| The recycling technology of asphalt pavement can effectively reduce the use of energy resources and dispose of old waste materials,which make waste profitable.It has great economic and environmental value,caters to the current mainstream concept of sustainable development of the international community,and is one of the inevitable trends of future development.However,at present,the recycling theory is not perfect,and the the good products and the bad one are intermingled.At present,there is no design theory and evaluation method of the asphalt regeneration materials.Therefore,It is of great significance for the development and wide application of recycled technology to establish and improve the design method and evaluation mothod of the asphalt regeneration materials.The goal of rejuvenator materials is to restore the performance of aging asphalt.So the design and optimization of regeneration materials can not be separated from the study of asphalt aging mechanism and its composition changes.Firstly,the thermo-oxidation aging,photo-oxidation aging and volatilization of light components of asphalt are systematically analyzed.The three ageing mechanisms are different,as well as the emergence conditions,components and the properties of asphalt materials.The test results show that the aging reaction of asphalt is mainly related to the source in stead of the asphalt label and mineral admixture.In addition to the sulfoxide,ketone and aromatic rings,there are some hydrogen bonds produced during the thermal and photo-oxidative aging of asphalt.The changes in the molecular characteristics of asphalt lead to changes in the interaction between the molecules,futher the colloidal structure of asphalt changed,which result in the aging hardening effect.The photooxidation aging of asphalt is not uniform,and the influence of ultraviolet radiation is limited.The deterioration of pavement structure under ultraviolet radiation is more due to some other diseases caused by the aging of surface asphalt.Whether the regeneration materials can rapidly diffuse into the old asphalt in a short time has a very significant impact on the performance of the asphalt layer on the surface of aggregate.In order to study the diffusion characteristics of different rejuvenators,molecular dynamics method was used.Firstly,25 kinds of aging asphalt molecules are generated from 20 kinds of new asphalt molecules based on the aging mechanism of asphalt,and then the aging asphalt model is constructed.According to the selected force field and molecular dynamics parameters,the molecular dynamics model of asphalt materials were generated.It has been proved that the models have similar properties with real asphalt materials and can represent asphalt materials to some extent.Then four typical petroleum-based molecules of four biooil-based molecules were selected for diffusion simulation analysis.It is found that the diffusion property is related not only to the structural characteristics of regeneration material molecules,but also to the intermolecular interactions within regeneration materials.Based on the simulation results,five typical diffusion modes are summarized and proposed.Based on the analysis of aging characteristics of asphalt and the molecular diffusion characteristic of regeneration materials,the design method of regeneration materials is proposed,and the design theory of regeneration materials is further optimized from the point of view of interface performance of asphalt regeneration layer.Then the asphalt rejuvenator and the corresponding recycled asphalt mixture were prepared combined with the mix design.At last,the comprehensive pavement performance of recycled asphalt concrete was verified.The results show that the high and low temperature performance of recycled asphalt mixture after 7 days of curing can basically meet the performance requirements of low-grade pavement.Firstly,the performance of asphalt regereration layer was evaluateed using the splitting test method and the pull-out test of asphalt regereration fusion layer.In order to compensate for the shortcomings of the evaluation method of asphalt mixture test,the low temperature beam test of FAM were further carried out.The test results show that the tensile strength of recycled mixtures increases with the increase of curing time,but the variation of tensile strain is not obvious.And the interface properties of asphalt regeneration layer can be effectively improved by adding polymer at room temperature.However,the interface strength can not be improved by adding bio-asphalt based regeneration materials at low temperature,while the tensile strain can be effectively increased.Then the beam test of FAM was used as a standard evaluation method of interface performance of asphalt recycling fusion layer after comparing the advantages and disadvantages of various test methods.Discrete element spherical bond model was used to construct the low temperature performance prediction model of asphalt mixture.The model established the relationship between FAM performance and the semi-circular bending test performance.It shows that the simulation results are in good agreement with the test results,and the model can predict the low temperature performance of the mixture well under specific conditions.Then,the influence of different indexes of FAM on the low temperature performance of mixtures was analyzed by using the discrete element model.Finally,the standard evaluation method of asphalt regeneration layer performance is determined through comparative analysis,and the relevant judgment standard is delimited according to the simulation and test result. |
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