Rapid Evaluation And Performance Study Of RAP Content In Recycled Asphalt Mixture Based On Infrared Spectrum

The content of Reclaimed Asphalt Pavement?RAP?determines the performance of recycled asphalt mixture.Rapid detection and evaluation of RAP content is the point to ensure the quality of recycled asphalt pavement.RAP has great variability,which limits its usage in recycled asphalt mixture.At present,the quality control of the recycled asphalt mixture is mainly focus on testing the mechanical properties,which cannot be used to assessed its quality quickly and accurately.Infrared spectroscopy may realize rapid non-destructive testing and has achieved rich results in the quality control of other building materials,which also provides ideas and theoretical support for this study.In this paper,the rapid evaluation method of RAP content is studied and validated by infrared spectroscopy analysis technology.The feasibility and accuracy of the prediction and evaluation of RAP content in recycled asphalt mixture are studied;The pavement performance indexes of recycled asphalt mixture with different RAP content are analyzed.The influence of RAP content on the pavement performance of recycled asphalt mixture is discussed in order to propose a RAP threshold to meet the corresponding indicators.The main research contents and results are as below.Two test methods for the reclaimed of aging asphalt in mixed asphalt and asphalt mastic were compared by infrared spectroscopy.The results show that each test method can effectively predict and estimate the content of aging asphalt.According to Lambert-Beer's law,the change of absorption intensity of carbonyl absorption peak with the content of aged asphalt is analyzed.The fitting lines of the two test results are parallel to each other,and the slope of the linear regression equation is basically the same.It shows that the proposed method for quantitative analysis and evaluation of infrared spectroscopy of recycled asphalt mixture is feasible.By collecting infrared spectra of recycled asphalt mixture with different RAP content,the content of RAP was evaluated by the changes of carbonyl and sulfoxide absorption peaks of oxidized products of aged asphalt.Carbonyl and sulfoxide index were used as predicting factors,and the evaluation model was established by linear regression fitting method,and the samples which were not involved in the model were selected to verify the model.The results show that the coefficient of determination R² of the evaluation model is between 0.87 and0.96,which is larger than the critical value of the coefficient of determination(R²_min?28?.0658),indicating a good linear correlation.The standard deviation is small,and the repeatability of parallel test is high.The predicted value of RAP content is closer to the actual value,and the error is about±5%.Therefore,infrared spectroscopy can be used to predict and evaluate RAP content quickly and accurately.The influence of RAP content on the pavement performance of recycled asphalt mixture is analyzed such as water stability,high temperature stability,low temperature crack resistance and durability.It shows that with the increase of RAP content,the water damage resistance of recycled asphalt mixture shows a trend of increasing first and then decreasing,increasing high temperature stability,weakening low temperature crack resistance,and the dynamic modulus and the number of repeated loads required for permanent deformation increase first and then decrease slowly.Taking all the performance indicators consideration,the maximum content of RAP is 40%when only adding new asphalt to regenerate,and the content thresholds of RAP which meet the requirements of different indicators are put forward.