Study On Fatigue Performance Of Full-thickness Asphalt Pavement

Full depth asphalt pavement is a kind of pavement structure form which directly paves asphalt mixture on the subgrade.The addition of flexible base can avoid early damage problems such as reflection cracks,reduce the thickness of pavement,save stones and prolong the service life of pavement structure.In this context,based on the foqingcong high-speed test road,through consulting domestic and foreign literature,indoor dynamic modulus test,fatigue test and calculation analysis,this thesis studies the fatigue performance of full depth asphalt pavement.The main contents are as follows.Firstly,the damage mechanism of full depth asphalt pavement is analyzed,and the main damage forms of full depth asphalt pavement are summarized.According to the main failure forms of full depth asphalt pavement,the design concept of full depth asphalt pavement is analyzed,and the design index suggestions are given.On this basis,three kinds of full depth asphalt pavement structure combination suggestions are put forward.Secondly,based on the structure of foqingcong test road,the mix proportion design and dynamic modulus test of asphalt mixture are carried out.The dynamic modulus of each asphalt mixture is tested by uniaxial compression test.The influence of temperature and frequency on the dynamic modulus and phase angle of asphalt mixture is analyzed,and the master curve of dynamic modulus is drawn.Four point bending fatigue test is used to test the fatigue life of each asphalt mixture,and the fatigue performance of each asphalt mixture is analyzed.The fatigue prediction models of asphalt mixture at home and abroad are comprehensively compared,and the fatigue prediction model with strain,stiffness modulus and asphalt saturation as parameters is established.The model is fitted with the test data,and the asphalt mixture parameters are added to establish the fatigue prediction model The fatigue prediction model of full depth asphalt pavement is established.On the basis of indoor test,the full depth asphalt pavement is calculated and analyzed by using French standard and French pavement design software Alice.Combined with fatigue prediction model,the fatigue life prediction value and traffic volume are compared;The effects of interlayer connection state,temperature,thickness and modulus of different structural layers on the bottom bending tensile strain and fatigue performance of asphalt layers are analyzed.Finally,the general situation of the test road is introduced,the modulus back calculation of the measured deflection data is carried out,and the back calculation modulus is compared with the measured modulus;combined with the previous indoor test and mechanical response analysis,the results show that the structure and materials of the test road meet the use requirements.The results show that the main failure modes of full depth asphalt pavement are top-down fatigue cracking,shear failure and permanent deformation.The tensile strain at the bottom of asphalt layer,allowable shear stress and compressive strain at the top of subgrade are proposed as control indexes,and three structural combinations of full depth asphalt pavement are proposed;The dynamic modulus decreases with the increase of temperature,and the change range is larger at lower temperature and frequency;The phase angle first increases and then decreases with the change of temperature,and the temperature corresponding to the peak value of phase angle decreases with the decrease of frequency;The dynamic modulus of asphalt mixture increases with the increase of frequency,and the lower the temperature is,the more obvious the trend is;The phase angle increases with the decrease of frequency below 35 ?,and decreases with the decrease of frequency above 35 ?;Fac-13 has the best fatigue performance,AC-25 has the worst fatigue performance,which indicates that increasing asphalt content in a certain range can improve the fatigue performance of asphalt mixture,and asphalt type will affect the fatigue performance of asphalt mixture;The fatigue prediction model with strain,stiffness modulus,asphalt saturation and asphalt mixture adjustment coefficient as parameters is established,and the mechanical response and fatigue analysis are carried out;The continuous connection of pavement structure can significantly improve the fatigue performance of asphalt pavement,reduce the tensile strain at the bottom of asphalt layer,and improve the fatigue life of pavement;Low temperature and high temperature will reduce the fatigue performance of pavement,especially at high temperature;The thickness of base course has the most significant influence on the tensile strain at the bottom of asphalt layer and the fatigue life of full depth asphalt pavement,followed by the thickness of binder course,and the thickness of wearing course and fatigue course has similar and small influence on it;The modulus of pavement cap has the most significant effect on the tensile strain at the bottom of asphalt layer and the fatigue life of full thickness asphalt pavement,followed by the modulus of base course,and the modulus of binder course and wearing course has relatively small effect.