Thermal Imaging of Hot-Mix Paving Operations for Quality Assessment: State of the Practice in Texas

In the mid-1990s, thermal imaging was identified as a technology that might locate segregation in hot-mix paving operations. In 2000, work started in Texas to evaluate the utility of infrared imaging for identifying segregation. Work conducted in Texas verified that temperature differentials did relate to changes in important hot-mix asphalt properties. This early work also showed that temperature differentials greater than 25°F (13.9°C) typically indicated problems in Texas mixes. With confidence in the utility of the technology, and recommended limits for temperature uniformity, Texas recently made substantial progress tailoring thermal data collection technology and data processing capabilities to hot-mix paving operations. The development and application of the current state of the practice for evaluating paving operations with thermal imaging in Texas are presented. The current methodology in Texas uses the Pave-IR system, which consists of a transverse bar with 10 infrared sensors immediately behind the paver, and the Pave-IR software package, which collects and displays the thermal profile in real time as the paving train progresses. In addition to real-time data display, Pave-IR can display in real time whether the paving temperatures fall within user-defined limits and, during paving, Pave-IR can provide a histogram of temperatures every 100 ft (30.5 m). Postprocessing functions in Pave-IR consist of data playback and review, spot temperature display, and creation of a histogram of the placement temperatures for the entire data file