A Research On The Fatigue Damage Of AsPhalt Overly On Old Cement Pavement Under Traffie Load

In order to study the anti-fatigue properties of the asphalt pavements and the process of fatigue cracks, many domestic and foreign scientific research organizations do a lot of calculation researches and laboratory experiments for the reflection cracks of the asphalt pavements. Nowadays, the study of the reflection cracks mainly concentrates on the calculations of the stress state of the crack ends and the stress intensity factor of the crack ends. Usually, the effect of the preventing cracks is compared by different measures of the preventing crack and the materials stress of the crack ends or the stress intensity factor, but the studies on the calculations of fatigue life and the relationships of the pavement structural parameters are seldom. In the aspect of experiments, the studies can't reflect the pavement's state of the overlaying layer comprehensively and truly and it is difficult to estimate the fatigue life of the overall structure. Especially, the theoretical research and entity engineering is still underway in our country on the new material and the structure of stress-absorbing and overlaying layer. So it is very necessary to make a study on the large fatigue experiment relaying on the experimenting road of the asphalt overlaying layer of some highway and the overlaying structure of the stress-absorbing layer system of some entity engineering.The thesis studies on the mechanism of the reflection crack coming into being basing on the existing research results by the analysis of fatigue and fracture. At the same time, the calculation is done for the life of the fatigue and fracture under the loading of vehicles by the method of the numerical simulation and experimenting. The calculation supplies a theoretical basis for the structure of the optimum asphalt overlaying layer. The work of the thesis is as below:Firstly, elastic fracture mechanics, the theory of fatigue and fracture and its numerical calculation methods are discussed detailedly. On the basis of these, the calculation method is given for the fatigue and expectancy life of the reflection crack. Secondly, some comparisons are done by using the huge fatigue experiment instruments and MTS taking the experiments of the fatigue breakage to different overlaying layer. The thesis makes a appraisal on the ability of the different styles asphalt overlaying, especially on the ability of the preventing reflection crack of the stress-absorbing layer structure. The result shows that the overlying structure setting the stress-absorbing layer has the best effect on resisting the reflection crack of the loading style and the overlying structure setting fiberglass grid has the second effect on resisting the same reflection crack.Thirdly, for the asphalt concrete overlaying structures of setting the STRATA stress-absorbing layer and not setting the STRATA stress-absorbing layer, some appraisals and comparisons are done for the fatigue life under the recycling loading of vehicles by the method of the numerical simulation. The calculation results show that the life of the overlaying structure setting the STRATA stress-absorbing layer of the asphalt concrete is far longer than that of the overlaying structure not setting stress-absorbing layer.