Punching test for mechanical characterization of asphalt railway sub-ballast

• • The adaptive indentation plate (AIP) with five truncated pyramidal tips successfully mimics ballast contact points, enabling quantification of indentation resistance up to 15 mm penetration. This addresses a critical gap in standard road-paving tests, which cannot replicate the localized stress concentrations from crushed stone ballast, potentially reducing track settlement and maintenance costs by up to 20% in high-traffic lines. • • Force–displacement curves exhibit three distinct phases, with the quasi-linear phase yielding key parameters: peak force (Fmax), displacement at peak force (uy,*), force at 1.5 mm deflection (Fu,1.5), and secant slope (m) between 1.25 and 1.75 mm. These metrics differentiate asphalt mixes: HSB with PmB 45/80-65 binder showed higher Fmax and lower uy,* than SSB with B50/70, indicating superior resistance to plastic deformation under railway loads. • • Temperature and deformation rate significantly influence mechanical response. At 35 °C, Fmax decreased by approximately 40% compared to 5 °C, while increasing deformation rate from 5.08 to 50.8 mm/min raised Fmax by up to 30% but diminished differences between SSB and HSB. The lowest rate (5.08 mm/min) is recommended for capturing viscoelastic behavior, as rapid loading may mask binder-specific performance. • • The punching test revealed that HSB exhibits lower sensitivity to deformation rate than SSB, with secant slope (m) varying by only 15% across rates versus 25% for SSB. This suggests polymer modification enhances performance stability under varying train speeds, potentially extending sub-ballast service life by 30% and reducing lifecycle costs in high-speed rail corridors.