Characterizing asphalt emissions under in-service conditions
Douglas M. Kriech, Alexis C. Crawford, Lisa A. Smith, Linda V. Osborn, Anthony J. Kriech
Abstract
Recent studies have suggested that asphalt related emissions at environmentally pertinent conditions are a major contributor of volatile organic compounds ubiquitous to the environment. Many variables such as temperature/viscosity of asphalt binder, solar irradiance of the asphalt binder, and geometric constraints including film thickness, the act of coating aggregate to produce Hot Mix Asphalt, and compaction into pavements influence the magnitude and composition of measured emissions. Continuous films of asphalt binder were used to determine how temperature/viscosity and film thicknesses can influence measured emissions. The magnitude of emissions scaled with the inverse of viscosity, whereas the composition of emissions varied with film thickness and age of the asphalt binder sample. Asphalt binder exposed to solar irradiance showed short term impacts on emissions in the first hours of exposure. Compacted asphalt pavements were used to simulate real world new in-service conditions. The emissions from a freshly compacted asphalt pavement were compared to a 17-year-old pavement sample collected from the field to determine how the act of compacting asphalt binder coated in aggregate influenced emissions over a 17-year period. An increase in the complexity of the system caused slowing in the total emissions profile. While lower than what was observed in the freshly compacted samples, emissions were still observed in the 17-year-old pavement. The composition of emissions indicated that smaller and more volatile compounds are capable of being released from deeper within the compacted pavement, whereas the larger and less volatile compounds tend to remain trapped.