Influence of Polymer and Rubber Modification on Fatigue Crack Propagation in Asphalt Mixtures: A Cyclic SCB and Paris Law Investigation

Fatigue cracking is a major distress limiting asphalt pavement service life, and Paris law–based fracture mechanics offers a more mechanistic understanding than conventional fatigue testing. However, systematic characterization across diverse modifiers, dosages, notch depths, and temperatures remains limited. This study investigates, for the first time, fatigue crack growth in asphalt mixtures modified with SBS, 611, and 701 elastomers, crumb rubber (CR), and Elvaloy + PPA using cyclic semicircular bend (SCB) testing under the Paris law framework. Tests were performed at 10‐, 20‐, and 30‐mm notch depths and 20°C/40°C, under stress‐controlled loading at 50% of the monotonic SCB peak load, evaluating a – N relationships and Log( da / dN )‐Log(Δ K ) curves. Fatigue life of the unmodified mixture ranged from ~400 to ~20 cycles, while the 4%‐611‐modified mixture performed best, reaching ~1500 cycles (three‐ to four‐fold improvement) and ~350 cycles (17‐fold improvement) under the most severe condition. Modification mainly reduced the Paris law coefficient C , not exponent n .