Diffusion Behavior And Regeneration Effect Evaluation Of Rejuvenator In Aged Asphalt

Asphalt pavement regeneration technology is a reliable choice to realize ecological protection and resource saving,and is a necessary means to realize the sustainable development strategy of road construction in our country.Among them,the diffusion behavior of the rejuvenator and the aged asphalt and the evaluation of the regeneration effect are the key to the regeneration technology.This article takes indoor simulated aging asphalt as the research object,firstly evaluates the degree of asphalt aging from the perspective of physical properties,chemical composition and rheological properties.Secondly,theoretical analysis methods and experimental testing methods are used to study the diffusion behavior of the rejuvenator.Finally,the regeneration effect of the aged asphalt is evaluated and the optimal content of the rejuvenator is obtained.The research results can provide theoretical foundation and technical support for the thermal regeneration technology of asphalt pavement.The main work completed in the thesis and the research conclusions obtained are as follows:（1）Through testing the viscosity-temperature characteristics,functional group content and rheological parameters of different aging asphalts.A quantitative analysis method for characteristic functional groups was established.Combining with the complex shear modulus G*,phase angleδ,rutting factor G*/sinδ,fatigue factor G*sinδ,complex viscosity η*,strain recovery rate R,irrecoverable compliance J_nr,and the changing law of the peak stress σP and asphalt aging degree under continuous increasing strain,the asphalt aging degree was evaluated.The results show that,after the asphalt is aged,the chemical composition changes,and the content of characteristic functional groups changes significantly.The 1700cm-1 carbonyl group（C=O）and 1030cm-1 sulfoxide group（S=O）are outstanding.The aging degree of asphalt can be quantitatively evaluated by the change of characteristic functional group index.Affected by the changes of components after aging,the ratio of viscoelasticity is imbalanced,the rheological parameters have changed significantly,the high temperature stability is improved,and the low temperature crack resistance and fatigue performance decrease.The aging degree of asphalt can be evaluated by the change of G*、δ、G*/sinδ、G*sinδ、η*、R、J_nr and σP.（2）Through the DSR frequency scanning test method,the complex shear modulus and phase angle of different aging asphalt are obtained,and the master curve is established using the principle of time-temperature equivalence.Combining with the WLF mathematical transformation equation and the numerical change of the shift factor,the glass transition temperature T_g of the aged asphalt is obtained.The correlation between T_g and the characteristic functional group index and rheological parameters of aging asphalt was explored,and the aging degree of asphalt was comprehensively evaluated.The results show that the characterization of asphalt’s low-temperature performance is significantly affected by the degree of asphalt aging;it is linear with the functional group index of hydroxyl and sulfoxide groups and their rate of change（IC=O,IS=O,WC=O,WS-=O）,respectively The distribution status,and the numerical changes are all positively correlated.Respectively,they are linearly distributed with rheological parameters(G*、δ、G*/sinδ、G*sinδ、η*、R、J_nr),and the value changes are positively correlated with G*、G*/sinδ、G*sinδ、η*and R,and negatively correlated with δ and J_nr.Through this correlation analysis,the aging degree of asphalt can be evaluated.Within the scope of this study,40h long-term aging asphalt has the greatest aging degree.（3）Based on the Vrentas-Duta free volume theory,a theoretical analysis method for the diffusion behavior of rejuvenator and aged asphalt was established,and the diffusion coefficient of rejuvenator was theoretically characterized.Through the calculation and analysis of the model parameters,the main influencing factors of the rejuvenator diffusion are explored,and the key issues and technical measures of the regeneration process are pointed out.Based on the diffusion model,the diffusion coefficients of rejuvenator and different aged asphalts were predicted.The results show that,based on the Vrentas-Duta free volume model,the diffusion coefficient of the rejuvenator can be characterized.Through the analysis of model parameters,it is known that selecting small molecule rejuvenators,increasing the initial content of the regenerating agent,increasing the system temperature,and reducing the degree of asphalt aging all improve the diffusion favorable way of speed.The theoretical model can effectively predict the diffusion coefficient of the rejuvenator.The results show that in the temperature range of 60～160℃,the diffusion coefficient satisfies the third-order polynomial distribution with the temperature change,and the limit temperature of the mechanical state of the aged asphalt is 100℃+T_g2,It is the mutation point of the diffusion coefficient.At this temperature,the aged asphalt enters the viscous flow state,and the diffusion coefficient increases significantly.（4）According to the self-designed diffusion test,the tracer method was used to test the diffusion behavior of the rejuvenator in the aged asphalt.Combining with the diffusion test,an analysis method for the diffusion coefficient of the rejuvenator was established,the diffusion behavior was quantitatively analyzed,and the reliability of the diffusion theory model was verified.The diffusion behavior of the rejuvenator under the actual distribution of the RAP asphalt membrane was estimated,so as to judge the rationality of the construction and production conditions.The results show that,CTBN and SBS are used as tracers to characterize the diffusion behavior of rejuvenator.The optimal labeling amount is 10%and 3%,respectively.By establishing a standard curve and taking the characteristic absorption peak area ratio A1739/A1458 as the judgment basis,it can effectively reflect the diffusion amount of the rejuvenator in the aging asphalt.Under the same conditions,increasing the temperature,extending the time and reducing the degree of asphalt aging can effectively improve the rejuvenator of the amount of diffusion.In the scope of this study,with the increase of temperature,the rejuvenator diffusion coefficient and the cumulative diffusion rate are consistent with the temperature,which conforms to Fick’s second law.Under preset conditions,the theoretical prediction value of the rejuvenator diffusion coefficient is basically close to the experimental calculation value.The Vrentas-Duta free volume model is used to predict the rejuvenator diffusion coefficient with certain accuracy.The mixing time stipulated in the production of recycled asphalt mixture is completely satisfied with the diffusion and miscibility behavior of the rejuvenator and the aged asphalt film,and make the aging asphalt have the prerequisites for regeneration.（5）Using the FTIR quantitative analysis method,the relationship between the content of the characteristic functional group and the dosage of the rejuvenator was established,and the reasonable dosage of the rejuvenator under this condition was obtained.Using DSR,MSCR and LAS test methods,the relationship between the parameters of the rejuvenator and the rheological parameters was established,and the reasonable dosage of the rejuvenator under these conditions was obtained.Based on the analysis results of the above-mentioned research methods,the optimal content of rejuvenator s for different aged asphalts to meet the performance requirements was determined.The results show that,regeneration is the reverse process of aging.After the rejuvenator is added,the characteristic functional groups and rheological parameters will change significantly,and the change trend is opposite to the asphalt aging process,and the regeneration effect gradually appears.Using the FTIR method to determine the optimal amount of rejuvenator based on the recovery status of the characteristic functional groups,it is not reliable;within the scope of this study,the optimal amount of rejuvenator is 11.303%and 15.790%for the 85min aging asphalt and 40h long-term aging asphalt.Under this condition,the regeneration effect of aged asphalt is good.