The rheological behaviour of non-shrinking cement pastes

Synopsis The effect of mixing, age and water/cement ratio on the rheology of non-shrinking cement pastes has been studied using a coaxial cylinders viscometer. Experiments under steady shear at constant rate, supported by thermogravimetry, gave information on the breakdown of structure. The rheology of non-shrinking cement pastes is broadly similar to that of ordinary Portland cement pastes. However, the rapid formation of ettringite increases the yield value and plastic viscosity. Prolonged mixing results in accelerated formation of ettringite and consequent stiffening of the paste which is also associated with reduced expansion in service. Structural breakdown takes place under continuous shear and the changes can be explained by the effect of shear on the amount of water bound in the ettringite crystals.