Mechanistic modeling and pull-off experimental validations of fatigue damage at bitumen–aggregate interfaces

Research on bituminous material fatigue has traditionally focused on tensile or shear damage of bitumen and asphalt mixtures, neglecting the critical bitumen–aggregate interfaces where microcracks initiate. Addressing this gap, the pull-off fatigue crack (POF-C) model was built to predict crack propagation at these interfaces under pull-off cyclic loading. The model, based on continuum damage mechanics principles, integrates force equilibrium and dissipated strain energy equilibrium. Pull-off fatigue tests were conducted on interfaces using limestone, tuff, and basalt aggregates, with #70 matrix bitumen and styrene–butadiene–styrene copolymer-modified bitumen, at temperatures of 15°C and 20°C, and with bitumen film thicknesses ranging from 0.2 mm to 0.8 mm. Dynamic modulus and phase angle data informed the model inputs. Predicted crack sizes closely matched measured results on fractured surfaces, demonstrating less than 2% prediction error. Scanning electron microscope tests confirmed the model's validity, showing numerous circular mesh depressions on fracture surfaces. The POF-C model accurately forecasts POF-C lengths across varied conditions, revealing three distinct stages of crack propagation: a rapid growth (∼0.025 mm/cycle), a stable expansion stage (<0.025 mm/cycle), and a slow fatigue stage (∼0 mm/cycle). The fatigue mechanism involves the development of microdamage into microcracks, their nucleation and aggregation, and macrocrack throughout the entire bitumen–aggregate interface.