| V Our country began to build highway from the mid-1980s, represented by high-grade highways, including semi-rigid and rigid pavement. During the high-grade highways having been built, 95% are semi-rigid materials for the base layer, and the asphalt concrete for surface (for short semi-rigid pavement). Semi-rigid base has high strength and capacity, the overall stability and good durability. So this structure provides a reliable guarantee for the realization of "strong-base and thin-surface". However, in this process of the use of the road, we found a lot of road damage phenomena such as the erosion, pumping, nte-shaped cracking and pot hole, cracking, rutting, cutting-slippage and humps, asphalt surface skipping off from the base layer. Of all damage arising in the semi-rigid pavement, the reflection crack in the asphalt pavement caused by the semi-rigid material itself such as shrinkage and the temperature reduction and other characteristics is particularly serious. In addition, the semi-rigid materials has poor water stability and poor drainage, therefore, it is easily to generate floating pulp and result decline in capacity when suffering water. The causes of these diseases are various. There are construction of factors (including that construction equipment is not advanced, level of construction technology is low, technical strength is insufficient, construction time is short, construction management is not good and etc.), project management reasons (such as poor road maintenance, improper interference by the executive and etc.), also, improper use of road materials and structural design considerations.How to solve the reflective cracks and poor drainage in the semi-rigid pavement is one of the problems needed to be solved urgently. The paper solves these two problems by using asphalt macadam as the pavement base and reasonable structure design.The first chapter introduces the study purpose and the situation at home and abroad as well as pavement structure characteristics and the deficiencies of semi-rigid pavement in JiLin Province. The necessary of using flexible base is noted aiming at the reflective cracks and other damage in the high-grade highway. LSPM flexible base and reasonably design in the pavement structure is adopted to solve these problems mentioned above. In addition, this chapter explained the main contents of the paper.The sencond chapter is devoted to the composition of the asphalt gravel design. And the following important conclusions are drawn:(1)Grading 5#has the maximum dry density, the minimum porosity and the maximum CBR value. However, it is noticeable high when the vibration molding method is used.(2)The density using vibration molding method is less than the density using compaction molding. This shows that the strength depends not only on the density, but also on the arrangement and combination of the aggregate, especially on the arrangement and combination of coarse aggregate. That if it can form a good skeleton structure with well squeezing.(3)The results show that the structure of graded gravel mixture may have different will not change when the coarse aggregate reached a certain number in a tight row. The structure will change with the action of outside force and tend to be dense stability status.(4)The mixture design is according to skeleton-dense principle with skeleton-squeezing and mixture dense taken into consideration. Skeleton is the main influencing factors of resilient modulus. And filler has greater impact on the control of permanent deformation.(5) The first-class of gradation 1 has the maximum content of coarse aggregate and the resilient modulus is highest. Gradation 4 has more particular with size 4.75 to 9.5mm and the resilient modulus is lowest. As for the resilient modulus, it is better to have more coarse aggregate. (6) The problem of permanent deformation is the most complicated. In absolute value terms, the permanent deformation of grade 4 is the largest with the same dynamic stress. If the dynamic stress is 15 Mpa, the deformation rate reaches 6mm firstly. If the dynamic stress is not more than the critical stress, the permanent deformation of grade 4 is not the largest. Only when it is over the critical stress, the permanent deformation increases rapidly.(7)The best interstitial coefficient is not a constant value relative to different grading.When calculating the best interstitial coefficient, the amount of fine aggregate should be slightly larger than the required amount filling the skeleton gap. That is within the scope of 0.7 to 0.9 and closer to 0.9. Chapter third discusses the flexible pavement structure, base on the test road, the application of flexible base layer in high-grade road, design method and design parameters. The following conclusion has obtained.(1)Through the comparison of the structure of test road LiaoYuan and TongHua with other pavement, the deflection of semi-rigid asphalt pavement is lower from an overall point of view. From an individual point of view, the deflection of flexible layer is not necessarily greater than the semi-rigid base layer asphalt pavement. From the representative deflection view, there is"abnormal"phenomenon. That is he deflection of semi-rigid base layer asphalt pavement is larger than the flexible base layer asphalt pavement.(2)In comparison of the deflection of Tonghua Test Road and Liaoyuan Test Road, it shows both from positive and negative aspects that the optimized combination of flexible base and semi-rigid base layer has good prospects both from positive and negative aspects. Nonlinear calculation results show that raising the elastic modulus of graded gravel base, reducing the thickness of graded gravel base layer and increasing the elastic modulus of semi-rigid base layer in some condition (For the ordinary HMA, the thickness of asphalt surface is 10cm, for the semi-rigid base layer, the thickness is 30cm and the thickness is 10-15cm for the graded gravel base.) can help to reduce the tensile stress of asphalt surface. Simultaneously, this can ensure that asphalt surface with smaller thickness can has high fatigue life.(3)Through the analysis of design method and design parameter, the necessary to establish flexible base layer quality control is proposed.Chapter four is the summarization of the paper. And also the study content and direction for further work are pointed out.
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