Rheology of cement grouts: On the critical shear rate and no-slip regime in the Couette geometry

The rheological properties of cement grouts play a key role in determining the final spread in grouted rock formations. In terms of flow properties, cement grouts are known to be complex thixotropic fluids, but their steady flow behavior is often described by the simple Bingham constitutive law. Due to their time dependent nature, the flow curves of cement grouts have been known to exhibit an unstable non-monotonic region, characterized by a negative slope below a critical shear rate. Within this paper, we focus on how this unstable region that is dominated by flow localization is affected by rheometer geometry and flow sweep measurement interval. We carried out controlled shear rate (CSR) flow sweeps on typical micro-cement grouts within different Couette geometries. Lastly, we discuss the effects of geometry and measurement interval on the resulting flow curves, with a focus on the critical shear rate that separates homogenous from non-homogeneous unstable flow.