Standardized Procedure for Analysis of Dynamic Modulus |E*| Data to Predict Asphalt Pavement Distresses

A standardized procedure is presented by which various asphalt concrete mixtures can be compared and their expected performance can be assessed in a uniform manner with the simple performance test suggested by NCHRP 9-19: Superpave Support and Performance Models Management. The frequency sweep data generated from the test are available in terms of dynamic modulus |E*| versus frequency at the measurement temperature under different levels of confining stress [0, 20, 30 psi (0, 0.14, 0.21 MPa)]. The moduli versus frequency data at different temperatures are unified to form a single curve for each mixture through a normalizing parameter. The temperature at which the normalizing parameter becomes equal to 1 is designated the specification parameter T_s (°C) for assessing mixture performance. Each unified curve is fitted with a constitutive equation from which model parameters are evaluated. Slope B₁ in the low-frequency region of the unified curve, when normalized with the term (T/T_s), results in a parameter that is related to asphalt pavement distress at high temperature T. It is shown that B₁/T_s is related to rut depths measured at different WesTrack (a full-scale test track) sections and the correlation improves with increasing confining stress. There is a good possibility that slope B₂ in the high-frequency region of the unified curve may relate to distresses in the intermediate temperature range, such as fatigue cracking. A preliminary check shows this may be true, but data are too limited to draw firm conclusions.