Research On The Formation Of The Voids Ratio Of Coarse Aggregate

Asphalt pavement is the main structure of road in China. Mineral aggregate gradation is one of the core content of HMA mixture proportioning design, the Superpave design method was commonly used internationally and the Marshall test design method which Chinese current using was also absorbed some important thoughts of the Superpave system such as S shape of grading curve, the basis of gradation selection is the VMA index, etc.Because of a lack understanding of the physical mechanism affected by VMA. The gradation design method in Chinese specification and the Superpave system were worked out several grading curves based on experience at first, then choose one reasonable curve through experiments. It has obvious temptation and grope for empirical features and also lack of theoretical properties. The starting 1-3 grading curves based on the designer’s experiences, therefore this design of gradation may couldn’t find qualified or the most suitable VMA grading, which were lack of thoughts and ideas about gradation optimization.Given the current situation of the study on this field and the thoughts gradation design should be divided into two parts, the coarse aggregate and fine aggregate. This paper focused on formation regularity of VCA gradation coarse aggregate. Using mathematical optimization to design tests plan, designed mixture ratio by uniform design table formed by the DPS data processing system. Choose AC-20 and AC-25 two kinds of coarse aggregate of asphalt concrete and gained 16(AC-20) and 25(AC-25) different ratios of coarse aggregate mixture, get their VCA results by taking lots of compaction test with the compaction process. Established the optimal regression equation through stepwise regression analysis method to analyze the test results and fully reveals the formation mechanism of skeleton clearance rate. Carried on the thorough analysis of coarse aggregate’s different grading curves by using the established regression equation. The research results showed that the coarse aggregate’s VCA of positive S-shaped curve was always larger than the reverse S-shaped curve; different positive S-shaped curves had different coarse aggregate VCA; further from the MTDL of S-shaped grading curve the VCA was larger; according to the MTDL mixture gradation of coarse aggregate, its density is not always the biggest, its smaller than the reverse S-shaped gradation of coarse aggregate density; differences of different situation can be given by the optimal regression equation here.