Research On Skeleton Structure And Performance Of Asphalt Mixture Based On Balance Mix Design

Both Marshall method and Superpave method are generally defined according to the characteristics of asphalt mixture design.One of the important indicators affecting the performance of the mixture is the amount of asphalt.Excessive use of asphalt will lead to rutting of the mixture,while insufficient asphalt content will lead to cracking,spalling or other durability problems.There is a lack of good relationship between the volume parameters and road performance used in the traditional asphalt mixture design method.The Balance Mix Design can better take into account the rutting and cracking resistance,which has gradually become a research hotspot.In this paper,AC-13 is selected as the design gradation,and the mix proportion of asphalt mixture is designed by Marshall design method,Superpave design method and Balance Mix Design respectively.Digital image processing of CT scanning images of asphalt mixture under three different design methods;The void distribution law and skeleton structure characteristics of Balance Mix Design and traditional asphalt mixture design method are studied;Water stability test and uniaxial compression dynamic modulus test are carried out on the specimens under different design methods,and the main curve of dynamic modulus is constructed to study the performance of asphalt mixture under Balance Mix Design and traditional asphalt mixture design method.The main research conclusions are as follows:(1)It is found that the optimum asphalt aggregate ratio obtained by Balance Mix Design,Marshall design method and Superpave design method are 5.0%,5.2%and 5.7%respectively.The analysis of density and pore characteristics of biased asphalt mixture is the characteristic of Marshall design method,which can ensure that the mixture has an appropriate volume proportion;The asphalt mixture specimen in Superpave design method is completed by rotating compactor,which can truly simulate the actual compaction in asphalt pavement construction;The Balance Mix Design pays more attention to the requirements of specifications for road performance,and the optimal asphalt stone ratio is relatively small..(2)Through digital image processing,the structural characteristics of asphalt mixture skeleton under three design methods are studied.The results show that the void fraction of the specimen is distributed in a " W" curve along the longitudinal direction;The voids measured by CT scanning are higher than those measured by indoor test;Under the Balance Mix Design,the average coordination number of asphalt mixture specimens is between 0.8 and 1.1.Compared with the other two design methods,the asphalt mixture skeleton structure designed by the Balance Mix Design is relatively stable.(3)Through the comparative analysis of the water stability of the mixture samples under three different design methods,it is found that the freeze-thaw splitting strength ratio of the samples under the traditional asphalt mixture design method and the Balance Mix Design is more than 80%,which is within the allowable range of China’s specifications.Among them,the water stability of the asphalt mixture under the Superpave design method is relatively good.(4)The results of uniaxial compression dynamic modulus test show that the dynamic modulus decreases significantly with the increase of temperature;The increase of loading frequency will lead to the increase of dynamic modulus.At low temperature,the dynamic modulus of asphalt mixture under Superpave design method is relatively large;The dynamic modulus of asphalt mixture under 35℃ and 50℃ Balance Mix Design is relatively large;In the region of low frequency load and high frequency load,the growth of dynamic modulus with frequency is relatively slow;In the middle frequency region,the dynamic modulus increases relatively rapidly with frequency.In the area of low-frequency load,the dynamic modulus of asphalt mixture under Balance Mix Design is larger than that under Marshall design method,while the dynamic modulus of asphalt mixture designed by Superpave design method is significantly smaller than that of the other two design methods.In the area of medium frequency load,the difference of dynamic modulus of asphalt mixture under the three design methods is small.In the area of high-frequency load,the dynamic modulus of asphalt mixture is the largest under Marshall design method.