Investigation of low temperature cracking in asphalt mixtures by acoustic emission

This paper investigates the use of acoustic emission (AE) to characterize microstructural phenomena and the corresponding macroscopic behavior during the low temperature fracture of asphalt mixtures. An acoustic emission system with eight channels of recording was used to monitor the failure process during testing at low temperature using the semi circular bend (SCB) configuration in three Superpave mixtures used at MnROAD facility. Algorithms to automatically detect the relative arrival time of the AE signal and to locate the AE source were developed. The analysis of the accumulated AE events illustrated the relationship between the micro damage and macroscopic behavior at different loading levels. The damage level under certain loading conditions was evaluated and preliminary results showed that the load level corresponding to the localization played a critical role in the damage process of the material. As a first step, the fracture energy of asphalt concrete specimen was related to the accumulated AE energy. By observing the distribution of microcracks with different energy levels, it was reasonably assumed that 95% of the total AE energy before peak load corresponded to the process zone and this zone was determined to be around 3-6 mm in width and 20-30 mm in length for the materials tested in this research effort.