Research On Gradation Design And Performance Of Cement Stabilized Macadam Of Framework Dense Structure

As a kind of semi-rigid base material,cement stabilized macadam material is commonly used road base in our country and there is the characteristics of high strength,good integrity and good economical benefit.However,in the actual use of cement stabilized macadam base,there are some shortcomings for this kind of material,such as easy to crack,easy to scour the surface.The problem of early damage of pavement caused by the defect of cement stabilized macadam base has become more and more serious.According to the distribution state of aggregate in the base material,the structures of the cement stabilized macadam base material are divided into three types,including suspended dense structure,framework dense structure and framework void structure.Among them,the advantages of the other two kinds of structures are assimilated into the framework dense structure while the road performance is superior,which provides an effective way for the cement stabilized macadam mixture to alleviate the above problems.Although there are many researches on the cement stabilized macadam mixture of framework dense structure in our country,there is no unified understanding on the design method and the gradation range,and then the application of the cement stabilized macadam mixture is affected.Based on the research and practice of the cement stabilized macadam mixture of framework dense structure at home and abroad,the composition design and performance of cement stabilized macadam of framework dense structure are studied in this paper.On the basis of fully considering the pavement structure layer function of the cement stabilized macadam mixture of framework dense structure,the composition structure and strength characteristics of the structure are analyzed.In order to ensure the formation of framework dense structure in the mixture,and facilitate the construction,at the same time,erosion resistance,crack resistance,fatigue resistance,and other superior performance,"balanced framework dense structure" is put forward,and the gradation range of "balanced framework dense structure" is given.On the basis of the idea of the Bailey method design of asphalt mixture,the method of coarse aggregate forming mutually embedded framework and using the reserved porosity for aggregate gradation design is established.The feasibility of bailey method and using the reserved porosity for designing the gradation of cement stabilized macadam of framework dense structure has been verified through the examination of design gradation.The performance of cement stabilized macadam mixture of framework dense structure is studied through some laboratory tests including unconfined compressive strength test,compressive resilience modulus test,erosion resistance test,dry shrinkage and temperature shrinkage test.The results showed that the compressive strength and compressive resilient modulus of cement stabilized macadam of framework dense structure with well-designed gradation significantly outperformed the suspended dense structure.The erosion amount of the two structural types of cement stabilized gravel increases as the scouring time goes on.Beginning within 15 mins,the erosion amount increases rapidly,and then gradually weakens,after reaching 30 mins it tends to be gentle.In the standard,it’s reasonable to adopt the erosion of 30 mins to appraise anti-erosion performance of cement stabilized macadam.Simultaneously,the average erosion rate within 28 d curing periods,the initial 15 mins can also be used to evaluate anti-erosion performance of cement stabilized macadam in order to save time.Under the same amount of cement,cement stabilized macadam of framework dense structure has lower coefficient of dry shrinkage and temperature shrinkage than the suspended dense structure,which can effectively improve the crack resistance of the base.The field construction technology and quality control of cement stabilized macadam of framework dense structure is discussed through in-situ test road.After more than two years′ vehicles loading,there are good road conditions and without any disease.The results showed that "balanced framework dense structure" of cement stabilized macadam base had good road performance.The long-term performance of the test section remains to be tracked.