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.
