The use of a thermal camera for quality assurance of asphalt pavement construction

The goal of the study was to assess the use of thermal camera to quantify the asphalt pavement homogeneity and to develop the quality assurance criteria to be used in paving contracts. In addition, the benefits of using thermal camera, for both the contractor and the client, were explored. Three test roads were studied in summer 2013 by monitoring paving work, interviewing contractors and taking core samples from the segregated pavement locations. At all sites thermal camera was mounted to the asphalt paver to record temperatures during paving work. Core samples were analyzed to determine pavement properties such as bulk and maximum density, binder content and gradation. Also mechanical properties stiffness and strength were measured. At all sites paving work was mill and fill type overlay with stone mastic asphalt mixture laid less than 40mm layer. As expected, study confirmed that truck-load segregation can be detected with thermal camera and severity of physical aggregate segregation correlates to temperature differentials. High level of segregation was detected when temperature between truck end and middle load differed more than 24 degrees C. However, not all temperature differentials are caused by physical segregation and certain trends in measured temperatures testified the presence of thermal segregation caused by the long hauling distance. A bonus calculation system provided by the thermal camera vendor was assessed at all three paving contracts. Bonuses were received only by keeping the paver moving as targets for the risk areas and cold spots were not met. No penalties were applied. More research is needed to recommend changes to the temperature assessment in the bonus system, but allowing variable paver speed to prevent paver stops is not recommended. The detrimental effects of truck-load segregation were mitigated by the higher compaction effort, which produced stronger mixture. To quantify this improvement, a follow-up study to monitor distress formation during the coming years is thus warranted.