Extension of the Reiner-Riwlin equation to determine modified Bingham parameters measured in coaxial cylinders rheometers

The determination of the exact rheological properties, in fundamental units, of cementitious materials has become gradually a necessary step in the domain of concrete science. Several types of rheometers and their corresponding transformation equations are described in the literature. In this paper, the Reiner-Riwlin transformation equation, valid for coaxial cylinders rheometers, is developed for the modified Bingham model, which is an extension of the Bingham model with a second order term in the shear rate. The established transformation is shown to be compatible with the Reiner-Riwlin equation for the Bingham and Herschel-Bulkley models. Its validation is further proven by means of numerical simulations applied on experimental data. The yield stress values for the three rheological models (applied on the same experimental data) are compared with the yield stress calculated by means of slump flow values. Results showed that the modified Bingham model results in the most stable yield stress values, which are independent of the non-linear behaviour.