Study On Application Performance Of Foamed Asphalt In Seasonal Freezing Environment

At present,the application of foam asphalt mixture in seasonal freezing zone is less,which is closely related to the environmental characteristics of seasonal freezing zone.In this paper,based on the environmental characteristics of the seasonal freezing area,the attenuation law and attenuation mechanism of the macroscopic properties of foam asphalt and foam asphalt mixture in the seasonal freezing area were deeply studied through the design of indoor simulation test.The main contents are as follows:(1)In this paper,70# matrix asphalt and SBS modified asphalt were foamed by using self-made foaming equipment.The optimal preparation process of foamed asphalt was determined by response surface method with water consumption,shear rate and foaming temperature as influencing factors,and the influence law of water content on the performance of foamed asphalt was studied.(2)Through design tests,the performance attenuation rules of foam asphalt under three environmental factors of high-temperature evaporation,low-temperature freezing and freeze-thawing cycle were studied,and it was found that the freeze-thawing cycle had more significant degradation effect on the macroscopic properties of foam asphalt than high-temperature evaporation and low-temperature freezing.The results show that under the freeze-thaw cycle,the foam asphalt is seriously affected by water-temperature aging,and obvious hardening occurs.The overall performance of foam asphalt declines,and after freeze-thaw for 30 days,the internal moisture basically disappears.(3)Through SEM test,DSR test and DSC test,the microstructure change rule of foam asphalt in seasonal freezing environment was analyzed.The SEM test results showed that the asphalt was fluffy after foaming,and there were circular cavitation.After freeze-thaw cycle,the cavitation disappeared,and the asphalt surface was fragmented and massive.DSR test results show that after repeated freeze-thaw cycles,foamed asphalt tends to be gelatinized and rutting factor increases.The storage modulus of the two kinds of bitumen decreased with the increase of temperature before and after freezing and thawing.At high temperature and low frequency,the recovery capacity of froth bitumen after freezing and thawing was similar to that of unfrozen and thawed bitumen.DSC test results show that the froth asphalt after freeze-thaw is not a uniform continuous phase,which shows that the phase Angle decreases unsteadily with the increase of frequency at a certain temperature.The addition of water will increase the glass transition temperature of asphalt,resulting in poor performance at low temperature.(4)According to the climatic and environmental characteristics of spring melt season,the treatment method of snowfall-snow water thawing-freezing was designed,and the method of using silane coupling agent to improve the anti-spring melt water loss performance of foam asphalt mixture was put forward.Results showed that silane coupling agent can improve the bubble Marshall stability of asphalt mixture,and obviously improve the foamed asphalt mixture of the soaking remnants stability and low temperature splitting strength,that silane coupling agent made up for the defects of foam asphalt internal aqueous adhesive power decline,foamed asphalt mixture can be effectively improved spring meltwater damage resistance.