Abstract
The purpose of this study is to determine the effect of cement C 3A content, temperature and composition of the immersion medium (water, gypsum and magnesium sulphate solution) on the rate of thaumasite formation in cement mortars. It also aims to ascertain how the C 3A content influences the composition of the salt formed. The mortar prisms for this study were made with two different cements, one with low and the other with high Al 2O 3 content, with or without gypsum and/or calcium carbonate. After hydration, curing and carbonation, the prisms were partially immersed in distilled water and stored at temperatures ranging from 0 to 5 °C for up to 5 years. Some of the prisms were immersed in a 2% (w/w) gypsum solution or in 1.4% (w/w) magnesium sulphate solution at ambient temperature. Samples were taken at different ages and mineralogical and micro-structurally characterised. Some of the specimens tested were observed to expand, in a process concurring with the formation of thaumasite or a solid solution of thaumasite and ettringite, at both ambient and cooler temperatures. A correlation was found between cement C 3A content and the composition of the deterioration product involved in the expansive process: thaumasite forms in mortars made with low C 3A cement, whereas mixed crystals or solid solutions of thaumasite and ettringite form in mortars made with high C 3A content cement.
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