| Due to the repeated effects of traffic load and climate environment,asphalt pavement is prone to crack problems.However,the existing maintenance technology is passive mode after the macro cracks appearing in the pavement,which has the disadvantages of long maintenance cycle,large resource consumption,high cost and so on.More advanced crack maintenance technology is urgently needed.Asphalt has a certain self-healing ability.The use of induction heating to improve the self-healing performance of asphalt concrete,so that the asphalt pavement will heal automatically when there are subtle cracks,which is the advanced maintenance concept advocated by domestic and foreign in recent years.However,the existing research mainly focuses on the recovery of the overall performance of asphalt concrete after induction heating,and lacks in-depth research on the crack gradient healing behavior caused by induction heating(the heating efficiency decreases with the depth of the test sample)and the influence of induction heating on the aging of asphalt cement at different depths of the pavement,which seriously restricts the preparation and application of induction heating self-healing asphalt concrete,healing effect optimization and induction heating equipment design.For this reason,this paper prepared the induction heating selfhealing asphalt concrete,studied the gradient heating characteristics under the action of induction heating and the gradient healing behavior of asphalt and asphalt concrete in different depths,established the prediction method of gradient healing effect,and explored the gradient aging behavior of asphalt cement under the action of induction heating.The main achievements are as follows:(1)According to the overall strength recovery,the optimal induction heating healing temperature of matrix asphalt concrete and SBS modified asphalt concrete is determined to be 100 and 130,respectively.The temperature distribution map of two kinds of asphalt concrete under the optimal healing temperature gradually decreases with the depth is established,which provides the basis for further research.And Based on the performance parameters of induction heating equipment,the relationship between induction magnetic field and induction temperature gradient is established.(2)According to the temperature gradient distribution after induction heating of asphalt concrete,the gradient healing behavior at different depths under induction heating of asphalt concrete was studied from two levels of asphalt cement and asphalt concrete.The self-healing properties of asphalt and asphalt mortar at different depths were studied by means of flow behavior factors,capillary flow performance,rheological model and parameters.The results show that the flow behavior factors and capillary flow activation energy of matrix asphalt in asphalt concrete are linearly related to the depth of specimen after induction heating.With the increase of specimen depth,the flow behavior factors of matrix asphalt decrease gradually,the viscosity index of asphalt increases and the self-healing property of asphalt decreases.(3)The strength recovery rate and crack healing rate of asphalt concrete at different depths under the action of induction heating were studied by strength recovery test and micro CT scanning test.The strength recovery rate and crack healing rate of asphalt concrete at 40 mm were 35.9%,23.9% and 22.8%,25.6% lower than that of the surface.The relationship model between the depth and healing efficiency of matrix asphalt concrete and SBS modified asphalt concrete was established based on the temperature gradient distribution and the asphalt self-healing initial temperature,the effective healing depth of two kinds of asphalt concrete is determined to be 52.5mm and 56.4mm respectively.The prediction method of gradient healing effect of asphalt concrete after induction heating is established.The healing performance of matrix asphalt concrete and SBS modified asphalt concrete after heating to five specific temperatures is simulated by using 15 mm thick thin-layer specimens.According to the temperature gradient distribution map of induction heating of asphalt concrete(to determine the corresponding depth of five specific temperatures),the asphalt concrete can be obtained in the healing characteristics of the gradient under this temperature gradient.(4)The change of asphalt properties after induction heating was studied by means of rheological properties,chemical structure and four component changes,and the effect of multiple induction heating on the aging degree of asphalt was proved.It is found that induction heating will lead to gradient aging of asphalt.After one induction heating,the complex modulus of asphalt increases,the phase angle decreases and the degree of change decreases with the increase of specimen depth.The carbonyl factor of asphalt in the upper,middle and lower layers of 45 mm thick trabecular specimen is1.50 times,1.17 times and 1.01 times of the original asphalt respectively.The change range of four components of asphalt increases slightly with the increase of specimen depth,and the starting temperature of asphalt self-healing increases slightly.After ten times of induction heating,the asphalt aged seriously,its carbonyl factor was 11.74 times of that of the original asphalt,the saturated content of asphalt decreased by 6.60%,the aromatic content decreased by 7.37%,the gum increased by 6.74%,the asphaltene increased by 7.23%,and the temperature of asphalt reaching near Newtonian fluid increased from 35.8 to 48.7.However,the aging asphalt concrete still has good induction heating self-healing performance.After 10 times of induction heating,the strength recovery rate of asphalt concrete can still reach 58.3%. |
