Shear strength parameters for porous asphalt mixtures: From macro to meso

The shear strength of asphalt mixtures significantly influences the rut resistance of flexible pavements. Existing methods predominantly address macroscopic aspects, failing to unveil the underlying mechanisms. Moreover, experimental determination of shear strength parameters is time-consuming, but there is a lack of simple prediction methods. This study explores correlations between macroscopic parameters (friction angle and cohesion) and key mesoscopic shear-related factors in Porous Asphalt Mixtures (PAMs) using multiscale triaxial compressive tests, dynamic shear rheometer tests, and sessile drop tests. The research reveals that PAM is influenced not only by aggregate interlock but also by stiff mastic, resulting in a reduced friction angle at a lower temperature. Regression analyses establish a prediction formula for PAMs, incorporating the friction angle of the aggregate skeleton and the complex modulus of the mastic. A correlation function, inspired by Griffith's fracture theory, was also proposed to link PAM's cohesion with the complex modulus and the work of cohesion of mastic, and the friction angle of PAMs. Predictions for PAM's friction angle and cohesion align well with macro-level experimental results, with all the coefficients of determination of over 0.94. These findings enhance the understanding of asphalt mixture shear strength formation and enable shear-resistance optimisation from meso-level.