# Ultrasonic Non-Destructive Testing of Accelerated Carbonation Cured-Eco-Bricks
## 4 Discussion of Results
### Co\({}_{2}\) Uptake  
The mass-gain method was used to calculate the CO\({}_{2}\) uptake within the samples. This method focuses on determining the CO\({}_{2}\) uptake of the entire sample as an average and providing an estimation of the CO\({}_{2}\) uptake by comparing the mass of the sample before and after carbonation. Equations (3) and (4) were used to compute the CO\({}_{2}\) uptake in all the samples.  
Free water is necessary to facilitate the dissolution of CO\({}_{2}\); however, excess of it obstructs its penetration through the available porous path. Hence, pre-conditioning in a dry environment (RH = 55 \(\pm\) 10%, T = 22 \(\pm\) 3 \({}^{\circ}\)C) to create more capillary spaces for CO\({}_{2}\) sequestration into the samples for durations not exceeding 18 h is recommended by research [49; 55].  
Figure 15 shows the carbon uptake values for the 0% TRC samples considering the 1.2 and 1.6 MPa compression pressures applied to each layer. Overall, the samples compressed with 1.6 MPa had better carbon uptake when compared to samples compressed with 1.2 MPa. It can be assumed that the 1.2 MPa compression was insufficient to produce good contact within the particles in the matrix. Hence, the lower carbon uptake resulted in the low compressive strengths obtained. Figure 16 shows the carbon uptake of the 0, 5, and 10% TRC samples considering 1.9 MPa compression. From the results, the 1.9 MPa compression was sufficient for effective CO\({}_{2}\) sequestration, as recommended by [PERSON] et al. [68]; hence, higher strengths were recorded.  
Based on the information gathered from Figures 15 and 16, the total CO\({}_{2}\) uptake of the samples produced in this study was about 15,912 g (15.9 kg), which is in line with studies carried out by [PERSON] et al. [33] and [PERSON] et al. [65].  
With the increasing awareness of achieving a net zero environment, a balance between the carbon dioxide emissions generated from construction activities and the amount removed through ACC is necessary. Hence, more research into ACC is encouraged, especially at the industrial level, to make the remarkable difference desired in climate change. Additionally, if brick-making factories can be set-up close to CO\({}_{2}\) emission sources, the CO\({}_{2}\) gas can easily be captured and utilized for curing. This will also allow costs to be saved for the long-distance transportation of the gas whereby leak risks are averted. Lastly, government and environmental agencies must establish incentives to motivate brick-making industries to accept and endorse the Advanced Carbon Technology (ACT). Incentives such as carbon capping, trading, and policies associated with taxation should be implemented to feature ACC as beneficial, thereby leading to a significant rise in annual CO\({}_{2}\) sequestration [12].  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Map Sum** & \multicolumn{2}{c}{**WC Samples**} & \multicolumn{2}{c}{**NWC Samples**} \\
**Spectrum** & **Wt \%** & **Wt \% Sigma** & **Wt \%** & **Wt \% Sigma** \\ \hline C & 13.77 & 0.07 & 17.69 & 0.10 \\ O & 53.28 & 0.05 & 49.30 & 0.07 \\ Na & 0.06 & 0.01 & 0.49 & 0.01 \\ Mg & 1.41 & 0.01 & 1.79 & 0.01 \\ Al & 2.95 & 0.01 & 11.73 & 0.02 \\ Si & 5.99 & 0.01 & 0.04 & 0.00 \\ P & 0.05 & 0.00 & 0.53 & 0.01 \\ S & 1.71 & 0.01 & 0.23 & 0.01 \\ K & 0.12 & 0.00 & 17.39 & 0.03 \\ Ca & 20.00 & 0.03 & 0.09 & 0.01 \\ Ti & 0.13 & 0.01 & 0.65 & 0.01 \\ Fe & 0.53 & 0.01 & 0.08 & 0.01 \\ Total & 100 & & 100 & \\ \hline \end{tabular}
\end{table}
Table 5: Elemental composition of 5% TRC (WC and NWC) samples.