Polymer-softener modified binder to control potential fatigue and thermal cracking in flexible pavements

Asphalt binder modification has been increased to minimize cracking potential and extend pavement service life. This would reduce maintenance costs, and hence total emissions over the pavement life-cycle. Two categories of modifiers are commonly used: Polymers and softeners. This study modified two Superpave PG 64–22 binders using four softeners and one styrene–butadiene–styrene (SBS) polymer to produce blends with PG 58–28, 70–28, and 76–28, and included two unmodified PG 58–28 binders for comparison. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, and cigar-tube test were used to evaluate oxidation, softener thermal stability, and storage-stability, respectively Cracking potential was assessed using binder parameters, including: ΔT c parameter for low-temperature cracking, fatigue damage tolerance parameter Δ|G*| peak τ , and stiffness at m = 0.3, S(at m=0.3), as a potential surrogate for ΔT c . Results show that selected polymer–softener-modified binders exhibited synergistic improvements, simultaneously increasing Δ|G*| peak τ and S(at m=0.3) relative to base and softened binders, while FTIR suggested softeners slowed SBS degradation. The study demonstrates that polymer–softener modification can be tailored to reduce potential fatigue and thermal cracking. This allows establishing a practical framework linking Δ|G*| peak τ and S (at m=0.3) to ranking modified binders, thereby supporting performance-oriented binder selection for flexible pavements. • Softeners slow SBS degradation in polymer-softener-modified binders. • Δ|G| peak τ can rank binders; softeners and polymers have synergistic effects to reduce cracking potential. • Dual modification increases Δ|G| peak τ and S(m=0.3), lowering cracking potential. • Polymer-softener modification sequence may allow use of thermally unstable softeners. • S(m=0.3) may act as a ΔT c surrogate for polymer modification evaluation.