Evaluation of fracture performance in porous asphalt mixtures reinforced by basalt and polypropylene fibers against runoff-induced degradation

Porous asphalt (PA) mixtures are vulnerable to fracture and durability loss when exposed to chemically aggressive runoff due to their interconnected void structure. Although basalt fiber (BF) and polypropylene fiber (PPF) are widely used to enhance mechanical performance, the comparative fracture response of fiber‑reinforced PA under sequential conditioning (oxidative aging followed by pH‑adjusted immersion) remains insufficiently understood. This study evaluates the fracture behavior of limestone- and granite-based PA mixtures reinforced with BF and PPF under acidic, neutral, and alkaline environments. PA mixtures were produced using 60/70 penetration grade bitumen and two aggregates with distinct mineralogical characteristics. A sequential conditioning protocol was adopted: short‑term aging (STA) and long‑term aging (LTA) were first simulated according to AASHTO R30, followed by vacuum saturation and five‑day pH conditioning in solutions ranging from pH 5 to 9. This sequence reflects pH-adjusted immersion where asphalt pavements undergo construction‑induced oxidative hardening prior to environmental chemical exposure from urban runoff. Fracture performance was assessed at intermediate temperature using semicircular bending (SCB) tests. Key indicators derived from the load-displacement curves included peak load (P max ), ultimate displacement, fracture energy (G f ), toughness index (TI), balanced cracking index (BCI), and dissipated energy ratio (DER). The results show that pH conditioning significantly reduces fracture resistance. Regarding P max , BF consistently outperformed PPF across most conditions, yielding higher load‑bearing capacity. However, PPF consistently provided greater deformation capacity and G f than BF. In limestone mixtures, PPF increased final displacement by about 36–77%, while BF produced a more moderate but stable improvement in fracture resistance. A similar trend was observed in granite mixtures, where PPF improved displacement by about 36–75% and BF by 17–49%. The environmental ranking was aggregate‑dependent: for limestone mixtures, pH 9 was the most damaging condition, whereas for granite mixtures, pH 5 often produced lower performance than pH 9. Fiber addition substantially increased fracture energy and crack tolerance, with improvements approaching 70% under favorable conditions. Aggregate mineralogy also influenced performance: limestone mixtures generally showed higher fracture resistance and greater stability across varying pH conditions than granite mixtures. Overall, the findings highlight the distinct roles of PPF in improving ductility and energy dissipation and BF in providing stable toughness enhancement, offering practical guidance for designing durable PA pavements exposed to chemically aggressive drainage conditions.