Secondary Regeneration Mechanism And Performance Evaluation Of Asphalt Based On Molecular Dynamics

Asphalt pavement regeneration technology is an effective method to recycle reclaimed asphalt pavement(RAP),and the regeneration effect of asphalt is the key to determine the road performance of recycled asphalt mixture.At present,a large number of primary recycled pavements in China are about to reach the design service life,and will face the problem of secondary regeneration.However,most of the research on asphalt regeneration mechanism and macro and micro performance evaluation still stays in the primary regeneration stage,and there are few related studies on asphalt secondary regeneration,which is not conducive to guiding the secondary thermal regeneration of asphalt pavement.Therefore,this paper studies the mechanism of secondary aging and regeneration of asphalt based on microstructure and molecular dynamics simulation,and evaluates the feasibility of simulation results through high and low temperature,rheological properties and fatigue properties.It has certain theoretical and engineering application value for promoting the progress and development of secondary regeneration technology of asphalt pavement in China.Firstly,the change law of physical properties of asphalt during the secondary aging process was studied,and the secondary long-term aging time was determined in combination with engineering RAP.Different types of primary and secondary recycled asphalt were prepared,and the physical properties of recycled asphalt were tested.The results show that the attenuation rate of physical properties of asphalt decreases and the aging resistance increases during the secondary aging process.The recovery level of physical properties of asphalt after secondary regeneration is not as good as that of primary regeneration asphalt,and its ductility index does not reach the new asphalt standard.Secondly,the changes of chemical composition and structure of asphalt before and after two regeneration were analyzed by TLC-FID and FT-IR tests.The results show that the asphalt experienced the volatilization of light components and the formation of oxidation products during the two aging processes,and the component ratio imbalance and oxide index increased more significantly during the secondary aging process.The recovery of component ratio after secondary regeneration is good,but the recovery effect of oxide index is not good,which means that the regeneration process is more reflected in four-component regulation rather than chemical reduction reaction.Then,three asphalt molecular models with different aging states were constructed and optimized based on the microstructure characteristics.Based on the dynamic simulation of single molecule and double layer diffusion model and performance test,the secondary regeneration mechanism of asphalt,the fusion behavior of old and new asphalt and the change trend of asphalt performance were analyzed.The results show that temperature and aging times are two important factors affecting the molecular characteristics of asphalt.The secondary aging asphalt has lower self-diffusion rate,higher energy in the system and smaller free volume fraction.The mutual diffusion speed of new and old asphalt after secondary aging is slower,that is,the secondary aging asphalt will hinder the integration and diffusion of new and old asphalt;regenerant can improve the diffusion rate of new and old asphalt during regeneration,but it can not improve the fusion degree of new and old asphalt during secondary regeneration.After the secondary aging of asphalt,the high-temperature shear modulus decreases and the low-temperature bulk modulus increases,and the secondary regeneration effect of the regenerant becomes significantly worse.Finally,the variation of the performance of the secondary recycled asphalt was analyzed by DSR and BBR tests.The results show that the rheological properties,high temperature performance and fatigue performance of asphalt after secondary aging are enhanced,and the attenuation range is lower than that of primary aging asphalt,but its low temperature performance is not as good as that of primary aging asphalt.The recovery level of high temperature performance and rheological properties of asphalt after secondary regeneration can reach the state after primary regeneration.The low temperature performance and fatigue performance continue to decay,and the recovery effect of secondary regeneration decreases.