Research On The Fatigue Healing Performance Of Asphalt Mixture Based On Semi-Circular Bending Test

With the continuous increase of road traffic volume and service life of pavements,some of the early asphalt pavements have been damaged to some extent.Studying the reason and law of pavement damage and improving the durability of pavements become the most important tasks for road researchers.Among them,fatigue failure is one of the main forms of asphalt pavement failure,which affects the performance of pavements to a great extent.At the same time,asphalt mixture itself has some fatigue damage healing ability during the process of fatigue damage accumulation,thereby delaying the time of fatigue damage on the pavements.It is of great importance to study the fatigue damage healing properties of asphalt mixtures to improve the durability of asphalt pavements.Firstly,the application values of semi-circular bending test(SCB)were summarized and the semi-circular bending test method was determined as the main test method in this paper.SMA-13 asphalt mixture was selected as the main research object and the mixture ratio design was conducted with all the raw materials which met the technical requirements.To control the porosity of the semi-circular specimens then reduce the variability of test,a number of pre-tests were carried out and the cutting process was strictly controlled,then the specimens that fit the test requirements were screened out.During the SCB test,the auxiliary measurement technology-Digital Image Correlation Technique(DIC)was introduced as an important way to obtain strain data.Secondly,three types of semi-circular specimens(0mm notch,15 mm notch,25 mm notch)were prepared for the following strength test and fatigue test respectively,then the tests were carried out.The fatigue equations based on stress ratio of semi-circular specimens were established.The results showed that the fatigue properties of the specimens decreased with the increase of the length of notch,while the sensitivity to stress of the three types of specimens had little difference.The axial displacement variations during the fatigue test were analyzed.The fatigue equations based on cumulative energy consumption and the relationship between energy consumption of the single load and stress ratio were established.The developments of the transverse strain in the main cracking zone under different load levels were compared and the relationship between strain curve and displacement curve was established.Due to the relatively small variability of fatigue life data,SCB specimens without notch were determined as the basic form of subsequent fatigue tests.Then,according to the above conclusions,the specimens without notch and the appropriate loading levels were selected in the following semi-circular bending fatigue test,which introduced three intermittent times(0.4s,0.8s,1.2s).The index of fatigue life growth rate was put forward to evaluate the healing performance.According to the index,the best healing time was determined to 0.8s in this paper and the fatigue equations based on stress ratio were established under the three kinds of intermittent times.The axial displacement variations and the developments of the transverse strain in the main cracking zone along with the development of load were analyzed.The fatigue equations based on cumulative energy consumption were established,and the healing inside the mixtures was evaluated from the energy point of view.Finally,a variety of asphalt mixture semi-circular specimens were prepared using different asphalt types and grading types.The strength test and the fatigue test under two loading modes were performed successively to evaluate the fatigue healing properties of different asphalt mixtures.The fatigue equations based on stress ratio were established and the influence of asphalt type and grading type on the strength and the fatigue healing performance were analyzed.The fatigue process under the two loading modes were compared and analyzed from the three aspects of displacement,energy and transverse strain in the main cracking zone as above.The study found that the higher the temperature classification of the asphalt used,the better the fatigue performance and healing performance of the corresponding asphalt mixture.Moreover,grading type also had an obvious effect on the healing performance.Based on the semi-circular bending test,this paper improved the test content and evaluation system of fatigue properties of asphalt mixtures,then enriched the research results.This is of great significance to improve the durability of asphalt pavement,thus the level of highway construction will be further enhanced.