MIXTURE TESTING, ANALYSIS, AND FIELD PERFORMANCE OF THE PILOT SUPERPAVE PROJECTS: THE 1992 SPS-9 MIXTURES

Abstract

A Specific Pavement Study, SPS-9, was initiated near the end of SHRP to validate the research and recommend specifications. To showcase the Superpave system, four SPS-9 pilot projects were built in the summer of 1992. These projects were intended to identify obvious problems in the system and would provide the first validation. By the time the states were expected to begin implementation in 1995 or 1996, the pilot projects would have three or four years of performance history. These performance results were expected to influence Superpave implementation. The SPS-9 pilot projects now have more than seven years of in-service performance. After seven years of service, the pilot SPS-9 projects built during SHRP in 1992 are still performing well. All four projects indicate rutting of approximately six millimeters or less after 3.6 to 16.5 million ESALs. None of the four projects would be considered rutting mixtures. Reflection cracking has been noted on the three projects (IH-94, IH-43, and IH-65) that used HMA overlays over the existing pcc pavement. This was not unexpected since the pcc pavement was not prepared by either the break and seat or pr rubbilization methods prior to the overlay. Mechanical property testing using the Superpave shear tester indicated that, for the four surface mixtures, the two selected performance tests-simple shear (SSCH) and shear frequency sweep (FSCH)-correctly ranked the observed rutting performance. Maximum shear strain (SSCH) at a normalized high temperature increased as the observed rutting increased. Shear stiffness (FSCH) at a normalized high temperature decreased as the observed rutting increased. Estimated shear stiffness at maximum pavement temperatures also correlated well with observed rutting performance.