Abstract
Synopsis: The rheology of concrete is often approached by using a particle-matrix model, which roughly can be described as coarser aggregate dispersed in a suspension of fines less than 125µm. Parameters determining the flow resistance of concrete matrix have been discussed. The following parameters are treated in some detail; w/c, cement type (mineralogy and fineness), silica fume dosage and plasticizers (type, dosage and time of addition).The influence of w/c of cement paste fit very well to the so called Krieger-Dougherty equation for suspensions where the apparent viscosity is dominated by the volume fraction of solids.There is a linear correlation between the flow resistance of cement pastes and the specific surface of the cements multiplied with a weighed sum of cubic C3A and C3S, or in other words the surface fraction of the most hydraulic active minerals in the fresh state. Cements ground from the same clinker show an exponential relation between fineness and flow resistance of pastes.Flow resistance of cementitious pastes decreases with increasing volume replacement of silica fume until 9 vol% and increases again thereafter.Polyether grafted polyacrylates (PA) are better plasticizers than naphthalene sulphonate-formaldehyde condensate (SNF) and sodium lignosulphonate (NLS). Unlike for SNF and NLS, paste show no improved rheology by delayed addition of PA.
