Validation of BTRHEOM, the new rheometer for soft-to-fluid concrete

An investigation was performed on the objectivity of a new rheometer for soft-to-fluid concrete, called BTRHEOM. Firstly, the influence of concrete wall friction on the measurement of the Bingham constants was studied by finite-element simulations. It has been shown that this influence is limited, in particular on the measurement of shear yield stress. However, the quality of the estimate of plastic viscosity can be improved by applying a reduction of 10% to the bulk value. Secondly, a series of comparative tests was conducted with two other rheometers with different operating principles. The comparison with the intrinsic values as measured by a big coaxial-cylinder viscometer, the CEMAGREF-IMG rheometer, showed a satisfactory result for yield stress, but not for plastic viscosity, probably due to the segregation of the coarse aggregate in the CEMAGREF-IMG rheometer. For two concretes without segregation, the two rheometers yielded the same values. Another comparison with the LAFARGE rheometer (a modified version of Tattersall's two-point test) showed a good correlation between the measurements with the two instruments. Finally, the slump test was modelled by a simple numerical approach, from which a linear relation between slump and yield stress was derived. This relationship agrees with the experimental results.