Effect of Testing Mode and Microcracks Healing on the Flow Number (FN) of Asphalt Concrete (AC)
Keywords:
Asphalt concrete, Constant strain, Constant stress, Flexure, Flow number, HealingAbstract
The FN of AC mixture is considered a critical parameter in the assessment of its performance and is influenced by strain, binder content, and the testing environment used for the evaluation of the rutting potential of AC mixtures when practicing the dynamic loading. In the present work, the effect of microcrack healing and the mode of testing were assessed. AC beam specimens have been recovered from the slab samples, which were compacted by a laboratory roller compactor, and fatigue testing for fatigue in the four-point bending beam 4-PBB under dynamic flexural stress DFS. Specimens of the AC mixture were divided into three sets: the first one practiced testing under a constant strain level of 200 microstrain. The second set was tested under a constant stress level of 100 kPa. The third set was subjected to a microcrack healing process, then tested under constant microstrain levels of (400 and 200). The variation in the FN among the tests was detected and analyzed. It was noticed that FN under a constant strain level of 200 microstrain is higher by 125% than that under a constant stress level of 100 kPa. The permanent strain of the AC mixture when tested with constant strain is six-fold higher than that of the AC specimen tested with constant stress. The fatigue life of the AC mixture when tested under constant strain, in general, is 24 times higher than that of the AC mixture when tested under constant stress. However, the healing process exhibited lower FN when compared with that before healing. The FN of the AC mixture declined by (50%, and 33.3%) under (400, and 200) microstrain levels after practicing the healing process. The permanent strain of the AC mixture declines after healing by 4.4%, while the fatigue life of the AC mixture increased by one-fold after the healing process, regardless of the adopted constant strain level.
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