Emissions of tar-containing binders: Field studies

Abstract

This study describes the measurement of emissions during field construction of asphalt pavements using tar-containing recycled asphalt pavement (RAP), which is known to release harmful substances, such as polycyclic aromatic hydrocarbons (PAH). At three different test sites, the main emission sources were identified and the total emission rates of fumes and PAHs of the paving process were determined. For this purpose, the paver was temporarily enclosed. While the screed area was the main emission source, the hopper area and freshly compacted pavement were also significant. In comparison with previous laboratory tests, the binder composition and the resulting emissions were comparable, except for Naphthalene. Benzo(a)pyrene (BaP) as a representative for carcinogenic PAHs was identified as a good leading compound, correlating well with the toxicity weighted sum of PAHs. In contrast, the unweighted, mass related sum of all EPA PAHs does not seem to be a good parameter to assess workplace concentrations because emissions by mass are dominated by the less hazardous 2-, 3- and 4-ring PAHs. Workplace concentrations for bitumen fumes and PAHs were below limit values in all three field studies. However, the margin was not large and the field tests were done under favourable meteorological conditions. Therefore, we suggest maintaining the current Swiss limit of 5000 mg EPA-PAH per kg binder in the RAP-containing hot mix.

Keywords:

• Recycling
• tar
• bitumen
• polycyclic aromatic hydrocarbons PAHs
• emission measurement
• field testing

Acknowledgments

The research project was funded by the Swiss Federal Roads Authority FEDRO. Special thanks to Regula Haag and Cornelia Seiler for the chemical analysis, to Joachim Mohr, Kerstin Zeyer, Peter Honegger, Hans Kienast, Christian Meierhofer and Roland Takacs for the sampling and sample preparation.