Research On Gradation Desigh Of SAC-16 Asphalt Mixture Based On Fractal Theory

With the rapid development of the highways, asphalt pavement which shared of the largest form of road surface type ushered in the golden age of development. In the number of significant growth at the same time, high temperature stability and durability shortage ware widespread lack. Generally considered, aggregate gradation plays a very important influence on asphalt mixture's performance. So the road workers to the world the gradation and aggregate particles itself more profound research.In the first chapter, this brief expounded in brief that the gradation played an important role in asphalt concrete pavement performance, analyzed and summarized the the existing design of several major grading methods have deficiencies.After much reading of literature and investigation found that, traditional method, using the experience index is difficult to linking the aggregate surface characteristics as well as other factors with the grading closely. In recent years, fractal geometry theory has been rapid development, has been widely applied to study unstable, irregular phenomena in nature, researching on those materials often punch but not smooth, broken but not continuous, has obvious advantages. Theory of fractal geometry in recent years gradually been applied to asphalt aggregate field of study such as microstructure, the volume characterization, grading curve shape analysis, particle analysis, the direction of uniformity has been successfully tried, depth study of this theory in the field of road materials is considered to have great potentials for development. The second chapter of this paper introduces the definition of the fractal, two basic principles and the most important parameter of fractal theory-fractal dimension.The process of reading the literature found that more fractal theory has been used to evaluate the grading curve, or to continuous gradation asphalt mixture one-dimensional design.Two-dimensional fractal design, just stop at the level of publicity derived and found no systematic design process. Therefore, in the third chapter, this one-dimensional basis of the formula to derive the two-dimensional formula, and instead of using the maximum nominal size of the largest particle size to calculating. Then, this study selected in the SAC-16 specification gradation range fractal evaluation of three curves, and with the AC-16 were compared, the comparison results show the SAC-16 using two-dimensional fractal design is correct, at the same time find out the coarse aggregate and fine aggregate sieve boundaries.In this paper, the coarse aggregate to VCA proven the most reasonable value, fine aggregate to achieve the maximum density as the basis and calculate the fractal dimension of coarse aggregate and fine aggregate value of Dc and Df, and as a parameter for the design of grading, filling the blank of the two-dimensional fractal grading formula is only used for the evaluation of the grading curve is not used in the design. The fourth chaper of this paper attempt to use Particle Flow Code PFC3D based on the principle of Discrete Element Method, to measuring the porosity rate of coarse and fine aggregate. The results show that this virtual experiments method has the accuracy and feasibility, and the method is simple, both save a lot of manpower, material and time, and pointed out the direction for carry out the virtual experiments in the future.In this paper, to SAC-16 graded asphalt mixture design process, for example, show the superiority and flexibility of fractal theory. Select the maximum nominal size by 97.5%, grading curve obtained broadly consistent with the value grading range. Difference is slightly higher content of coarse aggregate, slightly lower of the fine aggregate content. Finally, using road performance test for fractal gradation design results and grading median to testing and evaluating.