Study On Frequent Freeze-thaw Cycle Response Of Asphalt Mixture In Permafrost Areas

The special environment of permafrost regions in Qinghai-Tibet Plateau has a significant effect on the mechanical properties of asphalt mixtures, such as perennial low-temperature, fast cooling rate, temperature difference between day and night, intense and frequent freeze-thaw cycle. Pavement diseases are related to performance deterioration of surface asphalt mixture in special temperature conditions, in addition to the similar reasons of general area. At present, the design of asphalt pavement in permafrost regions has no design specifications for reference at home and abroad, and it still mainly draws on the design method of asphalt pavement in general icy area. This method doesn't consider the impact of long-term freeze-thaw cycle on selection of material parameters, and makes it different from the performance of the actual conditions, resulting in premature damage of asphalt pavement in permafrost regions.The result of uniaxial compression test shows that compressive strength and compressive resilience modulus of mixture are tended to be stable after about 8 times freeze-thaw cycles. at the optimum asphalt-aggregate ratio,the compressive strength and compressive resilience modulus loss minimum.The indirect tensile test of SBR modified AC-13 asphalt mixture concludes that cleavage strength, failure tensile strain and stiffness modulus are tended to be stable at 9 times,15 times and 20 times respectively. at the optimum asphalt-aggregate ratio, the compressive strength and compressive resilience modulus loss minimum, failure tensile strain increasing rate decreases with the increase of asphalt-aggregate ratio.The result of low-temperature bending test on SBR modified AC-13 asphalt mixture indicates that flexural strength and flexural modulus are gradually stabilized afterl2-15 times freezing and thawing, taking into account the low-temperature bending properties of AC-10 and AC-16 under optimum asphalt aggregate ratio. While flexural strain tends to be stable after 15 times, flexural modulus decreased rapidly.This paper concluded the reduction coefficient of compression characteristics, cleavage features and flexural properties with regression analysis when they tend to smooth fluctuations. After comprehensive analysis the law of asphalt mixtures with the variation of asphalt aggregate ratio, it is recommended that the frost resistance will be enforced by increasing asphalt-aggregate ratio appropriately.