Effect of Mixing Procedure on the Rheological Properties and Hydration Kinetics of Portland Cement Paste

Abstract

The mixing procedure used to make paste, mortar or concrete has an important influence on the hydration kinetics and rheological properties of cementitious materials. In this study, different shear mixing procedures were studied to evaluate the effect on the kinetics of hydration for Portland cement paste by isothermal calorimetry over 72 h. The rheological properties of the same pastes in terms of yield stress (Pa) and apparent viscosity (Pa.s) were also studied with the same mixing procedures: Manual, 2500 rpm and high shear mixing at 10000 rpm. To compare the heat flow over the time of each mixing procedure with the stiffening, an oscillatory rheometry evaluation with continuous flow was carried out. All the tests were carried out in triplicate and the variability was evaluated. The results show important differences in terms of enhancement of height of the main heat evolution peak and reduction of the induction period when the paste was mixed at 10000 rpm (high shear), moreover, the oscillatory rheometry showed that the high shear mixing reduced the stiffening time of the mix compared to manual mixing and 2500 rpm mixing.