Influence of binder composition on the thaumasite form of sulfate attack of concrete

The effects of cement types and mineral admixtures on the thaumasite form of sulfate attack of concrete were studied. Mortars made with addition of 30% limestone filler were stored in 2% magnesium sulfate solution at 5 ± 1°C for 1 year and their visual appearances, strength developments were measured at different storage times. X-ray diffraction (XRD) was used to determine the mineral composition of mortars. The results show that the relative resistance to thaumasite form of sulfate attack of the cements used in this study is outlined below, form best to worst: Sulphoaluminate cement plus ordinary Portland cement, sulphoaluminate cement, sulfate resisting Portland cement, ordinary Portland cement. The resistance to thaumasite form of sulfate attack of mortar is remarkably improved by the addition of silica fume or ground granulated blastfurnace slag (ggbs), and the better the resistance to thaumasite form of sulfate attack, the more the addition of ggbs is. The thaumasite form of sulfate attack is decreased to a certain degree by a lower replacement of cement with fly ash, but it is accelerated by the addition of a higher amount of fly ash due to its lower reactivity.