Study On The Thermo-oxidative Aging Mechanism Of Modified Asphalt Doped SBS

SBS modified asphalt has been widely used in asphalt pavement engineering and the waterproofing and antisepsis engineering of civil construction.The SBS modified asphalt will gradually occur performance cracking during the service process,due to the comprehensive influence of climate,working conditions,stress conditions and the other factors.This will cause the generation of pavement distresses and have a negative impact on the quality and life of the pavement and construction.Particularly,the thermo-oxidative aging is the main reason for the performance degradation of SBS modified asphalt.At present,the mechanism and influencing factors of thermo-oxidative aging of SBS modified asphalt at home and abroad are not clear enough.Further investigation is needed to improve the thermo-oxidative aging resistance of SBS modified asphalt.In order to improve the anti-aging property of modified asphalt,it is vital to explore the thermo-oxidative aging process and mechanism of modified asphalt,investigate the main factors affecting thermo-oxidative aging from the aspect of modified materials,and then put forward improving measures.Aiming at the residual diblock SB and Fe2+ in the polymerization process,the experiments were carried out using seven kinds of SBS with different residual diblock SB,SBS with different Fe2+ concentration,SBS with different graphene content and 70 matrix asphalt:Firstly,the basic technical properties and thermo-oxidative stability of different types of SBS were evaluated.Then,the thermal-oxygen aging test of SBS and its modified asphalt was carried out respectively under the same experimental condition.It was found that the increasing of the SB residual amount caused a drop for the glass transition temperature Tg1,the yellow index increased with time,and the C=C bond on polybutadiene block could easily be oxidized to carbonyl.The greater the molecular weight decay loss,the greater the thermo-oxidative degradation of the molecular structure.Fe2+ concentration had little effect on the glass transition temperature of SBS,but it had a significant effect on yellow index.With the increase of Fe2+ concentration,the yellow index increased,the content of methylene and C=C bond decreased,the carbonyl and ether bond increased,and the molecular weight decreased.This was due to the fact that Fe2+ accelerated the degradation of SBS chains and transformed SBS from macromolecule to small molecule.In addition,the addition of graphene alleviated the aging process of SBS.The decay of methylene and C = C bond slowed down,and there were no significant changes in carbonyl and ether bonds before and after aging.The addition of graphene reduced the formation of polar functional groups during aging and prevented polymer degradation.Secondly,the basic technical properties,thermo-oxidative stability and rheological properties of modified asphalt with different types of SBS are studied.Although the residual diblock SB improved the low temperature performance of modified asphalt,but it had a negative effect on the high temperature performance and thermal-oxidative aging resistance of asphalt.With the increase of Fe2+ content in SBS,the basic properties of modified asphalt decreased to some extent,but the effect of Fe2+ on the thermo-oxidative aging properties of modified asphalt was weaker than that on the modifiers.The addition of graphene can significantly improve the basic properties of modified asphalt before and after aging,especially at low temperature,and it can further improve the thermo-oxidative aging resistance of modified asphalt.Finally,the investigation on the pavement performance of SBS modified asphalt mixture was carried out.the SB content had a great influence on the high and low temperature performance and thermal-oxidative aging resistance of asphalt mixture.With the increase of SB content,the dynamic stability was reduced and the low temperature bending tensile failure strain was increased.The high temperature rutting resistance and low temperature cracking resistance of SBS modified asphalt mixture after aging were both decreased,but the change of water damage resistance was not obvious.The change of Fe2+ content had little effect on the high temperature performance and water damage resistance of SBS modified asphalt mixture.When the Fe2+ concentration reached 8 ?g/g,the high temperature stability was slightly enhanced.However,after aging,the change of Fe2+ content had a significant impact on the low-temperature performance of SBS modified asphalt mixture.When the Fe2+ concentration reached 8 ?g/g,the low temperature bending tensile failure strain was reduced by about 30% compared with the asphalt mixture without Fe2+ content.SBS modified asphalt mixture had a slight increase in high and low temperature properties and water damage resistance by adding appropriate amount of graphene.The main function of graphene was to improve the thermo-oxidative aging resistance of the mixture.The low temperature bending tensile failure strain of graphene mixture before and after aging was only slightly reduced.Considering the changing trend of road performance and economy before and after aging,the appropriate content of graphene is 1.0%.The above experimental results show that the presence of residual diblock SB reduces the thermo-oxidative stability of SBS and weakens the coupling between the blocks.Under the thermo-oxidative condition,the breakage probability of polymer chains increases,and the chains are easy to degrade.The presence of Fe2+ promotes the formation of active free radicals,decreases the activation energy of polymer chain reaction,and promotes the thermo-oxidative aging process of SBS.The graphene can cover the SBS polymer chains and bond with the unsaturated bonds and polar groups of SBS,reduce the oxidation of unsaturated bonds and polar functional groups of SBS,enhance the thermo-oxidative stability of SBS and improve the thermo-oxidative aging resistance of SBS modified asphalt.