Assessment of low-temperature cracking in asphalt materials using an acoustic emission approach

An acoustic emission (AE)-based approach to evaluate low-temperature cracking susceptibility of both asphalt binders and asphalt mixtures is presented. The AE binder testing approach consists of a thin film of asphalt binder bonded to a granite substrate exposed to decreasing temperatures ranging from 20°C to -50°C. Because of the differential thermal contraction between the granite substrate and the asphalt binder, thermal cracks develop in the asphalt binder. The initiation/propagation of these thermal cracks leads to a release of mechanical elastic energy in the material, i.e., acoustic emission activity that is recorded and used in determining the embrittlement temperature of the binder material. The AE-based embrittlement temperature showed excellent correlations with thermal cracking predictions based upon the binder rheological properties. Similar results were also obtained when asphalt concrete mixture samples were exposed to temperatures ranging from 20°C to -50°C. The AE-based approach for low-temperature characterization of binders and asphalt concrete mixtures is a rapid and reliable testing method that yields results with better repeatability (lower coefficient of variation) than the traditionally used methods based upon the binder rheological properties. Current results using AE source location also indicate that the AE approach could be used to quantitative evaluate the effectiveness of rejuvenators on aged asphalt pavements.