Research On Properties Of Micro Asphalt Gravel Mixture Materials As Base Course

With the increasing of road traffic volume,the service life of the traditional semi-rigid base road structure has obviously not been able to meet the demands of heavy load traffic,which inevitably leads to road cracks and other disasters.In recent years,it was found that graded broken stone materials have nonlinear mechanics characteristics,permeability and better construction economic,if laying graded broken stone materials between asphalt layer and semi-rigid base can effectively reduce the elastic modulus difference between these two layers and have the effect of transitional buffer,The strain energy which transfer from the base can be absorbed by its nonlinear mechanical characteristics,furthermore reduce the possibility of cracking.But the elastic of graded broken stone materials have poor restorative,under the stress can easy to produce larger plastic deformation,and its stiffness is small,so they are difficult to be compacted.When serious,the road surfaces will have cracks,rutting and other diseases.,so how to improve the overall performance of the graded broken stone materials are particularly important.Micro asphalt gravel mixture materials are half integrity of materials which between graded broken stone and asphalt mixtures,they are new base transitional materials composed by mainly of graded broken stone and a small amount of asphalt mortar,pitch binder to improve the overall performance of graded broken stone materials and construction convenience.In this paper,the indoor experiment and numerical simulation are combined to study the properties of the new type of base transitional materials-micro asphalt gravel mixture materials.The main research work in this paper including the following tips:?1?Choosing the raw materials of micro asphalt gravel mixture materials which have good performance of preparing.This paper chooses the SBS modified asphalt as materials binder,and based on the multilevel embedded squeeze theory to optimize the gradation design of micro asphalt gravel mixture materials,and determine the optimal gradation.Selecting the gradation median of transition layer gradation stone which used to governance the reflection cracks and the gradation median of semi-open graded asphalt macadam AC-20.They are both recommended by Standard?JTG D50-2006?.Comparing these two different gradation median during the subsequent mix proportion experiments,determining structural rationality of micro asphalt gravel mixture materials which choosing the best asphalt mixtures gradation design.The results show that micro asphalt gravel mixture materials which prepared by optimal gradation have good skeleton property.?2?According to the technical requirements of base materials of asphalt gravel mixture materials,determining the reasonable range of asphalt amount in different gradation composition by cohesiveness test and leakage tests.The CBR index can be used as the index of mechanical properties to reflect the anti-deformation ability of the micro asphalt gravel mixture materials when they as the base buffer materials.So in the reasonable range of asphalt amount,CBR test can determine the optimum asphalt content in different gradation composition.Micro asphalt gravel mixture materials which have excellent performance should have enough structure strength and stiffness.So used micro asphalt gravel mixture materials which made by the guide of the optimum asphalt content to continue cohesiveness test and resilience modulus test.The experimental results are used to evaluate the using properties of micro asphalt gravel mixture materials.The optimum mixture ratio of micro asphalt gravel mixture materials which used SBS modified asphalt as binder which provided theoretical basis for subsequent numerical analysis.The results show that 2.6%content of SBS modified bitumen is the optimum mixture ratio of the micro asphalt gravel mixture materials,the gradation composition recommend type A.Micro asphalt gravel mixture materials prepared by this mix proportion have good cohesiveness and structural stability.?3?The material parameters are determined by the mixture ratio test,based on the theory of pavement fracture mechanics.Using ABAQUS software to establish a composite road structure model which made by micro asphalt gravel mixture materials.Study the variation characteristics of base course crack tip stress intensity factors of road structures which made by micro asphalt gravel mixture materials to confirm the rationality of using micro asphalt gravel mixture materials as base transitional materials to control road reflection cracks.Furthermore,the influence of the thickness variation on the stress intensity factor at the crack tip is analyzed.The results show that,after laying micro asphalt gravel mixture materials on the base course,crack stress intensity factor K₁ will reduce 31.8%,it means that micro asphalt gravel mixture materials can reduce crack stress intensity factor and prevent cracks extend to the surface layer.When micro micro asphalt gravel mixture materials thickness at the range of 10 to 25cm,while the thickness increases 5cm,stress intensity factor only increases 4.0%,that means the variation of thickness has little effect on the stress intensity factor at the crack tip.?4?Compared with the gradation broken materials,micro asphalt gravel mixture materials have some advantages such as good performance of cohesion,structure strength and rigidity.This paper innovative put forward the view that can layered set micro asphalt gravel mixture materials.In addition,a certain stiffness gradients should be formed between each layer of them to formation a kind of transition buffer structure.This can reduce the elastic modulus difference between the base layer and the surface layer.Using ABAQUS software,evaluating the applicability of this kind of layered structure by key mechanical indexes,such as the deflection on the surface,the stress at the bottom of the asphalt surface,tensile stress of semi-rigid base layer bottom and so on.The results show that,using layered structure and the form of counter gradient at 50MPa are helpful to reduce the road mechanics index and prolong the life of road.