Study On The Prediction Of VMA Of Asphalt Mixture And The Sectional Design Method For Gradation Design

Gradation design is one of the key contents in asphalt mixture design.Gradation design affects the performance of the pavement directly.Voids in mineral aggregate(VMA)is an important technical index in Gradation design.Both Marshall design method and Superpave design method use VMA to determine the gradation.But the two methods use more experience instead of theoretical calculation.Moreover,gradation depends on complicated asphalt mixture experiment to determine VMA.If VMA doesn't meet the requirements,a new gradation design should be done.These experiments will waste a lot of time and energy.To improve the efficiency of gradation design of asphalt mixture,physical modeling,mathematical deduction,laboratory test and theoretical analysis are used to study following contents.(1)The model of the VMA of aggregates without asphalt(VMAa)and the variation prediction of VMAa;(2)Sectional design method for gradation design;(3)Analyze on the relationship of VMA and VMAa;(4)The effect of the passing rate of 2.36mm sieve(Pcf)on high-temperature properties of asphalt mixture.Conclusions obtained from the study are summarized as follows:(1)Sectional design method for gradation design has been found.The predictive model of VMAa is built.VMAa will decrease first and then increase with the increase of Pcf,with a trend of opening upward parabola.(2)The experimental VMA decreases first and then increases with the increasing of Pcf,with a trend of opening upward parabola.It is similar with the rule of prediction model of VMAa.(3)With the help of prediction model of VMA-VV and VMA-Pa,VMA can be predicted based on volume parameter of asphalt mixture in initial asphalt content(predicted asphalt content),which has great significance to gradation design.(4)Dynamic stability of asphalt mixture first increases and then decreases with the increasing of Pcf,with a trend of opening downward parabola.When Pcf is less than the pass ratio through 2.36mm sieve of dense framework(Pcf0),mix is in skeleton state,VMA decreases with the increasing of Pcf,and dynamic stability increases;When Pcf is more than or equal to Pcf0,mix is in suspended-dense state,VMA increases with the increasing of Pcf,and dynamic stability decreases;When Pcf is equal to Pcf0,VMA is the minimum value,dynamic stability will be the maximum,which proves that asphalt mixture has the best high-temperature stability in dense framework.