Microstructure changes in mortars attacked by sulphates at 5 °C

In this study mortars have been produced using ordinary Portland cement (CEM I – 32.5) and limestone cement with 15% limestone addition (CEM II/A-LL – 32.5). The mortars were immersed in a solution of 5% Na2SO4 at 5 °C for 6 months and the caused deterioration was observed visually at a regular basis. The deterioration product of the surface of both mortars has been identified as thaumasite by the means of XRD, FT-IR, DTA and SEM/EDAX analysis. The damage caused due to formation of thaumasite in both mortars was approximately the same and not influenced by the addition of limestone. Furthermore, expansion and compressive strength of the mortars were studied as a function of time and it was proved they were not influenced by thaumasite formation at the age of 6 months.