Polyethylene terephthalate modification of asphalt is mostly referred to as PET. PET is typically used in single-use applications such as water bottles and food packaging; however, large corporations are now reusing up to 100% of their waste PET to produce new plastic bottles and other items. The most typical applications for PET are water bottles and food packaging. Because of its high strength-to-weight ratio, PET was discovered to be a perfect candidate for its application in asphalt pavements, making it a suitable plastic in the asphalt sector to reduce environmental pollution and improve bitumen material qualities. PET was discovered to be a promising choice for its employment in asphalt pavements due to its great chemical resistance to organic compounds and water. Unfortunately, PET and recycled PET are relatively expensive polymers, especially when certified as "food grade," since the majority of their applications are for food-grade containers. This is due to the fact that PET and recycled PET are mostly used in the food business. PET's exceptionally high melting temperature (about 260 degrees Celsius) also precludes its employment as a bitumen modifier. Several studies, however, have demonstrated that using PET as a polymer modifier for bitumen enhances a variety of the mixture's properties. Recently, an article was published that presented a review of the application of PET for pavement performance. El-Naga and Ragab used PET to modify bitumen and assessed its impact on the overall characteristics of PET-modified bitumen and PET-modified asphalt mixes. PET was employed to modify the bitumen. The PET modification reduces the material's penetrability while increasing its softening point, ductility, and viscosity. When compared to typical asphalt modifiers, the results showed higher Marshall stiffness modulus, indirect tensile strength, and rutting stiffness. The amount of PET employed in the modified asphalt mixture increased the value of air spaces as well as voids in mineral aggregates. 
Furthermore, the findings of a rheological study conducted by Bary and colleagues revealed that the addition of 4% PET significantly lowered the phase angle and enhanced the complex shear modulus. The addition of polypropylene (PP) to bitumen causes significant changes in the characteristics of the resulting PP-modified bitumen. The addition of PP to the binder resulted in an increase in the softening point while simultaneously decreasing the penetration value. As previously noted, the most common PP concentrations used are between 3 and 5%; the penetration value has been demonstrated to drop between 18 and 30% for 3% PP and between 38 and 50% for 5% PP. According to, a rise in the softening point of 3% and 5% PP, respectively, were discovered to be between 4 and 30% and 11-43.5%. The addition of polypropylene (PP) increased the viscosity of the bitumen while decreasing the ductility; specifically, the ductility was reduced by 20% at a 5% PP concentration. Before employing certain polymers for bitumen modification, several parameters must be considered, including particle size, mixing duration, and the interaction between the binder and the modifier. These observations suggest that these aspects should be taken into account. In terms of rheological properties, bitumen modification with polypropylene (PP) improved the rheological properties of PP-modified bitumen at high temperatures and low frequency. This resulted in greater resistance to persistent deformation. After bitumen was modified with PP, the complex shear modulus increased, the phase angle decreased, and higher G*/sin values were obtained. It has been established that different forms of PP, including aPP, iPP, and sPP, can be employed efficiently for bitumen modification [30,246]. Despite the fact that aPP has a low crosslink density, Nekhoroshev et al. discovered that a bitumen binder treated with aPP increased its adhesion properties. 
Al-Haidri et al. investigated the effect of two different grades of PP modifiers and discovered that both isotactic polypropylene (iPP) and atactic polypropylene (aPP) increased stress resistance, reducing the frequency of distress and increasing the in-service life of the pavement. However, as compared to iPP, the outcomes from aPP at 2% concentration were superior. Schaur et al. included four unique PP polymers: one atactic polymer, two isotactic polymers with different molecular weights, and one isotactic polymer having polar (anhydride) side groups. In contrast to the long-chain iPP, which indicated a polymer with a heterogeneously distributed chain, they determined that the short-chain polymer was finely dispersed. The aPP has a smaller effect on the mechanical characteristics of PMB than iPP. As a result, a partial network of polymer-rich phases forms within PMB. The maPP, on the other hand, significantly improves mechanical characteristics. Awad and Awad and Al-Adday investigated the use of polypropylene (PP) as a bitumen modifier, concluding that the addition of PP resulted in enhanced stability when compared to standard bitumen devoid of PP. A number of research on storage stability were published, and many of them suggested that the use of PP causes phase separation. However, Giavarini et al. proved that adding 3% polyphosphoric acid (PPA) by weight of bitumen to PP can reach acceptable storage stability values. This would help to lessen the impact of the previously noted disadvantage. Other methods of modification include the addition of maleic anhydride to polypropylene (PP) and the use of PP pyrolysis products as an intermediate step before using the polypropylene to change binders. It has been established that polypropylene, whether virgin or waste, is a reasonably good polymer for bitumen modification. Despite the fact that there is a general lack of studies that evaluate the fatigue performance of asphalt mixes enhanced with PP, this is the case. 
Bitumen Modification
However, because PET does not melt during the bitumen modification process (it can only operate as a filler), its relative size should be carefully studied when DSR tests are conducted, especially when a gap of 1 mm is used. The addition of PET to bitumen resulted in an increase in the G*/sin value, indicating improved rutting resistance. Leng et al. evaluated the MSCR parameters (%recovery and Jnr) of PET modified bitumen binder at two different pressures: 0.1 kPa and 3.2 kPa. In comparison to pure binder, the %recovery of modified binder was substantially higher, and the Jnr value of modified binder was noticeably lower. Furthermore, increasing the amount of polymer in the mixture increased the percentage of material retrieved while decreasing Jnr. Al-Jumaili used PET (with a size range of 2.36 mm to 4.75 mm), crumb rubber (with the same size range as PET and added via the dry process), and waste engine oil to modify bitumen. According to the findings, a composition containing 9% crumb rubber achieved the highest levels of tensile strength and water resistance. When a higher amount of PET was added to the bitumen, the tensile strength values increased to their maximum. The Marshall's overall stability was considerably improved by using 9% crumb rubber, 12% PET, and 5% waste engine oil. The study, however, did not investigate the potential of a lack of adhesion between the PET particles and the bitumen. According to the findings of another study, both the SBS and PET mixes improved fatigue response, although the SBS blends demonstrated superior fatigue behavior to the PET blends. 
The fatigue properties of SBS-modified bitumen were compared to those of PET-modified bitumen in this study. According to Cong et al. fatigue behavior is connected to surface energy, which means that the higher the surface energy, the longer the product would survive before exhibiting signs of wear and tear. Furthermore, it was revealed that the surface energy of the SBS-modified binder was greater than that of the unmodified bitumen; as a result, the SBS modification increased fatigue life. The PET-modified mix demonstrated greater fatigue resistance than the SBS-modified bitumen in the same trial at low strain levels and a 6% PET loading. Similarly, it has been proposed that the addition of PET to bitumen has an effect on thermal cracking at low temperatures, i.e., PET-modified bitumen blends are more prone to breaking under the influence of heat. The process of combining PET and bitumen is also critical to overall performance. As previously stated, there are two methods for combining polymers with bitumen: the dry process and the wet process. Both of these strategies are discussed in greater detail below. However, because of the exceptionally high melting temperature of PET, which makes it difficult to manufacture homogeneous blends, the wet method is not regarded as a viable choice for PET. Despite this, investigations on PET modification of bitumen utilizing the wet technique have been published. Moghaddam et al. investigated the wet mixing of PET with bitumen. They discovered that PET-modified bitumen had significantly greater resistance to permanent deformation and that a higher PET concentration had stronger resistance to permanent deformation. Choudhary et al. described a dry method and a modified dry process for PET modification of bitumen (heated aggregates were combined and coated with PET first, then bitumen was added and blended). 
They discovered that the modified dry method performed better and was more resistant to moisture-induced damage. In general, PET-modified bitumen generated from either technique exhibited greater resistance to deformation. This was accompanied by a high Marshall quotient, strong stability, and low flow. PVC accounts for approximately 10.1% of total European plastic manufacture. It is commonly used to make profiles, cable insulation, garden hoses, and window frames. PVC has earned the moniker "poison plastic" due to the fact that it contains a variety of poisons. Dioxins are generated when PVC-based goods are burned or melted at high temperatures. PVC is supposed to emit a substantial amount of hydrochloric acid when heated to a high temperature (HCl). [Citation required] Even if it is not burned, it is believed that polyvinyl chloride (PVC) can emit hydrochloric acid (HCl). Because HCl is highly hazardous, producing it by heating PVC can cause broad damage to both instruments and the environment. To alleviate the detrimental consequences of PVC's high chlorine concentration, it has been proposed that chlorine be eliminated through chemical treatment. There have been indications that chlorine can be removed from the surface of PVC by nucleophilic substitution of ligands such as amines and hydroxy. Given that PVCs have a thirty-year lifespan, there is no reliable strategy for dealing with this highly hazardous material. Furthermore, the tactics of collection, transportation, and disposal are still not carried out in a suitable manner, particularly in developing countries. The disposal of such materials without any type of management causes a number of serious environmental issues, including groundwater contamination. 
PVC was utilized in certain studies as a polymer modification of bitumen; however, the researchers were unable to achieve successful results due to the polymer's high melting point (approximately 298 degrees Celsius). PVC was used in several studies to modify bitumen, although the results were mixed. Other investigations used PVC from a variety of sources, including window frames, wires, and pipes, or did not specify the source of the PVC at all. The following mixing conditions were needed for PVC modification of bitumen: a temperature range of 140-190 degrees Celsius, a mixing time range of 20 minutes to three hours, a particle size range of 0.075-2 millimeters, a concentration of 1-20% PVC by weight of the bitumen, and a mixing speed range of 1300-3750 revolutions per minute. Despite the fact that PVC was used as a filler in the production of PVC-based bituminous mastics, it was discovered that adding PVC to bitumen boosted both the conventional and rheological properties. When PVC was added to basic bitumen, the penetration value generally decreased while the softening point value increased significantly. The addition of 5% PVC to the bitumen reduced the penetration value by 57% while increasing the point at which it softened by 26%. When 5% PVC was added to bitumen, the viscosity increased by up to 300%, but the ductility decreased. PVC alteration of bitumen resulted in a rise in the complex shear modulus and a decrease in the phase angle. This was seen from a rheological standpoint. The larger complex shear modulus and smaller phase angle aided in better rutting resistance at high temperatures, which may indicate greater pavement durability. In any of the studies to change the base bitumen, PVC was the only additional modifying ingredient that was used. Fang et al. employed organic montmorillonite at concentrations of 0.05%, 0.15%, and 0.25% to improve the characteristics of PVC-modified bitumen. 
They discovered that storage stability was increased, especially at 5% PVC. This was true when all three concentrations of organic montmorillonite were applied. Another study combined a chemical modifier with PVC to improve the properties of modified bitumen. The findings of this study revealed that the polymer dispersion in bitumen was considerably improved. Neither the likelihood of fuming nor the possibility of emissions from PVC heated at high temperatures was explored during the investigation. Polypropylene (PP), which currently accounts for 21% of global plastic output and 19.1% of European plastic production, is used in a wide range of applications such as microwave-safe containers, food packaging, pipes, and automotive components. PP is a thermoplastic linear hydrocarbon with a crystalline level in between HDPE and LDPE. PP can be molded into a number of shapes. PP has been extensively used to achieve the goal of improving the properties of bitumen by polymer modification. Polypropylene (PP) is reported to increase bitumen's stability, Marshall properties, and indirect tensile strength. It is also claimed that PP-modified bitumen mixtures have increased rutting resistance and fatigue life. The following are the ideal mixing parameters for polypropylene and bitumen, according to published research: 165-180°C mixing temperature, 1-2 hours mixing time, 120-4000 rotations per minute mixing speed, and 1-6% polypropylene concentration by weight of the binder. The most commonly used dosage values for PP for polymer modification of bitumen are 3% and 5%.