白云石和石灰石微粉对水泥砂浆强度和水化产物的影响

Effects of Dolomite and Limestone Powders on Strength and Hydration of Cement Mortars

为探究白云石微粉在水泥基材料中的物理化学效应和安全高效应用途径，以石灰石微粉为参照，在研究白云石微粉取代量和细度对水泥砂浆强度影响的基础上，采用X射线衍射和热重法研究了白云石微粉对复合胶凝材料浆体水化产物的影响。结果表明：白云石和石灰石微粉对水泥砂浆强度的影响规律类似，砂浆强度几乎均随取代量增加而降低，而且两者所致的强度绝对值差异不大。白云石微粉取代量大于10％时砂浆3d强度明显降低，而石灰石微粉在取代量达20％时，对砂浆3d强度几乎没有影响。随龄期延长，两种微粉对砂浆强度影响的差异减小。养护至28d，取代量≤10％时，两种微粉对砂浆强度的影响几乎没有差异；进～步延长龄期至90d，在取代量为5％～30％范围内，两种微粉同掺量时砂浆的强度相当。提高白云石微粉细度可小幅改善混合水泥早期强度。与石灰石微粉类似，白云石微粉参与水泥水化反应，生成碳铝酸盐，但两者参与反应的速度、程度和机制略有差异。取代量为30％时，白云石和石灰石在浆体中的反应程度3d时分别为3．06％、3．54％，90d时则分别为7．46％和5．91％。与石灰石微粉相比，白云石微粉成核效应弱、早期反应活性低，导致其对砂浆早期强度的积极效应不及石灰石微粉；直接生成碳铝酸盐和去白云石化反应的共同效应明显促进白云石微粉的中后期反应速度和程度，并进而促进砂浆中后期强度发展。

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.