Study On Unsaturated Freeze-thaw Damage Behavior Of Emulsified Asphalt Cold Recycled Mixture

With the continuous increase of highway mileage in China,China gradually shifted its focus from highway construction to highway maintenance.As a consequence,the recycling of old road waste has become a major environmental issue,and with the continuous development of regeneration technology The development and application have achieved good results.The laying of emulsified asphalt cold recycled mixture has become more and more common,but the recycled mixture used in the lower layer and base layer of the pavement has been found to have characteristics of early loosening or spalling damage after a large number of investigations.This causes damage to the mixture,so this article studies this early failure mechanism and pave the way for future research on similar materials and similar damage.This type of damage to the cold-recycled mixture layer of emulsified asphalt is actually different from water damage caused by dynamic water pressure.Therefore,this article first conducts a field environmental investigation of the freeze-thaw cycle of the cold-recycled layer,taking Shenyang and its surrounding areas as an example.Obtain the actual freeze-thaw cycle temperature,define the unsaturated water absorption,and finally determine the conditions of the indoor test,that is,the freezing temperature is-20 ±2?,the melting temperature is 10±0.5?,and the cycle period is 6h(freezing 4h,thawing 2h).The unsaturated water absorption of the test piece is controlled at 40%-60%.Based on the determined indoor test conditions,the mix ratio design of the mixture and the non-saturated freeze-thaw cycle test after the test piece is formed,respectively,for different numbers of cycles(0,5,10,15,and 20times)The road performance test of the mixture was conducted.After 20 unsaturated freeze-thaw cycles,the penetration strength was reduced by about 50%,the-10? split strength was reduced by about 55%,and the freeze-thaw split strength ratio was reduced by 26.3%.The overall performance shows a law of decay.When the porosity is measured,the porosity is increased by 1.4% compared with the non-freeze-thaw.The ultrasonic non-destructive testing of the test piece is performed accordingly,and the conclusion is consistent with the change of the porosity.Use the results of the split test to model the mechanical model,use the constitutive relationship of damage mechanics and the random damage characteristics of the micro-prototype,and use Wei-bull distribution to derive the damage evolution equation and damage of the unsaturated freeze-thaw cycle of the emulsified asphalt cold-recycled mixture.Constitutive equation.The feasibility of the model is proved by actual experimental results.Finally,from a micro perspective,using scanning electron microscope(Scanning Electron Microscope)or scanning electron microscope(SEM),this article takes micro-images of the surface of emulsified asphalt cold-recycled aggregate aggregates with different freeze-thaw cycles.It was observed that the amount of cement hydration products decreased after freezing and thawing cycles,and the length became shorter.The original three-dimensional structure gradually disappeared,and the asphalt wrapped on the surface of the aggregate also gradually peeled off,which reduced the adhesion between the asphalt and the aggregate.At the macro level,the voids of the mixture are gradually connected,the porosity is increased,the size of the mechanical indicators is attenuated,and the damage is continuously increased,and the road performance is reduced.Through the research in this paper,the causes and mechanisms of the early failure of the emulsified asphalt cold-recycled mixture in actual roads are revealed from the macro and micro levels,and a damage mechanics model is established for reference in future related research.