# Investigation of Crack Propagation and Healing of Asphalt Concrete Using Digital Image Correlation
2  
[PERSON] 1  
1 Faculty of Applied Engineering, University of Antwerp, 2020 Antwerp, Belgium;  
[EMAIL_ADDRESS] (C.V.); [EMAIL_ADDRESS] (A.M.);  
[EMAIL_ADDRESS] (B.R. ); [EMAIL_ADDRESS] (G.J. ); [PERSON]RESS] (B.J. );  
[PERSON](W.V.d.b. ); [PERSON]W.V.d.b. ); [PERSON]S.V.) 2  
[PERSON] 1  
1 Faculty of Applied Engineering, University of Antwerp, 2020 Antwerp, Belgium;  
[EMAIL_ADDRESS] (C.V.); [EMAIL_ADDRESS] (A.M.);  
[EMAIL_ADDRESS] (B.R. ); [EMAIL_ADDRESS] (G.J. ); [EMAIL_ADDRESS] (J.B.);  
[PERSON](W.V.d.b. ); [PERSON]W.V.d.b. ); [EMAIL_ADDRESS] (S.V.) 2  
[PERSON] 1  
1 Faculty of Applied Engineering, University of Antwerp, 2020 Antwerp, Belgium;  
cedric.vThe significance of healing has been proven by multiple researchers through different laboratory tests [5]. In one experiment, the change in the stiffness of asphalt mixtures due to temperature and fatigue damage growth and healing during rest periods were evaluated using the impact resonance method. These experiments showed an increase in the dynamic modulus of the damaged specimens after a rest period. It was also proven that a higher healing temperature increases the amount of healing that occurred during the rest periods [6]. Another method to investigate the healing is through dynamic mechanical analysis performed on asphalt mortar to characterize fatigue damage and healing under strain-controlled torsional testing. These experiments illustrate the effects of microdamage healing due to rest periods and the increase of the dynamic modulus after the rest period, and consequently an increase in the fatigue life of asphalt mixtures [7]. However, damage formation and healing are not the only important factors in fatigue experiments. During fatigue experiments, reversible and non-reversible mechanisms happen at the same time. The non-reversible mechanisms are damages caused by self-heating, permanent deformation, and structural damages, and the reversible mechanisms are healing, thixotropy, and steric hardening. Currently, there are no models that can quantitatively identify the contribution of all these phenomena [4; 8]. However, while investigating the mechanical recoveries of asphalt mixtures, it is important to take into account that healing is not the only influential phenomenon. Non-linearity, thixotropy, and steric hardening can also generate similar mechanical recoveries during the unloading stage. Different methods have been suggested by researchers to quantify the healing in asphalt. Some approaches introduce parameters that provide a relative comparison of healing between mixtures and some provide a more absolute measure of healing through proposed parameters [9]. A popular method is to use [PERSON]'s extended nonlinear elastic-viscoelastic correspondence principle [10] to characterize both the microdamage and microdamage healing during the damage process. Using this method, some healing indices have been defined and it has been demonstrated that longer rest periods result in more healing, and consequently greater fatigue life [11]. In another study, this approach has been used in the dynamic shear rheometer tests with a specifically designed intermittent loading sequence to define a healing rate, as the rate of dissipated energy recovery per unit of rest time, to quantify the healing potential of asphalt binders. The results of that study indicate that binder type, strain level, and temperatures have an important impact on healing [12]. An alternative method to determine the healing rate of asphalt mixtures is based on the recovered dissipated creep strain energy (DCSE) per unit time. This method was used to determine the healing properties of different mixtures and determine the influential factors on their healing capacity [13]. The healing factor currently used by the Flemish road agency for mixture design was developed in 1974 [14] and is 7.1 for all mixtures. This value is outdated and can lead to mistakes in design and faster deterioration of the road construction [15].