Characterization of the granular-to-fluid state process during mixing by power evolution in a planetary concrete mixer

Adding product into the mixer exerts a strong and rapid impact during concrete mixing. Experimental data obtained from a planetary mixer in a full-scale concrete plant under laboratory conditions show that the state of mixture progress with mixing time is well described by the mixing power evolution. More specifically, a reliable method for detecting the time corresponding to the transformation of a mixture from a cohesive granular material into a granular paste (i.e. the so-called "transition time"), through use of a mixing power measurement, will be presented herein. Moreover, once this transition has been achieved, mixing power consumption will be related to mixture rheology and then to mixer geometry by means of a simplified hypothesis. This equation can also be obtained via a dimensionless analysis. Lastly, it will be shown that mixture behavior beyond the transition point is well fitted by a hyperbolic equation. The corresponding mixing power evolution can then be predicted by the level of power at this transition time. These results are suitable for application to online process monitoring. (c) 2008 Elsevier Ltd. All rights reserved.