Flow properties of freshly prepared ettringite suspensions in water at 25 °C

The rheology of a complex, heterogeneous mineral colloid was rationalised using models devised for model rod systems. Mixing a calcium hydroxide slurry with an aluminium sulphate solution produces a suspension of rod-shaped ettringite particles. Ettringite rod suspensions exhibit non-Newtonian flow behaviour, which depends on the shape of the particles, their size distribution, concentration and surface properties as well as the suspension medium characteristics. We have measured the shear viscosity of suspensions of ettringite rods with a median aspect ratio, ri∼ri∼ 8, at 25 °C as a function of particle volume fraction, ϕ, in the range 0.0001–0.08. It was found that the viscosity of the suspensions increased with ϕ  , and showed a marked change of slope at ϕ∼0.01ϕ∼0.01, which we identified as the minimum overlap concentration ϕ*ϕ*. Above ϕ*ϕ*, the system is in the semi-dilute regime. At ϕ>ϕ*ϕ>ϕ*, when Perot>1Perot>1, hydrodynamic interactions between rods become increasingly significant, and we observe shear-thinning behaviour. The high effective hydrodynamic volume of rotating rods, resulting in much lower values of the maximum packing fraction, ϕcϕc, than for spheres, dominates the rheological behaviour of ettringite suspensions.

The ettringite particles were well-characterized by electron microscopy so that the effect of shape and size on the shear rheology was successfully studied.Figure optionsDownload as PowerPoint slide