Study Of Anti-aging Agents On The Performance Of SBS Modified Asphalt And Mixture

Asphalt aging is an important cause of pavement durability and has become a leading factor in triggering pavement maintenance.In addition to optimising the mixture grade design,the addition of asphalt ageing inhibitors is also an important measure to improve the durability of asphalt mixtures.For the anti-ageing agents to improve the performance of asphalt and its mixtures,most of them are limited to the verification of the conventional performance of asphalt and the road performance of mixtures at high and low temperatures,but not in-depth analysis of the microscopic properties of asphalt,rheological properties and the comprehensive road performance of its mixtures from different ageing stages.Different anti-ageing agents do not have the same effect on asphalt ageing resistance due to differences in their material properties and mechanism of action.Based on this,three anti-aging additives,graphene,gum powder and petroleum resin,were selected and blended with SBS modified asphalt using a melt blending process to prepare three composite modified asphalt of graphene/SBS,gum powder/SBS and petroleum resin/SBS,and to carry out research on the influence mechanism and performance.The main research work of the thesis is as follows:Considering the temperature and time dependence of asphalt under dynamic shear conditions,the rheological evaluation system of asphalt in different aging conditions is improved.And using Burgers and VECD viscoelastic continuous medium damage functions,a mathematical model of non-linear viscoelastic damage before and after asphalt ageing was established to reveal the correlation between the evaluation indicators.The test results showed that there was a good correlation between the medium temperature fatigue yield stress and the high temperature rheological complex modulus of asphalt.The peak widths in the stress-strain curves,the failure damage characteristic points and the damage characteristic curves were taken into account to provide a more accurate description of the fatigue damage evolution of asphalt.The graphene interlayer structure can effectively inhibit structural damage under the coupling of thermal and mechanical stresses,effectively reduce oxygen penetration and diffusion,improve the rutting factor ageing index,reduce the amount of non-recoverable creep flexibility by 7.1%,improve the stress sensitivity,and enhance the high temperature stability of asphalt before and after ageing.The gum powder increased the elastic component of the SBS modified asphalt,improved low temperature performance and fatigue performance,and reduced relaxation time by 14.8% and retarded delay time by 12.6% after long-term ageing.The increased viscous composition of the petroleum resin improves the low temperature movement of the molecular chain segments,but has a negative effect on the high temperature performance enhancement and has the worst fatigue properties after long-term ageing.The ageing mechanism of SBS modified asphalt was analyzed at the microscopic scale,and the improvement effect of anti-ageing agents was quantitatively and qualitatively evaluated.The asphalt-aggregate two-phase system interface was established by surface free energy theory,revealing the failure mechanism of material composition,ageing state and environmental conditions on the adhesion strength of the interface.The test results showed that the ageing process of SBS modified asphalt was accompanied by both the oxidation of functional groups and the pyrolytic fracture of the modifier.Graphene,gum powder and petroleum resins can,to varying degrees,retard the rate of degradation of polar functional groups carbonyl and sulfoxide group formation and polybutadiene during ageing.There were no new characteristic peaks in the preparation of the three composite modified asphalt,and there was only a difference between the peak strength and weakness of the SBS modified asphalt,which was physically blended.The anti-ageing agent was homogeneously dispersed in the bitumen and had good compatibility with both SBS modifiers.The fluorescence results of the gum powder mostly showed a loose flocculent structure that broke up and reorganizes,eventually forming a semi-solid continuous phase system;the petroleum resin had a more stable phase distribution and the most complete interwoven network.Based on surface free energy theory,ageing behaviors decreased the adhesion properties by changing the contact angle between the asphalt and the test fluid,increasing the cohesive work of the asphalt and the exfoliation work of the asphalt-aggregate system,and decreasing the adhesion work.Petroleum resins had the most significant improvement in asphalt adhesion properties,but graphene had the most significant improvement in the water stability of asphalt in the ageing stage.The effect of different ageing stages on the service life of asphalt pavements is considered,and the effect of anti-ageing agents on the road performance of asphalt mixtures is clarified through indoor simulation of thermal-oxidative short-term ageing and thermal-oxidative and UV coupled long-term ageing.A prognostic model for the dynamic modulus master curve of the mix was constructed based on the time-temperature equivalence principle and the generalized Sigmoidal function.The test results showed that the model had a high accuracy in fitting the dynamic modulus of asphalt mixtures at different stages of ageing,and that the main modulus curve ordering showed a consistent variation pattern with the rheological properties.The glue powder optimized the inter-aggregate interlocking and void distribution characteristics and improved the low temperature performance of the mixtures.Petroleum resins can substantially increase the adhesion between the asphalt and the aggregate and maintain high water stability properties under dynamic water pressure.This study uses a combination of macro and micro analysis,and comprehensive qualitative and quantitative analysis to construct a systematic evaluation system,which reveals in depth the anti-aging enhancement mechanism of graphene,gum powder and petroleum resin on SBS modified asphalt.On the basis of asphalt rheological properties,microscopic characteristics and mixtures road performance,the correlation between asphalt ageing microscopic indicators and macroscopic performance is established to provide theoretical basis and technical support for improving the anti-ageing performance of asphalt pavements.