Strength and hydration products of cement mortars with dolomite powders cured at 40℃ and 60℃

To clarify the physical and chemical effects of dolomite powder (DM) in cement, the strength of blended cements mortars with dolomite powders replaced at different contents (i.e. 10%, 20% and 30%, mass fraction) and cured at 40℃ and 60℃ were investigated. A limestone powder (LS) was used for the comparison purpose. The hydration products of blended cements were examined by X-ray diffraction. The results indicate that DM and LS both show their effects on the mortar strength at different replacement contents of DM and LS and curing temperatures. At 40℃, LS shows a positive impact on the promotion of the early strength, compared to DM, but this difference reduces and even reverses with the increase of the replacement content and the curing age. When the replacement content is over 20% and the curing duration is 90 d, the strength of mortars with DM is greater than that with LS. Comparing to LS mortars, increasing the curing temperature to 60℃ gives a promoting effect on the strength of mortars with DM, and the effect is more pronounced with the increase in the replacement content. When cured at 40℃, LS and DM both involve in reaction, forming monocarboaluminate (Mc) hydrates at early ages, but developing a few hydrotalcite (Ht) in DM pastes at 90 d. At 60℃, however, single sulphur calcium aluminate (AFm) is formed in blended cement pastes instead of Mc. When the curing duration increases, no significant change in the hydration products in the LS pastes, and the amount of AFm decreases and AFm disappears while Ht develops and increases considerably with the increase of DM replacement content in the DM pastes. DM gives a more intense chemical effect at a high temperature and a late duration. Compared to the dedolomitization of aggregate leading to alkali carbonate reaction instead of brucite and calcite, Mc and/or Ht were formed in the reaction of dolomite powders in the paste. The reaction of dolomite powders with aluminous constituent in the paste has a positive effect on the promotion of the strength of mortars.