水泥-粉煤灰浆体流变特性及其机理研究

Rheological characteristic and its mechanism of cement-fly ash paste

采用Rheolab QC型旋转黏度计研究水泥-粉煤灰浆体的流变性能,分析粉煤灰掺量和剪切速率对浆体的流变模型、屈服应力、塑性黏度、触变性、临界剪切速率以及剪切增稠作用的影响。研究结果表明:随粉煤灰掺量增加,基于Bingham模型进行描述的水泥-粉煤灰浆体剪切应力与剪切速率的线性相关性逐渐降低。浆体的屈服应力、塑性黏度、触变性和临界剪切速率等流变参数随着粉煤灰掺量的增加而降低,当粉煤灰掺量约为50%时,各流变参数均降为最低。在较低的剪切速率下水泥-粉煤灰浆体的塑性黏度显著减低,浆体呈现显著的剪切稀化,然后随剪切速率的增大浆体的塑性黏度增大,浆体出现了剪切增稠。增大粉煤灰的掺量,降低了浆体由剪切变稀向剪切增稠转变的临界剪切速率,使浆体在较低的剪切速率下出现剪切增稠。粉煤灰颗粒在水泥浆体中的"滚珠效应"、"减水润滑效应"以及"比表面积效应"是造成浆体流变性能变化的重要原因。

The rheological properties of cement-fly ash pastes were studied by a rotation viscometer with type of Rheolab QC. The influence of fly ash content and shear rate on rheological model, yield stress, plastic viscosity, thixotropy, critical shear rate and shear thickening were investigated. Results show that with ash content increasing, the linear dependent between shear stress and shear rate of compound paste based on Bingham model decreases. Yield stress, plastic viscosity, thixotropy and critical shear rate of cement-fly ash paste are on the decline with the increasing fly ash content. When fly ash content is 50%, all rheological parameters above are the lowest. Plastic viscosity of compound pastes shows remarkable shear thinning behavior under low shear rate. Plastic viscosity of pastes increases with shear rate increasing, and then the compound paste shows shear thickening behavior. With the increase of fly ash content, the critical shear rate of compound paste decreases, resulting in shear thickening in low shear rate. “Ball effect”, “water reducing and lubricating effect” and “specific surface area effect” are the reasons causing the change of rheological properties of compound paste.