## 3 Methods for Incorporating Waste Plastics into Asphalt Pavements
The dimensions and morphology of plastic particles substantially affect the efficacy of the modified asphalt. Plastics utilized as modifiers may exist in forms including pellets, flakes, fibres, powders, or strips. Smaller particles facilitate superior dispersion and coating, improving compatibility and minimizing the possibility of phase separation, while bigger or irregularly shaped particles might result in inconsistent blending, reduced compaction, or the formation of voids. Uniformity in particle size is crucial for attaining desirable aggregate gradation and mixture workability [10; 11; 30]. Multiple factors affect the efficacy of each approach, such as plastic type and melting point, mixing temperature, time, shear rate, particle shape, and dosage. Plastics having melting points lower than asphalt mixing temperatures, such as LDPE and HDPE, are more appropriate for the wet method as they can liquefy and integrate with the binder under standard processing conditions. Conversely, higher-melting polymers such as PET and PS, which remain solid at asphalt mixing temperatures, are more appropriate for the dry method, serving as solid fillers or partial aggregate substitutes [17; 18; 27; 36]. Compatibility and homogeneity present significant challenges, particularly in the wet method. The molecular weight, polarity, crystallinity, and asphaltene content of bitumen affect the interaction between plastic and binder. Poor compatibility may result in phase separation, yielding non-uniform mixes and diminished performance. Investigated solutions encompass the incorporation of compatibilizers (such as maleic anhydride-grafted polyolefins and polyphosphoric acid) or the functionalization of plastic surfaces to enhance adhesion with bitumen [11; 21; 28]. The proportion of plastic waste is generally optimized between 3 and 8% by weight of binder in the wet method, and may exceed 10% in the dry method, dependent on particle size and desired qualities. Exceeding optimum thresholds may result in heightened stiffness, decreased fatigue lifespan, and impaired workability [11; 27; 31]. Laboratory investigations and field experiments have confirmed the efficacy of these approaches. Field applications in India, Australia, and Europe have demonstrated good performances of dry-processed roads with LDPE, HDPE, and PET at doses of approximately 8-10%, demonstrating enhanced rutting resistance and durability in both tropical and temperate regions. Nonetheless, field validation across varying traffic loads and climatic conditions is still constrained [11; 14]. Every method possesses advantages and disadvantages. The wet method provides superior binder modification and durability but requires greater energy and equipment expenditure, and poses dangers of storage instability. The dry method is economical, simpler to implement, and allows for increased plastic content; yet it may lead to diminished moisture resistance and decreased binder-plastic interaction. The mixed method provides a compromise, potentially enhancing distribution and diffusion while reducing the need for equipment modifications, although managing mixing conditions is more complex [11; 14]. Table 2 presents a comparative overview of recent studies investigating different incorporation strategies, emphasizing critical characteristics such as plastic kinds, doses, mixing settings, and the advantages and disadvantages of each method. Incorporating waste plastics into asphalt presents distinct advantages from both environmental and economic standpoints, such as diminished landfill utilization, reduced demand for virgin polymers, and a lowered environmental impact, demonstrated by a 17-25% reduction in greenhouse gas emissions, dependent on the type and quantity of plastic used. Economically, savings are realized by substituting a portion of the binder or aggregates with less-expensive waste plastics, although initial expenses may increase due to the needs of processing, sorting, and quality assurance.