## 5 Test Materials and Equipment  
### Effects of CO\({}_{2}\) Absorption on the Rheological Properties of Cement Paste  
(1) Rheological curves of cement paste after CO\({}_{2}\) absorption  
(a) Mechanical vibration  
The rheological curves of the cement pastes after absorbing CO\({}_{2}\) under mechanical vibration are shown in Figure 4a. The shear stresses of the net cement pastes in different groups are summarised in Table 4. It can be seen from Figure 4a and Table 4 that the initial shear stress of the net cement paste under mechanical vibration is 7.56 Pa. At shear rates \(<\)120 L/s, the shear stress increases slowly with the shear rate. At shear rates \(>\)120 L/s, the shear thickening increases quickly and the shear stress increases in a straight line. At CO\({}_{2}\) AA = 0.44%, the paste-thickening phenomenon occurs and the initial shear stress increases to 17.5 Pa. With increases in shear rate, the shear stress increases slowly and the rate of increase declines to some extent. At CO\({}_{2}\) AA = 0.88%, the initial shear stress increases further to 25.1 Pa and the trend is very similar to that at 0.44%. At CO\({}_{2}\) AA = 1.32%, the shearing resistance continues to increase, while the initial shear stress increases to 29.6 Pa. Under this circumstance, the rheological curve rises at a slow rate. At CO\({}_{2}\) AA = 1.76%, the thickening phenomenon is more obvious. The trend when the initial shear stress is increased to 46.5 Pa is similar to that at 1.32%. Shear thickening becomes more obvious at CO\({}_{2}\) AA = 2.20%. The initial shear stress reaches 77.6 Pa and the rheological curve has a parabolic shape. (b) Ultrasonic vibration stirring  
The rheological curves of cement pastes after CO\({}_{2}\) absorption under ultrasonic vibration are shown in Figure 4b. The shear stresses of the net cement pastes of all groups are summarised in Table 5. It can be seen from Figure 4b and Table 5 that in the initial stage of the shear rate of net cement pastes under ultrasonic vibration, the shear stress is 12.8 Pa. At shear rates of 0-90 L/s, the shear stress increases slowly. At shear rates \(>\)90 L/s, shear thickening increases in a straight manner. At CO\({}_{2}\) AA = 0.44%, the initial shear stress increases to 40.2 Pa and the paste thickening increases obviously. At shear rates of 0-120 L/s, the shear stress increases slowly. The thickening accelerates at shear rates \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 & 7.56 \(\pm\) 1.35 & 12.3 \(\pm\) 3.45 & 20.1 \(\pm\) 5.96 & 34.5 \(\pm\) 4.53 & 60.1 \(\pm\) 6.75 \\
0.44 & 17.5 \(\pm\) 3.54 & 22.5 \(\pm\) 4.89 & 32.5 \(\pm\) 7.32 & 48.5 \(\pm\) 4.14 & 74 \(\pm\) 7.03 \\
0.88 & 25 \(\pm\) 4.79 & 30 \(\pm\) 6.24 & 38 \(\pm\) 6.46 & 55 \(\pm\) 6.29 & 77.5 \(\pm\) 8.21 \\
1.32 & 29.6 \(\pm\) 5.21 & 35 \(\pm\) 6.35 & 45 \(\pm\) 8.23 & 57 \(\pm\) 6.31 & 74.2 \(\pm\) 8.13 \\
1.76 & 46.5 \(\pm\) 8.18 & 53.6 \(\pm\) 8.2 & 60 \(\pm\) 8.86 & 68.2 \(\pm\) 8.92 & 80 \(\pm\) 8.88 \\
2.20 & 77.6 \(\pm\) 8.06 & 94.1 \(\pm\) 8.12 & 107.5 \(\pm\) 10.11 & 117.5 \(\pm\) 10.36 & 112.3 \(\pm\) 10.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Shear stresses of cement paste after CO\({}_{2}\) absorption under mechanical agitation (Pa). Figure 4: Rheological curves of cement pastes after CO\({}_{2}\) absorption under (**a**) mechanical and (**b**) ultrasonic agitation. >120 L/s, resulting in a linear increase in shear stress. At CO\({}_{2}\) AA = 0.88%, the initial shear stress increases to 55.1 Pa and the curve is similar to that at 0.44%. When the CO\({}_{2}\) AA is increased to 1.32%, the initial shear stress increases to 69.1 Pa. Under this circumstance, the rheological curves increase at a steady rate without obvious growth. At CO\({}_{2}\) AA = 1.76%, the thickening phenomenon is more significant and the initial shear rate increases to 105 Pa. At CO\({}_{2}\) AA = 2.20%, shear thickening continues to increase and the rheological curves also increase slowly.