Study On Creep Characteristics Of Reinforced RAP Material

In recent years,with the rapid development of road traffic engineering in China,the total mileages of roadways with asphalt concrete pavements are increasing gradually.Despite the prosperity of transportation industry,large quantities of waste asphalt pavements are inevitably produced due to the continuous increase of traffic loads,extension of service cycle and improper maintenance.In order to respond to the Chinese ecological civilization construction and avoid waste of resources and environmental pollution caused by solid waste stacking,it is urgent to recycle waste asphalt pavement materials to form recycled asphalt pavement materials(RAP).In recent years,the main research direction of Chinese scholars on RAP material is focused on the use of RAP as pavement materials.In order to expand the application area and increase the utilization ratio of RAP materials,this paper proposes to reuse RAP material as retaining wall fills.Through systematic laboratory tests and theoretical analysis,the main research results are as follows:(1)Raw RAP material was obtained from a road maintenance company in Zhenjiang city.The basic physical and mechanical properties of the crushed RAP material were tested,including proctor test,specific gravity test and sieving test.By analyzing the physical and mechanical properties of RAP material,it is determined that RAP material is comparable to gravel soil with good particle size distribution and permeability.It can be used as a substitute for natural aggregate in the project of retaining wall engineering.(2)An improved direct shear apparatus is adopted to conduct direct shear tests on geogrid reinforced and non-reinforced RAP material under different compaction temperatures.Test results show that shear strength of RAP material increases with the increase of compaction temperature and vertical stress.A linear relation between shear strength and vertical stress can be fitted.Compared to non-reinforced RAP,geogrid reinforced RAP shows obvious strength improvement,especially in the increase of cohesive strength.A linear relation between shear strength and vertical stress for geogrid reinforced RAP can also be fitted as a function of compaction temperature and vertical stress.(3)An improved direct shear creep apparatus is used to perform direct shear creep tests on geogrid reinforced and non-reinforced RAP material under different compaction temperatures.Test results indicate that with the increase of compaction temperature,creep strain decreases,critical shear stress ratio increases and time to creep rupture is lengthened.Time to creep rupture decreases with the increase of vertical stress.Shear strain increase with the increase of ratio of vertical stress and shear stress.The creep of RAP material is smaller after adding geogrid even in the same compaction temperature,while critical shear stress ratio is larger and time to creep rupture is longer.Creep rate of non-reinforced and geogrid reinforced RAP material decrease with the increase of compaction temperature.At the same compaction temperature,creep rate of geogrid reinforced RAP is smaller than that of non-reinforced RAP.The creep process of non-reinforced and geogrid reinforced RAP material is similar at different compaction temperatures and the effect of shear stress ratio on creep rate of RAP material is mainly on the different values of initial creep rates.(4)Classical Singh and Mitchell’s three-parameter creep model can be used to predict the creep rate curve of geogrid reinforced RAP material.The effect of compaction temperature on three parameters of creep model is investigated and results show that that influence of compaction temperature on parameter m is not obvious and the parameter ? increases with the increase of compaction temperature.The parameter A decreases with the increase of compaction temperature.A modified three-parameter creep model is established for geogrid reinforced RAP material considering the effect of compaction temperature based on the data fitting.The validity of the modified creep model is verified by comparing the model calculated and test results.