Study On Macro-microscopic Voids Of Warm Mix Asphalt Based On The Fractal Theory

WMA(Warm mix asphalt) is a kind of building material with better road performance, energy saving and environmental protection, Which is in line with the trend of development in the western region of China’s future pavement materials, to accelerate the construction of the national highway network, highway reconstruction project and the new silk road network and it is of great significance to promote the development of ecology and economy in western region.The compaction degree of asphalt pavement has great influence on the strength and durability. Good compaction is helpful to improve the pavement bearing capacity and durability, which can meet the effect of traffic load and the change of the environment of the asphalt pavement. The degree of compaction is one of the indexes to evaluate the degree of compaction of asphalt mixture, and the macro-micro voids are very important to the study of compaction characteristics.This paper which based on the comparative analysis of WMA and HMA(hot mix asphalt).Firstly, reveals the internal distribution of aggregate gradation, puts forward the three stage design idea of fractal gradation, so as to realize the mineral aggregate gradation orientation design. Secondly, comparatively analyses the relationship between mineral aggregate gradation, asphalt aggregate ratio and degree of compaction and the voids of HMA formed by the method of Marshall by the orthogonal experiment; The relationship between fractal parameters(coarse gradation fractal dimension, fractal dimension and fine graded coarse level with quantity the relationship between the ratio) and HMA volume index of Marshal is analyzed by the single factor experiment method; In addition, The specimen of the target gradation is formed by different compaction times under the Marshall, SGC and rolling molding, analyses the Change rule between HMA volume parameters and compaction times and finds out the best compaction standard of different molding methods of WMA basing on HMA; At the same time, analyses the Change rule of WMA and HMA between volume index and the mineral aggregate gradation under different molding methods; Finally, analyses the relationship between macro-micro voids and different factors, and the correlation of macro-micro voids of WMA are analyzed.Through the research we can draw the following conclusions:(1)Comparative analysis of WMA, put forward the three stage design ideas of WMA and give the design flow chart based on the volumetric principle of WMA and HMA, WMA Compaction Characteristics and modified asphalt viscosity temperature curve(2)Giving the Cartesian coordinate system, graded approximate line representation and fractal gradation evaluation model based on the fractal characteristics of continuous gradation, Interlocking skeleton gradation and gap gradation; Combined with the existing the research results, proposes the three components of aggregate gradation fractal design method which is combined by the fractal dimension, the asphalt mixture gradation design and asphalt mixture road performance test analysis, and the two degree domain fractal gradation formula was optimized.(3)The relationship between macro-micro voids of WMA and HMA and coarse, fine, coarse level matching ratio, asphalt aggregate ratio and degree of compaction is analyzed by the orthogonal test and single factor test under the Marshall.(4)WMA is more difficult compacting than HMA, there is a good correlation between WMA and HMA and asphalt aggregate ratio, aggregate gradation and compaction times; SGC forming process of rubbing force is conducive to the asphalt mixture in the movement, resulting in the asphalt mixture compacting easily, so WMA design should be based on the SGC method; In the process of compaction,the relative thickness of the voids is a sine(cosine) waveform in constant evolution; void distribution fractal dimension can reflect the test about beam forming process.