Influence of Dynamic Flexural Stresses (DFS) on Flow Number (FN) of Asphalt Concrete (AC)

Abstract

The flow number (FN) of asphalt concrete (AC) pavement is the number of dynamic loading cycles at which the Visco-plastic strain hardening of the AC mixture reaches saturation. It varies among the deformation types (resilient, permanent, and total). An attempt has been taken in the present work to identify such variation in the FN when the AC mixture is subjected to dynamic flexural stresses (DFS). Beam specimens of AC were prepared with optimum binder content, conditioned and tested at 25˚C environment at the chamber of the pneumatic repeated load system (PRLS). Linearly Variable Differential Transformer (LVDT) was used to monitor the deformation (total, permanent, and resilient) of the AC beam under each load cycle. The DFS was applied (0.1 sec. load duration and 0.9sec. rest period) to the specimen and the flexural deformation at the central third of the beam specimen was measured under each load repetitions. It was observed that the FN is (60, 280, and 300) at (resilient, permanent, and total) deformation respectively. The deformation at failure was (0.2, 5.3 and 5.5) mm for (resilient, permanent, and total) parts of deformation respectively. It was concluded that linear regression model is formed before reaching the FN with high coefficients of determination. However, after reaching the inflection point which represent the FN of the AC mixture, a power regression model is formed with acceptable coefficients of determination. It is recommended to use the obtained mathematical models for prediction of FN of AC mixtures and to distingush between the types of deformation when practicing DFS processes.