Research On The Theory And Method Of Skeleton Dense Gradation Design Of Hot-mix Asphalt Mixture

With the rapid development of economy and the increase of traffic volume,the traditional grading design methods of asphalt mixture lack optimization design ideas,which is one reason of the frequent occurrance of pavement premature failure.Asphalt mixture of dense framework type is the focus of domestic and foreign experts and scholars,which has the beter road performance because of its high cohesion and internal friction.At present,there are many researches on grading design methods of skeleton dense,but there are few applications in engineering because of many unsolved problems.In view of this,the study on the theory and method of skeleton density gradation design is necessary.Based on the previous research,this paper proposes a set of theory and method of skeleton dense gradation design through model calculation,in which the parameters of the skeleton are obtained from the asphalt mixture.The gradation design process includes:(1)the grading design of coarse and fine;(2)The initial design of the two gradation curve(include a skeleton gap gradation and a suspension dense gradation),and the skeleton dense parameters inversed according to the Marshall specimen parameters;(3)Calculating the best amount of fine materials;(4)Selecting the final amount of fine material which determine the final skeleton density gradation.(5)The secondary optimization,which is needed when the voids in mineral aggregate do not meet the requirements.In addition,if the quantity of the initial design gradation curve is enough,such as 5,the best amount of fine materials can be directly obtained from the variation curve of VMA,in which the VMA of skeleton dense gradation is minimal.Based on the theoretical model formula,the interference coefficient is redefined.The stacking test of coarse materials indicates that the coarse material gradation directly affects the bulk porosity of the coarse material and affects the interference coefficient.Research shows that the correlation degree in the gray relational analysis can reflect the different coarse material gradation and the correlation degree is related to the porosity of coarse material,so the correlation degree can be used as an index to judge interference coefficient.The interference coefficient model is established by analyzing interference effect based on MATLAB,which can intuitively reflect the influence mechanism of the interference coefficient.The separation particle size of coarse and fine is identifie as 2.36mm according to the interference coefficient model within the grading range.The existence of skeleton dense gradation is confirmed by the Marshall test of AC-13,AC-20 and AC-25.At the same time,the change law of VMA is analysed.Through the study on the change law of the skeleton dense parameters which inverse from compacted asphalt mixture,the two parameters are not significant turning or stabilized on the state of skeleton dense.Two kinds of methods are proposed to obtain the skeleton density gradation include the model caculation and the graphical method,and the corresponding design method and suggestion are given.At the same time,the skeleton density areas of each type of asphalt mixture are givenBy analyzing the shear strength and dynamic stability of different gradation types,the skeleton density gradation has excellent performance,in which shear strength and dynamic stability are better than the skeleton gap gradation and suspension compact gradation;when the VMA is the same,the skeleton gap gradation performance is superior to the suspension compact gradation.