| The aging of asphalt mixtures is the main reason for the change in asphalt properties,so it is important to study the aging of asphalt in asphalt mixtures.The current common approach is to first extract the bitumen in the asphalt mixture and then evaluate the extracted asphalt.Such tests require the use of organic solvents to extract and distill the asphalt in the asphalt mixture,which will affect the accuracy of the asphalt aging results,and the micro-toxic reagents will also be harmful to the body of the tester.Low-field NMR technology has the advantages of rapid testing,accurate results and non-destructive samples during testing,and has been gradually applied to the field of asphalt and asphalt mixtures in recent years.The purpose of this project is to explore the use of low-field NMR technology to study the performance of asphalt in asphalt mixtures,conduct non-destructive and rapid inspection of asphalt aging in asphalt mixtures,explore the characteristic parameters of obtaining low-field NMR spectra of asphalt and asphalt mixtures,and the inherent laws between asphalt aging,and study the feasibility and reliability of low-field NMR technology to test the aging degree of asphalt mixtures.The parameters of low-field NMR spectroscopy studied in this study include the number of flaccid peaks,shape,transverse relaxation time T2,total area of relaxation peak normalization,proportion of main peaks,peak width and experimental variables.Asphalt aging adopts conventional test infrared spectral parameters.Firstly,the LF-NMR test was performed on the asphalt mixture of the same specimen,the setting temperature was 40-100℃,and the holding time was 10 min,20min and 30 min,and the influence of temperature and holding time on the results of low-field NMR spectroscopy was studied,and the optimal test temperature and holding time were determined.Secondly,the low-field NMR test was carried out on the asphalt mixture with different aging degrees,the relevant parameters on the transverse relaxation time T2 and the semaphore spectrogram were analyzed,and the aging rate and aging terminal value were found to fit the aging rate and aging terminal value with the regular variation parameters of the aging time,and the relevant aging equation was established.Third,the extraction experiment of the mixture with different aging degrees is carried out,and the conventional test and evaluation method of the proposed aging asphalt is carried out-infrared spectroscopy test,and the carbonyl and subsulfite indices are analyzed,the relevant aging rate and final value are fitted,and the aging equation is established.The aging equation of the low-field MRI test is compared with the aging equation of the infrared spectral test,and the law of the low-field NMR test is analyzed to evaluate the aging degree of the asphalt mixture.Modified asphalt and basalt were selected to make AC-10,AC-13,OGFC-13 three graded asphalt mixtures,and the short-term aging was simulated indoors by manual acceleration standards,followed by long-term aging at three different time points.The results of the study show that:(1)The low-field NMR test spectrum of the asphalt mixture has a certain relationship with the test temperature.The optimal test temperature is 60 ℃ and the holding time is ten minutes.(2)The low-field NMR spectroscopy parameters of asphalt mixtures with different aging degrees are different,but the change trend of the total area of relaxation peak normalization is related to the aging time.(3)The rate of change and the final value of aging of the asphalt mixture fitted by the low-field NMR test are consistent with the laws obtained by the infrared spectroscopy fitting of conventional experiments.(4)There is a nonlinear relationship between the carbonyl and subsulfoxide index of aging asphalt in the asphalt mixture and the aging time.According to the carbonyl and sulfoxide index and the aging time,the relevant aging equation is fitted,and the content of carbonyl group and sulfoxide group increases with time,but the rate of change is different. |
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