Fatigue Properties Of Asphalt And Asphalt Mastic Considering Self-Healing

The fatigue cracking of asphalt mixture mainly occurs in the asphalt or asphalt mastic,which seriously affects the service life and service level of asphalt pavement.Therefore,it is of great significance to study the fatigue performance of asphalt and asphalt mastic.As a viscoelastic material,asphalt has self-healing ability when no load acts,thereby restoring part of the strength and macroscopically showing an increase in fatigue life.There are many kinds of methods for determining the fatigue life of asphalt materials and indicators for self-healing of asphalt materials,but the methods for determining fatigue life underestimates the fatigue performance of asphalt materials and these self-healing indexes are not suitable for evaluating self-healing properties of asphalt materials based on a pulsed loading.Therefore,the failure criterion of asphalt and asphalt mastic was studied,the advantages and disadvantages of existing methods for determining fatigue life of asphalt materials were analyzed,the fatigue life prediction equation considering self-healing performance and the self-healing evaluation index were established,which were extremely crucial to prolong the life of asphalt mixture and to design the durable pavement.In this paper,three kinds of asphalt and six kinds of asphalt mastic were studied.The time-scan test of the material was carried out by dynamic shear rheometer to study the fatigue performance.The intermittent time was introduced in the fatigue test to simulate the self-healing phenomenon of the material.In order to accurately evaluate the fatigue performance of asphalt and asphalt mastic,this paper analyzed the existing methods to determine the fatigue life of materials and the defects of self-healing evaluation indicators.And the point of stress change and the recovery modulus ratio were proposed to assess the fatigue performance and self-healing properties of asphalt and asphalt mastic.The main conclusions are as follows:(1)By comparing the fatigue life determined by the stress change method with the fatigue life determined by the existing methods,it can be known that the asphalt material still has the ability to withstand the loading when failure criterion is satisfied.And the existing methods for determining the fatigue life of the asphalt material are not suitable to characterize fatigue properties of asphalt materials.Although the fatigue life determined by different methods differs greatly,there is a good correlation between different lifetimes.The fatigue life of asphalt and asphalt mastic shows a rapid decline and then slowly decays with the increase of stress level,and satisfies the power function equation.Under the same stress level,the fatigue performance of 50# asphalt is optimal,and SBS modification can improve the fatigue performance of 70# asphalt.From the overall analysis,the optimal powder-to-rubber ratio of 50# asphalt mastic is 1.0,and the optimal powder-to-rubber ratio of asphalt mastic is 1.2.(2)Asphalt and asphalt mastic are accompanied by the change of dissipated energy in the fatigue test and self-healing test.The rate of dissipated energy change is an important indicator of fatigue performance.The larger the value,the smaller the fatigue life.In this paper,the relationship between the rate of dissipated energy change and the fatigue life is established.This formula contains 101 groups of fatigue and selfhealing test data of asphalt and asphalt mastic at different stress levels and intermittent time,which can be used to estimate the fatigue life of asphalt materials.(3)The recovery modulus ratio can be obtained by calculating the ratio of the average value of modulus of the fixed stage to the initial modulus,which can quantify the self-healing properties of the asphalt materials.This value has a good correlation with the fatigue life growth rate.And it has a good linear relationship with the 0.25 th power of the intermittent time,which satisfies the molecular diffusion theory.The selfhealing properties of 50# asphalt mastic increase with the increase of powder to rubber ratio,while 70# asphalt mastic is opposite.The increase of stress level inhibits the selfhealing ability of matrix asphalt,but larger stress levels will improve the self-healing properties of SBS modified asphalt within the range of small stress levels.