Direct Measurements of Volatile and Semivolatile Organic Compounds from Hot- and Warm-Mix Asphalt

Emissions from the production and paving of hot-mix asphalt are increasingly being scrutinized. The introduction of warm-mix asphalt (WMA) technologies could potentially lead to a reduction in these emissions. However, the measurement of these emissions is both complex and expensive. To overcome these obstacles, the University of California Pavement Research Center has developed a simplified protocol that can be used in addition to conventional methods and that allows direct comparison of emissions from different mixes measured at the pavement surface during construction. A portable flux chamber is used to capture and directly measure emissions before, immediately after, and 2 h after compaction. Emissions are collected in activated charcoal sorbent tubes and analyzed by using gas chromatography–mass spectrometry in the laboratory to identify individual compounds. The protocol was evaluated during the construction of a test track that will be used in an accelerated pavement test to compare the performance of three rubberized hot-mix asphalt controls against seven rubberized WMA sections. The measured reactive organic gases included selected volatile and semivolatile organic compounds. The results demonstrated that WMA technology type, temperature, and level of compaction greatly influence emissions characteristics. On the basis of the success of the pilot study, the project is being extended to measure other types of emissions, including polycyclic aromatic hydrocarbons, and to assess real-time analysis methods.