Evaluation of Induced Healing of Laboratory Aged Mixes Based on Semi-Circular Bending Test Results

Aging in asphalt pavements results in reduced serviceability and flexibility of pavements. Aging is not commonly considered as distress, but it substantially effects the rate of evolution of various distresses. One of the common distress observed in aged asphalt pavements is cracking. If cracks/micro-cracks are healed during their initial formation, the service life of the pavement will be increased. Otherwise, there will be the risk of crack propagation that results in more cracking and loss of pavement strength. It is well known that asphalt mixes have capability of self-healing their cracks/micro-cracks when they are exposed to high temperatures. Cracks/micro-cracks in asphalt mixes can be healed through an induced healing process. Induced healing of asphalt mixes by applying external electromagnetic radiation is an innovative technique to repair cracks/micro-cracks. Applying external energy through electromagnetic radiation increases the temperature of the asphalt binder in mixes, allowing it to move and fill the cracks/micro-cracks. Flowing and crack filling of asphalt binder play a significant role in induced healing characteristics of mixes. As temperature of the asphalt binder is increased, its viscosity will be decreased drastically. When asphalt binder gets to Newtonian fluid temperature or higher, the melted binder moves inside the cracks and micro-cracks and subsequently, the cracks will be healed. The aim of this research was to evaluate the effects of different aging levels on induced heating-healing of asphalt mixes. In order to impose different aging levels, asphalt mixes were aged in oven for 3, 5, 7 and 9 days at 85 ºC. Activated carbon was added to mixes so that to enhance electromagnetic sensitivity of mixes. In addition, effects of activated carbon on mechanical properties and microwave heating rate of mixes were determined. Results indicated that activated carbon, as a powder-based additive, improves electrical conductivity, induced heating-healing rate of asphalt mixes. In addition, it was shown that aging phenomenon in asphalt mixes decreases their heating rate, which was more pronounced in higher aging level. Lower heating rate of asphalt mixes resulting in lower efficiency of induced healing of mixes. For evaluating healing capability of mixes that were subjected to different aging levels, Semicircular Bending tests (SCB) was conducted at intermediate and low temperatures. It presented that induced healing efficiency of mixes decreased as the aging level and the notch length in SCB testing were increased. The adverse effects of aging on induced healing process can be attributed to increased viscosity of the asphalt binder in mixes, which limits moving capability of melted asphalt binders to move through damages and properly heal the cracks. Moreover, it resulted that, lower heating rate of aged mixes can be considered as another reason of reduction in induced healing efficiency. The results indicated that increased notch lengths not only affects load at fracture and fracture energy of mixes, but also it plays a significant role in induced healing efficiency of mixes. For further evaluation of the healing ability of asphalt mixes, combination effects of aging, notch lengths and testing temperature parameters were also investigated. Notch length and testing temperature was found to have significant effects on induced healing efficiency of mixes. In addition, the results indicated that induced healing efficiency of low temperature cracked asphalt mixes were more than that of asphalt mixes that were cracked at intermediate temperatures. The results suggest that the necessity of considering aging level in analyzing induced heating-healing process of asphalt mixes.