Study On Crack Propagation Behavior Of Asphalt Mixtures Based On CT Rael-Time Observation

Cracking is one of the major distress types of asphalt pavements. Expected life of pavements, pavement condition and maintenance cost are directly related to pavement cracking. It is crucial to have a sufficient understanding of cracking mechanism in order to produce a sound and safe material and structural design of asphalt pavements. This dissertation reports an orchestrated research on crack initiation, propagation, and failure in asphalt pavements.Simulation, surveying, observation, and measurement of cracking in pavement structures have been reported in literature in last three decades. However, cracking process in asphalt mixtures in a three dimensional scale is still a great challenge to road engineers. Using SIEMENS SOMATQM plus X-ray CT (COMPUTED TOMOGRAPHY) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. Marshall samples of AC20, SMA16, ATB25 were used under uniaxial compressive stress state. Stress and strain behavior was observed during the compressive failure process of asphalt mixtures. The tests reported here provide important theoretical fundamentals to study the cracking behavior and failure mechanism of asphalt pavement mixtures. Major conclusions of this research are summarized as follows.(1)Based on past experience and literature review, cracking mechanism of asphalt mixtures was analyzed. Stress-strain behavior was found to have a close relationship of cracking propagation in asphalt concrete materials. Study of cracking behavior of asphalt mixtures should be conducted in a micro-scale level to have a real simulation of crack propagation.(2)Failure process under compressive pressure was recorded using CT images and CT numbers. The direct responses in density change of Marshall samples under a CT-compressive process is the change of CT numbers. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. Voids are found to have a significant influence on damaging behavior of mixtures and play a governing role in deformation development. Loading rate is a critical factor influencing cracking velocity and cracking density. Temperature determines the ultimate capacity of...