## 2 Experimental Programme
### Recycled Aggregate Properties  
In this experimental campaign, RA were randomly withdrawn from each recycling plant that produces several types of CDW. To better understand the composition of the RA used in the production of concrete mixes, a visual analysis was carried out. Table 3 shows the composition of the four types of RA. The RA used have a high percentage of \"concrete, mortar and natural stone\", which is estimated to be between 69% and 84% of their total content (by mass). The percentages of \"masonry--clay materials\" are quite variable (between 1% and 29%). [PERSON] et al. [34] analysed several sources on the composition of CDW and also concluded that concrete and ceramic materials are the main sources of inert materials. RA from Ambilei have a large amount of glass, which reaches 15.4% of their composition. In turn, RA from Vimajas stands out in terms of the amount of bituminous materials found, which corresponds to 10.5% of these RA. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Cement** & & **0.115 L/L** & **351 kg/m\({}^{3}\)** \\ \hline \multirow{6}{*}{Fine Aggregates} & 0–0.063 & 0.000 L/L & 0 kg/m\({}^{3}\) \\  & 0.063–0.125 & 0.016 L/L & 42 kg/m\({}^{3}\) \\  & 0.125–0.25 & 0.044 L/L & 114 kg/m\({}^{3}\) \\  & 0.25–0.5 & 0.050 L/L & 130 kg/m\({}^{3}\) \\  & 0.5–1 & 0.057 L/L & 148 kg/m\({}^{3}\) \\  & 1–2 & 0.066 L/L & 172 kg/m\({}^{3}\) \\ \hline \multirow{6}{*}{Coarse Aggregates} & 2–4 & 0.076 L/L & 198 kg/m\({}^{3}\) \\  & 4–5.6 & 0.041 L/L & 111 kg/m\({}^{3}\) \\ \cline{1-1}  & 5.6–8 & 0.046 L/L & 124 kg/m\({}^{3}\) \\ \cline{1-1}  & 8–11.2 & 0.047 L/L & 127 kg/m\({}^{3}\) \\ \cline{1-1}  & 11.2–16 & 0.121 L/L & 327 kg/m\({}^{3}\) \\ \cline{1-1}  & 16–22.4 & 0.122 L/L & 329 kg/m\({}^{3}\) \\ \hline Water & & 0.182 L/L & 182 kg/m\({}^{3}\) \\ \hline Voids & & 0.017 L/L & - \\ \hline Total & & 1.000 L/L & 2354 kg/m\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Materials and mixing proportions of the natural aggregate concrete (NAC). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Composition (\%)** & **FRA Ambilei** & **FRA Vimajas** & **CRA Valnor** & **CRA Retria** \\ \hline Concrete, mortar and natural stone & 83.7 & 75.2 & 70.8 & 69.1 \\ Masonry—clay materials & 0.9 & 11.6 & 28.6 & 28.6 \\ Glass & 15.4 & 1.0 & 0.5 & 2.1 \\ Bituminous materials & 0.0 & 10.5 & 0.0 & 0.0 \\ Others & 0.0 & 1.7 & 0.1 & 0.2 \\ Total & 100.0 & 100.0 & 100.0 & 100.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Composition of recycled aggregates. In Tables 4 and 5, it is possible to observe the results of the physical characterization carried out on several aggregates used. When compared to the NA, the RA exhibit a lower density and higher water absorption, which derives from their nature and higher porosity. It is found that all RA have a higher shape index than the NA, which can lead to a lower workability of the concrete mixes with RA, compared to that of NAC. It was also observed that the RA present a higher level of fragmentation than the NA, possibly due to their composition. Table 6 shows the results obtained in the chemical tests carried out on the different recycled aggregates. By performing these tests, the aim is to know which chemical components in these aggregates can be detrimental to the concrete mixes. These components will influence how curing takes place, as well as the protection of the steel rebars, among other aspects. There are compounds that significantly alter the curing rate and the quality of the hardening of concrete, one of them being humus [35]. The humus test, carried out according to EN 1744-1 [28], only performs a qualitative analysis, signalling the existence or absence of organic matter. Regarding the RA analysed, a negative result for the presence of hummus was obtained for the RA from all the recycling plants. Table 6 shows that the biggest concern regarding the results of the chemical tests is the amount of lightweight contaminants existing in the various RA.