Infrared Thermography Revolutionizes Hot-Mix Asphalt Paving

Hot-mix asphalt (HMA) surfaces comprise about 90% of the highways and roads in the U.S. Highways and are typically engineered to last 15 years or more, but many have been failing early due to potholes, cracks, raveling, and other problems. This premature road failure unnecessarily wastes millions of taxpayer dollars every year. This paper describes a series of research studies that were conducted jointly by the Washington State Department of Transportation (WSDOT) and the University of Washington to determine the reason for the premature failure of HMA paved roads, beginning in 1995. The studies used infrared (IR) thermographic and follow-up in situ nuclear density testing, laboratory analysis, and field evaluations. Study results confirmed that a major cause of premature mat failure stems from temperature differentials within the hotmix during laydown. Further research and actual road construction experience has confirmed that reblending the hot mix immediately prior to laydown can reduce or eliminate the problem. WSDOT has used these findings to supplement its HMA density specification with a new density test method for selected HMA construction projects in 2002 and thereafter.