## 2 Materials and Methods
### Life-Cycle Assessment of the Material Alternatives
#### 2.4.2 Functional Unit and Methodology  
The functional unit for this study was the road subbase layer of the class III type national road, where the materials are mainly produced outside of the construction area. The production of the materials comes within the product system. The functional unit for the study was a 1 km long national road of class III with a pavement width of 6 m and roadbed width of 9 m, has and with a subbase layer of 0.3 m thickness, using conventional and alternative materials. The substitution was assumed to be 100% of the subbase material layer through (a) m-sand, (b) CDW, (c) GBF slag, (d) EAF slag, and (e) fly ash. The primary goal of this study was to evaluate the potential environmental benefits of using recycled materials and determine which of the alternative mixes were relatively more or less sustainable. The normal scenario involves comparing conventional river-sand-based subbase layers and alternative-material-based subbase, without considering the avoidance of using alternative materials. The avoidance scenario involves comparing the conventional subbase layer and alternative material subbase layers with the avoidance process to technosphere factors. A cradle-to-gate approach was considered. In terms of the system boundaries, the onsite installation process, other layers, and service life in conventional or alternative subbase layers were assumed to be similar, so they were not considered in the analysis.  
The LCA was carried out using the Ecoinvent 3.6 database (www.ecoinvent.org, accessed 1 January 2022) and the software SimaPro 9.2 ([[https://simapro.com/](https://simapro.com/)]([https://simapro.com/](https://simapro.com/)), accessed 1 January 2022) [75]. The study adopted the ReCiPe 2016 Midpoint (H) V1.04/World method to assess the impacts. This method was introduced in 2008 [76] and combines the strengths of other methods such as CML and Eco-Indicator 99 [77]. The primary objective of the ReCiPe method is to transform the long list of life-cycle inventory results into a limited number of indicator scores. These indicator scores express the relative severity of an environmental impact category. This method was chosen because of its advantages, with a broad set of midpoint categories, and utilizing an impact mechanism with global scope [78]. The following impact categories expressed through the respective indicators were considered:  
* Global warming potential (infrared radiative forcing increase), in kg CO\({}_{2}\)eq;
* Mineral resource scarcity (ore grade decrease), in kg Cu eq;
* Fossil resource scarcity (upper heating value), in kg oil eq;
* Terrestrial acidification (proton increase in natural soils), in kg SO\({}_{2}\)eq;
* Freshwater eutrophication (phosphorus increase in freshwater), in kg Peq;
* Fine particulate matter formation (PM2.5 population intake increase), in kgPM\({}_{2.5}\) eq;
* Stratospheric ozone depletion (stratospheric ozone decrease), in kg CFC\({}_{11}\)eq;
* Ozone formation (terrestrial ecosystem tropospheric ozone increase), in kg NO\({}_{\infty}\)eq;
* Cumulative energy consumption (Total of used primary energy), in KJ.