Research On The Method Of Determining The Optimum Asphalt Content Of Asphalt Mixture

China’s highway construction has made great progress,but the quality of some of the highway need to be further improved.In addition to material and construction,a very important reason to early damage of new highway asphalt pavement is the design of mixture ratio.This paper is to research the design of determing asphalt content in mixture ratio design,and study the effects of different asphalt content to pavement performance.It give the method of determing optimum asphalt content based on the test of pavement performance,and the method of predicting asphalt film thickness based on fractal prediction.Different from the the traditional methods of Marshall,in the test method to determine the optimum amount of asphalt mixture,introduced the mixture pavement performance index,and considered the effects of overload on pavement performance of mixture.According to the characteristics of upper layer,middle layer and lower layer selecte SMA-16,AC-20,AC-25 mixture to do the research,every layers selects four kinds of gradation,and each gradation with five groups asphalt content to do the test of rut and freeze-thaw rut,studying on the effects of different asphalt content to high temperature and water stability of asphalt mixture.On the basis of index adds mixture density,porosity,voids in mineral and asphalt saturation to determine the asphalt minxture optimum content that can meet the pavement performance.Experiment low temperature bended performance in optimum asphalt content of each gradation,to check low temperature performance of mixture,all in compliance with the requirements.The key to estimated asphalt content is to determine the reasonable asphalt film thickness.In this paper,the method of fractal theory is introduced in the determination of asphalt film thickness,today fractal theory is very popular in the international,and it is a new theoretical tool to statistical a large number of existence of the self similar characteristic in the nature.This paper use fractal theory to describe asphalt mixture,first derive the fractal representation of gradation size distribution function and aggregate gradation.Then to deduce fractal representation of mixture porosity and volume,thereby obtaining fractal representation of the surface area.To find out the relationship between surface area and volume fractal dimension,basis of the volume fractal dimension to calculated surface area fractal dimension,in that to calculate the fractal surface area of mixture.,finally according to the fractal surface area reach the result of asphalt film thickness of mixture.For the optimum asphalt content determined by the test method of this paper,calculated its asphalt film thickness,and given the appropriate range of asphalt film.