Development Of A New Evaluation Method For Fatigue Performance Of Asphalt Materials Based On Relaxation Tests

As one of the main distresses of asphalt pavements,fatigue failure has been extensively studied in recent years.However,the existing fatigue performance evaluation methods are more complex to a certain extent,and the reliability needs further research.Many scholars have shown that the rheological properties of asphalt binders are significantly related to the road performance of the asphalt mixtures.Therefore,to fully explore the rheological properties of materials,it is necessary to study the relaxation properties of asphalt materials.And based on related theoretical studies,there is an essential correlation between the slack properties of asphalt materials and their fatigue properties.Therefore,further study of its relevance is of great significance for proposing new methods for evaluating fatigue properties of materials.In this paper,the relaxation properties of asphalt binders were investigated,and simple relaxation tests were performed on asphalt and mortar with different penetration grade,aging conditions,and modified conditions.The results showed that the relaxation curve of most asphalt materials shows a regular change in the test temperature,but the relaxation curve does not change with the loading strain within a certain range.Based on preliminary test results,a repeated stress relaxation recovery test was designed to study the essential relationship between rheological properties and fatigue properties of asphalt materials.The test was divided into two parts: the first part is the stress relaxation phase,and the second part is the strain recovery phase,which is used to test its relaxation performance and elasticity performance,respectively.At the same time,combining a simple relaxation test result with a reasonable set of test parameters for the new design test,this new test method can effectively measure the relaxation behavior and elastic behavior of asphalt materials,and can be used as a test for stress relaxation and elastic properties.The above two relaxation test methods were used to test the performance of selected materials,and the corresponding evaluation indexes of stress relaxation performance and strain recovery capability(relaxation time,relaxation rate,initial stress and strain recovery rate)were proposed.The analysis of the test results using four evaluation indicators shows that the relaxation rate and strain recovery rate of the materials can be used to characterize the relaxation properties and elastic properties of the materials,respectively.Therefore,the new relaxation test can be used as a test method for the rheological behavior of materials,and the corresponding indicators proposed can evaluate the viscoelastic properties of materials.The fatigue properties of the selected materials were tested by the linear amplitude sweep test(LAS),and the damage curves of the materials were analyzed in combination with the viscoelastic continuous damage cumulative model to obtain the corresponding fatigue parameters A and B.By comparing the fatigue and relaxation properties of the material,the relationship between the relaxation properties of the material and the fatigue properties was explored.The results show that the fatigue parameter B and the relaxation rate of the asphalt material have a good linear relationship,and the fatigue parameter A has a good exponential relationship with the strain recovery rate.The relationship between fatigue parameters and rheological properties of the material has been well fitted and the fitting degree is high.Based on the two sets of functional relationships,a fatigue performance prediction equation based on repeated stress relaxation recovery test method for materials was established.There is a close correlation between the relaxation properties of the material and its fatigue properties,and the fatigue performance of the material can be accurately analyzed and evaluated through the corresponding stress relaxation test.