Estimation of low-temperature cracking threshold for asphalt binders using an acoustic emission approach

An acoustic emission (AE) approach to evaluate low temperature cracking susceptibility of asphalt binders is presented. Thin films of asphalt binders were bonded to granite substrates and exposed to temperatures ranging from 15°C to - 50°C. Differential thermal contraction between granite substrates and asphalt binders induces progressively higher thermal stress in the binders resulting in thermal crack formation, which is accompanied by a release of elastic energy in the form of transient waves. Using piezoelectric sensors (Digital Wave, Model B-1025), a four-channel acoustic emission system was used to record the acoustic emission activity during the binder/granite cooling process. Assuming the cracking temperature (T_cr) to be the temperature at which the AE signal energy exceeds a pre-selected threshold energy level, this AE testing approach was found to be sensitive and repeatable for predicting cracking temperatures (T_cr) in four SUPERPAVE core asphalt binders. These AE-based T_cr predictions showed strong correlation (R² = 0.9) with predictions based on either AASHTO TP1 or MP1A protocols. Unlike TP1 and MP1A protocols, the presented AE approach does not require the use of sophisticated software for predicting thermal stresses, and no assumption is required regarding the testing cooling rate and the binder coefficient of thermal contraction.