Papers by Author: Yan Jun Qiu

Abstract: Cracking has long been accepted as a major mode of premature failure in flexible 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. 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 SOMATOM plus X-ray CT (computerized 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 were used under uniaxial compressive stress state. Stress and strain behavior was observed during the compressive failure process of asphalt mixtures. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. Research results show that loading rate is a critical factor influencing cracking velocity and cracking density.

Abstract: The fracture resistance of asphalt materials significantly influences the service life of asphalt pavements and consequently affects the maintenance and rehabilitation costs of the pavement network. Therefore, there is significant interest in understanding the mechanism of fracture in asphalt pavements and in developing analysis tools that would lead to the selection of asphalt materials with increased fracture resistance. Study of cracking behavior of asphalt mixtures should be conducted in a micro-scale level to have a real simulation of crack propagation. Using SIEMENS SOMATOM plus X-ray CT (computerized tomography) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. 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 are change of CT numbers. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. The tests reported provide important theoretical fundamentals to study the cracking behavior and failure mechanism of asphalt mixtures.

Abstract: 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 necessary to promote the understanding of cracking mechanism of hot mix asphalt (HMA) based on fracture mechanics. 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. This paper reports a research effort of dynamic observation of the micro-fracture process of asphalt mixture under compressed condition using CT (computerized tomography) method. Through CT scanning, the clear CT images, which include the microcrack compressed, growth, bifurcation, development, the crack fracture, and the asphalt concrete sample failure were obtained. The CT numbers, CT images and the other data were analyzed. Analysis of the relationship between of CT number and volumetric strain suggests that damage value at zero volumetric strain can be used as threshold point in damage analysis. Corresponding stress value can be used as maximum allowable stress in design practice.

Abstract: Various asphalt pavement distresses, such as longitudinal cracking, thermal (transverse) cracking, and reflective cracking, are directly related to the fracture properties of the asphalt materials used in the pavement layers. The fracture resistance of asphalt materials significantly influences the service life of asphalt pavements and consequently affects the maintenance and rehabilitation costs of the pavement network. Therefore, there is significant interest in understanding the mechanism of fracture in asphalt pavements and in developing analysis tools that would lead to the selection of asphalt materials with increased fracture resistance. This paper reports a research effort of dynamic observation of the micro-fracture process of asphalt mixture under uniaxial compressed condition by using CT (computerized tomography) method. CT images were analyzed to investigate the process of micro-fracture of asphalt concrete. Research results show that the abnormal belt of density damage of asphalt concrete is the initiation belt of cracking and the turning point in the curve of stress and density distress increment is the point of cracking failure of asphalt concrete.

Abstract: Water damage of asphalt concrete pavements has been one of the major distresses in highway engineering. Engineering experiences and research results indicate that this damage is due to the extortionate air voids of bitumen mixtures. Paranormal porosity of asphalt mixture is largely the result of the poor controlling of compact degree during paving process. The quality of asphalt pavement is subjected to the controlling methods of compacting of bitumen mixtures. Ultrasonic is an excellent method for non-destructive testing used in various engineering fields. It is also a potentially effective tool to be applied in the control and evaluation of the compaction quality of bitumen mixtures. This paper presents the results of a study aimed at the applicability of ultrasonic technology for evaluation of porosity and compaction quality of bitumen mixtures. It is shown that this technology, which has been successfully used for many years for evaluation of Portland concrete structures, might be used in asphalt pavement engineering to provide a simple, quick, and objective methodology for control and evaluation of the compact quality of bitumen mixtures. The results of laboratory testing demonstrate the potential of this technology.

Abstract: The furthest dangerous cracking type of asphalt pavement is usually considered of the simplex
type crack(namely shear crack) under traffic load, but the so-called
type crack should be the compound cracking at the concurrence of I type crack (namely splay crack) and
type crack. In order to study the compound type crack propagation behavior of asphalt concrete, a three point bending beam with compound type notched has been designed. Asymmetry-gap small girder specimens of asphalt concrete are adopted in the test, and the central testing equipment is MTS. A series of compound type three point bending beam tests have been performed to simulate compound type crack initiation and growth. The propagation of compound type crack is studied by a newly developed numerical code, Rock Failure Process Analysis (RFPA2D).it is shown that the crack initiation angle and the peak load increased as the distance of the preexisting crack from the midpoint of the beam increased, the crack propagation path follows some regularity in general and the main force of crack propagation is still tensile stress. Through this work, the understanding of the mechanism about damage and early destroy of asphalt pavement can be advanced and it can provide guidance for asphalt pavement design and maintenance.