Study On The Effect Of Freeze-thaw Cycle On Cracking Characteristics Of Warm Mixed Rubber Powder Modified Asphalt Mixture Under Fatigue Load

In recent years,rubber powder modified asphalt mixture has been widely recognized for its superior performance at high and low temperature.The domestic and foreign experts put forward the warm-mixing technology for the problems of high energy consumption and high emission.And the effect of warm-mixing technology on the performance of rubber powder modified asphalt mixture has become the focus and hotspot content.In the cold regions of the north,the road surface is often covered with ice or snow in winter.In order to ensure the safety of traffic,the snow salt is usually used to melt the snow.That keeps the road in a freeze-thaw cycle of salt solution for a long time.And under the repeated loads of vehicles,the fatigue cracking and failure become the main failure forms.Because of its advantages of non-contact,high precision and full-field measurement,the digital image correlation(DIC)technology has become a reliable method to study the deformation and fracture characteristics of asphalt mixture.Based on the above background,warm mixed rubber powder modified asphalt mixture(CR-WMA)and Hot mixed rubber powder modified asphalt mixture(CR-HMA)were used as the research object,and the fracture mechanics and the damage mechanics were used as the theoretical basis in this paper.Based on the DIC technology,the effects of different salt concentrations and freeze-thaw cycles on the fatigue cracking characteristics of asphalt mixture modified by rubber powder before and after warm mixing were studied.First,a semi-circular bending repeated loading test is used to measure the displacement field and strain field of the warm-mixed rubber powder modified asphalt mixture in the loading process by using the DIC technique.On the basis of this,the cracking position was judged and the effect of salt freeze-thaw cycle on its cracking characteristics was analyzed.Then,the fatigue damage is defined by analyzing the characteristic cloud images of the displacement field and the strain field during loading.And the effect of freeze-thaw cycle on its fatigue damage characteristics was studied.Finally,the fatigue fracture parameters are fitted based on the Paris formula of fracture mechanics.And the effect of freeze-thaw cycle on fatigue fracture characteristics was analyzed.The results show that the damage resistance and fracture resistance of CR-WMA and CR-HMA decreased with the increase of freezing and thawing cycles;The damage resistance and fracture resistance of CR-WMA and CR-HMA decreased first and then increased with the increase of salt concentration,and the damage resistance and fracture resistance of 8% salt were the worst;The damage resistance,fracture resistance,freeze thaw resistance and salt erosion resistance of CR-WMA are better than those of CR-HMA.