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 Behavior. © 2012 RILEM

Challenges Encountered During Measuring Rheological Properties Of Mortar And Concrete

Performing rheological measurements of mortar and concrete is not a straightforward task as many challenges can alter or invalidate the outcome of a rheological experiment. This chapter summarizes the most common challenges for flow curve measurements, which are the type of flow behavior, achieving the reference state, plug flow, shear and gravity-induced particle migration, hydrodynamic pressure, heat of vaporization, correct choice of rheological transformation equations and model, air, and wall effects. Some of these challenges are also detailed separately for static yield stress measurements. For each challenge, the physical background, consequence on the measurement outcome and any detection or prevention strategy are described. To adequately perform rheological measurements, all challenges need to be addressed, which can be a daunting task as some prevention strategies can increase the risk for a different challenge to affect the measurement. Developing a suitable measuring and analysis procedure is a critical task to the success of rheological measurements of mortar and concrete

Avoiding Inaccurate Interpretations of Rheological Measurements for Cement-Based Materials

Rheology is a high quality tool to evaluate the effect of variations in constituent materials and mixture proportions on fresh properties of cement-based materials. However, interpreting rheological measurements is relatively complicated, and some pitfalls can lead to wrong conclusions. This paper offers a review of measuring devices and transformation equations used to express rheological parameters in fundamental units. The paper also discusses some of the major issues that can lead to errors during the interpretation of rheological measurements. Although the Bingham model is mostly used for cement-based materials, some non-linearity has been observed, necessitating the selection of an alternative rheological model, which could influence the rheological parameters. Other measurement errors related to thixotropic and structural breakdown, plug flow and particle migration are also demonstrated. The paper also discusses the challenges of using numerical simulations to derive rheological parameters for complicated rheometers or industrial devices, such as a concrete truck

Influence of plug flow when testing shear thickening powder type self-compacting concrete in a wide-gap concentric cylinder rheometer

When testing powder type self-compacting concrete (SCC) in a wide-gap concentric cylinder rheometer, sometimes a plug state arises, introducing an error in the obtained rheological flow parameters. In this paper, the classification of plug state inside a wide-gap concentric cylinder rheometer is illustrated for a nonlinear (Herschel-Bulkley) flow behaviour, which is not seldom observed in the case of powder type SCC. For a linear (Bingham) flow behaviour, the classification of plug inside a concentric cylinder rheometer is already well described in literature. The applied methodology is adapted to the nonlinear case. With a plug state, a solid state arises inside the sheared test material, so that it is rotating as a rigid body. When applying a stepwise decreasing rotational velocity sequence, plug will begin at the outer, rotating cylinder and propagates towards the inner, stationary cylinder as the velocity of the outer cylinder will further decrease. This means that, with a plug state and assuming no slippage in the transition zone from the viscoplastic to the solid state, the outer boundary condition of the integration equations of the Couette inverse problem solution must be corrected to the rigid body velocity at the boundary between the viscoplastic and the solid state (i.e. the plug radius R_p). For each rotational velocity of the outer cylinder N_p, the corresponding plug radius R_p can be calculated. However, these calculations are based on the assumption that the calculated rheological parameters are correct to begin with. Nevertheless, it was found that even if plug was occurring in some of the measurements when testing powder type SCC, it did not introduce a large error to the rheological parameters. In fact, the error generated by plug flow on the rheological flow parameters always remained within their 95% confidence intervals in case of the shear thickening powder type SCC mixes tested.status: publishe