Development and rheological characterization of warm mix asphalt binders with the coupled organic additive

• Synergistic action of NO and PEL in the developed coupled organic additive reduces viscosity significantly. • Competing dominant effects of PEL and NO influenced the rheological properties. • Fatigue and low-temperature cracking resistance were significantly enhanced. Wax-based warm mix additives are widely applied for their ability to enhance the rutting resistance of asphalt. However, they often compromise low-temperature performance, increasing fatigue cracking risk and reducing pavement durability. To address this, a coupled organic additive (COAPN), composed of polyethylene wax (PEL) and naphthenic oil (NO), was developed to improve asphalt workability by reducing viscosity while maintaining rheological performance at both high and low temperatures. Asphalt binders (COAWMA) with varying COAPN contents were evaluated through a series of tests. The results showed enhanced penetration and ductility, with FTIR confirming physical modification and good thermal stability. The synergistic effect of PEL lubrication and NO weakening of intermolecular forces significantly reduced viscosity with increasing COAPN content, and the cumulative viscosity reduction effect reached its optimum at 2 % content. DSR results indicated non-monotonic trends in the G ∗ , δ , G ∗ /sin δ , and G ∗ sin δ of COAWMA due to alternating dominant effects of NO and PEL. At 2 % COAPN, rutting resistance remained comparable to matrix asphalt while fatigue factor reduction expanded from 4.6 % at 1 Hz to 6.3 % at 10 Hz, demonstrating enhanced fatigue resistance. BBR results revealed progressive improvement of low-temperature crack resistance with increasing COAPN content.