# Impact of Industrial Application of Fast Carbonation of Recycled Concrete Aggregates
## 2 Pilot Installations
### Carbonation in a Rotating Drum at the Vicat Crcchy Cement Plant  
The rotating drum constituting the pilot installed in the Vicat plant in Crcchy was already described in a previous paper [10]. The main points are summarized here: it was 11 m long and had a radius of 2 m (Figure 4). The RCA and the CO\({}_{2}\)-enriched cement gas circulated in counterflow. The rotary movement associated with the lifters welded to the tube linings allowed all the surfaces of the aggregates to be brought into contact with the gas. The gas feeding the drum came from a spike in the chimney of the cement plant. The temperature of the gases was between 40 and 60 \({}^{\circ}\)C and had a CO\({}_{2}\) content varying from 11 to 16%. The relative humidity in the drum was 90%. The drum rotated intermittently at 4 rpm for 2 min every 15 min with an optimal residence time of 60 min for 3 t of RCA. The contents was then drained for 10 min at a speed of 10 rpm. The particle size distributions of these materials (sand and gravel) before and after carbonation in the rotating drum are given in Figures 1 and 2. There was little change in the grain size distribution of the 0-4 mm fraction. For the recycled gravel, the enrichment of \begin{table}
\begin{tabular}{c c c c c c} \hline
**Recycled Aggregates** & **Water Absorption (\%)** & **Porosity (\%)** & **Ca(OH)\({}_{2}\) Content (\%)** & **CaCO\({}_{3}\) Content (\%)** & **Soluble Fraction in** \\ \hline RS fraction 1–4 & 7.2 \(\pm\) 0.9 & 15.9 \(\pm\) 1.5 & 0.8 \(\pm\) 0.2 & 32.9 \(\pm\) 0.3 & 34.1 \(\pm\) 5.5 \\ RG & 6.6 \(\pm\) 0.6 & 15.0 \(\pm\) 1.2 & 2.3 \(\pm\) 0.1 & 32.6 \(\pm\) 0.3 & 38.2 \(\pm\) 6.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Initial characterization of recycled aggregates. Figure 3: Phenolphthalein spraying on recycled aggregates RS (**left**) and RG (**right**). the fraction lower than 4 mm was weak (+5%) and could be avoided in a future installation using a screening system at the drum exit. Thus, the carbonation process in the rotating drum used here did not generate excessively finer particles as a consequence of the possible mechanical disintegration of the recycled sand and gravel. Two carbonation campaigns took place in December 2019 and August 2020. In the first campaign, the moisture content of the sand at the inlet was approximately 14.5% and 13.9% after re-carbonation. Similarly, the moisture content of the gravel was 13.6% at the inlet and 12.5% at the outlet. The RCA's water content did not change significantly despite a high relative humidity in the drum. In both cases, these moisture contents were well above the laboratory-determined optimums of 5.8% for sand and 2.6% for gravel [9]. For the second campaign, an attempt to dry via spreading the RCA on the ground in a thin layer for more than 6 months did not bring the water contents to levels comparable to the optimum. This spreading did, however, promote the natural carbonation of the RCA and therefore a lower amount of CO2 was captured. The addition of a drying system to a future industrial installation should therefore be considered. The carbonation intake was measured by comparing the loss on ignition between 550 \({}^{\circ}\)C and 950 \({}^{\circ}\)C of carbonated and non-carbonated RCAs. The test was inspired by the norm EN 196-2 \"Chemical analysis of cement\". The principle is to measure the loss of mass of test samples of a size that can be adapted to the particle size of RCA at different temperature levels imposed in a furnace. A quantity of around 500 g was used. Here, the mass of the samples was measured at 80 \({}^{\circ}\)C, 550 \({}^{\circ}\)C, and 950 \({}^{\circ}\)C. ATG measurements were first used to verify that the temperatures corresponding to the release of water and those corresponding to the release of CO2 were well separated by the 550 \({}^{\circ}\)C level. The ATG measurements were also used to verify the consistency of the values obtained with the loss on ignition measurement.