Comparison of Laboratory Cracking Test Results with Field Performance of Moderate and High RAP Content Surface Mixtures on the NCAT Test Track

In 2006, a group of experimental test sections was built on the National Center for Asphalt Technology Test Track to evaluate surface-layer mixtures containing 20 and 45 % Reclaimed Asphalt Pavement (RAP) with variations in the Superpave performance grade of the virgin binder. This paper discusses several laboratory tests that have been proposed as indicators of cracking susceptibility and how the results of these tests conducted on the mixtures used in the test sections compare with the observed cracking performance on the Test Track after five years. The cracking tests performed on the mixtures were the bending beam fatigue test, the Energy Ratio method developed at the University of Florida, the simplified viscoelastic continuum damage method developed at the North Carolina State University, and the Overlay Tester developed at the Texas Transportation Institute. On the track, the test sections performed very well, but exhibited a range of low-severity cracking, mostly near the edges of the wheelpaths. Cores were extracted to confirm that the cracks were limited to the surface layer. The field cracking performance indicates that the performance grade of virgin binder affects cracking resistance. The creep strain rate, measured as part of the Energy Ratio method, and the Overlay Tester results best matched the field performance of the test sections.