# A Review of Sustainable pavement Aggregates
## 4 Waste in Civil Engineering  
### Reclaimed Asphalt Pavement (RAP)  
Roods are essential infrastructure for the economic growth of nations and global technological exchange; however, their construction and maintenance require an enormous amount of natural resources that negatively impact the environment [64]. For instance, the rehabilitation of civil structures generates large volumes of solid waste by demolishing elements that have met the design lifespan, destined for open-air landfills, putting humanity's habitat at risk [65]. The rehabilitation of asphalt pavements generates a large amount of removed material called RAP (reclaimed asphalt pavement) capable of being reprocessed [66]. According to the US EPA IWEM transport and destination model, the negative environmental effects of RAP leaching on pavement construction report a low risk to human health [67]. The main source of RAP is the milling process, which reduces the size of fragments (Figure 3) of the removed pavement when the machine speed is slow at high milling depth [68]. The depth of the milling is determined by the condition of the binder and the original level to be rehabilitated [69]. The RAP contains residual asphalt  
Figure 2: Glass waste aggregate, adapted from [56]. (**a**) Coarse Glass Aggregate, (**b**) SEM image of glass powder.  
binder which increases the viscosity of the mixture improving the tensile response [70]. The RAP content in hot asphalt mixes (HMA) should not exceed 30% for good performance [71]. Warm mix asphalt (WMA) exhibits the same low-temperature behavior and fatigue as HMA with a recycled RAP content of up to 40% [72]. The low-temperature crack resistance decreases if the RAP content increases in the mixture [73]. However, the higher the RAP content in the mixture, the greater its stability, reducing the asphalt content and increasing resistance to transit loads [74]. Marshall stability improves with lower asphalt cement demands for 75% RAP content in HMAs registering 29.32 kN [75]. In turn, 60% of RAP in hydraulic concrete mixtures presents 6.13% savings in its manufacturing cost and a 10% increase in compressive strength [76]. Additionally, Cold Recycled Mixtures (CRM) consume higher compaction energy to increase their stiffness when the content of air voids increases due to the decrease of the rated maximum RAP size [77]. The homogeneity of the asphalt layers improves when the rigidity of the mixture is reduced with rejuvenating additives [78]. The incorporation of RAP in warm blends with polyethylene wax-based additive (RH-WMA) equates to the indirect tensile strength (ITS) of hot mix asphalt (HMA), favoring a lower consumption of compaction energy [79]. Blends with RAP that include rejuvenating additives increase fatigue resistance and, therefore, increase pavement life [80]. Incorporating polypropylene fibers negatively affects the mechanical properties of the mixtures combined in a ratio of 70/30 aggregates of RAP and rock powder, r [81]. Nevertheless, asphalt mixtures with RAP at 50% of their weight report a Marshall stability value equal to 21.4 kN that allows a depth in the formation of grooves of 9.89 mm and a crack resistance of 1750 kPa using hydrated lime as a filler; while its fatigue resistance decreases with high deformation; however, it reaches a resilient modulus equal to 4200 Mpa [82]. Finally, the incorporation of optimal amounts of additives improves the mechanical properties of the mixtures, increasing stability and reducing wear loss, which extends the durability of the pavement [83].