| In the context of the "Dual Carbon Strategy" and "Transportation Powerhouse Strategy",extending the service life of asphalt pavement has become particularly important,as the aging resistance and healing ability of asphalt to some extent determine the service life of pavement.Therefore,this paper comprehensively considers these two aspects and uses Tinuvin P and nanomontmorillonite to prepare modified asphalt,providing ideas for extending the service life of asphalt.However,the dispersion effect of directly adding nano-montmorillonite into asphalt is poor,and how to determine the dosage of the two modifiers used together to achieve the best synergy is also a problem that needs to be studied.Therefore,this paper chooses a suitable modifier to organically modify nano-montmorillonite,making it have better hydrophobicity and dispersibility.Based on this,a preparation scheme for modified asphalt is designed and optimized,resulting in superior performance of modified asphalt.In addition,this paper studies the performance of modified asphalt through a series of experiments and molecular dynamics software,revealing the mechanism of Tinuvin P and nano-montmorillonite improving the aging resistance of asphalt.The paper first studied the organic modification method of nano-montmorillonite.Three modifiers,namely,KH-560,octadecyl dimethyl benzyl ammonium chloride(ODBAC),and coconut oil amide propyl betaine(CAB),were used to modify the montmorillonite organically.Based on the results of Fourier transform infrared spectroscopy and X-ray diffraction experiments,it was found that all three modifiers could effectively organicize the nano-montmorillonite.However,in terms of increasing the interlayer spacing of the nano-montmorillonite,ODBAC was found to be the most effective due to its longer carbon chain and larger branched molecule,and it could form a vertical double-layer intercalation structure between the montmorillonite layers.KH-560 was less effective,and CAB was the least effective.Therefore,ODBAC was ultimately selected to prepare organically modified nano-montmorillonite(OMMT).Secondly,a process consisting of single-factor experiments→PB screening experiments→response surface optimization → experimental verification was designed and used to comprehensively consider the dosages of the two modifiers and the five factors of shear temperature,shear rate,and time in the preparation process of modified asphalt,combined with the three major indicators and 135℃ Brookfield viscosity value of asphalt.The optimal preparation conditions for modified asphalt were determined to be Tinuvin P dosage of 5.5%,OMMT dosage of 3.5%,shear temperature of 136℃,shear time of 30 minutes,and shear rate of15,000 rpm.After preparing modified asphalt under these conditions,the three major indicators were tested,and it was found that the measured values differed from the predicted values by only3%.Therefore,the process of single-factor experiments →PB screening experiments →response surface optimization →experimental verification can be used to explore the optimal preparation conditions for modified asphalt.Then,a comparative analysis was conducted on the performance of Tinuvin P/OMMT modified asphalt and matrix asphalt.Four aging indicators were introduced: penetration ratio,retained ductility,softening point increase,and viscosity aging index.By comparing these four indicators between the modified asphalt and matrix asphalt,it was found that the modified asphalt has better anti-aging and healing capabilities than the matrix asphalt.Through macroscopic healing experiments and microscopic infrared and ultraviolet spectroscopy experiments,it was found that OMMT can delay the reaction between asphalt and oxygen and improve the healing ability of asphalt,while Tinuvin P can absorb most of the UV light in the range of 280-400 nm,explaining the reason for the improvement of anti-aging performance of modified asphalt.Finally,molecular dynamics simulations were performed using software to investigate the effects of Tinuvin P and OMMT on asphalt properties.An 8-molecule model was used to construct the asphalt matrix,and the accuracy of the model was verified by density and surface energy calculations.Based on this,three modified asphalt models were established: Tinuvin Pmodified,OMMT-modified,and Tinuvin P/OMMT-modified asphalt models.Molecular dynamics simulations were conducted on these models,and the system energy,free volume fraction,and mean square displacement were calculated.Results showed that Tinuvin P can reduce the system energy of asphalt,thereby enhancing its resistance to UV aging.Both Tinuvin P and OMMT can reduce the free volume fraction of asphalt,increasing its internal stability and resistance to thermal-oxidative aging.OMMT can also improve the healing ability of asphalt due to its larger interlayer spacing.Furthermore,the mechanisms by which Tinuvin P and OMMT enhance the anti-aging and healing properties of asphalt were explained at the molecular level. |
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