Experimental Study Of Asphalt Mixture Of Different Gradation On Fatigue Property

Under the rapid economic development in China, road transport has got a rapid development. Nowadays, asphalt pavement is widely used in freeway and urban road because of its comfortable driving, smooth surface, short construction period and some other advantages. Some pavement performances, e.g. well comfortableness and durability, are essential to asphalt pavement.The cause of asphalt pavement fatigue failure is analyzed by combining the previous researches at home and abroad with test. According to the design of orthogonal test, four gradations, fine AC-13, coarse AC-13, AC-16and AC-20are put forward, three bitumen-aggregate ratios, OAC-1%, OAC and OAC+1%are presented, and four stress ratios,0.5,0.6,0.7and0.8, are also discussed. In accordance with the standard, specimens are made. Firstly, do ultrasonic testing(UT). UT can not only analyse the change rules of asphalt concrete under various factors, but also lay a good foundation for the flexural strength test. Secondly, do flexural strength test to got the failure rules. Finally, do fatigue test to research the change rules of fatigue life under different gradations, various bitumen-aggregate ratios and diverse stress ratios.Based on the experiment analyses, the change of bitumen-aggregate ratio and gradation will affect both the wave velocity in UT and flexural strength greatly. There is a best bitumen-aggregate ratio, OAC, in the test, which is obtained from Marshall test. Both the wave velocity in UT and flexural strength increase with the increase of asphalt content when bitumen-aggregate ratio ranges from OAC-1%to OAC. And when bitumen-aggregate ratio is OAC, both the wave velocity and flexural strength reach the max value. While when bitumen-aggregate ratio continues to increase, both the wave velocity and flexural strength decline. The wave velocity and flexural strength of fine AC-13is bigger than those of coarse AC-13. Coarse AC-13is bigger than AC-16. And AC-16is bigger than AC-20. That's to say, the smaller the gradation, the larger the wave velocity and flexural strength. Based on the correlational study, regression equation (?) is got from linear regression. And the correlation coefficient R2is0.9134. There is a good correlation between flexural strength and wave velocity. And this can provide a theoretical support to predict the performances of asphalt pavement by UT. When bitumen-aggregate ratio is OAC, regression equation of fine AC-13is (?) and correlation coefficient R2is0.9677. Regression equation of coarse AC-13is (?) and correlation coefficient R2is0.9865. Regression equation of AC-16is (?) and correlation coefficient R2is0.9443. And regression equation of AC-20is (?)and correlation coefficient R2is0.9702. Hence, flexural strength can be forecasted by regression equation before bending test.Through the fatigue test, fatigue life of asphalt concrete decreases along with the gradation of aggregate increasing. Fatigue life of fine AC-13is longer than coarse AC-13. Coarse AC-13is longer than AC-16. And AC-16is longer than AC-20.Bitumen-aggregate ratio to fatigue life is in line with that to wave velocity and flexural strength. So, fatigue life increases with the bitumen-aggregate ratio increasing. And when bitumen-aggregate ratio is OAC, fatigue life is the longest. While bitumen-aggregate ratio continues to increase, fatigue life decreases. Moreover, fatigue life drops with the stress ratio increasing. Therefore, fatigue life of stress ratio0.5is longer than that of stress ratio0.6. Stress ratio0.6is longer than stress ratio0.7. And stress ratio0.7is longer than stress ratio0.8.This research will provide a certain theoretical guidance and practical guidance for the design and construction of asphalt pavement.