## 6 Critical Discussion  
The incorporation of waste plastics into asphalt pavements has drawn academic and industrial attention in the last five years, driven by escalating plastic pollution, policy shifts towards circular economy purposes, and advancements in bitumen modification technology. This review highlights potential mechanical and environmental advantages while also exposing considerable contradictions, methodological unravelling, and unresolved \begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**References** & **Plastic Type** & **Incorporation Method** & **Key Findings** & **Conditions** & **Environmental Impacts** \\ \hline
[4] & Various & Wet and dry & Poor compatibility leads to phase separation and plastic loss; increases & Environmental exposure, field sim. & Elevated risk of MPs from poorly compatible blends \\ \hline
[13] & PET, HDPE & Dry &
\begin{tabular}{c} RPM increased pavement life by 14–65\%, reducing maintenance; road roughness raised \\ vehicle emissions \\ \end{tabular} & FlexPaveTM, AASHTOWare & Net benefit only if roughness is controlled; major landfill diversion \\ \hline
[12] & LDPE, PS & Wet and dry & \
\begin{tabular}{c} Plastic-modified asphalt \\ outperformed SBS in all \\ except for ozone depletion; transport and processing \\ energy contributes \\ significantly to the total \\ environmental impact \\ \end{tabular} & Full LCA: cradle to installation & Full LCA: cradle impacts; wet method tends to result in cleaner environmental impact &
\begin{tabular}{c} Using waste \\ plastics generally \\ better than SBS in terms of \\ environmental \\ impacts; wet \\ method tends to result in cleaner \\ environmental \\ outcomes over \\ the long term \\ \end{tabular} \\ \hline
[90] & PE (LDPE, HDPE) & Wet and dry methods & Wet process showed stronger environmental gains than dry; recycling locally amplifies benefits & Case study in Victoria, Australia &
\begin{tabular}{c} Wet method \\ better for GHG; \\ dry method is \\ constrained by synthetic \\ aggregate \\ replacement \\ efficiency \\ \end{tabular} \\ \hline
[39] & PE & Not specified &
\begin{tabular}{c} 5\% PE saved \textgreater{}1 ton \\ bitumen and diverted \\ 1.125 million plastic \\ bags/km \\ \end{tabular} & 5\% PE binder & Significant plastic waste diversion and material savings \\ \hline
[89] & PET & Dry method with up to 40\% RAP & \begin{tabular}{c} 2\% PET + 40\% RAP reduced \\ life cycle costs by 31.8\% and \\ GHG emissions by 37.6\% \\ \end{tabular} & \
\begin{tabular}{c} 2\% PET binder, \\ up to 40\% RAP \\ \end{tabular} &
\begin{tabular}{c} Significant reduction in both \\ cost and emissions \\ with recycled \\ content synergy \\ \end{tabular} \\ \hline
[37] & \begin{tabular}{c} Hard \\ polyolefins \\ + graphene \\ \end{tabular} & Wet (modifier, granulate) & \begin{tabular}{c} Impact reductions of \textasciitilons \\ (standard thickness \\ scenario) and \textasciitilons \\ (reduced thickness) \\ \end{tabular} & \
\begin{tabular}{c} 0.5\% plastic \\ modifier; \\ 20-year LCA \\ \end{tabular} &
\begin{tabular}{c} Circular use \\ of hard \\ plastics enables \\ substantial impact \\ mitigation and \\ durability gains \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont._environmental issues that must be addressed prior to the determination of sustainable or risk-informed broad adoption. Studies on mechanical performance consistently indicate enhancements in rutting resistance, stiffness, and high-temperature durability, especially when LDPE, HDPE, or PP are utilized within optimized dosage ranges (generally 3-8 wt% of binder for wet methods and up to 10 wt% of aggregate for dry methods). However, above these thresholds, other investigations (e.g., [39]) observed diminished workability, higher brittleness, and increased viscosity, indicating a limited performance range.