Combustion of Asphalt and Concrete in Case of Fire in Roads

The present study concerns the comparison of the behaviour at high temperature of an asphalt and that of concrete, the purpose being to define the parameters of choice of the material for the construction of roads, in particular in tunnels. To do this, laboratory tests of fire, thermal behaviour and chemical analysis of the asphalt studied were carried out. The tests showed at which temperature the asphalt ignites if exposed to fire and how long after the beginning of the fire this phenomenon would take place. Specimens of asphalt were exposed to a rise of temperature according to the ISO fire curve. Temperature charts were recorded. Visual observations completed the combustion tests and gave a detailed analysis of the behaviour of the asphalt at high temperature. The results of similar tests on concrete allowed a comparison between the behaviour of asphalt and that of concrete. Study of toxicity (chemical analysis of smokes and gases emitted during the combustion of the asphalt) was also carried out. This study showed that asphalt ignites between 428°C and 530°C. The first vapours emitted are felt 5 minutes after the beginning of the heating. The asphalt ignited 8 minutes after the beginning of the heating. Once the material was burning, the temperature charts showed that asphalt has a strong calorific power. After the test, only aggregates are still present but are not bound together any more by the binder. Because of this the material loses its mechanical characteristics and can no longer fulfil its main purpose. Concrete is incombustible, contrary to asphalt. It does not emit smokes. It does not change shape with high temperature and it keeps a large part of its mechanical characteristics. Toxicity study showed that the combustion of asphalt produces many pollutants whose dangerousness is proven.