Temperature dependency of VOCs release characteristics of asphalt materials under varying test conditions

Asphalt pavement is increasingly used in paving and roofing. However, the release of volatile organic compounds (VOCs) from asphalt harm both the environment and humans. Various methods were applied to characterize the VOCs for better understanding and inhibiting. However, asphalt VOCs have huge heating temperature dependency, which makes the asphalt VOCs' characterization complicated. In this research, three kinds of heating conditions, thermal gravimetric (TG) analyzer, pyrolysis (PY) analyzer, and thermal desorber (TD), were compared to determine the temperature dependency of VOC release characteristics. Gas chromatography and mass spectrometer (GC-MS) were then coupled for VOC detection. Results indicated that the TG heating condition can surely simulate the volatilization of VOCs from some asphalt that is not in contact with air (no oxygen) during the actual construction process, while PY and TD represent the substances released by the asphalt due to the boiling point at a certain temperature and under the actual construction process, respectively. The components detected by TG heating condition are both large and small molecules, while PY and TD heating condition will detect large molecules or small molecules, respectively. The VOC composition results under various heating conditions reflect the chemical reaction law of asphalt molecules in the heating process. When heating asphalt binders to a higher temperature, macromolecular substances will gradually crack and oxidize into small molecular substances, sulfides and nitrides. With the increase of temperature, the change trend of VOC components under different conditions is different.