Asphalt Mixture’s Fatigue Performance Based On The Random Load Spectrum

Asphalt pavement is repeated effect by vehicle load in its working time, and the stress or strain caused in the structure is longtime in the overlap changing state,so the strength of asphalt mixture is diminishing. After loading a certain number, when the stress of the pavement is greater than the strength of decreased structure, the pavement comes to fatigue failure. Vehicle load is a kind of random load, so the stress or strain caused in the pavement structure layer has randomness. At present, most of the domestic and foreign researchers study constant amplitude loading (stress/strain) fatigue test. The research of asphalt mixture’s fatigue performance using variable amplitude loading is still rare. Therefore, this article adopts four points bending rectangular beam fatigue test method to estimate the asphalt mixture fatigue life under random amplitude strain. Therefore, the asphalt mixture fatigue life based on random amplitude strain is investigated by four points bending rectangular beam fatigue test in this article.First of all, the loading schema and mechanical model is selected to calculate the strain response of the pavement structure based on overloading model in this article. The tensile strain of surface course of both inversion structures and road semi-rigid base asphalt pavement are calculated by using SHELL pavement design software BISAR3.0. The most unfavorable position of strain in the pavement structure layer is determined by comparing the strain condition based on different loads, at the road depth direction and transverse direction. The existing references’ axle load spectrum is simplified, then it is conversed to the strain spectrum of the most disadvantageous position in inversion structure. This point’s strain spectrum is affirmed conforming to the Gaussian distribution after statistical analysis.Secondly, the four-point bending fatigue test of modified asphalt SMA13 mixture is carried out in five different strain levels by using UTS015 beam fatigue test machine of Australia, then the fatigue life equation is established based on the five different strain levels. Three kinds of strain spectrums which are conforming to Gaussian distribution are established for laboratory loading; then the asphalt mixture bending fatigue test based on these strain spectrums are carried out; the fatigue life of the asphalt mixture based on these strain spectrums are determined.Finally, through the calculation and analysis of existing life forecast model, a fatigue life prediction model of asphalt mixture under the action of random amplitude strain is set up. Compared with conventional Miner theorem forecast model, this model based on continuous fatigue damage theory can better predict the fatigue life of asphalt mixture under the action of random strain spectrum. The error between this prediction model and random strain fatigue test results is not big. This model has good applicability to predict the fatigue life of asphalt mixture, which is based on the fatigue equation of the constant strain test and the actual road surface function of load spectrum.