## 1 Introduction  
The majority of the roads in United States are surfaced with asphalt material, indicating the importance of this material in U.S. transportation infrastructure. In asphalt roads located in cold regions or in milder climate regions with large daily temperature fluctuations, a major form of deterioration is associated with the formation of low-temperature cracks, a.k.a., thermal cracks, in the pavement. Thermal cracks are categorized into two groups based on their formation mechanism: (1) \"single-event thermal cracks\", which occur in cold climates due to fast cooling rates; and (2) \"thermal fatigue cracks\", which develop after several cooling cycles in regions with a milder climate and large daily temperature fluctuations [1; 2; 3; 4]. Thermal cracking phenomenon demonstrates itself as a group of parallel, evenly-spaced, transversely-oriented, surface-initiated cracks in pavements. A typical thermal cracking pattern in asphalt pavements is depicted in Figure 1a. As the temperature decreases, thermal stresses build up in the pavement due to the tendency of the \"restrained\" continuous layer of asphalt pavement to contract. The distribution of thermal stresses through the pavement thickness is non-uniform, with the highest stresses occurring at pavement surface, see Figure 1b. Thermal cracks happen when the thermally-induced stresses exceed the material fracture strength. On the local scale, another source of thermal stresses in asphalt pavements is the thermal contraction mismatch between aggregates, i.e., crashed stone, and the surrounding asphalt mastic material. As the pavement temperature drops, asphalt mastic tends to contract more (often more than ten times) than the aggregate particles, causing increasing thermally-induced stresses in the pavement structure. At the same time as the temperature drops, the asphalt mastic becomes increasingly more brittle with less resistance against fracture. As a result, microcracks develop within the asphalt mastic when the thermally-induced tensile stresses overcome the fracture resistance of mastic material. In addition to mastic cracking, another type of damage, i.e., debondings, also occurs at low temperatures at the interfaces between asphalt mastic and aggregates, see Figure 2. Repair and rehabilitation of low-temperature cracks in pavements costs millions of dollars every year. In addition, damaged pavements also develop higher surface roughness, which leads to vehicle damage. A study by [PERSON] and [PERSON] showed that the presence of cracks in pavements would add over $300 per vehicle per 19,000 km (12,000 mi) driven in user costs [5]. Asphalt roads also suffer from oxidative aging [6; 7]. Figure 3a shows two images of the same pavement section: one taken right after the construction and the other 19 months later when the pavement has already encountered some level of oxidative aging. Figure 3b shows a schematic diagram illustrating the typical steep gradation of material properties (e.g., complex modulus) caused by oxidative aging at the pavement top material layer. Computer models have already been developed to estimate the change in material properties due to oxidative aging for given climatic conditions [7]. In addition to changing the asphaltenes to maltenes ratio [6], oxidative aging also increases the stiffness of the top material layers, see Figure 3b, which increases the pavement vulnerability to cracking in cold  
Figure 1: Thermal cracks as a result of oxidation; (**a**) typical thermal cracking pattern in asphalt pavement, (**b**) thermal cracking formation and non-uniform distribution of thermal stresses through the pavement thickness. Figure 2: Schematic depiction of thermally-induced stresses within the asphalt mastic causing microcracks in the mastic and mastic-aggregate debondings. environments. Oxidative aging is an important issue in asphalt pavements that negatively affects low temperature cracking of asphalt materials.