Review of fume-generation mechanism, test methods, and fume suppressants of asphalt materials

Asphalt pavements are widely used in road engineering owing to their good skid resistance, ease of maintenance, and high driving comfort. However, large amounts of toxic fumes are produced during petroleum asphalt heating, asphalt mixture preparation, and pavement construction. This review clarifies the fuming mechanisms and hazards of asphalt fumes with the aim of promoting the application of fume-suppression asphalt(s) and reducing the emission levels of asphalt fumes. First, starting from the fuming mechanisms of hot asphalt, the composition and hazards of asphalt fumes are described. Second, existing indoor and on-site asphalt fume testing methods are discussed. Finally, the inhibitory effects and mechanisms of different types of fume suppressants are discussed separately to provide a reference for the popularization and application of fume-suppression asphalt. The review shows that the existing descriptions of the fume-generation mechanisms are based on physical phenomena, and there is a lack of systematic research at the chemical level. An indoor asphalt fume test is usually conducted using a fume-generation and collection device, where the main test object is an asphalt binder. Therefore, it is difficult to simulate real fuming conditions in these tests. A field testing mainly evaluates the concentrations of different types of asphalt fumes, and there is a lack of standardization of asphalt fume test methods and emission specifications. Existing asphalt fume suppressants mainly include polymers, flame retardants, warm mixing agents, adsorbents, and nanomaterials; traditional fume suppressants such as polymers, flame retardants, and warm mix agents have poor fume-suppression effects or reduce the pavement performance. Meanwhile, nanomaterial-based fume suppressants have good fume-suppression and improved pavement performance to some extent; however, they are still in the early stages of exploration. Therefore, future research should focus on asphalt fume-generation mechanisms, asphalt fume-evaluation methods and specifications, and environmentally friendly nanomaterial-based fume suppressants.