Fwd Asphalt Pavement Overlay Design

Overlays or resurfacings are the most frequently used technique in asphalt pavement maintenance and rehabilitation. Overlays are used not only to improve surface characteristics of the pavement, but also to strengthen existing pavements to support future traffic loadings and hence to prolong the service life of the pavements effectively. The research purpose of this paper is on the thickness design of strengthening asphalt overlays, and the research way is based on analyzing the using of Falling Weight Defiectometer in the area of pavement design and analyzing the priority of FWD -this kind of nondestructive deflection testing equipment, the emphasis is using of the testing results and research production of FWD in overlay design. The mainly research results includes the following aspects:1. Describing all kinds of overlay design procedures and its advantages and disadvantages in detail, especially the overlay procedure used in our country's pavement design criterion. It indicates that although this procedure has introduced the mechanistic-empirical method, but still is not perfect in design theory: one is about bearing capacity evaluation method and device. The currently used device -Benkelman Beam is dropping behind the development of the pavement testing service; the other is about the mechanistic method that used in overlay design. It simplifies the original pavement and subgrade as a whole half infinite space, this is not true in the real layered pavement structure. Therefore, the overlay design procedure of our country should be improved with the development of the pavement nondestructive testing devices.2. An idea is put forward that the moduli backcalculated from deflection data of FWD were used in overlay thickness design method by combining the hot questions about FWD research in recent years. The key point of this usage is developing related testing criterion and regulations of FWD through research testing in large scale and in many areas in our country, meanwhile the backcalculating method also need improved further. In addition , the back-calculated moduli should be corrected to the normal design condition, then it can be used in the final overlay design.3. A new mechanistic-empirical based on FWD procedure is developed in this paper according to the information from the other country and our own. The mechanistic model and damage model of this method is reviewed theoretically. Finally, we use this new method and the other several procedures using currently to calculate a case example. It indicates that this method can derive a effective result comparing to the other existing procedures, but for the real use in the true pavement overlay design, we should still to improve it in the empirical part of this method to get more accurate results.