Research On The Experiment Of Aggregate Segregation

Asphalt concrete pavement is the main type structure of road in china.Asphalt mixture segregation is one of the main reasons for early damage of asphalt pavement.At present,much research of the segregation of shaping pavement has carried out at home and abroad,which includes the evaluation criteria of segregation,the effects of segregation on pavement performance and so on.As all those researches belong to the analysis after the segregation is formed,so it is difficult to control the production of segregation at the mix design phase.Aggregate gradation design is one of the core content of the hot mix asphalt mixture design.According to the asphalt pavement construction technical specification of China and Supercave system of American,the main technical index of the gradation design is the void in mineral aggregate at present.However,the same VMA may corresponds to multiple gradation curves with different shapes,so if the relationship between the shape of gradation curve and the degree of segregation could be established,the gradation curve which meets the requirement of VMA and has smaller segregation degree could be designed.It provides feasible theoretical and technical support for the optimal design of gradation.Coarse aggregate is the main component part of the mineral aggregate of asphalt mixture.The segregation degrees of coarse and fine aggregate decide the segregation degree of asphalt mixture.In this paper,coarse aggregate was regarded as the object of the study at first.According to the simulation tests of discharging process of aggregate bin,the segregation degree evaluation index was put forward,and so the relationship between segregation and coarse aggregate gradation curve was achieved.In allusion to the coarse aggregate of AC-16 and AC-20 asphalt mixture,16(AC-16)and 25(AC-20)different test ratios of coarse aggregate mixture were gained by the uniform design method.Segregation degrees of different ratios of coarse aggregate were obtained by a large number of segregation tests.The optimal regression equation was established through the stepwise regression analysis method to analyze the test results,and the relationship between the shape of gradation curve and segregation degree was analyzed utilizing the regression equation.The results show that:For AC-16 and AC-20 gradation,the segregation degree(SD)of coarse gradation curve with positive S-shape is smaller than the MTDL gradation curve,and the SD of coarse gradation curve with reverse S-shape is bigger than the MTDL gradation curve;when the intersection of the positive S-shape curve and the MTDL is located at the 9.5?13.2mm particle size section,the SD is smaller;further the inflection point away the MTDL,smaller the SD of positive S-shape curve is,but bigger the SD of reverse S-shape curve is;through result analysis of segregation test of coarse aggregate of AC-25 characteristic gradation curve,it is also proved that the research conclusions are applicable to AC-25 coarse aggregate part.Secondly,in order to verify whether the conclusions are applicable to asphalt mixture,the segregation tests of asphalt mixture were carried out on the positive S-shape,reverse S-shape and MTDL gradation in the range of AC-16,AC-20,and AC-25 gradation.By comparing the test results with the prediction results from the regression model,it is indicated that,the addition of asphalt and fine aggregate did not change the SD sort result of positive S-shape curve,MTDL and reverse S-shape curve,but due to the bonding of asphalt,the segregation of asphalt mixture decreases to a certain extent with that of coarse aggregate.