Paper Number
SC16 

Session
Suspensions, Colloids and Granular Media

Title
Granular physics in yield-stress fluids: Carbopol suspensions versus wet concrete

Presentation Date and Time
February 14, 2017 (Tuesday) 10:25

Track / Room
Track 1 / Audubon B

Authors (Click on name to view author profile)

1. Koch, Jeremy A. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)
2. Castaneda, Daniel I. (Angelo State University, Department of Engineering)
3. Lange, David A. (University of Illinois at Urbana-Champaign, Civil and Environmental Engineering)
4. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Jeremy A. Koch¹, Daniel I. Castaneda², David A. Lange³, and Randy H. Ewoldt^1
1Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL; ²Department of Engineering, Angelo State University, Angelo, TX; ³Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL

Speaker / Presenter 
Koch, Jeremy A.

Text of Abstract
Wet concrete is often cited as an example of a yield-stress fluid, and modeled as a Bingham or Herschel-Bulkley material. We show this is an incomplete understanding to rationalize simple but important flow phenomena in wet concrete. Specifically, we will describe how granular physics must be considered. As a motivating phenomenon, we consider the practice of vibrating wet concrete during placement to induce flow and remove air voids. A simple yield-stress fluid (an aqueous polymer microgel particle suspension, Carbopol) cannot recreate the phenomenon, falsifying the hypothesis that traditional yield-stress fluid models embody the key physics. Instead, we show that a granular hard-particle suspension (millimetric glass beads in silicone oil) succeeds in recreating the phenomenon. We use vibration-dependent and depth-dependent shear rheology to further show that concrete and mortar display noticeable granular physics, as indicated by (i) vibration-induced loss of the yield stress, consistent with the granular suspension model of Hanotin et al. (2015), and (ii) depth-dependent flow resistance. These are also recreated by the glass beads in oil, but not the Carbopol suspension. A dimensionless group rationalizes why Carbopol suspensions (whose microstructure is indeed ‘granular’) do not have the granular signatures of depth- and vibration-dependent rheology. These results have implications for understanding the unseen phenomenon of air bubbles rising in concrete, but moreover, the depth- and vibration-dependent rheological signatures add a new dimension to categorizing the vast realm of yield-stress fluids more generally.

Reference: Hanotin, C., S. Kiesgen de Richter, L. J. Michot, and Ph. Marchal, "Viscoelasticity of vibrated granular suspensions," Journal of Rheology (2015).