Using Infrared Thermography to Detect and Measure Segregation in Hot Mix Asphalt Pavements

This paper summarizes the findings from the recently completed National Cooperative Highway Research Program (NCHRP) 9–11 Segregation in Hot Mix Asphalt Pavements which details the use of infrared technology for detecting and measuring segregation. Infrared thermography can be used to detect localized areas of cooler mix during typical hot mix asphalt (HMA) construction. These areas are the result of portions of mix which have cooled differentially (temperature segregation) as well as coarse aggregate-rich areas (gradation segregation). Coarse areas tend to have both more and larger air voids around the aggregate particles which allow these areas to cool faster. This is seen in the infrared image as cold spots in the freshly laid mat. Results indicate that a temperature differential of 10, 16. 21 and greater than 21 °C from the maximum temperature in a given infrared photograph correlate with levels of segregation of none, low, medium and high, respectively. These levels of segregation are defined by statistically significant increases in air voids, decreases in mixture stiffness, increase in numbers of sieves with a greater percent retained and decreases in asphalt contents.