Effects of dolomite and limestone powders on strength and hydration of cement mortars

To clarify the physical & chemical effects of dolomite powders in cement and their high efficient & safe application in cementitious materials, the strength of cement mortars blended with dolomite powders at various replacement levels and finenesses were investigated when limestone powder was used as a reference. The hydration products of blend cements were examined by X-ray diffraction and thermogravimetry. The results indicate that strength of cement mortars blended with dolomite and limestone powders decreases with the increase of replacement levels, and there is a slight difference between the powders in affecting the actual value of strength. Incorporation of dolomite powder for promoting the early strength and flexural strength of mortars is not pronounced, but mortars with both the powders develop the comparable strength at middle and later stages. The early strength of mortars can be slightly improved when the fineness of dolomite powder used increases. Similar to limestone powder, dolomite powder is involved in chemical reaction in cement paste, in addition to portlandite, ettringite and C-S-H, which are identified and carboaluminate hydrates are formed. However, the reaction rate, degree and reaction mechanisms of the two powders are different. The reaction degree of dolomite (3.06%) is slightly less than 3.54% of the limestone powder at early stage, and its reaction degree is 7.46%, which is greater than that of the limestone at late age (i.e., 5.91%). Compared to limestone powder, dolomite powder dissolves slowly, thus giving a lower reaction degree at 3-d period, but a higher reaction degree is reached due to the combination of direct formation of carboaluminate hydrates and dedolomitization reaction at the middle and late periods.