## 3 Results and Discussion
### Effect of Carbonization Pressure on CO\({}_{2}\) Sequestration and Rheological Properties of CGBS
#### 3.1.2 Effect of Carbonization Pressure on Rheological Parameters of CGBS  
The rheological properties of a slurry are important indicators for measuring its flow and workability in engineering applications [21]. The relationship between shear stress and shear rate in the slurry system is explored; then, the rheological model is fitted to determine the yield stress and plastic viscosity of the slurry, which can provide a theoretical basis for determining the slurry ratio and selecting parameters in engineering [22; 23; 24]. Figure 6 shows the shear rate-shear stress and apparent viscosity-shear stress curves of CGBS. It can be found that under the same shear stress, the shear stress and apparent viscosity of the slurry increase after CO2 is stored at different pressures. The reason is that the calcium carbonate and hydration products produced after CO2 is stored adhere to the surface of the particles, resulting in poor fluidity of the slurry [25]. Figure 6b shows the curve of apparent viscosity changing with the shear rate. It can be found that with the increase in the shear rate, the apparent viscosity first gradually decreases and then tends to stabilize, indicating that the slurry has shear thinning behavior [26]. Repeated measures ANOVA was conducted on the shear stress of CGBS obtained at different carbonization pressures, and the results of the within-subjects effect tests are shown in Table 3. From Table 3, the F-value of the carbonization pressure factor is 19,385.7, and the \(p\)-value less than 0.001, which shows that there is a significant difference in the shear stress of CGBS corresponding to the different carbonization pressures. Figure 5: CO2 sequestration capacity of CGBS at different pressures. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Source** & **Test Methods** & **F** & \(\mathbf{p}\) \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Carbonization \\ pressure \\ \end{tabular} } & Mauchly’s Test for Sphericity & 19,385.7 & *** \\  & Greenhouse–[PERSON] & 19,385.7 & *** \\  & Huynh–[PERSON] & 19,385.7 & *** \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Within-subjects effect tests. The H-B model is used to fit the experimental data, and the rheological equation is [27]  
\[\tau=\tau_{0}+\eta\gamma^{n} \tag{2}\]  
When n = 1 and \(\tau_{0}\) = 0, it is a Newtonian fluid; when n = 1 and \(\tau_{0}\) > 0, it is a Bingham fluid; when n > 1, it is an expansion fluid; when n < 1, it is a pseudo-plastic fluid. The fitting results are shown in Table 4, and R\({}^{2}\) is greater than 0.99, which indicates a good fitting effect. Figure 6: Rheological parameters of CGBS at different carbonization pressures. (**a**) Shear stress–shear rate. (**b**) Apparent viscosity–shear rate relationship. Yield stress is the maximum stress that prevents the slurry from plastic deformation, and plastic viscosity is a property that hinders the flow of the slurry, reflecting the deformation rate in the slurry system [28; 29]. The relationship between the yield stress and plastic viscosity of CGBS with carbonization pressure is shown in Figure 7. It can be seen that with the increase in carbonization pressure, the yield stress of the slurry increased from 127.16 Pa to 189.49 Pa, an increase of 0.49 times; the plastic viscosity increased from 0.04 Pa\(\cdot\)s to 0.11 Pa\(\cdot\)s, an increase of 1.75 times. It can be seen from the figure that when the carbonization pressure is 0.7 MPa, the yield stress of the slurry increases sharply. This may be caused by the production of a large amount of calcium carbonate, which corresponds to the results of Section 3.1.1 above. As shown in Figure 8, the thixotropy of the slurry is usually represented by the hysteresis loop formed by the shear stress rising and falling cycles, and its integrated area can represent the thixotropic characteristics of the slurry [6; 30]. The magnitude of thixotropy depends on the number of flocculation structures that hinder the flow inside the slurry, which is an important indicator for measuring rheological properties [31].