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Title: Detailed Analysis and Interpretation of Flow Curves from Round-Robin Tests (RRT) on Concrete Rheometers

Author(s): Feys

Publication: Web Session

Volume: ws_S22_Feys2.pdf

Issue:

Appears on pages(s):

Keywords:

DOI:

Date: 3/28/2022

Abstract:
Within the RRT on concrete rheometers, several devices and geometries were employed to measure flow curves of purposefully designed concrete and mortar mixtures. These include the ICAR, eBT-V, Viskomat XL, RheoCAD with vane and helix, as well as the 4SCC Rheometer with mixing and modified Tattersall Mk-II tools. All rheometers with vane geometries allow for the calculation of fundamental rheological properties, while the others only deliver relative units. The presentation at hand includes an analysis of raw data meant to quantify yield stress and plastic viscosity values for the vane configuration rheometers. The analysis includes the concept of baseline values for yield stress and viscosity, based on an extensive weighted average procedure. A comparison between each vane rheometer and corresponding baseline values shows significantly high correlation coefficients above 0.80 for the yield stress and above 0.95 for viscosity. Discrepancies in values between rheometers are attributed to the differences in calibration or assessment of torque and rotational velocity. The deviations of each value for the rheometers compared to the average relationship with the baseline can be traced back to concrete composition and to a lesser extent to the rheometer they have been measured in. For high viscosity values, rheometers tend to show higher spread in the viscosity data, and yield stress seems more sensitive to an increased coarse aggregate content and an increased yield stress-to-viscosity ratio. As a consequence, when extrapolating the findings to conventional vibrated concretes, measures on (dynamic) yield stress is expected to induce even higher sensitivity and noise into the data. Lastly, the team has discovered that extending the duration of the measuring procedure with approximately a factor of 2.5 has serious negative consequences on measuring concrete, but not for measuring mortar.