Characterization of the Distress Modes and in Situ Material Properties of Highway Asphalt Pavement with Long Service Life

A 36-year-old, heavily trafficked highway asphalt pavement was analyzed in detail. The variation in structural capacity was assessed by a falling-weight deflectometer (FWD). Trenches were cut to examine the distresses in the pavement structure. Sample cores were taken for the study of distress modes, volumetric characteristics, and mechanical properties of the asphalt mixtures. Asphalt binder was extracted from the cores for the study of rheological properties. Rutting, cracking, fracture at the pavement bottom, and debonding at the interfaces were found to be the major distress modes. Air voids (AVs) were found to vary greatly in the samples and to be particularly high at the construction joints and at the pavement bottom. The total AV contents are primarily attributed to a few large voids, not a large number of seemingly disconnected voids. The stiffness of the road samples was much higher than that of the new mixture of the same type, and the average stiffness of the samples from the wheel path is lower than that of the samples from the nonwheel path. The increased stiffness by aging apparently reduces the sensitivity of the samples to stress change in fatigue tests. All binders in the different layers of the pavement were found to be severely aged, and pavement depth and mixture type significantly affect aging rate. Possible reasons for the durability of the pavement and pitfalls that may need to be avoided are discussed. The findings are important for the development of long-life flexible pavements.