Study On Material Design And Shrinkage Characteristic Of Semi-flexible Pavement

Semi-flexible pavement material is a kind of composite material which is made by pouring special-performance cement mortar into high-connected macroporous matrix asphalt mixture(voidage between 20%-35%).Semi-flexible pavement owns flexibility of asphalt concrete pavement and rigidity of cement concrete pavement.The trait of semi-flexible pavement is of good rutting resistance,meanwhile,it has better integrity and lower rigidity compared with cement concrete pavement.However,due to the characteristics of grouting material cement mortar and the influence of external environmental factors,the shrinkage behavior arise and finally cause cracks on semi-flexible pavement?In order to find out the shrinkage performance of semi-flexible pavement material,based on the review of previous researches,this paper focus on mixture design relying on“CAVF”(Course Aggregate Void Filling Method),and successfully designs macroporous asphalt mixture which is of required voidage.Also,it conducts experimental verification of real voidage and cement mortar grouting rate.Through analyzing the shrinkage of cementitious material and considering the feature of semi-flexible pavement material,this paper summarizes five main types of shrinkage which are chemical shrinkage,plastic shrinkage,autogenous-shrinkage,drying shrinkage and temperature shrinkage.Here,autogenous-shrinkage and drying shrinkage are selected to be studied.The corresponding experimental methods of semi-flexible pavement are put forward after modifying the existing shrinkage deformation measuring methods based on the analysis of semi-flexible pavement material feature.Based on analyzing the causes of semi-flexible pavement material shrinkage,this paper starts shrinkage research from the perspective of three design parameters which are design voidage,water cement ratio and cement mortar types.Starting from the law of shrinkage of cement mortar,this paper aims to figure out the influences of different design parameters on semi-flexible pavement material shrinkage and the relationship between autogenous-shrinkage and drying shrinkage.Also,suggestion of material design are put forward to improve autogenous-shrinkage and drying shrinkage behaviors.Based on the shrinkage models of cementitious material,the discussion on shrinkage models of semi-flexible pavement material are conducted.On account of research review and a series of experiments,the specimens of different shrinkage experiments are made,and the proper experimental methods are worked out.By means of data processing and graphic analysis,the shrinkage characteristic of semi-flexible pavement material can be concluded as follows: Cement mortar is the major factor which leads to autogenous-shrinkage and drying shrinkage.The drying shrinkage of semi-flexible pavement material is more severe than autogenous-shrinkage.With the increase ofwater-binder ratio,dry shrinkage gets increased.With the increase of design voidage,both autogenous-shrinkage and drying shrinkage get increased.Different types of grouting material have significant effect on drying shrinkage of semi-flexible pavement material.The suggestion on improving autogenous-shrinkage and drying shrinkage behaviors is optimizing design method by increase design voidage and decrease water-binder ratio.It has been found that the autogenous-shrinkage model of semi-flexible pavement can be established through revising the autogenous-shrinkage model of cement paste.The one element logarithmic regression method has a good characterization effect on dry shrinkage of semi-flexible pavement material.