authors show, that TSA-s can be appearence in concretes because of the followings reasons: Presence of SO42- or S2- ions in the ground solles or in ground waters; Presence of CO32- in the cement or the additional materials of concretes; Presence of SO42- or S2- in the technological waters; Low temperature (t < 15 degrees C) of concrete. On the basis of the registered several hundreds appearences of TSA, authors collected the thaumasites into following groups: Thaumasites as results of grounds with sulphates or sulphides around the concrete; Thaumasites, appearenced in concretes because of exhaust or escape-gases, around the building construction made from concrete; TSA-s as results of streaming sea-water around the construction made from concretes; Thaumasites because of injured mortars used for concretes.