Research And Application Of Inverted Structure Of Graded Crushed Stone Asphalt Pavement In Qiandongnan Prefecture

Reflection crack is one of the most serious defects of semi-rigid base asphalt pavement structure.The rainy season lasts for a long time in Qiandongnan Prefecture,which is prone to water damage and other problems related to reflection cracks,seriously affecting the life of the pavement.The inverted structure can prevent reflection cracks.Based on the project of "research and application demonstration of graded crushed stone asphalt pavement inverted structure in Qiandongnan area" of Guizhou Provincial Highway Bureau,combined with G242 Jinping Datong Liping Gaotun highway,this paper studies the inverted structure of crushed stone in Qiandongnan Prefecture.The main contents and achievements are as follows :(1)According to the influence of the maximum particle size of graded crushed stone on the performance and the characteristics of the crushed stone material in Qiandongnan Prefecture,31.5mm is used as the maximum particle size of graded crushed stone base,and the mechanical properties of the foundation of the intermediate graded crushed stone in the selected quarry are tested.It is found that the crushing value and the content of needle and flake of the graded crushed stone materials in this area are higher,but they basically meet the requirements of the code.According to the existing research results,the parameters of the general grading design method Taylor method and the grading recommended by the code are determined.Based on the theory of multi-stage extrusion,the skeleton structure of coarse aggregate is completed,and the proportion of coarse and fine aggregate is determined by indoor test and theoretical calculation.(2)Combined with CBR test and triaxial test,the performance of the mixture was studied,and the composition of graded crushed stone was selected.The relationship between stress and strain of graded broken stone is explored,and the influence of gradation,confining pressure,deviator stress,bulk stress and moisture content on dynamic modulus is studied.The non-linear characteristics of graded crushed stone are analyzed.Uzan model can accurately represent the non-linear characteristics of resilient modulus of graded crushed stone materials in Qiandongnan Prefecture.(3)Based on two-dimensional digital image processing technology,the relationship between aggregate contact characteristics and mixture performance is explored.The results show that the skeleton type gradation with good contact characteristics is not good enough due to the internal load transfer mode and the high crushing value of the material.In order to obtain a more stable grading performance,a grading design method based on variability is proposed,and the passing rate of key sieve holes is obtained according to the indoor test results.(4)Through simulation calculation,it is found that compared with the semi-rigid base asphalt pavement,the inverted structure can prevent the occurrence of reflective cracks,but it is easy to produce Top-Down cracks and has a short fatigue life.According to the change rule of modulus and thickness of each structural layer,the typical inverted structure asphalt pavement under heavy,medium and light traffic is recommended.Through the design,laying and testing of the test road,the accuracy of indoor test and numerical simulation,the adaptability of construction technology and inverted structure are verified.