## 4 Circularity Assessment of Each Scenario
### Scenario 1: Maintaining Material Linearity Throughout Its Lifespan  
This scenario assessed the circularity of the building structure under a linear economic model in which resources are extracted, manufactured, and disposed of. As noted in Section 1, this scenario was predominant, and it was therefore assumed to represent the current situation.  
Based on this background, it was assumed that all elements in this scenario have been produced through resource extraction and become waste without being maximised in their use through circularity strategies. The only exceptions are biodegradable materials: these undergo a physical, chemical, thermal, or biological decomposition process, which breaks them down into carbon dioxide, biomass, and water [91].  
Following the hierarchical structure of the CARES-F [62], the material level was analysed first. The circularity assessment at this level is defined by the Material Circularity Index (MCI), which considers the material scenario conditions, their technical and functional lifespans, as well as the impact of their transportation on input and output flows. Since the structure is made of reinforced concrete, the materials that become structural elements, as well as those involved, including packaging, formwork, and material losses, were taken into account. Table 1 presents the 12 most representative materials based on their total mass, while Figure 11 shows their respective MCI.  
The circularity assessment at the element level is represented by the Element Circularity Index (ECI). This index considers the MCI of the materials that constitute each structural element and their individual DP. The outcomes of this analysis for the reinforced concrete elements that comprise the building structure are depicted in Figure 12.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**LoW 1 Code and Description**} & **Representative Material** & **Participation Mass Ratio** \\ \hline
170101 & Concrete & Concrete (H-25) & 93.33\% \\ \hline
170405 & Iron and steel & Steel rebar (B 500 S) & 2.82\% \\ \hline
170405 & Iron and steel & Small steel material & 1.08\% \\ \hline
150111 * & Metallic packaging containing a hazardous solid porous matrix & Metallic packaging & 0.55\% \\ \hline
170405 & Iron and steel & Supplementary steel material or special parts & 0.54\% \\ \hline
170201 & Wood & Pinewood planks (shuttering) & 0.45\% \\ \hline
170201 & Wood & Pinewood boards (shuttering) & 0.43\% \\ \hline
170405 & Iron and steel & Welded wire mesh (ME B 500 T) & 0.13\% \\ \hline
170604 & Insulation materials & EPS waffle pod for slabs (0.6 \(\times\) 0.6 m) & 0.11\% \\ \hline
150103 & Wooden packaging & Wooden packaging & 0.10\% \\ \hline
170405 & Iron and steel & Steel panel formwork (50 \(\times\) 50 cm) & 0.10\% \\ \hline
150101 & Paper and cardboard packaging & Cardboard box & 0.10\% \\ \hline \hline \end{tabular}  
* European List of Waste (LoW) [92].
* Potentially hazardous waste.  
\end{table}
Table 1: Representative materials of the building structure (Authors’ own).  
Lastly, the System Circularity Index (SCI) was determined based on the previously defined ECI and the AP. This evaluation reflects that the SCI for this scenario is 24.1%.