## 3 Results and Discussion
### Economy  
The data for economic assessment varies considerably between regions. This is because local conditions highly affect the cost of labour and market costs of recovered materials. Regulatory constraints and regional financial conditions also limit the economic viability of selective demolition in a free market. Considering this evidence, the economic implications of concrete mixes made with various incorporation ratios of FA and RCA, both with and without SP, were assessed by analysing a case study in Portugal (Table 4). The results show that the cost of the concrete mixes decreased slightly with the incorporation of RCA (up to 4% with fine RCA, and 7% with coarse RCA, contents). Furthermore, the cost decreased by 9% and 18% when OPC was replaced by 30% and 60% of FA, respectively. Contrary to the incorporation of RCA and FA, the use of 1% SP led to about a 13% higher cost. However, the results show that by incorporating 60% of FA in NA concrete or by incorporating 30% of FA in RCA concrete, the high cost of concrete with SP can be offset. In addition, by incorporating RCA in FA concrete, even when SP is used, the cost is lower than that of the reference concrete (Figure 4). Bearing this in mind, it is not reliable to directly compare the cost of concrete mixes when their performances are different  
Figure 3: Ranking the concrete mixes based on the mechanical performance ratio (MPR) at 28 and 365 days. (Section 1). Therefore, the cost efficiency of the concrete mixes is studied in Section 3.3 by considering their mechanical performance. A study by [PERSON] et al. [26] estimated the average cost of NA and RCA concrete according to 23 and 20 international studies, respectively. It shows that, for strength class C30/37 and C50/60, the average costs were 43 \(\upxi\)/m\({}^{3}\) and 57 \(\upxi\)/m\({}^{3}\), respectively. These values were lower than those of the total material costs, final costs of this study and the commercial cost of concrete. This is due to the fact that the mentioned study estimated the cost of concrete mixes without considering the cost of the mixing procedure, company profit, and more. As with this study, it showed that the cost slightly decreased (42 \(\upxi\)/m\({}^{3}\) for C30/37 and 48 \(\upxi\)/m\({}^{3}\) for C50/60) when RCA was used. Furthermore, other studies [5; 37; 38] reported that the cost of concrete significantly decreased by using FA. Figure 5 presents the relationship between compressive strength and cost of 1 m\({}^{3}\) of concrete for the concrete mixes in this study (M1-M18 sp) and commercial concrete mixes obtained from Portuguese suppliers [35]. There is a strong relationship between the two parameters with a determination coefficient of 0.90 and 0.99 for concrete mixes obtained by the current study and Portuguese suppliers. Generally, the price of raw materials depends on the region and supplier. Therefore, Equation (4) is proposed to compare the results of the reference concrete with those of the other mixes made with various incorporation ratios of FA and RCA, with or without SP, even if the price of these raw materials changes. As seen in Figure 6, the results can be represented by the line of equality with a high coefficient of determination (R\({}^{2}\) = 0.98). \[C_{mises}=C_{ref.}+2*\left(5\cdot FA\%\text{-}C_{FA}+8\text{-}Coarse\ RCA \%\text{-}C_{coarse\ RCA}+5\cdot fine\ RCA\%\text{-}C_{fine\ RCA}-3\cdot SP \%\text{-}C_{SP}\right) \tag{4}\]  
where C\({}_{mises}\), and C\({}_{ref. }\), is the cost of 1 m\({}^{3}\) of other mix and of the reference concrete \"M1\"; FA%, \(Coarse\ RCA\%\). \(fine\ RCA\%\) and \(SP\%\) are the incorporation ratios of these raw materials; C\({}_{FA}\), C\({}_{coarse\ RCA}\), C\({}_{fine\ RCA}\) and C\({}_{SP}\) is the cost of 1 kg of these raw materials.