Analysis Of Asphalt Overlay Structures On Existing Cement Concrete Pavements

With the effect of vehicle loading and environmental factor, the performance ofPCC pavement declined gradually and the service performance and bearing-capacityof PCC pavement cannot meet the requirement of future transportation. The newasphalt overlay can be directly placed on the existing cement concrete pavement tomake the full use of the residual strength of old PCC pavement and improve theperformance of pavement.This paper is based on the reconstruction project of Yiyang to Changde freeway.Aiming at the reflective cracking generating easily in asphalt overlays over directlythe old cement concrete pavement, combining with the real engineering project whichthe research is based on, two three-dimensional finite element models for doweledjoint concrete pavements and asphalt overlay structures over the old cement concretepavements were used to investigate the factors influencing the deflection at PCC slabedge, and mechanic characteristics of asphalt overlay near the crack tip to forecast thefatigue life due to reflection cracking in the asphalt overlay. Here are mainly aspectsin the study:(1) Study the deflection near joints for doweled joint concrete pavements, withemphasis on the effect of variation of modulus of each structural layer on deflectionand differential deflection near the joints of slabs. Based on the quality standards(deflection is not more than0.2mm and differential deflection is not more than0.06mm) for treatment of old PCC pavements, proper combinations of modulus ofstructural layers are proposed to order to facilitate subsequent analysis of the asphaltoverlay structures.(2) Analyze stress intensity factors at the crack tip when crack has propagated tothe middle of the divided asphalt sub-layers, on the basis of the fracture mechanicstheory and finite element calculation.(3) According to the results of stress intensity factors, acquire the stress intensityfactor at the crack tip when crack has propagated to the middle of the divided asphaltsub-layers, which represent the average level of intensity factor as the crackpropagates throughout the divided asphalt sub-layers. Analyze the fatigue life ofasphalt concrete layers. Establish the prediction models to fatigue life of reflectioncrack on the basis of Paris law and the mechanism of pavement cracking. Calculate the fatigue life of reflection crack in asphalt concrete layers with the model. Theresult indicates that when the modulus of each layer is under the condition ofdeflection less than0.2mm and differential deflection less than0.06mm, the fatiguelife of asphalt overlay can meet the design requirements.