## 5 Test Materials and Equipment
### Effects of CO\({}_{2}\) Absorption on the Rheological Properties of Cement Paste
(Note: N = 10, mean \(\pm\) S.D. N presents number of samples). (c) Analysis of shear stress in cement pastes after CO\({}_{2}\) absorption  
Firstly, the shear stresses of cement pastes before and after CO\({}_{2}\) absorption under mechanical vibration were compared. At CO\({}_{2}\) AA = 0.44%, shear thickening was obvious at shear rates of 30 L/s, 60 L/s, 90 L/s, 120 L/s and 150 L/s. The shear stresses of cement paste were 131.5%, 82.9%, 61.7%, 40.6% and 23.6% higher before CO\({}_{2}\) absorption than afterwards. Moreover, the shear thickening of cement paste became more obvious with increases in CO\({}_{2}\) AA and was accompanied by continuous increases in shear stress. Second, compared with mechanical agitation, the shear stresses of cement slurries without CO\({}_{2}\) input under ultrasonic agitation were 69%, 83%, 87%, 66% and 53% higher at shear rates of 30 L/s, 60 L/s, 90 L/s, 120 L/s and 150 L/s, respectively. At CO\({}_{2}\) AA = 0.44%, the shear stresses of the cement slurry were 128.6%, 105.3%, 69%, 59.2% and 39.5% higher, respectively. At CO\({}_{2}\) AA = 0.88%, the shear stresses of the cement pastes under ultrasonic agitation were 120%, 108.3%, 94.7%, 68.2% and 60.6% higher compared to those under mechanical agitation. At CO\({}_{2}\) AA = 1.32%, the shear stresses of cement pastes under ultrasonic agitation were increased by 133.4%, 120.6%, 88.9%, 70.2% and 61.2%, respectively. At CO\({}_{2}\) AA = 1.76%, the shear stresses of cement pastes under ultrasonic agitation were increased by 125.8%, 108%, 103.5%, 98.2% and 87.5%, respectively. At CO\({}_{2}\) AA = 2.20%, the shear stresses of cement pastes under ultrasonic agitation were increased by 80.9%, 64.2%, 55.8%, 51.1% and 66.9%, respectively. Based on the above comparison, the shear stress of cement paste was significantly increased by CO\({}_{2}\) absorption under mechanical stirring. Meanwhile, the shear stress was higher after ultrasonic vibration than mechanical vibration, indicating that ultrasonic vibration can more effectively increase the shear stress of carbonised cement paste. Comparison of the rheological curves in Figures 4 and 5 shows that after CO\({}_{2}\) absorption under both types of vibration, the cement pastes generally showed positive relationships of shear stress with CO\({}_{2}\) AA and shear rate. All curves increase at low rates and some present linear trends after reaching a certain shear rate. Although there are similarities between the curves, they change differently. \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 & 12.8 \(\pm\) 3.4 & 22.5 \(\pm\) 3.1 & 37.5 \(\pm\) 6.4 & 57.2 \(\pm\) 6.8 & 91.8 \(\pm\) 7.2 \\
0.44 & 40 \(\pm\) 5.7 & 46.2 \(\pm\) 4.0 & 55 \(\pm\) 7.2 & 77.2 \(\pm\) 7.2 & 103.2 \(\pm\) 8.2 \\
0.88 & 55 \(\pm\) 5.2 & 62.5 \(\pm\) 7.6 & 74 \(\pm\) 8.2 & 92.5 \(\pm\) 8.1 & 124.5 \(\pm\) 8.1 \\
1.32 & 69.1 \(\pm\) 6.0 & 77.2 \(\pm\) 8.3 & 85 \(\pm\) 8.1 & 97.4 \(\pm\) 8.3 & 119.6 \(\pm\) 9.2 \\
1.76 & 105 \(\pm\) 9.8 & 111.5 \(\pm\) 9.2 & 122.1 \(\pm\) 9.1 & 135.2 \(\pm\) 10.1 & 150. \(\pm\) 10.2 \\
2.20 & 140.4 \(\pm\) 12.6 & 154.5 \(\pm\) 11.4 & 167.5 \(\pm\) 12.9 & 177.5 \(\pm\) 12.1 & 187.4 \(\pm\) 13.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Shear stresses of cement pastes after CO\({}_{2}\) absorption under ultrasonic agitation (Pa).