Forensic Investigation Report for MnROAD Ultra-thin Whitetopping Test Cells 93, 94 and 95

Status:  Complete
Report Date:  11/07/2005


Three instrumented ultra-thin whitetopping (UTW) pavement test sections were constructed in 1997 at the Minnesota Road Research facility (MnROAD). The sections were installed on the interstate highway portion of MnROAD to accelerate the traffic loadings compared to typical applications of UTW. By spring 2004, significant deterioration of the sections had occurred. Prior to replacement of the three test sections in fall 2004, a forensic investigation of the distresses was carried out. The focus of this report was to describe the forensic investigation procedures carried out, and to summarize findings from the investigation. The investigation revealed that the performance of ultra-thin whitetopping test cells at the MnROAD project was related to traffic volume, wheel placement, and layer bonding. Distresses were more frequent and severe in the higher-volume driving lane. Panel sizes that place wheelpaths near the edges of UTW slabs resulted in accelerated distress and poor performance. Bonding of UTW to the underlying asphalt layer was essential for long-term performance. Reflective cracking occurs in bonded concrete overlays for thicknesses less than 5 inches (over 6 inch minimum asphalt layer). Large polyolefin fibers did provide some benefit to crack containment in UTW, but added significant cost to the concrete mix.

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