Study Law Cracking Damage Of Asphalt Concrete Overlay Layer

Periodic maintenance and rehabilitation can prolong the road's service life. An asphaltic overlay is applied to the old pavement surface in good time, which not only enhances the strength of the pavement, but also improves the using performance of the old pavement instead of doing lots of rebuilding works. Therefore, The thickness of asphalt concrete overlays is less than the thickness of the reconstructed pavement . Therefore, Using the asphalt overlays often provide the most economical form of rehabilitation. A major drawback of this kind of rehabilitation is the reflection cracking of the overlay, whereby the cracking pattern existing in the original pavement is extended into and through the new overlays. Reflection cracking is the main cause for early deterioration of bituminous concrete overlays , and therefore its prevention is an important consideration in the design of overlays. This thesis utilized a mechanic-empirical approach the for prediction of reflection cracking life of asphalt concrete overlays. A mechanic-empirical approach was utilized in developing the present design procedure. The achievements we obtained was listed as the following:1. Compared the representative equipments for detecting the deflection of pavement structure, especially describes the Following Weight Deflection (FWD) which is used widely in the world. We introduced the working principle of its detecting system, using performance and technological index in detail. Whereby a strong technology reference for introducing the FWD equipments was supplied to domestic engineers.2. A mechanic model which can reflect the real case of the pavement cracking was developed ,and analysised the cracking model in the overlays. Meanwhile, described the theory and methodology of the fracture mechanics. Based on these results, discussed the method of calculating the crack stress intensity factor by using fracture mechanics.3. In order to obtain the modulus of each layers and the subgrade . A back-calculating method which is based on the system identification principle was presented and supply the reliable technology for the overlay design.4. Based on the pavement mechanics models ,fatigue cracking theory of fracture mechanics was used to investigate the rule of reflection cracking. Furthermore, combined with the pavement engineering, the availability of this method was tested well.