Rheological Measurement of Suspensions Without Slippage: Experimental and Model
Alex Olivas, Michelle A. Helsel, Nicos Martys, Chiara C. Ferraris, William L. George, Raissa Ferron
The conclusion of international studies was that the optimal approach to calibrate concrete rheometers would be to develop a non-Newtonian standard reference material (SRM) that contained inclusions similar in size to aggregates used commonly in concrete. This could be achieved by using a multi-stage approach where each stage corresponds to a different level of complexity of the fluid. The first stage would be to create a paste reference material, as was done in the SRM 2492 . The second stage would be to mimic the mortar phase of a concrete, and SRM 2493  accomplishes that goal. The third, and final stage, is the creation of the concrete SRM 2497, that is currently in development at NIST. During the certification of SRM 2493, it was found that differences in rheometer's geometry affect the accuracy of the rheological measurements. In order to gain fundamental insight about the impact that different rheometer's geometries have on measurements of suspensions, a comprehensive analysis was conducted on three different rheometry families. The analysis included both experimental testing and computer simulation. The comparison between the model and rheological results showed that the increased viscosity due to the addition of the 1 mm beads significantly higher in the Couette model than in the experimental data. It was also determined that some geometries, such as a double spiral, resulted in a higher viscosity than a simple serrated cylinder or vane. This finding led to the inference that slippage should also be considered. Ultimately, this report highlights that industrial rheometers experience slippage issues caused by their rheometry choice and boundary conditions (free surfaces), and discusses the most accurate alternative available for calibrating rheometers.
, Helsel, M.
, Martys, N.
, Ferraris, C.
, George, W.
and Ferron, R.
Rheological Measurement of Suspensions Without Slippage: Experimental and Model, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.TN.1946
(Accessed September 23, 2023)