# Improvement of Recycled Aggregates Properties by Means of CO\({}_{2}\) [PERSON]
## 4 Results and Discussions
### Parametric Study of the Accelerated Carbonation Test on RCAs
#### 4.1.5 Effect of the Temperature on the CO2 Uptake  
Figure 10 shows the effect of the temperature on the CO2 uptake at the same optimum water content (2.8%) that was obtained for OC 12-20 in the accelerated process in a desicator.  
The values for the process in the desiccator at 20 \({}^{\circ}\)C and in the incubator at 20 \({}^{\circ}\)C were similar. The passage from the desiccator to the incubator indicated the repeatability of the carbonation tests within the same temperature range. A maximum CO2 uptake of 12.1 g/kg was obtained at 40 \({}^{\circ}\)C, with an increase of around 34% in the CO2 uptake. An increase in temperature increased the diffusion of CO2 in the pores of the RCA, impacting the diffusion coefficient of the gas through a thermoactivated effect. Conversely, the dissolution of portlandite decreased with the temperature. The fact that the temperature increased the carbonation potential indicates that the diffusion of CO2 is the dominant factor, compared with the dissolution of portlandite, as described by [PERSON] et al. [39]. In their study, [PERSON] et al. determined the effect of the temperature on the depth of carbonation for a CEM I cement paste. An increase in temperature from 20 \({}^{\circ}\)C to 80 \({}^{\circ}\)C increased the depth of carbonation.  
[PERSON] et al. [38] suggested that for a cement paste with a water-to-cement ratio of 0.7 in an SSD state, increasing the temperature to 100 \({}^{\circ}\)C results in an increase in the CO2 uptake. These results are consistent with ours.  
The effect of the water content on the CO2 uptake was studied at 40 \({}^{\circ}\)C. The plot in Figure 11 shows a comparative analysis for OC 12-20 of the effect of the water content on  
Figure 10: Effect of the temperature on CO2 uptake (water content of 2.8%) (one accelerated carbonation test for these RCAs at this same water content).  
the CO\({}_{2}\) uptake between the process of carbonation at 20 \({}^{\circ}\)C in the desiccator and the test at 40 \({}^{\circ}\)C in the incubator.  
As can be seen in Figure 11, the optimum water content was 2.8% for both temperatures, and the maximum CO\({}_{2}\) uptake was 9.6 g/kg in the desiccator and 12.1 g/kg in the incubator. Between 20 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, the temperature sped up carbonation without shifting the optimum water content. The temperature can affect the water content of the RCA. Thus, as [PERSON] et al. [38] concluded in their study, an optimum temperature below 100 \({}^{\circ}\)C can improve the maximum CO\({}_{2}\) uptake, and after this optimum temperature, an excessively high temperature inhibits the carbonation process by complete evaporation of the water in the pores of cement-based materials.  
With regard to the effect of the temperature on the optimum relative humidity, [PERSON] et al. [39] observed, for an ordinary cement paste, that an increase in temperature did not have a significant impact on the optimum relative humidity. The modification in the relative humidity as a result of the temperature had a small impact on carbonation. This conclusion is consistent with our results: the CO\({}_{2}\) uptake for OC 12-20, sourced from ordinary concrete, achieved its maximum value at the same water content, regardless of the temperature.  
In Figure 11, the plot showing the rates of CO\({}_{2}\) uptake at 40\({}^{\circ}\) C exhibits less difference between the highest and lowest values as the water content changes than the plot for 20 \({}^{\circ}\)C. For example, the increase in CO\({}_{2}\) uptake between a water content of 2.1% and 2.8% was about 55% at 20 \({}^{\circ}\)C and about 8% at 40 \({}^{\circ}\)C. At a water content of 5%, the reduction in CO\({}_{2}\) uptake attained 59% at 20 \({}^{\circ}\)C, but it was only about 25% at 40 \({}^{\circ}\)C. The effect of the water content on carbonation was thus most apparent at 20 \({}^{\circ}\)C, because the RCA with this water content dried less at this temperature.