## 1 Introduction
The higher the oxidative aging level of asphalt pavements, the higher the extent of thermal cracking damage in the material. A great deal of research efforts has been directed towards the characterization and prevention of thermal cracks in pavement. The Superpave tests developed under the Strategic Highway Research Program (SHRP) in the 1990s have significantly improved the performance tests to assess the behavior of asphalt pavements by providing fundamental material tests over a broad range of production and service temperatures. However, the Superpave tests were not developed for (1) the characterization of highly modified binders, (2) the characterization of asphalt pavements containing recycled materials such as Reclaimed Asphalt Pavement (RAP) or Reclaimed Asphalt Shingles (RAS), and (3) the characterization of warm-mix materials. In addition to Superpave performance tests [8; 9; 10; 11; 12], studies conducted by several researchers [13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29] also provide valuable and significant insight into the estimation of asphalt materials low-temperature performance. Acoustic Emission (AE) has been used extensively for damage detection and assessment of several materials including concrete, steel, wood, and rock. However, there has been limited application of AE for evaluating damage mechanisms in asphalt materials. [PERSON] and [PERSON] [21] used AE techniques to detect crack initiation and propagation in indirect tensile (IDT) specimens at \(-23\)\({}^{\circ}\)C. The study found that failure by fracture is indicated by a sharp increase in total AE counts, and that significant AE counts occur at about 80% of the peak load. [PERSON] and [PERSON] [22] used AE to monitor temperature cycling tests with restrained asphalt concrete specimens at low temperatures (\(-10\)\({}^{\circ}\)C to \(-40\)\({}^{\circ}\)C). They observed that the repeatability of AE measurements is good, that the AE activity (i.e., number of events) correlates with the thermal fracture temperatures, and that the AE activity in restrained specimens at low temperatures is caused by defect initiation in the binder. [PERSON] et al. [23] used AE measurements to detect crack initiation and propagation in restrained specimens at low temperatures (\(-32\)\({}^{\circ}\)C to \(-20\)\({}^{\circ}\)C). They concluded that the Styrene-Butadiene-Styrene (SBS)-modified  
Figure 3: Oxidation of asphalt concrete pavements: (**a**) pavement section right after the construction (left), and the same pavement 19 months after construction (right); and (**b**) Schematic diagram illustrating the steep gradation of material properties (e.g., complex modulus) caused by oxidative aging at the pavement top material layer. mixes produced less AE activity than unmodified mixes. [PERSON] et al. [24; 25; 26; 27; 28] used AE techniques to characterize fracture in semi-circular bend asphalt specimens at low temperatures (\(-20\)\({}^{\circ}\)C). They also concluded that large amounts of accumulated AE events occur at 70% of material strength, that the maximum intensity of AE peaks correlates with the development of macro-cracks, and that the location of AE events suggests that a several centimeter-sized process zone forms before the peak load. [PERSON] and [PERSON] [29; 30] used an AE spectral analysis approach to characterize fracture in semi-circular bend asphalt specimens at low-temperatures, and concluded that an AE approach could be used for evaluation of asphalt pavements. All of this research work led to the development of standards by the American Association of State and Highway Transportation Officials (AASHTO MP1, 1998; AASHTO TP1, 1999; AASHTO MP1A, 2001) [8; 9; 10] that allowed the estimation of the low-temperature performance of binders based upon their rheological properties.