## 2 Recycled Material Analysis
### Blast Furnace Slag  
Based on technical performance, BFS is ranked as the second most desirable reusable material for highway pavement construction, while it is ranked fifth and sixth in economic and environmental terms, respectively [5]. There are three main types of slag: iron blast furnace slag, oxygen furnace steel slag, and electric arc furnace slag. BFS is available in four main forms: air-cooled, pelletised, granulated, and ground. This paper only covers the application of the ground and granulated varieties of BFS (GGBFS). GGBFS can be used as a filler in asphalt as well as a supplementary cementitious material in concrete pavement. Although BFS is a free material (as an industrial by-product), the energy required for the crushing and grinding of BFS should be included in the input energy calculations of the raw materials phase. For example, [PERSON] [31] estimated that the input energy required for the processing of slag is 722 kJ/kg. Notably, BFS is a hydrophobic material and has high absorption. As a consequence, the OBC of asphalt mixtures containing BFS is higher than that of control asphalt mixtures, which reduces the environmental benefit. Because of the higher OBC, mixtures containing BFS are prone  
Figure 4: Effect of MR6, MR8 and MR10 on the performance of the mixture, plotted based on data reported by [PERSON] and [PERSON] [29]. to asphalt bleeding at higher temperatures. Asphalt bleeding is a functional failure that decreases the skid resistance of the pavement surface which negatively impacts safety. Therefore, optimal BFS content for asphalt mixtures should be determined individually for various asphalt types and service conditions. [PERSON] [32] recommends the maximum skid resistance associated with mixtures containing 30% BFS; however, optimal BFS content is likely to be mixture-specific. Analysis of structural consistency of asphalt mixtures containing BFS indicates a decrease in rutting potential [33; 34]. Moreover, analysis of long-term performance ageing found that BFS mixtures had higher stiffness, reflecting the higher absorption of the binder by BFS granules, resulting in a reduced effective binder content. It follows that mixtures containing BFS are more prone to ageing, which may reduce the service life of asphalt surfaces. However, physicochemical ageing depends on many factors, including construction temperature, aggregate type and gradation, binder type, ambient temperature, service condition, field compaction and densification due to traffic loading. Further investigation on the short and long-term ageing patterns of BFS mixtures is required. Additional research should also be conducted on the synergistic performance of BFS and WMA, because the higher stiffness of BFS mixtures might be offset by the reduced binder ageing associated with WMA production temperatures. Use of BFS as a supplementary cementitious material in concrete also increases the sustainability of concrete pavements. The main disadvantage of using BFS in concrete pavements is slower early-life strength gain which may result in longer curing periods and delays in opening pavements to traffic. Chemical additives can be used to accelerate the hydration of the cement paste and reduce curing time. However, incorporation of extra chemical materials reduces the sustainability benefits associated with the incorporation of BFS. The benefits and drawbacks of its use should be considered in LCA analysis. It is also important to understand that the environmental footprint associated with different BFS sources can be significantly different. For example, [PERSON] [35] and [PERSON] et al. [36] reported that the use of BFS can decrease greenhouse gas emission by around 50%, while a LCA case study conducted by [PERSON] et al. [37] showed that the total environmental emissions decrease by only 7%, a result which is consistent with the findings of [PERSON] & Hellweg [38].