Research On Pavement Performance Of Concrete Containing Reclaimed Asphalt Pavement And Application In Composite Pavement

Asphalt pavements that China has laid over the past decade have gradually entered the medium and long term conservation period,so that a large amount of reclaimed asphalt pavements(RAP)are produced every year.Using reclaimed asphalt pavements in cement concrete pavement,can not only reduce the exploitation of natural aggregate resources and protect the natural ecological environment,but also help to solve the problem of reclaimed asphalt pavements.In this paper,the application of reclaimed asphalt pavements in cement concrete are studied,the scope of research is performance index of RAP,optimization of gradation,mix design,pavement performance,disease characteristics of HMA/PCC,and application of RAP concrete to provide theoretical support for the application of reclaimed asphalt pavements in cement concrete.Meso-structure of the RAP was studied based on the X-ray CT scanning technology,the key factor in the evaluation of RAP performance is the number of fine aggregates attached to the coarse aggregate.The distribution of aggregates and asphalt in RAP micrographs was analyzed by VGStudio MAX image processing tool,and the RAP performance test results show that the attached fine aggregates can be expressed by the 2.36 mm sieve passing rate in the mineral gradation of RAP,which were subjected to particle size,asphalt content and the degree of aging of asphalt,and then the amount of fine material in RAP particles which is a new index is put forward for evaluating the performance of RAP and gradation optimization.Based on the compressible packing model of granular materials,the optimization method of concrete gradation is proposed.The method can be used to optimize the gradation of new aggregate concrete,but it is not applicable to RAP.In this paper,the gradation optimization method is modified by the amount of fine material in RAP particles,so that the method can be applied to the optimization of RAP concrete gradation.Using the aggregate gradation with the best available concrete to correct the method,it is not only optimized for the grading of concrete,but also ensures the excellent workability of the concrete.Based on the principle of concrete mix design,the concrete model was established based on the modified compressible packing model.The concrete volume balance equation and the cement dosage formula were established,and then a RAP concrete mix design was formed,an example is given to verify that the method is practicalBased on the RAP mix design method proposed in this paper,concrete with RAP content of 33%,67% and 100%,and fiber concrete with 80% RAP content were designed,and a series of anti-bending strength,compressive strength and wear resistance tests were carried out,Test results found that RAP has a negative effect on the flexural strength,compressive strength and abrasion resistance of concrete,when the content of RAP exceeds a certain proportion,the anti-bending performance,impact resistance and abrasion resistance of concrete cannot meet the requirements of specification.The anti-bending performance of RAP concrete can be improved by adding fiber,but little effect to the impact resistance and abrasion resistance.So it is recommended that RAP concrete can be used in the pavement structure except for the surface layer.Indirect tensile test method for cement concrete was studied,in view of the convenience of the indirect tensile test method and the correlation between indirect tensile strength and flexural strength,an indirect tensile test method is proposed to evaluate the flexural behavior of concrete.The indirect tensile test of RAP concrete was carried out under the conditions of-9?,20? and 60?.The results showed that the elastic strength and indirect tensile strength of concrete decrease and the toughness increases with the increase of RAP content.RAP can improve the anti-bending performance of concrete in low temperature environment.RAP reduces the indirect tensile strength,fracture energy and toughness of concrete in high temperature environment,which is disadvantageous to the anti-bending performance of concrete slab.Aiming at the problem of the decrease of anti-bending performance of RAP concrete in high temperature environment,the indirect tensile strength of high temperature is proposed as the design index of pavement,and the indirect tensile strength of different traffic grade highway is given for RAP concrete.In addition,the practicality of the index was verified by the indirect tensile strength of fiber concrete with 80% RAP content at different temperatures.Based on the rut estimation model and Abaqus finite element software,the rut and interlayer shear damage of the HMA/PCC pavement structure were studied.The HMA/PCC pavement structure with smaller asphalt layer thickness,smaller modulus of RAP concrete,larger modulus of asphalt concrete and better interlayer bonding state has less rut permanent deformation.And the HMA/PCC pavement structure with smaller asphalt layer thickness has greater shear stress between layers.Based on the design concept of pavement disease prevention and control,the design method of RAP concrete in HMA/PCC pavement structure is put forward.The upper limit of thickness of asphalt layer is designed by using permissible permanent deformation of asphalt layer,and the thickness of asphalt layer is allowed to be measured by adhesive layer,concrete layer thickness is design by composite plate model,indirect tensile test to control the anti-bending performance of RAP concrete to guide the application of RAP concrete in HMA/PCC.The research of this paper has promoted the application of RAP in the composite pavement structure,which not only can improve the recycling of pavement materials,but also improve the value of RAP utilization,prolong the service life of road and achieve the purpose of energy saving and environmental protection and resource recycling.