*3.1. Rheological Decsription of Tested Hydromixture*

The flow curves of hydromixtures with mass concentrations of 21.30%, 28.14%, 35.00%, 42.75% and 50.00% without addition (denoted as 'pure') and with deflocculant addition (denoted as '+DFL') are presented in Figure 3. The rheometric measurements were compared with the results calculated for the Bingham plastics model where the solid line indicates the fit of the rheological model to the experimental data. The shape of the flow curves indicates that the tested hydromixtures belong to the group of non-Newtonian, pseudo-plastic fluids.

Non-Newtonian fluids are generally highly viscous systems throughout the technically important range of the shear rate and are very difficult to transport in a pipeline.

**Figure 3.** The experimental flow curves of tested hydromixtures with a mass concentration of: (**a**) 21.30%; (**b**) 28.14%; (**c**) 35.00%; (**d**) 42.75%; and (**e**) 50.00%.

The flow curves of hydromixtures were described by the Bingham model as follows:

$$
\pi = \pi\_y + \eta\_p \cdot y \tag{1}
$$

where *η<sup>p</sup>* is plastic viscosity and *τ*<sup>y</sup> is a yield stress.

The rheological properties of the tested hydromixtures can be described by the rheological Bingham plastics model in the shear rate range from about 8–10 s−<sup>1</sup> to 100 s<sup>−</sup>1. This range of shear rate occurs in the hydromixture flow in the analyzed pipeline.

In Table 2, the parameters of analyzed hydromixtures with deflocculant (+DFL) and without the addition of deflocculant (pure), such as density (ρm), yield stress value (τy), plastic viscosity (*ηp*) and the coefficient value of fitting the mathematical model to the experimental data (R2) are shown.


**Table 2.** Rheological parameters of the tested hydromixtures.
