Investigation On The Performance Of Granulated Crumb Rubber Asphalt Mixture For Curing Track Bed

As a new structure type of railway track,elastic curing track bed can avoid the inherent limitations of railway ballasted track and slab track.Therefore,it is being popularized and applied gradually.However,the elastic curing track bed represented by the polyurethane curing track also has some problems such as difficult construction and high cost.With the further development of China’s railway network,it is of great research significance to provide more excellent materials for elastic curing track bed.Based on the engineering experience of highway asphalt mixture,and the performance requirements of materials for railway curing track bed,the feasibility of applying granulated crumb rubber asphalt mixture to railway curing track bed is creatively put forward in this work.And the corresponding technical support for the subsequent construction of curing track bed using granulated crumb rubber asphalt mixture for high-speed railway is provided.Firstly,the Marshall test of asphalt mixture was used to determine the optimum asphalt content and mixing process of granulated crumb rubber asphalt mixture with equal volume replacing 0%,3%and 6% aggregate,and the best maintenance time of mixture was also determined.The mechanical properties of granulated crumb rubber asphalt mixture under repeated load were investigated by indoor Uniaxial Compression Test and composite specimen Interface Shear Test.The test results show that the static modulus of granulated crumb rubber asphalt mixture decreases to 170～320MPa after repeated loading,and the maximum change rate is 22%.The residual cumulative deformation of the mixture is also within the requirements of the elastic track bed.The Interface Shear Test results of composite specimens show that the shear strength of interface at service temperature meets the requirements of lateral stability of railway track bed.Secondly,the Dynamic Creep test was used to evaluated the long-term stability of curing track bed of granulated curmb rubber asphalt mixture.Results show that the mixture with 3% granulated rubber content is not easy to accumulate permanent deformation rapidly.Based on the horizontal shift factor of creep compliance master curve,the creep behavior of mixture under different temperature conditions can be equivalent converted,which provides a prediction method for the long-term cumulative deformation of curing track bed using granulated crumb rubber asphalt mixture.The pseudo strain of granulated crumb rubber asphalt mixture can better describe the elastic response and permanent deformation behavior of the mixture.Moreover,the dissipation pseudo strain energy caluated based on the pseudo strain of granulated crumb rubber asphalt mixture under repeated load has a good correlation with its permanent deformation resistance.Finally,on the basis that the mechanical properties and long-term stability of granulated crumb rubber asphalt mixture met the requirements of elastic track bed,the cracking resistance of granulated crumb rubber asphalt mixture before and after the effect of environmental factors was characterized via the Semicircle Bending test(SCB).The results show that the fracture strength and critical fracture energy of granulated crumb rubber asphalt mixture decrease with the increase of granulated rubber content,freeze-thaw cycle and aging effect,but the fracture energy increases with the increase of granulated rubber content.The results of fracture energy and damage curve of nonlinear zone show that aging effect imposes greater influence on the cracking resistance of granulated crumb rubber asphalt mixture than freeze-thaw cycle,and 3% granulated rubber content contributes to the maintainance of the cracking resistance of the mixture.The results of SCB test based on Digital Image Correlation(DIC)show that the inflection point and mutation of time history curve of the horizontal strain at cracking tip can be selected as the starting point of different stages of cracking generation and propagation.The cracking propagation time ratio shows that the addition of granulated rubber reduces the cracking propagation speed and prolongs the cracking propagation duration before and after the environmental effects.From the distribution of strain field at the moment of macroscopic cracking formation,the change of cracking propagation path and strain band distribution before and after the effects of environmental factors can be detected.And the conclusion from macroscopic test can be verified from the perspective of microscopic strain field distribution.