石灰石粉对水泥-粉煤灰砂浆流变行为影响的研究

Effects of limestone powder on rheological properties of cement-flyash mortar

采用RHEOLAB QC型旋转黏度计研究石灰石粉对水泥-粉煤灰砂浆流变性能的影响,并采用Bingham流体模型拟合了所测浆体的屈服应力和塑性黏度,采用POWER LAW流体模型拟合所测浆体的流变指数。研究结果表明:在水泥砂浆中分别掺入石灰石粉和粉煤灰后,显著降低了砂浆的屈服应力,改变了砂浆的塑性黏度,增大了砂浆的流变指数,降低了砂浆剪切变稀的程度,改善了砂浆的工作性。水泥-粉煤灰砂浆中,随着石灰石粉掺量的增加,砂浆的屈服应力和塑性黏度均增大,当石灰石粉掺量不大于14%时,砂浆的屈服应力增大不显著,当石灰石粉掺量低于8%时,砂浆的塑性黏度增大不明显。当石灰石粉掺量大于22%以后,砂浆流变指数降低,砂浆剪切变稀的程度增大。石灰石粉的密实填充、形状尺寸、比表面积和浆体体积等四大效应是造成砂浆流变性能变化的重要原因。

The effect of limestone powder on rheologieal properties of cement - fly ash mortar was studied through rotation viscometer with the RHEOLAB QC type. Moreover, the Bingham fluid model was introduced to fit the yield stress and plastic viscosity, and the Power Law fluid model for the theological index. The results show that the addition of fly ash and limestone powder to cement mortar decreases yield stress of mortar obviously, changes plastic viscosity of mortar, increases rheological index and decreases the degree of shear thinning of mortar, thereby improving workability of cement mortar. In cement - fly ash mortar, with the increase of limestone pow- der, yield stress and plastic viscosity of mortar increase. When the content of limestone powder is no less than 14% , the increase of yield stress of mortar is not obvious. And when the content of limestone powder is no more than 8%, the increase of plastic viscosity is not remarkable. After the content of limestone powder is beyond 22% , rheological index of mortar decreases, showing the increase of degree of shear thinning. The research find- ings show that the effects of limestone powder of dense packing, shape, specific surface area and paste volume result in the change of rheological properties of mortar.