Flexible pavement construction remains one of the most material-intensive activities in civil engineering, relying heavily on virgin aggregates and bituminous binder. Both materials require energy-intensive extraction and processing, and their supply is increasingly shaped by environmental regulation, cost volatility and sustainability targets. These pressures have accelerated the adoption of recycling strategies that reduce embodied carbon and conserve natural resources. Reclaimed Asphalt Pavement (RAP) is among the most viable options in pavement engineering because it contains high-quality aggregates and aged binder recovered from milled or reconstructed asphalt layers. When correctly processed and blended with virgin materials, RAP reduces consumption of newly quarried aggregates and can partially replace virgin binder demand. This creates direct cost savings and delivers measurable environmental benefit through reduced extraction and reduced bitumen production impacts. The engineering challenge lies in the rheological condition of the aged binder. Oxidative aging increases stiffness, raises viscosity and reduces ductility. While increased stiffness can enhance rutting resistance under high temperatures, it may also reduce strain tolerance and increase thermal and fatigue cracking risk. For this reason, RAP mixtures require robust volumetric control and performance-informed testing rather than relying solely on traditional empirical criteria. This study evaluates how RAP percentage and binder content influence mixture performance and identifies a practical RAP range that maximises benefits without compromising durability.