Life Prediction Of Asphalt Overlay Of Old Cement Concrete Pavement Based On Reflection Crack

With the rapid development of economy,a large number of cement pavements built in the early stage have been damaged to varying degrees,and the focus of highway construction has gradually shifted from building new roads to repairing and reforming the original roads.Overlaying asphalt pavement on old cement concrete pavement is one of the main technical measures adopted in the reconstruction of old cement pavement at home and abroad,but it is easy to cause the reflection crack to destroy the overlaying pavement in a short time.Was not recognized at home and abroad of the old cement concrete paving asphalt layer design system,the current pavement design specification only paving asphalt layer on the measures for prevention and reflection crack,the guidance of empirical and defines the fatigue cracking at the bottom of the asphalt layer as a standard of asphalt pavement damage,gave no setting detailed Suggestions of the anti-cracking measures,and not considering crack extension process in asphalt layer.In view of this,this paper combined with the linear elastic fracture mechanics theory and finite element method,set up different structure parameters of asphalt overlay on old cement concrete layer 3d model,paving layer structure are analyzed and calculated in a separate under the coupled action of vehicle load and temperature load on the mechanical response,cracking life and fracture propagation life,paving layer structure under different working conditions are given advice,structural parameters of the prevention and reflection crack and establish related life forecast model based on the reflection crack.The main research results are as follows:(1)Under the action of single vehicle load,the mechanical response at the bottom of the overlay in the form of direct overlay structure is improved by a force transmission bar,which is about 14.06%.For all kinds of overlay structures without force transfer rod,increasing the thickness of direct overlay asphalt layer and the thickness of stress absorption layer can reduce the load stress.With the increase of axle load,the mechanical response of overlay increases almost linearly.The distribution of the force transmission rod has different effects on the crack initiation life,crack propagation life and total life of different overlay structures,and the effect on the overlay structure with graded gravel layer is the least.(2)Under the temperature-load coupling action,the maximum principal stress in the dissipation coupling stress of graded gravel layer is the best.Increasing the thickness and modulus of the direct overlay asphalt layer can reduce the maximum tensile strain at the bottom of the overlay,thus affecting the crack initiation life of the overlay,while the change of the modulus of the geosynthetic material has the least effect.With the increase of temperature drop,the mechanical response of overlay increases almost linearly.(3)Under the temperature-load coupling action,the crack initiation life of the direct over-paved structure occupies a larger proportion of the total life,while the crack propagation life of the other three types of over-paved structures is more significant.(4)Parameters with the best anti-reflection effect under the action of load and coupling: directly overlay asphalt layer thickness of 10～12.5cm,1000MPa;The thickness of graded gravel layer is 10 cm,and the modulus is 400Mpa4.The thickness of the stress absorbing layer is 2.5cm,and the dynamic modulus is less than4000 MPa.Tensile modulus of geosynthetics ≥1000MPa;In areas with small temperature difference,it is suggested to adopt the stress absorbing layer,whose life is1.5 times longer than that of the asphalt layer directly over-laid.Stress absorbing layer or graded gravel layer can be used in the area with large temperature difference,and the life of the stress absorbing layer can be increased by 3.4 and 3.1 times respectively compared with that of the asphalt layer.(5)The life prediction models of different overlaying structures with and without transmission rods under load and different overlaying structures without transmission rods under coupling action were established respectively.The life prediction models of asphalt overlaying structures without transmission rods can be rapidly estimated according to the corresponding parameter values,which provides a reference for overlaying design and maintenance.Finally,the prediction model is verified based on the actual project.