Research On Fatigue And Self-Healing Properties Of Aging Asphalt

Asphalt fatigue resistance is an important factor to long-term performance of asphalt pavement,and one of the hotspots in long-standing.In recent years,the view of self-healing has an important influence on the fatigue properties of asphalt has been reached consensus for researchers and agreed that the fatigue properties study of asphalt pavement must consider the impact of self-healing properties,can only reflect the fatigue performance more realistically.However,at different stages of asphalt pavement service,fatigue performance and self-healing propertiy will change significantly,which are closely related to the aging of asphalt.Starting from evaluation method of asphalt fatigue and self-healing performance,this paper has researched fatigue and self-healing performance of different degree aging asphalt under stress and strain modes,as well as influence of intermittent time,degree of damage and other factors on self-healing properties,and then has analysised the relationship between self-healing properties and fatigue performance.The 70# asphalt and SBS modified bitumen were aged in different time(0/85/255min)by rotating thin film oven tests(RTFOT),and effect on penetration,penetration index,ductility,softening point and viscosity of aging was analyzed.Also the effect on 70# asphalt was compared to SBS modified bitumen.The existing research method for fatigue characteristic of asphalt binder was modified from test temperature,loading level,specimen preservation method,parallel plate selection and extra asphalt trimming after understanding the method deeply.Then a suitable method for fatigue characteristic of aging asphalt was put forward,thus the accuracy and stability of test results were improved obviously.Different aging degree's 70# asphalt and SBS modified bitumen was conducted fatigue test by DSR,and three methods including 50% complex shear modulus(50%G~*),rate of energy dissipation(DR)and cumulative dissipated energy ratio(DER)were used to analyze the test results.It shows that the fatigue life of asphalt grows with aging degree increasing under stress mode,while the variation law of fatigue life with aging degree is not clear under strain mode,and the fatigue life dosen't all the same that determined by different methods.The higher aging degree,the greater initial complex shear modulus of asphalt.The process that complex shear modulus changes with loading times is related to asphalt type,aging degree,loading form and loading level under repeated loading.Phase angles of different aging asphalts increase slowly at firstand then decrease rapidly after a turning point appear suddenly under strain mode;while the phase angle's changing process of 85 minutes aged asphalts are same with unaged asphalts under stress mode,but after 255 minutes aged,asphalt phase angles increase all the time,also with a turning point,and the rate of increasing is much greater after the point.The higher degree of aging,the faster increasing rate of phase angle.The cross-sectional shapes of asphalt specimens after fatigue destruction were compared with each other.It shows that the cross section of 70# asphalt has appeared hairline crazing and annular groove in succession with aging degree increasing.While the cross-sectional shape of unaged SBS modified asphalt seems undulating hills,fuzzy hairline crazing can be seen after 85 minutes aging,and hairline crazing becomes clearly visible while aging time reaches 255 minutes.Four healing index were chosen to evaluate the healing characteristic of aged asphalt binder.These index includes growth rate of complex shear modulus(HI~1),complex shear modulus ratio(HI~2),load number ratio(HI~3),ratio of fatigue damage rate(HI~4).The results show that shortcomings can been seen on all healing index,but by contrast,HI~3 reflects the resilience of asphalt comprehensive performance much better;moreover,HI~2 can reflect the complex shear modulus recovery capability of asphalt,and the healing index is almost free from the impact of loading form.Penetration,ductility,softening point and viscosity can be broadly reflect the self-healing ability of aged 70# asphalt;but for SBS modified asphalt,it can not predict impact of aging on self-healing property according to softening point and viscosity.The influences of aging degree,intermittent time and damaged degree on the self-healing performance of 70# asphalt and SBS modified asphalt were investigated.As aging degree increasing,the self healing performance of asphalt will decrease gradually,and the aging has a greater effect on 70# asphalt than SBS modified asphalt.The self-healing performance of asphalt will be improved by increasing the intermittent time,and the intermittent time has a greater effect on SBS modified asphalt than 70#asphalt.the lower damaged degree,the better self-healing performance of asphalt,and the damaged degree before intermittent has a greater effect on unaged SBS modified asphalt than unaged 70# asphalt.