# Pathway to Carbon Neutrality in the Cement Industry: CO2
## 3 Materials and Methods  
### Materials  
According to the legislation of the European Union concerning CDW management, CDW must be sent to recycling plants that are responsible for its treatment (Waste Framework Directive 2008/98/EC). In this study, 7 types of recycled aggregates (RAs) were collected directly from recycling plants, in situ demolitions and concrete industry wastes (Table 1). Concrete aggregates, with well-known compositions, were also produced in a laboratory to be compared with other recycled aggregates. The selected RAs were divided into the following categories: mixed recycled aggregates (based on a miscellany of rubble); recycled concrete aggregates (mainly composed of concrete and mortar waste); RAs from concrete samples produced in a laboratory (control concrete, CA-L). In CA-L, the binder used was a cement type CEM II/A-L 42.5 R according to the EN 197-1 [54], having around 15% limestone filer. The concrete specimens produced with this cement were kept underwater to prevent natural carbonation. At about 3 months of age, the specimens were dried at 40 \({}^{\circ}\)C until constant mass; afterwards, the samples were grinded and sieved in order to produce a representative sample based on a granulometric curve to be analysed before and after CO\({}_{2}\) exposure. The constituents of RAs were classified based on the European standards EN 933-11 [55] and EN 13242 [56]. The procedure involves an initial separation of the floating parcels from the non-floating ones. Once the non-floating portion is obtained, the remaining portion is separated and classified into various constituents as stated in the standards. The classification of RAs according to EN 933-11 [55] is also presented in Table 2. The CA-L is composed of 260 kg/m\({}^{3}\) cement, 50 kg/m\({}^{3}\) limestone filler and 1900 kg of coarse and fine aggregate. The cementitious fraction (Rc--concrete, concrete products, mortar and concrete masonry units) is the major component of the recycled aggregates, with emphasis on RCAs. This fraction has a direct influence on the carbonation effectiveness of the RAs from CDW. Therefore, it is expected that the greater the amount of Rc, the higher the carbonation potential of the sample. However, this potential is also affected by other factors, such as age, exposure and type of binder, which can reduce the fraction of carbonatable compounds in Rc. The recycled aggregates collected in recycling plants were in stockpiles exposed to the air, and it is not known where the material came from. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Aggregate Type** & **Designation** & **Origin (Collected at)** & **Location** \\ \hline \multirow{3}{*}{Mixed recycled aggregates (MRAs)} & MRA-RP1 & Recycling plant 1 & Pero Pinheiro, Portugal \\ \cline{2-3}  & MRA-RP2 & Recycling plant 2 & Figueira da Foz, Portugal \\ \cline{2-3}  & MRA-RP3 & Recycling plant 3 & Seixal, Portugal \\ \hline \multirow{3}{*}{Recycled concrete aggregates (RCAs)} & RCA-I81 & Concrete producer & Alhanda, Portugal \\ \cline{2-3}  & RCA-IS1 & Demolished in situ & Settibal, Portugal \\ \cline{2-3}  & RCA-RP1 & Recycling plant 1 & Pero Pinheiro, Portugal \\ \cline{2-3}  & RCA-RP2 & Recycling plant 4 & Bucelas, Portugal \\ \hline Control concrete aggregates (CA) & CA-L & Concrete produced in laboratory & Lisbon, Portugal \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Recycled aggregates studied.