## 5 Test Materials and Equipment
### Comparative Analysis of the Rheological Properties of Carbonated Cement Paste  
(1) Comparative analysis of viscosity Viscosity curves of net cement pastes after carbonation under mechanical and ultrasonic vibration are shown in Figure 8a,b. Tables 9 and 10 show the viscosity values more clearly. The viscosity values were estimated for cement-paste shear rates of 30 L/s, 60 L/s, 90 L/s, 120 L/s and 150 L/s and CO\({}_{2}\) AA values of 0%, 0.44%, 0.88%, 1.32%  
AA = 2.20%, the viscosities under ultrasonic vibration were 80.9%, 64.2%, 55.8%, 141.5% and 136.5% higher. Comparison of the two vibration modes shows that the viscosity after ultrasonic vibration is higher than that under mechanical vibration, indicating that ultrasonic vibration can effectively increase the viscosity of fresh cement paste. Moreover, the viscosity of cement paste increases gradually with increases in CO\({}_{2}\) AA under both vibration modes. At CO\({}_{2}\) AA = 0.44%, the viscosity changes the least with increases in shear rate. At CO\({}_{2}\) AA = 0.88%, 1.32% and 1.76%, the viscosity presents similar variations but increases to some extent. At CO\({}_{2}\) AA = 2.20%, the viscosity value changes the most. (2) Comparative analysis of yielding stress  
The yield stress of cement paste carbonated under ultrasonic vibration, which was derived from the ultrasonic rheological model, is shown in Figure 9. Mechanical vibration was used as the control group. The yield stress under mechanical vibration was derived from the H-B model. It can be seen from Figure 9 that CO\({}_{2}\) AA = 0%, 0.44%, 0.88%, 1.32%, 1.76% and 2.20%. At these values, the yield stresses of cement paste under ultrasonic vibration were 12.2%, 32.7%, 45.1%, 46.3%, 26.5% and 31.3%, respectively, which were higher than those under mechanical vibration. Under ultrasonic vibration, the yield stresses were 247%, 35.4%, 17.1%, 26.4% and 31.3% higher, respectively. According to the measured data, ultrasonic vibration can effectively improve the yield stress of carbonated cement paste. The yield stress of carbonated cement paste is positively related to CO\({}_{2}\) AA. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**CO\({}_{2}\) AA/\%** & **30 L/s** & **60 L/s** & **90 L/s** & **120 L/s** & **150 L/s** \\ \hline
0 & 0.59 \(\pm\) 0.15 & 0.36 \(\pm\) 0.11 & 0.41 \(\pm\) 0.15 & 0.42 \(\pm\) 0.18 & 0.58 \(\pm\) 0.12 \\
0.44 & 0.61 \(\pm\) 0.16 & 0.58 \(\pm\) 0.12 & 0.54 \(\pm\) 0.12 & 0.57 \(\pm\) 0.12 & 0.92 \(\pm\) 0.34 \\
0.88 & 1.63 \(\pm\) 0.47 & 1.02 \(\pm\) 0.35 & 0.81 \(\pm\) 0.23 & 0.62 \(\pm\) 0.12 & 0.6 \(\pm\) 0.22 \\
1.32 & 2.2 \(\pm\) 0.51 & 1.32 \(\pm\) 0.35 & 0.93 \(\pm\) 0.34 & 0.74 \(\pm\) 0.23 & 0.62 \(\pm\) 0.22 \\
1.76 & 2.22 \(\pm\) 0.52 & 1.2 \(\pm\) 0.55 & 0.83 \(\pm\) 0.33 & 1.57 \(\pm\) 0.66 & 1.49 \(\pm\) 0.66 \\
2.20 & 4.71 \(\pm\) 0.82 & 2.62 \(\pm\) 0.82 & 2.15 \(\pm\) 0.81 & 1.55 \(\pm\) 0.56 & 1.38 \(\pm\) 0.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Viscosity values of net cement pastes carbonated under ultrasonic vibration (Pa-s). Figure 8: Viscosity curves of cement paste carbonated by (a) mechanical and (b) ultrasonic vibration. The shear stresses of fresh cement pastes before and after adding water reducer are compared next. At shear rates of 30 L/s, 60 L/s, 90 L/s, 120 L/s and 150 L/s and before carbonation, the shear stresses of fresh cement pastes with added water reducer were 92.2%, 86.2%, 81.9%, 76.4% and 71.5% lower than those without water reducer. At CO\({}_{2}\) AA = 0.44%, the shear stresses of cement pastes were 79.8%, 73.6%, 55.6%, 50.6% and 83.3% lower, respectively. At CO\({}_{2}\) AA = 0.88%, the shear stresses of cement pastes were 70.5%, 67.2%, 53.6%, 41.5% and 32.6% lower, respectively. At CO\({}_{2}\) AA = 1.32%, the shear stresses were 61.2%, 54.3%, 47.9%, 39.1% and 36.9% lower, respectively. At CO\({}_{2}\) AA = 1.76%, the shear stresses were 52.5%, 47.9%, 46.6%, 44.4% and 42.4% lower. At CO\({}_{2}\) AA = 2.20%, the shear stresses were 48.6%, 45.6%, 40.3%, 37.6% and 37% lower, respectively.