Rheological properties of cement slurry
The rheological properties are characterized by liquidity, susceptibility to deformation under the influence of the acting force and maintaining homogeneity at the same time. The listed features are important from the point of view of the concrete mix, the fluidity and stability of which depend on the freedom of movement of the aggregate grains in the slurry. They can change, because immediately after mixing cement with water, a chemical process begins between them, and the water becomes saturated with calcium and alkali ions, thereby increasing its viscosity. Hence, the durability of rheological features is important, which can change significantly when admixtures and / or additives are introduced into the slurry. The initial rheological characteristics depend primarily on the quantity ratio of water to cement (W/C), in turn, on the degree of thoroughness of mixing them. The rheological properties can be quantified by setting the flow resistance limit with rheometers (tension, where the layers of grout shift to each other (Well) and internal friction. The disturbance of the constancy of rheological features may be caused by flocculation (clumping into lumps = conglomerates) cement grains, false binding, strong temperature change, separation of the ingredients of the leaven, e.g. due to excess water or low water resistance by cement. Coarse-grained cement slurries change faster (specific surface < 2500 cm²/g) because of low waterbondness and with fine grains (p.w. > 4500 cm²/g) Due to excess water.
The situation is most favorable, when each grain of cement is separated from the others and surrounded by a layer of water. The thinner the layers are, the more stable the rheological properties over time, and the whole mass of grout is more homogeneous.