Study On Mechanism And Performance Evaluation Of SBS And Crumb Rubber Composite Modified Asphalt

With the development of economy,axial load and the amount of traffic on the pavement are gradually increasing,and modified asphalt of a single modifier has gradually failed to meet the requirements of pavement performance in some cases.On the other hand,SBS modified asphalt and crumb rubber(CR)asphalt has its own advantages and disadvantages.For example,the SBS modified asphalt has excellent performance but high price,CR modified asphalt is environmentally friendly and low in cost,but its performance is not stable.Therefore,in order to utilize the complementary advantages between different modifiers and then produce more excellent modified asphalt.Researchers proposed SBS/CR composite modified asphalt.Based on the summarization of domestic and foreign researches,this paper systematically studies the properties of SBS/CR composite modified asphalt,the mechanism of composite modification,and the road performance of the composite modified asphalt mixture.Firstly,"wet process" is used to prepare different modified asphalt.Through the traditional asphalt evaluation system and Superpave asphalt binder evaluation system,the performance of modified asphalt are evaluated comprehensively.The test results show that SBS and CR can reduce the penetration and improve the softening point and viscosity of the binder.The effect of composite modification is better.The results of dynamic shear rheological test and the performance grading show that composite modified asphalt possess outstanding resistance to deformation at high temperature and fatigue.The results of bending beam rheometer show that the low temperature performance of the composite modified asphalt has not been significantly improved.From the results of the master curve,the viscoelastic properties of the composite modified asphalt are improved.Taking comprehensive consideration of performance test results,the optimal content of modified asphalt is selected.Then,the mechanism of composite modification is investigated by Fluorescence Microscopy,Fourier Transform Infrared Spectroscopy,Gel Permeation Chromatography,and Scanning Electron Microscopy.Fluorescence images show that SBS and CR were uniformly distributed in the modified asphalt and the particle diameter was reduced,indicating that the modification process occurred and particle swellen.Composite modified asphalt forms a good network structure.FTIR shows that no new functional groups are generated during the process,and only chemical bonds are destroyed and recombined.GPC tests show that different modified asphalts have different macromolecule content,SBS and CR can increase the proportion of large molecule size,thus improving asphalt performance.According to the area ratio of the polymer peak and asphalt peak,SBS and CR can promote each other in the composite modification process,allowing the asphalt to better absorb with the modifie;SEM test results indicate that during the modification process,the light components in the asphalt penetrate and diffuse into the crumb rubber particles,so that the asphalt transforms from a sol structure to a sol-gel structure,and the temperature sensibility decreased.Next,the performance of composite modified asphalt mixture which produces by "dry process" with AC-13G gradation was verified,and the dynamic creep tests show that the high-temperature stability of mixture increased significantly.The fracture energy and flexibility index obtained by the semi-circular bending test show that the mixture has a higher modulus but lower toughness and is vulnerable to brittle failure.The results of the immersion Marshall test and freezing and thawing split test show that the composite modified asphalt mixture has good water stability.Finally,it was proved that the three-phase system of aggregate,CR and asphalt has been formed through SEM of the composite modified asphalt mixture,and in the dry process,CR particles swell and are wrapped by asphalt and adhered to the aggregate.The results of performance test of the asphalt binder extracted from mixture which produced throght dry process prove that in the dry process,the modifier can also sufficiently modify the asphalt.