Gilbertson, Craig

Under the auspices of the Long Term Pavement Performance (LTPP) program eight SPS-5 overlay sections were constructed in Manitoba in 1989 and Minnesota in 1990. In addition to a control section the variables included mix design (virgin or recycled materials), overlay thickness (50 or 125 mm), and type of surface preparation (minimum or extensive). Over the past 15 years these sites have been monitored to evaluate and compare the pavement performance. The pre-rehabilitation condition record of the Manitoba test site was that it was rough with fatigue and block cracking evident. The predominant distress of the pre-rehabilitation condition of the Minnesota site was recorded as severe depressed transverse cracks. As much of the original amount of cracking has reflected through the applied bituminous overlays, none of the design options have outperformed the others in preventing or reducing the severity of reflective cracking. This paper concludes that the SPS-5 study has demonstrated that given pavements in the original condition of these two test sites, the use of the more expensive options of milling, thicker overlays, and virgin bituminous material have not resulted in significant pavement performance gains. Thus the lowest cost design alternatives (minimal surface preparation, thin overlay, and RAP in HMA mixture) would be chosen as the most cost-effective overlay design options.

This report reviews Manitoba's and Minnesota's Specific Pavement Studies (SPS-5) projects. The studies focus on investigating the performance of hot mix asphalt (HMA) overlays on HMA pavements and involve nine core test sections. The SPS-5 design variables in test sections include a control section (do nothing), amount of preparation of the existing surface (mill, no-mill), overlay thickness (50-mm, 125-mm), and the type of overlay material (virgin, recycle). Researchers plan to study the Manitoba and Minnesota SPS-5 projects, part of the Long-Term Pavement Performance (LTPP) Project, until 2010, when each project reaches the approximate age of 20 years. This project update includes a field review by the authors, a review of the existing monitoring data, and an estimate of the expected performance and cost expectations for upcoming years until 2010. Currently after 10 years all sections, excluding the control section, still are performing well. As a result at this point, researchers recommended the least costly treatment, 50-mm recycled asphalt overlay with no surface preparation, for pavement rehabilitation.