Summary

Bitumen, a product of petroleum distillation, is heated and then mixed with crushed mineral materials (aggregate) to form the hot mix asphalt that is used for paving most roads. The gases, vapours and particles emitted when the bitumen or asphalt is heated are composed of a complex group of chemical compounds that are regulated under the name of asphalt fumes, in particular in Quebec’s Regulation respecting occupational health and safety. If bitumen does not adhere to the aggregate according to the prescribed standard, an anti-stripping agent (chemical additive) is added to it. This type of bitumen, which we will call high stripping resistance (HSR) bitumen, has been used in Quebec for approximately 15 years.

For several years, paving workers have been complaining about irritation of the eyes and respiratory system following the use of HSR bitumen with this type of additive. However, the substances emitted during paving with HSR bitumen with an anti-stripping agent have been studied very little. The first two objectives of this study were to characterize in the laboratory the fumes emitted by HSR bitumen with an additive and then identify the specific chemical compounds in this type of bitumen that are suspected to be irritants or sensitizers. The third objective was to develop a sampling and analysis method for the compounds identified in this study so they can later be assessed in the workplace.

Two complementary approaches were used in the lab: a headspace (HS) generating system coupled with gas chromatography–mass spectrometry (GC-MS) and a reactor generating system. Three mixtures of bitumen and additives (anti-stripping agent), called S, V and W here, were selected for this study, based on the frequency of their use by Quebec’s Ministère des Transports, de la Mobilité durable et de l’Électrification des transports.

The two approaches enabled the identification of several compounds contained in the emissions produced during generation with single additives, including amines, amides, amino alcohol, glycols and glycol ethers. During generation of fumes with bitumen, the HS-GC-MS approach revealed only a limited number of compounds that were specifically attributable to the presence of the additive, namely pyrazine (S, V and W), ethylene glycol (W), diethylene glycol (W) and triethylene glycol (W).

Based on their irritant nature and their representativeness among all the compounds identified, 10 compounds were systematically assessed in 74 reactor generation tests, using an optimized version of IRSST method 363 (Amines in the air). The results showed that most of the compounds evaluated were attributable to the presence of the additive in the three types of bitumen studied. The compounds with the highest concentrations during the generation tests were the following: piperazine (S, V and W), ethylenediamine (S, V and W), ethanolamine (W), diethanolamine (W) and diethylene glycol (W). The temperature at which the bitumen was heated in the reactor proved to be the main determinant of the concentrations measured. Air samples taken in an asphalt mixing plant directly above the tank of bitumen with an additive (S) at 160–165 °C revealed results on the same order of magnitude as those obtained in the laboratory for the same bitumen, confirming that the results obtained with the reactor approach were valid and thus that all of the study’s objectives were achieved.

This research allows one to conclude that the presence of additives in bitumen may increase the irritant potential of asphalt fumes. Nevertheless, more detailed assessments in the workplace are required to confirm workers’ exposure level to these irritants.