Research On Anti-cracking Performance Of Semi-rigid Base Course In High Altitude Mountain Highway

Semi-rigid base course road having the characteristics of high carrying capacity and good economic benefit,was widely applied in highway construction in China,but it is easy to crack prematurely,especially in high altitude mountains.On the base of the special climate conditions such as large temperature difference and extreme temperature,this thesis studies on anti-cracking performance of semi-rigid base course.Based on the Wenma highway,this thesis aims to improve the crack resistance of semi-rigid base course in high altitude mountainous areas,from the aspects of material composition,evaluation index,cracking mechanism.The main content includes:(1)Comparing with the semi-rigid base of the various types of cracks generated conditions,this thesis combines with high altitude mountain conditions,and analyzes its shrinkage mechanism.The reasons for the cracking of semi-rigid base course were explained and the theoretical basis for anti-cracking measures were provided.(2)According to the special conditions of high altitude mountain,combined with the previous evaluation of dry shrinkage performance and thermal shrinkage performance indicators,this thesis put forward a comprehensive high altitude mountain anti-cracking performance indicators.(3)A kind of anti-cracking design is proposed to meet the conditions of engineering area,that is adding polyvinyl alcohol fiber to cement stabilized macadam.The advantages of polyvinyl alcohol fiber in the application of semi-rigid base in high-altitude mountainous area are discussed,and the economic analysis is made.(4)The length of 10 mm polyvinyl alcohol fibers are the best dispersion under the same mixing conditions.Different groups of mix proportions were prepared and the compaction test was carried out to find the maximum dry density and the optimum water content.Through the testing of the crack resistance of polyvinyl alcohol fiber cement stabilized macadam,reasonable mix proportion is determined.The results show that the shrinkage coefficient of cement stabilized macadam is reduced after the incorporation of polyvinyl alcohol fiber,and the relationship between age and material crack resistance is also analyzed.(5)On the base of mechanical properties test,this thesis analyzes the effect of testing period,fiber dosage and cement dosage on compressive strength,tensile strength and modulus of resilience.The result shows that after the addition of polyvinyl alcohol fiber cement stabilized macadam early strength is lower,higher later.Addition of polyvinyl alcohol fiber can reduce the elastic modulus of cement stabilized macadam.(6)The frost resistance test of polyvinyl alcohol cement stabilized macadam was carried out.The results show that the incorporation of polyvinyl alcohol fiber can improve the frost resistance of cement stabilized macadam and adapt to the climatic environment of high altitude mountainous area.(7)Compared with cement stabilized macadam under different fiber dosage for anti-erosion test,showing that the mechanical properties and the erosion resistance of the cement stabilized macadam are improved after the incorporation of the polyvinyl alcohol fiber.