# Improvement of Recycled Aggregates Properties by Means of CO\({}_{2}\) [PERSON]
## 4 Results and Discussions
### Impact of Accelerated Carbonation on the Properties of RCAs
#### 4.2.1 Impact of Natural and Accelerated Carbonation on the Water Absorption Coefficient  
Figure 13 shows the effect of carbonation on the WAC. For RB 1-4, the WAC of the non-carbonated RCA (RB 1-4 (reference)) was equal to 8.9% [22]. After natural carbonation from 6 years of storage, the WAC of the NC-RB 1-4 decreased by 48% compared with the reference. After accelerated carbonation with a CO2 uptake of 8.9 g/kg, the WAC of RB 1-4 decreased by 69% compared with the reference. Moreover, for RB 1-4 C, because of accelerated carbonation with a CO2 uptake of 17.3 g/kg (at 100% CO2), the WAC of RB 1-4 C decreased by 39% compared with NC-RB 1-4. This decrease in the WAC was due to the clogging of the pores by calcium carbonates that were formed during accelerated carbonation. In the literature, [PERSON] et al. and [PERSON] also observed a reduction in the WAC after accelerated carbonation [51; 52]. Natural carbonation had an effect on the WAC; 6 years of storage reduced the WAC to around 50%. This process also had an effect on accelerated carbonation and the WAC. Indeed, a CO2 uptake of 8.6 g/kg for NC-RB 1-4 during natural carbonation led to a 39% reduction in the WAC after accelerated carbonation. However, the greatest effect of \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **OC 1-4** & **OC 12-20** & **HPC 1-4** & **HPC 12-20** \\ \hline CO2 uptake (g/kg) & 21.8 & 9.6 & 11.4 & 6.5 \\ SFSA (\%) & 29.8 \(\pm\) 4.0 & 24.8 \(\pm\) 4.6 & 27.1 \(\pm\) 6.9 & 28.8 \(\pm\) 9.7 \\ Portlandite rate (\%) & 1.3 \(\pm\) 0.1 & 1.7 \(\pm\) 0.1 & 1.2 \(\pm\) 0.1 & 1.4 \(\pm\) 0.1 \\ CaCO3 rate (\%) & 67.9 \(\pm\) 0.5 & 67.4 \(\pm\) 0.3 & 64.9 \(\pm\) 0.3 & 64.0 \(\pm\) 0.1 \\ Porosity (\%) & 7.6 & 6.3 & 7.2 & 8.4 \\ WAC (\%) & 2.9 & 3.4 & 2.9 & 3.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Properties of carbonated RCAs (RCAs from laboratory concretes). Figure 13: Effect of carbonation (natural and accelerated) on the WAC (one WAC measurement for each RCA after carbonation). carbonation on the WAC was attributed to accelerated carbonation, with a reduction of up to 69%. On the other hand, in the case of RB 1-4 C, which had undergone partial natural carbonation and was then subjected to the accelerated carbonation process (17.3 g/kg CO\({}_{2}\) uptake), accelerated carbonation improved water absorption, with a decrease in the WAC of 39%. This was equivalent to the decrease in the WAC after 6 years of natural carbonation. In conclusion, as shown in Figure 13, natural and accelerated carbonation improved the water absorption of the RCAs by decreasing the WAC. However, accelerated carbonation decreased the WAC more. The effect of natural carbonation combined with accelerated carbonation was substantially the same as that of accelerated carbonation on its own. For CB 1-4, after accelerated carbonation with storage of 49.9 g/kg of CO\({}_{2}\), the WAC was equal to 3.0%. With respect to the reference, the decrease in the WAC was around 52%. The correlation between the decrease in the WAC and the CO\({}_{2}\) uptake for RCAs sourced from demolition concretes is presented in Figure 14.  
For RCAs obtained from laboratory concretes, the trend was similar (Figure 15). This shows that carbonation has a repeatable effect on the WAC, regardless of the type and fraction of the RCA, as a result of the formation of calcium carbonates in the pores in the RCA. The decrease in the WAC was also correlated with the formation of calcium carbonates during carbonation tests (Figure 16). Due to the effect of accelerated carbonation and a CO\({}_{2}\) uptake of 8.6 g/kg (Figure 13), the WAC of RB 1-4 decreased by 39% compared with NC-RB 1-4 because of the formation of 1.7% CaCO\({}_{3}\). In the same way, for RB 1-4 C, the CO\({}_{2}\) uptake was equal to 12.6 g/kg (with 15% CO\({}_{2}\)), and the decrease in the WAC was around 31% because of the formation of 15% CaCO\({}_{3}\) due to accelerated carbonation.