# A Review of Sustainable pavement Aggregates
## 2 Plastic Waste  
_Polyethylene Terephthalate (PET)_  
PET is a plastic waste that is abundant in the world due to its versatility in application for the packaging industry [26]. Recycling is a third option (Figure 1) in the treatment of plastic waste that is deposited in the open or incinerated, releasing components harmful to the mammalian reproductive system [27]. The reuse of PET is on trend to improve the properties of traditional bitumen, harmonize it with the environment, and point out the reduction of production costs inherent in asphalt concretes [28]. PET is a binder additive capable of meeting the expectations of asphalt cement [29]. The British company MacRebur made a mixture of binders for paved roads that contains the equivalent of eighty thousand plastic bottles per ton. These volumes represent a considerable reduction in the discharge of plastic into the soil which allows it to interact with the environment as an inert pollutant [30]. If the PET goes through an aminolysis treatment where its flakes and Triethylenetetramine (TETA) react chemically, it becomes an additive, which improves the adhesion between the asphalt cement and the aggregates, reducing the moisture-induced damage of the asphalt mixture [31]. In addition, PET combined with a silicon nanomaterial forms a sustainable hybrid additive that makes SMA (Stone Mastic Asphalt) mixtures more rigid, improving resistance to deformation and traffic; with a reduction of up to 0.04% in the infiltration rate (drain-off) [32]. On the other hand, due to the high melting point of PET, it is also considered as a substitute aggregate for asphalt mixtures after a mechanical reduction process [33]. PET is cut into small flakes, which are integrated into the hot asphalt mix, as physical recycling; capable of improving resistance to detachment and rutting with a proportion between 2% to 10% of the weight of the mixture [34]. Mixtures containing crushed PET flakes have high porosity, and the texture is similar to semi-dense asphalt mixtures (SDA) that reduce road traffic noise [35]. Crushed PET, with particles between 0.1 mm and 2 mm, is a replacement for sand in semi-dense asphalt mixtures (SDA) that makes them more ductile, but difficult to compact; They also present a reduction in cracking due to low temperature and resistance to permanent deformation at high temperature [36]. Therefore, exposing PET to gamma radiation increases its mechanical and thermal properties with a positive impact on its resistance; showing a Marshall stability with a range of 4.5% to 5.5% for an asphalt mixture with a content between 0.2% and 0.8% of PET fibers; considering a linear relationship between the increase in asphalt or PET content that increases the Marshall flow value [37]. Additionally, the use of plastic waste as a partial replacement for fine aggregates in concrete pavements can improve the compressive strength and durability of the pavement [38]. The incorporation of polyethylene terephthalate plastic waste as an aggregate in concrete can reduce porosity and improve the compressive strength of the material [39]. On the other hand, the addition of thermoplastics such as high-density polyethylene and polypropylene in the hydraulic concrete with a replacement percentage of up to 12% does not negatively affect the corrosion behavior in the reinforcing steel [40]. Therefore, the use of recycled plastics in concrete pavements contributes to environmental sustainability by reducing the amount of plastic waste in landfills [41].