Performance Effect Of Asphalt Mixture Under Salt Freeze-Thaw Cycles

The north is in an environment of snowy and low temperature in winter, so the roads will generate ice-frozen and snow which affect the traffic safety and smoothness. The deicing agent is often utilized to clear the road after snowfall, which will let roads long-term being the environment of salt frozen cycle, thereby destroy, the internal structure of the road. The road workers have done lots of research on the mechanical properties of asphalt being freeze-thaw with water and expound the mechanic of asphalt pavement damage. Also, some scholars have studied the erosion of deicing salt solution to pavement. Connecting the pre-existing related research results, in this paper, the bituminous mixture is studied with the experiments of freeze-thaw split, marshall stability, bending creep and uniaxial dynamic modulus, under different condition of freeze-thaw cycle. These experiments are used to study the variation of mechanical properties of bituminous mixture specimens before and after freeze-thaw cycle, and to contrastly analyze the variation of high temperature performance of ordinary bituminous mixture with the salt freezing cycle and bituminous mixture added snow melt salt with freeze-thaw, and furthermore the microstructure of bituminous mixture specimen that before and after salt freeze test was observed by scanning election microscope.The results verify that:(1)After freeze-thaw cycle, splitting strength and Marshall stability of bituminous mixture were decreased generally. The 4% salt solution environment has little effect on splitting strength and resistance to water damage. With the increase of the number of freeze-thaw cycles, splitting strength and Marshall Modulus are smaller, while the damage of road structure is greater.(2)Asphalt mixture is damaged larger, the flexibility and low temperature deformation are deteriorated in the environment of water freeze-thaw cycles. However, deicing salt environment can enhance the deformability of asphalt mixture.(3)The influence degree of the three factors about freeze-thaw cycles for splitting strength, Marshall stability and beam bending creep parameters of asphalt mixture is: the number of cycles> freezing temperature> salt concentration of the solution.(4) The dynamic modulus was decreased with the temperature increasing or the loading frequency decreasing. The change law of the phase angle is more complex with the transform of temperature and load frequency. In the same temperature and frequency, compared to the common specimens under freeze-thaw cycle, the dynamic modulus of specimens added the self melting snow is higher, while the phase angle is lower.(5)The microstructure: After freezing salt circulation, salt crystals appear on the surface of the mixture which will pierce bituminous membranes. In the short-term freeze-thaw situation, the corrosive of salt solution creates chipping and peeling in structural layer of asphalt. With the further increasing of the number of freeze-thaw, the saline water in the asphalt mixture internal will frozen or crystallization, leads to the further damage of mixture structure When the specimens molded, self melting snow will replace part of the slag and are closely with asphalt. Along with the number of freeze-thaw increased, self melting snow was released slowly. In experimental cycle-index, the variation of internal microscopic structure of asphalt mixture with self melting snow is not obvious.