## 3 Sustainability Assessment of RFA Incorporation Ratio Based on Multi Criteria Decision Analysis  
The objective of this section is to generate a framework for assessing the optimum replacement ratio of sand or natural fine aggregates with RFA from CDW. A multi criteria decision analysis framework was developed by [PERSON] et al. [108] as shown in Figure 13, which combines the functional, economic and environmental parameters of concrete to assess its sustainability. This is achieved in four main steps: First, the alternatives that are to be compared need to be defined. Second, based on this data, the different alternatives are evaluated for their functional, environmental and economic parameters. Third, these impact factors would be normalized according to the equation below for a factor between 0 and 1. Finally, based on user-defined weights, these three factors are to be aggregated together to form one sustainability index upon which the alternatives are to be ranked, and the optimal one is selected. Figure 13: The support method for the assessment of the relative sustainability of building technologies proposed multi criteria decision analysis framework for sustainability assessment. In light of the presented findings from the literature, the selected parameters and corresponding predictive models were summarized in Table 6. The authors of this paper chose to include only a selected few functional and environmental properties of concrete but rather followed the trend set by similar studies such as [PERSON] et al. [9] and [PERSON] et al. [109]. Three scenarios were assumed for the transportation distances since it proved as a vital variable in the comparison, especially in the environmental and economic impact. The assumed values for D1, the transportation distance between the natural aggregates source and the concrete batch plan, were 150, 100 and 50 km. Similarly, the values for D2, the distance between RFA and the concrete batch plan, were assumed as 50, 100 and 1  
The results present enough evidence to support a claim that the incorporation of any increment of RFA to replace natural fine aggregates has an adverse effect on the overall functional performance of concrete. Nevertheless, it could be also concluded as per the comparison shown in Figure 14, regardless of the transportation distance, and due to the much higher purchase cost assumed for RFA, any incorporation % would yield a more expensive concrete alternative. On the other hand, the EI of the studied alternatives incorporating a range of RCA% (10% to 100%) showed sensitivity to the relative transportation distance of natural aggregates and RFA. Agreeing with the aforementioned data from the literature, when the distances travelled by NA double that assumed for RFA, which is described in this study as scenario 1, the concrete alternatives with RFA showed enhance environmental performance. As shown in Figure 15, mid-point indicators such as abiotic depletion potential (ADP) and the consumption of non-renewable primary energy (Pe-NRe) testify that alternative 10, which suggests the full incorporation of RFA instead of natural sand, is 80%, 60% and 40% better after normalization compared to the NA conventional concrete alternative considering scenarios 1, 2 and 3, respectively.