Modeling asphalt mastic modulus considering substrate–mastic interaction and adhesion

Microscopic aggregate–mastic interaction and adhesion lead to macroscopic modulus nonuniformity of asphalt mastic on aggregate surface. This nonuniformity is ignored in multiscale models of mixture and causes prediction errors. This study aimed to establish a macromechanical model considering microscopic aggregate–mastic interaction and adhesion to characterize the mastic modulus in contact with aggregate substrates. Frequency sweep tests were conducted to measure the modulus of mastic with different thicknesses, and the measured mastic was simplified as a mechanical model comprising viscoelastic elements series. By introducing a piecewise function of thickness, the measured modulus was deduced as an expression containing the contribution of the affected layer and bulk phase. Four model parameters described the microscopic interaction, adhesion, affected range, and modulus of bulk mastic, respectively. The model was applied to the mastic modulus on different substrates, and results effectively demonstrated the applicability. The temperature and frequency dependence and time–temperature superposition of interface mastic modulus and bulk mastic modulus were observed, and it demonstrated the model's ability to characterize mastic viscoelasticity. Moreover, evaluation of the gap between the measured and real moduli on a substrate showed the necessity of considering interaction and adhesion.