Analysis of Long-Term Effectiveness of Thin Hot-Mix Asphaltic Concrete Overlay Treatments

Abstract

Thin hot-mix asphalt (HMA) concrete overlays are preventive maintenance treatments used to address minor distresses, increase ride quality, and extend pavement life. This paper determines the long-term effectiveness of such treatments by using three measures of effectiveness: treatment service life, increase in average pavement condition, and area bounded by the performance curve. For each measure of effectiveness, the pavement performance indicators used are the international roughness index (IRI), rutting, and pavement condition rating (PCR). For each measure of effectiveness and performance indicator, treatment benefits were found to lie within a wide range because of the effect of varying levels of weather severity, traffic, and route type. The service life of the treatment ranges from 3 to 13 years (IRI performance indicator), 3 to 14 years (rutting), and 3 to 24 years (PCR). When the increase in average pavement condition is used as the measure of effectiveness, the results show that such treatments offer 18% to 36% decrease in IRI, 5% to 55% reduction in rutting, and 1% to 10% increase in PCR. For the area enclosed by the performance curve, thin HMA overlay effectiveness ranges from 40 to 360 IRI years (where IRI is in inches per mile), 0.13 to 0.76 RUT years (where RUT is in inches), and 7 to 130 PCR years (where PCR is on a 0 to 100 scale). The wide ranges of thin HMA overlay effectiveness for each combination of measure of effectiveness and performance indicator is suggestive of the sensitivity of the treatment effectiveness to levels of traffic loading and weather severity, and route type. The effectiveness of thin HMA overlay treatments is of interest to pavement professionals and is a vital input in the quest for cost-effective long-term pavement preservation practices.