Abstract
The mixing process used for cement, gypsum, mortar, or concrete has a strong effect on the hydration kinetics and setting properties, so that a standard mixing protocol has to be followed, including the mixing time and the addition sequence of the different components. In order to study the effect of the mixing on the hydration kinetics, rheological and calorimetric measurements have been performed on cementitious materials prepared with different mixing designs. The product viscosity was directly measured with an instrumented mixer from the start of the mixing and during the addition of the different constituents to enable an accurate measurement of the mixing energy. The acceleration of the hydration kinetics is associated with (i) the generation of finer particles that act as nuclei for the precipitation of the hydrates and (ii) an increase of the temperature due to the friction between the grains; therefore, a longer and more intense mix tends to accelerate the hydration kinetics. We show in this work that the retardation of the hydration kinetics of cementitious materials, which appears with the addition of plasticizer, is not only chemical but also physical, as a modification of the rheological properties has an additional effect on the setting properties.
