Thaumasite: Its Relevance to Sulphate Corrosion in Concrete

The destruction of concrete and mortar in environments rich in sulphates and carbonates is termed sulphate attack: in terms of topical chemical changes, it is attributed to thaumasite1 added to ettringite. The scope of sulphate ingress (as opposed to durability) into concrete has been recorded based on a decrease of flexural strength, changes in length, and observation. Phase changes studies have confirmed beyond doubt the relevance and role of thaumasite and thaumasite sulphate attack (TSA) to concrete, but the latter must not be overestimated. Thus, the amount of thaumasite in destructed concrete bodies, as well as quantification of the TSA portion of overall deterioration caused by sulphate attack on construction material, remain the subjects of ongoing discussion in the research and technology of concrete and mortar.

The first step in damage to concrete and mortar and the constructions based on them is observable in the formation of ettringite and conjugated mass and volume changes leading to cracks, which enable water to access the original material. Repeated (cyclical) wetting and drying increase both the permeability of the

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