Mixing of a wet granular medium: Influence of the liquid addition method

Mixing is an important operation in the elaboration of concrete. This process generally involves high energy consumption. The method by which the liquid is added influences this consumption. The liquid can be added progressively with a constant flow, instantaneously at the beginning of the mixing process, or in several stages. Our results show that the power usually consumed with a progressive liquid addition can be reduced by adding liquid in several stages, by modifying the number of additions and by varying the amount of liquid added for each addition. For a final-state mixture, oversaturated in liquid, instantaneous addition provides the lowest energy consumption. However, for a final state that is less saturated, the lowest energy intensity is obtained by adding the liquid in two stages. The first amount corresponds to a saturation rate located in the funicular regime, and is higher than the second amount. Finally, for saturation states located before the capillary regime, a progressive increase in the energy signal is observed after an instantaneous addition of the liquid. Moreover, the capillary state is obtained using an amount of liquid for which this state is not usually reached by progressive addition. This phenomenon is more pronounced where the particle size is reduced and the rotation velocity increased. (C) 2010 Published by Elsevier B.V.