Monitoring the Failure Stages in Asphalt Concrete Mixture throughout its Fatigue Life

Abstract

After practicing the dynamic stresses from environmental change and vehicular loading, signs of failure initiation appear in asphalt concrete throughout its service life in the form of rutting, cracking, or other types of distress. In this work, an attempt has been made to detect the stages of failure initiation in asphalt concrete at the laboratory testing conditions. The role of constant strain level and asphalt binder content were assessed through a detailed testing program. Various mixtures of asphalt concrete were prepared with optimum binder content and with (± 0.5 %) asphalt binder below and above the optimum requirements. The prepared asphalt concrete mixtures were subjected to laboratory roller compaction into a slab mold. Beam specimens were obtained from the slab samples and tested for fatigue life using three constant strain levels of (750, 400, and 250) micro strain under dynamic flexural stresses at 20℃ environments. Four stages of failure have been detected throughout the elapsed time consumed to reach the failure. A significant influence of the binder content on controlling the starting and end point of each failure stage could be detected. However, the influence of constant strain level is more pronounced as the binder content increases. The elapsed time consumed by the asphalt concrete to exhibit failure increased by (0.5, 6, and 39) folds while the flexural stiffness declined by (20, 60, and 80) % for (750, 400, and 250) micro strain levels respectively as compared with the mixture prepared with lower binder content. The elapsed time consumed by the mixture to show the failure stages of asphalt concrete increased by (33.3, 16.6, and 50) % for (750, 400, and 250) micro strain levels respectively when the asphalt binder content is higher than the optimum.