Investigation On Properties Of Rejuvenated SBS Modified Bitumen And Their Mixture Based On Structure Reconstruction

Poly(styrene-b-butadiene-b-styrene)block copolymer(SBS)modified bitumen has been widely applied in highway construction because of its superior low-temperature crack resistance and high-temperature stability.However,SBS modified bitumen will be aging to the asphalt pavement diseases with the effect of the environmental factors such as heat,oxygen and ultraviolet light.Through the milling and repaving for road,a lot of waste SBS modified bitumen mixtures are thus produced.If those waste mixtures are not effectively utilized,it will not only have a great impact on the ecological environment,but also lead to a great waste of the resources such as bitumen and aggregate.The aging of the binder is the main determinants for performance deterioration of bituminous mixture,while the aging of SBS modified bitumen binder includes the changes of chemical components caused from the reaction such as dehydrogenation and oxidation in bitumen,and the destruction of molecular structure casused from the degradation of polymer modifier.At present,the component reduction of asphalt matrix is the main rejuvenation method for aged SBS modified bitumen,while there has been no effective methods for restoring the molecular structure of the modifier,so the better improvement for the performances of aged SBS modified bitumen and its mixture can't be achieved.Therefore,it is of great significance to investigate the rejuvenation and utilization of waste SBS modified bitumen mixture.To restore the whole performance of SBS modified bitumen,the research idea of rebuilding the molecular structure of aged SBS using reactive compounds is put forward in this paper.Firstly,the changes of molecular structure of SBS under the aging conditions of heat and oxygen are investigated and the aging mechanism of SBS is discussed;then,the reconstruction effects of reactive compounds 1,4-butanediol two glycidyl ether(BUDGE)and 4,4-two phenyl methane diisocyanate(MDI)on aged SBS are studied and the reconstruction mechanism is analyzed;moreover,the reactive rejuvenating systems(BUDGEs,MDIs,BUDGE-MDIs,etc.)including the bituminous component reducing reagent(FCC oil slurry)and epoxy or/and isocyanate compounds are used for the reaction-rejuvenation of the aged SBS modified bitumen,while the effects of the reaction-rejuvenation on the molecular structure,physical and rheological properties of aged SBS modified asphalt are investigated;finally,the optimized reactive rejuvenating systems are applied in the rejuvenation of aged SBS modified bitumen mixture,and the road performances of rejuvenated SBS modified asphalt mixture are evaluated.The main conclusions are drawed as follows.(1)The analysis of Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)indicate that the oxidation and degradation of SBS will be occurred during the aging process,and some degradation products with the oxygen-containing groups such as-OH,C=O,-COOH etc.,will be formed.The short-term thermo-oxidative aging only causes the chain breaking of PB segment in the main chain structure of SBS,and has no significant effect on PS segment.However,with the prolongation of aging time,the degradation of PS segment will continue to be done in addition to PB segment.The results of Gel permeation chromatography(GPC)and Thermogravimetric analysis(TGA)show that thermal aging will cause a significant decrease in the molecular weight,a wider molecular weight distribution and a great decrease in thermal stability of SBS.(2)FTIR analysis demonstrates that BUDGE can react with aged SBS to form reactive products containing ether and ester group structure,whereas MDI can react with aged SBS to form reactive products with amide structure.GPC tests indicate that the molecular weight of the reactive products obtained from the reaction between BUDGE or MDI and aged SBS can be more obviously improved,and their molecular weight distributions become narrower,which illustrates that BUDGE and MDI can individually connect the reactive aged products of SBS,and to some extent,rebuild the molecular structure of aged SBS.(3)Results of physical and rheological properties demonstrate that the epoxy reactive rejuvenating system(BUDGEs)can effectively improve the low-temperature ductility,flexibility and fatigue resistance of aged SBS modified bitumen,while it has an obvious reduction on the high-temperature stability.However,the isocyanate reactive rejuvenating system(MDIs)can improve the high-temperature stability of aged SBS modified bitumen,while it will cause a lower improvement on the low-temperature ductility,flexibility and fatigue resistance.The synergistic reactive rejuvenating system(BUDGE-MIDs)can not only significantly improve the low-temperature ductility,flexibility and fatigue resistance of aged SBS modified bitumen,but also preferably restore its high temperature stability.(4)The reaction rejuvenation experiment of second-aged SBS modified bitumen indicates that the rejuvenation effect of BUDGE-MDIs on second-aged SBS modified bitumen becomes weak,however,which can still improve the low-temperature ductility,flexibility,fatigue cracking resistance and high-temperature deformation resistance.After rejuvenation of second-aged SBS modified bitumen with addition of BUDGE-MDIs,the elastic modulus of rejuvenated SBS modified bitumen keeps a lower level and the elastic-plastic transformation rate becomes obviously slower.When the tensile strain exceeds the elastoplastic transition point,its behavior gradually changes to viscous deformation.(5)Road performances of rejuvenated SBS modified bitumen mixture suggest that both BUDGEs and BUDGE-MDIs can significantly improve the moisture damage resistance of aged SBS modified bitumen mixture,and the load and water resistance of rejuvenated SBS modified bitumen mixture can be also remained after a second water damage test,in particularly,BUDGE-MDIs rejuvenating system can well improve its low-temperature cracking resistance of aged SBS modified bitumen mixture,and maintain a higher high-temperature stability.(6)The observations for the fracture appearance of rejuvenated SBS modified bitumen mixture indicate that both BUDGEs and BUDGE-MIDs can improve the low-temperature adhesion force between aged SBS modified bitumen binder and aggregates,and significantly reduce the occurrence of the large-area loose holes of binder when the mixture is broken at low temperature.