The Research On Fracture Parameters A And N Of Asphalt Mixture

Asphalt pavement has become a major construction type of roadway because of its driving comfort.However, reflective crack is one of the serious problems of asphalt pavement diseases in both old cement pavement overlay asphalt layer and new semi-rigid base asphalt pavement. Reflective cracks allow rainwater to flow into the pavement cracks and then seep along the base crack down to soften the soil base,or stagnate between overlay and substratum. The mixture of grassroots and asphalt is scoured by dynamic water pressure on the effect of traffic load, thus leading to extensive damage to the asphalt surface with decreased pavement strength. Nevertheless, the emergence of reflective crack does not mean a complete destruction to a road. The rainwater will not enter the interior roads to increase damages as long as the reflective cracks do not extent to the top.To investigate the characteristics of reflection cracks extension, fracture mechanics to the crack propagation rate of research is need to know. So Paris formula, the foundation of prediction mode of modern engineering applied crack propagation is applied:Where N is the load of the cumulative fatigue life role; C is the crack length; Δ is the stress intensity factor under the action;K is a given load change amplitude; A, n are the material fracture parameters. In this paper, we try to get fracture parameters A and n values in Paris formula,aiming at specific environmental factors and material factors of Wuhan area,based on the combination of existing research results and Overlay Tester method. To support the subsequent estimates of fatigue life of asphalt mixture(crack initiation, crack extension) Several processes are included. Firstly, this paper gives a brief introduction to the existing asphalt mixture at home and abroad of low temperature performance test methods; And then crack propagation model is established through numerical finite element analysis software for analyzing the actual reflection cracks of asphalt pavement and extension; Overlay Tester calculation model is built at the same time, for analyzing the stress intensity factors of SIF with the length of crack extension under the experiment condition.Next Overlay Tester is operated to lap the relationship between the maximum load and load frequency, combined with relationship between the regression of the normalized lap maximum load and crack propagation length, the relationship between the crack propagation length and loading times can be obtained; A and n values are easily calculated according to Paris formula; Finally, based on the actual temperature and the materials in Wu Han,verifying A、n values by Overlay Tester.