Research On Main Influencing Factors Of Reflective Crack In Typical Pavement Structure Of Trunk Highway

Recently,reflective crack has become one of the major distresses in pavements of domestic trunk highway.Reflective crack is the transverse crack arising in semi-rigid base due to the excessive tensile causing by temperature and traffic load,then propagating to the surface.It can not only destroy the performance but also cause the failure of the pavement structure in severe cases.Therefore,this paper studied on main influcing factors of reflective crack to provide suggestions for the future pavement structure design of trunk highway.Firstly,aiming at the pavement structure consisting of semi-rigid base,a literature survey on the typical pavement structure of domestic trunk highways and their conditions of reflective crack was conducted.A pavement structure that“4cm AC-13+6cm AC-20+20cm cement（5%）stabilized crushed stone+20cm cement（3%）stabilized crushed stone”was selected as the basis of the following finite element modeling（FEM）.The mechanism of reflective crack formation and propagation was described.According to this,main influencing factors to be studied were decided,including:modulus,temperature contraction coefficient,surface layer thickness,bonding state between surface and base,and temperature et.al.Secondly,a FEM model was built to study the process of crack formation in the base.The nonlinear spring element was selected to represent the bonding state between surface and base and its feasibility was verified.Then different temperature fields were selected and added to the model together with the traffic load.It was concluded that the most unfavorable position of the longitudinal tensile stress of base layer was below one of the wheel in the standard double-wheel load.The order of the influence of various factors on its maximum value was:temperature contraction coefficient of base layer>temperature difference≈dynamic modulus of base layer>surface layer thickness>bonding state between surface and base>dynamic modulus of surface layer>temperature contraction coefficient of surface layer.The study also showed that the use of high modulus asphalt could not prevent the base layer from cracking.After that,another FEM model was built to study the process of crack propagation.During this process,the eccentric load was more likely to cause the propagation of reflective crack than a symmetrical one.The morphology of the crack preset in base layer changed from“upper narrow to lower wide”to“upper wide and lower narrow”before and after the crack penetrating in the surface layer.The study has shown that the temperature contraction coefficient of surface layer influenced the propagation of reflective crack most,followed by the thickness and dynamic modulus of the surface layer,and the influence of the dynamic modulus and temperature contraction coefficient of the base layer was small.When the temperature contraction coefficient of asphalt mixture didn’t exceed to 1.6×10^-5/℃,the reflective crack would not arise in the surface layer in the condition that the temperature drop was lower than23.8℃in twenty-four hours.Besides,the long-term use of the pavement would promote the propagation of reflective crack.According to this,the relational expression between the pavement life and the temperature drop corresponding to the crack arising in the surface layer has been proposed.Finally,prevention measures of reflective crack has been researched.The results indicated that both the measure of setting pre-cracks in the base layer and adding the middle layer between surface and base layer could prevent reflective crack,however,it was not recommended when the temperature drop was above 15℃in twenty-four hours.In addition,it was suggested to take measures of combining increasing the thickness of the surface layer and reducing the temperature contraction coefficient of the surface layer.Based on this,a regression formula between the two and the temperature drop that the road surface could withstand was proposed.