External sulfate attack on portland cement incorporating high-volume of dolomite powder pre-cured at 20? and 60?

This work focuses on the sulfate resistance performances of Portland cement (PC) incorporating different amounts (0 similar to 60 wt%) of dolomite powder (DM) pre-cured at different temperatures (20 degrees C and 60 degrees C). The results show that the PC-DM samples pre-cured at 20 degrees C for 28 d and then eroded by sulfate solution for 180 d exhibit the worse appearances and higher expansion values than the reference PC sample. On the opposite, the sulfate resistance performances of the PC-DM samples pre-cured at 60 degrees Care better than those of the PC sample. Furthermore, with the increase of the DM content, the sulfate resistance properties get better and better. The degradation of the pore structure may act as a major factor for the poor sulfate resistance of the PC-DM samples pre-cured at 20 degrees C. However, for the PC-DM samples pre-cured at 60 degrees C, the poor pore structure does not increase the risk of sulfate erosion. This is mainly due to that the formation of hydrotalcite (Ht) results in the decomposition of monosulfate, and SO42- may also be bound firmly by Ht in the PC-DM samples, thus contributing to the excellent sulfate resistance. Additionally, brucite can be identified in the PC-DM samples pre-cured at 60 degrees C , especially with high DM dosages (=40 wt%).