Rheological behavior of cement pastes from MRI velocimetry

From MRI measurements, it is shown that in a flowing cement paste the thixotropic effects dominate over short time scales, while aging effects become significant over larger timescales. The steady state behavior, defined as flow properties in the intermediate period, exhibits a yielding behavior which differs from the prediction of usual yield stress models. The transition from the solid to the liquid regime is abrupt: the shear rate changes suddenly from zero to a finite value (critical shear rate) when the shear stress overcomes a critical value. These critical shear rates and shear stresses are independent of the flow conditions so that they may be considered as intrinsic material parameters. It was also shown that these results are consistent with usual macroscopic observations from conventional rheometry. (c) 2005 Elsevier Ltd. All rights reserved.