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 125?m. Parameters determining the flow resistance (taken as the area
under the shear stress versus shear rate curve) of concrete matrix have been
discussed. The following parameters are treated in some detail; water-to-cement ratio
(w/c), cement type (including mineralogy and fineness), silica fume dosage and
plasticizers (type, dosage and time of addition).
It is shown, for instance, that the w/c for a cement fit very well to the so called
Krieger-Dougherty equation for suspensions where the apparent viscosity is
dominated by the volume fraction of solids.
Another finding 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 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 (LS).
Unlike for SNF and LS, paste show no improved rheology by delayed addition of PA.