**3. Utilizing the AFM images as a basis for asphalt healing model**

From Atomic Force Microscopy (AFM) scans, it was found that bitumen is not a homogeneous bulk material as microstructures are observed in almost all the bitumen (Loeber et al., 1996, 1998; Pauli et al., 2001, 2009, 2011; Jäger et al., 2004; Masson et al., 2006). All the previous studies showed that bitumen appeared to have some form of 'phase separation' dependence on its temperature history, storage time and crude source. Changing the temperature of the bitumen showed a movement of the phases and sometimes resulted in an overall homogeneous material, where the clusters seem to have 'melted' back into the matrix structure. The ability of bitumen to phase separate and redistribute its phases depends on the thermal or mechanical energy input. Recently, based on this phase separation phenomena under certain kinetic conditions, Kringos et al. (2009a) developed a healing model by assuming the bitumen matrix has two types of phases (i.e., phase α and phase β), as shown in Fig. 2.

Fig. 2. AFM evidence of phase separation in bitumen (Pauli et al., 2011)
