## 2 Multi-Disciplinary Aspects of Reutilizing Waste Materials
### Legislative and Health Concerns  
Another crucial factor that can limit the extensive use of recycled materials into asphalt mixtures is the compliance with all applicable local laws, as well as any upcoming legislation [30]. For instance, the resistance to a wide implementation of RAP in surface courses due to legal constraints has already been acknowledged previously [1]. Therefore, the current levels of utilization exhibit variance, since some countries either partially permit or fully restrict the use of waste materials. For instance, according to [PERSON] et al. [55], RAP use is prohibited in surface courses that adhere to Belgium's Flemish Road Standard SB250 v3.1. Other safety considerations do exist for the case of glass, as in urban road environments, glass particles can harm automobiles and/or hurt people, because of the danger of being dislodged by moving vehicles over a pavement surface [56]. Because of this, there is a propensity to \"not trust\" waste glass when it comes to applying it in heavy-duty motorways with fast-moving vehicles [36]. Conversely, it appears that parking spaces and quieter roads are better cases for using waste glass.  
Surface courses may also be subject to even stricter legislation because of possible leachates and health issues from waste material use, tire-pavement noise, etc., which is particularly important in urban and suburban areas. The investigation of recycled materials in pavement construction and reconstruction projects shall not exclude such components that are strictly related to the quality of living of human beings [55]. Indeed, Figure 5 shows the example of the mechanism of groundwater table leaching. Pollutants that may seep from the pavement's surface into the underlying soils and groundwater aquifers can endanger ecosystems and the environment. This factor has not received the research attention it deserves. Shortly after construction and up to the \"end-of-life\" phase of the pavements, leaching is a persistent worry pertaining to the pavement's lifespan [57].  
Figure 5: The leaching mechanism for the case of RAP.  
Leaching can occur from the usage of waste materials in asphalt pavements as well as from their disposal or stockpiling, which makes the assessment of the leaching potential rather difficult. While leaching potential can be evaluated using laboratory and field testing, the latter is uncommon and challenging due to the extended time required to finish the assessment and form meaningful conclusions.  
According to pertinent research, in order to create more accurate simulations, it is imperative to take into account as many environmental factors as possible that are close to the recycled pavement, such as humidity, frequency of rainfall, air temperature, and wind speed. Lastly, leaching needs to be evaluated in conjunction with the effects of the soil layers surrounding the pavement and in the space between the pavement and the groundwater table [57].  
Governments, businesses, and academia may all work together to more efficiently develop and create new test protocols and evaluation techniques. In addition to the performance standards, it is important to consider any possible harm to the health and safety of paving crews and other employees. Legislative issues about the use of waste materials that need to be taken into account can be undoubtedly raised by such reasons [18]. From this perspective, any reluctancies about using waste materials or unawareness of good practices could be replaced by a robust and informative knowledge background.  
Finally, the aspect of GPP, mentioned earlier, is again recalled toward a greener lifecycle of recycled mixtures. Wherever applied, GPP aims to establish minimum environmental criteria. Thus, in road engineering, GPP can even promote a minimum rate of recycled materials within the road construction layers and consequently foster the development of virtuous practices. This is an issue that definitively affects both road engineers and designers, as well as the road stakeholders.