An analysis of the mechanism of microdamage healing based on the application of micromechanics first principles of fracture and healing
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The selection of asphalt mixture constituents and properties to promote fracture fatigue resistance has been a formidable challenge in bituminous, materials, and pavement engineering. The fatigue process is considered as the result of the competing process of crack growth and crack healing. The former is one of microcrack development and growth. During the period of microcrack growth, microdamage healing significantly influences the process. The significance of the process of healing on fatigue damage was confirmed via laboratory testing, in which a very considerable recovery of dissipated pseudo energy was shown following rest periods. The significance of the healing process was also confirmed from field data showing recovery of stiffness measured by surface wave methods. A discussion on the mechanism of healing was presented based on first principles of fracture and healing. These principles showed that the surface energy of the mixture constituents and mixture compliance affected fracture and healing speeds. The effect of surface energy on the healing process was demonstrated via a comparison of bitumen surface energies determined for different bitumens to the rate of healing of mixtures containing those bitumens. A micromechanics fracture and healing model linked to a finite element analysis of direct tensile, controlled-strain fatigue tests established the link between surface energy, fracture, and healing.
