Nano-structure And Components Of The Recovered Asphalt Binders From Weathered Asphalt Mixtures

At present,asphalt mixtures are frequently selected for pavements in all levels of highway due to the continuous improvement of asphalt properties.The aging of asphalt binders always,however,causes various problems to asphalt pavement failures.Asphalt binder would easily become hard and brittle after aging,which seriously affected the performance of asphalt pavements.In addition,the maintenance and repair of the asphalt pavement will not only largely consume natural resources,but also hamper the traffic flow.The change of nano-structure of asphalt binder is inevitably initiated by its chemical components and the structure type of asphalt colloid is influenced,which would consequently affect the performance of asphalt pavements.The relationships between the chemical component,nano-structure and performance properties of asphalt binder are t key interests of the research project.The objectives are to understand the aging mechanism of asphalt binders by using chemical components and the nano-structure of asphalt binders.To this end,this study selected two kinds of asphalt binders recovered from weathered asphalt mixtures of OGFC-13 in an accelerated weathering machine.The recovered asphalt binders were tested for their four components in composition,nano-structure by Atomic Force Microscope(AFM)in morphology and rheological properties by Dynamic Shear Rehometer(DSR)in mechanics.The weathering time for the asphalt mixtures,the aged binders were recovered from,were 0,1,000,2,000 and 3,000 hrs.In addition,SHRP aging processes of both short and long terms were carried out as control.The results showed that:(1)with the increasing of weathering time,the contents of asphaltene and resin within all the aged asphalt binders were raised,but the aromatic and saturated reduced.The index Ic of asphalt colloidal of the two weathered binders are different,but steady.The SHRP aged binders had the similar trend as found from the wearthering machine.But the Ic of SBS modified asphalt increased from 0.411 to 0.734.(2)With the increasing of weathering time,the three indexes ISAD,Rq and Rmax by AFM of the weathered asphalt binders were all increased.Again,the weathering machine and the SHRP aging processes owned the similar trend.However,"bee-structure" of asphalt binder nano-structure exhibited different change rules under the two aging ways.(3)There existed good relationships between the four components of the two weathered asphalt and their rheological properties.Asphaltene and resin increased more,and saturates and aromatics reduced more,rheological properties of asphalt binder would degrade more.In addition,it found that there was a low correlation coefficient between the four asphalt components and the freeze-thaw splitting ratio of OGFC-13 mixtures,which indicated a lower relationship between water damage of the asphalt mixture and properties of its asphalt binder.(4)As the three AFM indexes of two weathered asphalt binders increased,their rotational viscosity,anti-rutting factor and fatigue cracking also increased.There would be more deterioration of asphalt rheological properties,as the size of "bee-structure" existed on asphalt nano-structure increased.In addition,there also had low correlation coefficients between two AFM indexes and the freeze-thaw splitting strength ratio of OGFC-13 mixtures,and worse than those of asphalt components.(5)As the resin and asphaltene of the two weathered asphalt increased,the three AFM indexes linearly increased and the size of "bee-structure" became larger.Regardless of the two aging methods of either by weathering machine or SHRP aging process,the modifier SBS can both retard the influence of four asphalt components onto the asphalt nano-structure,as it reduced all the linear correlation coefficient analyzed.