Research On Cumulative Superposition Mechanism Of Asphalt Mixture Fatigue Damage

With the rapid development of China's road traffic industry,asphalt pavements of varying degrees have experienced various levels of damage under increasing traffic pressure.Among them,fatigue cracking of asphalt pavement has become one of the main forms of destruction of asphalt pavement.For a long time,the fatigue damage mechanism of asphalt mixture is very complicated.Domestic and foreign scholars have studied fatigue damage and cumulative superposition for nearly 70 years.Usually,the consideration of the self-healing property of asphalt mixture is neglected in the study of the cumulative damage mechanism of asphalt mixture.A large number of studies have shown that the asphalt mixture has certain fatigue damage healing ability under certain conditions.When designing the asphalt mixture at home and abroad,the self-healing ability of the asphalt mixture is usually less considered,making the engineering design more conservative,resulting in problems such as cost and energy waste.The research group has studied the cumulative damage mechanism of fatigue damage based on self-healing asphalt mixture.It is of great social value and road value to study the fatigue performance of the bituminous mixture that is self-healing-compensated,but at present there is a relative lack of research in this country.In this paper,the cumulative fatigue damage mechanism of asphalt mixture is studied through the laboratory test method.By adding the discontinuous time to simulate the actual pavement working state,the cumulative fatigue damage equation with intermittent time is obtained,and the existing fatigue determination methods are proposed.First of all,analyze the influencing factors of self-healing,in order to quantitatively evaluate the self-healing ability of asphalt mixture and the influence of various factors on theself-healing properties of asphalt mixture,determine the reasonable evaluation index of self-healing ability.Through the analysis of the influencing factors of self-healing,the choice of asphalt and the design of asphalt mixture were carried out.Secondly,four-point bending fatigue test of indoor trabecular beam was used to test the fatigue of the different asphalt and type mixture respectively with and without pause time under single-stage load.Analyze the fatigue damage evolution of asphalt mixture,determine the parameters of fatigue,and establish the fatigue equation.Different fatigue tests were performed on different asphalt mixtures with and without multi-stage loading.The cumulative fatigue damage superposition mechanism of asphalt mixture was analyzed,fatigue parameters were determined,and a fatigue prediction model was established.Finally,by comparing fatigue life prediction equation with or without pause time,Miner's rule for predicting fatigue life and data analysis charts,combined with the actual pavement fatigue cracking situation,the experimental termination condition in the current fatigue test,namely the bending stiffness modulus is reduced.50% of the initial stiffness modulus proposed corresponding improvement suggestions.This article studies the analysis results:(1)Through the addition of different breaks in the fatigue test,the influence of the self-healing ability of the asphalt mixture on the fatigue life is judged.It is found that the stiffness modulus of the asphalt mixture is increased by increasing the duration of the rest period.Get different levels of improvement.As the rest period increases,the degree of stiffness modulus recovery of the mixture also increases,and the corresponding asphalt mixture also has an extended fatigue life.As the damage increases,the healing ability of the asphalt mixture gradually weakens.(2)By analyzing the fatigue data of asphalt mixture under single-stage load without considering self-healing performance,it is found that the actual fatigue life and the selected fatigue life prediction equation have a poor correlation,and thus the obtained various Fatigue test parameters modify the original fatigue life prediction equation.After verification,the fatigue life prediction equation has a high correlation with the actual fatigue life.(3)Based on the actual fatigue life of the asphalt mixture under single-stage load based on strain control,the two-stage simple load and cyclic load tests are designed,and the data analysis chart,cumulative damage amount,and fatigue life prediction value are obtained through analysis of test results.The asphalt mixture is divided into three stages when subjected to constant amplitude loading.The first stage is the stage where the stiffness modulus drops sharply.In the second stage,the stiffness modulus decreases slowly,and the slope of the stiffness modulus curve is small.In the third stage,due to the gradual expansion of internal cracks in the specimen,the stiffness modulus rapidly decreased.In the two-stage load conversion,the stiffness modulus of the asphalt mixture will be restored to some extent.When switching from a high-strain load to a low-strain load,the recovery of the stiffness modulus is larger than when the load is converted from low to high.This is due to the fact that when the load is transferred from a high level strain to a low level strain,There is residual stress at the higher levels of the upper level of strain.Whether it is a single stage load or a two stage load fatigue test,there is no damage under the existing standard test termination conditions.It is found that the existing specifications are conservative on the requirements of the fatigue test and may cause a gradation design.Be conservative and lead to the waste of resource materials.Through the calculation of the fatigue damage factor D,it can be found that the fatigue damage factor D of the asphalt mixture under the two-stage equal-amplitude load with strain control is greater than 1,indicating that the fatigue cumulative damage evolution process under two-stage load is nonlinear.The fatigue life predicted by using the Miner's rule is basically less than the actual fatigue life of the test piece,indicating that the estimated fatigue life using this model is relatively conservative.(4)Through the analysis of fatigue test results of asphalt mixture considering self-healing ability,it was found that the fatigue life and the phase without self-healing ability are both in the fatigue test under single-stage load and two-stage load.The ratio has been greatly improved.First of all,after increasing the interval time in the single-stage load,the overall change trend of the stiffness modulus has not changed basically,and it still presents two basic stages.The overall single modulus modulus decline trend is relatively slow.Secondly,in thesimple loading mode of two-stage load,the fatigue damage factor of the fatigue test after rest period is much larger than one,which means that the cumulative fatigue damage evolution process of increasing rest periods is also nonlinear.Using Miner's rule to estimate the fatigue life of asphalt mixture,it is found that the estimated life is far less than the actual fatigue life of the material.(5)Through the overall analysis of this paper,we can find that the termination condition of the fatigue test in the current specification is too conservative,even if the test piece is still in the stiffness mode at the end of the test in the ordinary asphalt mixture fatigue test without increasing the rest time.The amount decayed steadily in the transition phase and did not enter into the crack propagation period.The modulus did not decrease rapidly and did not reach the critical point of failure.It is recommended to use the inflection point of the residual stiffness modulus in the data analysis diagram drawn from the fatigue test results as the termination condition of the fatigue test.The purpose of this paper is to analyze the mechanism of fatigue cumulative damage of asphalt mixture based on the self-healing ability of asphalt mixture,and provide theoretical support for fatigue limit design method considering self-healing ability.