Influence of plug flow when testing shear thickening powder type self-compacting concrete in a wide-gap concentric cylinder rheometer
Author(s): G. Heirman, D. Van Gemert, L. Vandewalle, E. Toorman, J.E. Wallevik, O.H. Wallevik
Paper category: Symposium
Book title: 3rd International RILEM Symposium on Rheology of Cement Suspensions such as Fresh Concrete
Editor(s): O.H. Wallevik, S. Kubens, S. Oesterheld
Pages: 283- 290
Total Pages: 8
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, 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 Rp).
For each rotational velocity of the outer cylinder Np, the corresponding plus radius Rp 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 occuring 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.
Online publication: 2009
Publication Type: full_text
Public price (Euros): 0.00