Influence of Recycling and Healing on Flow Number (FN) of Reclaimed Asphalt Pavement (RAP)

Abstract

Healing the microcracks of AC mixture is a sustainable property which prolongs the useful life of the AC pavement. Recycling of aged flexible pavement is a sustainable process used to extend the life of the pavement. In the present work, Reclaimed Asphalt Pavement (RAP) was obtained from the in-service field pavement and recycled with a mixture of binder and carbon black. Laboratory specimens of Marshall size were prepared from both recycled and the control RAP mixtures and tested under dynamic indirect tensile stress (DITS) and dynamic double punching shear stresses (DDPSS) at moderate temperature of 20°C. A constant stress level of 138 kPa was implemented. The testing was conducted in the pneumatic repeated load system PRLS with constant loading frequency of 60 cycles per minute. The dynamic loading sequence for each cycle is 0.1 seconds of load duration and 0.9 seconds of rest period. The test was terminated after 1200 cycles of dynamic stress which allowed for the initiation of micro cracks. Specimens were stored in an oven for 120 min at 60 °C to allow for crack healing by external heating technique. The healed specimens were subjected to another round of DITS and DDPSS and the variations in the permanent microstrain (PM) and FN were recorded. It was observed that the FN declined by 212 % after recycling and declined by 44.4 % after healing when tested by DITS. PM increased by 14.2 after recycling while it declined by 166 % at failure for both aged and recycled mixtures after healing. However, FN of AC mixture declined by 18.2 % and declined by 66.6 % after healing. PM increased by (100, and 340) % for recycled and after healing under DDPSS cycles respectively. The recycling index before healing is lower by 50 % for DITS test as compared with that at DDPSS test. However, the recycling index after healing is lower by 30 % for DITS test as compared with that at DDPSS test. On the other hand, the healing index at failure showed no significant variation among the testing mode. FN is recommended as a sound measure for the efficiency of recycling process.