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 National Cooperative Highway Research Program (NCHRP) project 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 sub S (deg C) for assessing mixture performance. Each unified curve is fitted with a constitutive equation from which model parameters are evaluated. Slope B sub 1 in the low-frequency region of the unified curve, when normalized with the term (T/T sub S), results in a parameter that is related to asphalt pavement distress at high temperature T. It is shown that B sub 1/T sub 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 B sub 2 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.
Samenvatting