Research On Evaluation Method Of Anti-reflection Crack Capacity Of Asphalt Pavement Structure

Reflection cracks are common pavement diseases in our country.Many pavements need to be re-paved with new pavement structure because of reflection cracks,which cause huge economic losse.At present,it has become an urgent problem to be solved.Therefore,the anti-reflection cracking ability of asphalt mixture is studied from the perspective of materials,and the anti-reflection cracking fatigue equation is established.On this basis,it is of great significance to evaluate and estimate the anti-reflection cracking ability of asphalt pavement structure and provide guidance for pavement design.In this paper,compound beam specimens with a prefabricated crack were prepared for the asphalt mixture of pavement structure in Hebei section of expressway from Beijing to Xiongan New Area.The failure test and fatigue test of two loading modes(composite mode and flexural-tensile mode)were carried out,and the whole process of reflection cracks from initiating to penetrating was observed by Digital Image correlation method(DIC).The ABAQUS finite element software was used to model and calculate the compound beam specimens and the pavement structure of Xiongan New Area expressway.Finally,the anti-reflection cracking ability of the pavement structure of Xiongan New Area expressway was estimated.Main conclusions were as follows:MTS was used to carry out two kinds of failure load tests on composite beam specimens(composite mode and flexural-tensile mode),and DIC technology was used to observe the whole process of cracks initiation and propagation.Experimental results showed that:1)The initiation strains of flexural-tensile failure of three composite beam specimens(SMA-13、AC-20C、AC-25C)wree 0.0488,0.0221 and 0.0457,and the initiation strains of composite failure were 0.0285,0.0332 and 0.0323,respectively.2)The cracks propagation path could be obtained by DIC.The cracks propagation modes of composite failure and flexural-tensile failure were different.Taking the composite mode failure of AC-20C composite beam specimens as an example,a secondary crack that extended from top to bottom generated and connected to the primary crack during the primary crack propagation.During the secondary crack propagation,the primary crack basically did not expand.The secondary crack propagation passed through the bottom of the specimen and then returned to the main crack propagation stage.DIC technique was used to observe the whole process of crack propagation of composite mode fatigue and flexural-tensile mode fatigue.The experiment results showed that:1)the secondary crack propagated from top to bottom,and the secondary crack connected with the primary crack to generate new primary crack.The secondary crack also generated when the newly formed primary crack propagated,and this process was cyclic until the specimen was fractured.2)The concept of crack propagation considering primary and secondary crack propagation was proposed.Logistic function was used to fit the relationship curve of primary and secondary cracks propagation with the loading cycles of fatigue load,and the correlation was good,and the function curve equation of crack propagation and fatigue life was obtained.3)At the simultaneous stage of primary and secondary cracks propagation,it was found that the secondary crack propagation rate was much larger than the primary crack propagation rate by comparing the primary and secondary crack propagation rate.At this time,the secondary crack propagation was dominant.The linear fitting of the secondary crack propagation with the fatigue loading times showed that the linear correlation was above 0.9.4)The reflecting crack propagation mechanism based on DIC observation was explained.The reflecting cracks caused by composite and flexural-tensile modes fatigue loads had general laws and their own characteristics.ABAQUS software was used to calculate flexural stresses at the bottom of composite trabecula specimens,and combined with the fatigue life of asphalt mixture,the anti-reflection crack stress model of asphalt mixture was established.The bottom bending stress of pavement structure in Xiongan New Area was calculated.Finally,the anti-reflection crack ability of highway pavement structure in Xiongan New Area was estimated based on fatigue life standard.