Research On Fatigue Behavior Of Unbonded Concrete Overlay Pavements Using A Nonwoven Geotextile As An Interlayer

Cement concrete pavement is one of the main forms of rigid pavement design,which is widely used in our country.With the increasing traffic demand,many pavement structures begin to appear different degrees of damage,which needs to be repaired.The unbonded concrete overlay(UBCO)is usually used to repair the severely damaged pavement.Asphalt concrete is usually used as the interlayer in the traditional UBCO.However,the asphalt will bond the new and old concrete layer,can not play the role of isolation,is not conducive to the prevention and treatment of reflective cracks.Thus,a new UBCO with the nonwoven geotextile interlayer is more widely used.However,the existing design rules of overlay structure are more based on engineering experience and lack sufficient theoretical support.Therefore,the mechanism of fatigue crack propagation in pavement structure,a clear understanding of the structure function of non woven geotextile layer,the overlay thickness for a reasonable design,and to predict the fatigue life of the pavement structure is of great significance.In this paper,the basic properties of nonwoven geotextiles are introduced firstly.Based on the working mechanism of the fabric in the overlay structure,the tensile properties and out of plane compressive properties of the fabric have been studied.The results show that the thermal bonded nonwoven geotextile is the ideal material for the interlayer,and the three-dimensional model of the interlayer is established.Then,this paper reviews the existing overlay design theory,based on linear elastic fracture mechanics(LEFM)and combine the Paris Law with the extended finite element(XFEM)with the help of ABAQUS,a three dimensional fatigue fracture model of UBCO with nonwoven geotextile as an interlayer is established.In addition,the fatigue propagation mechanism of reflective cracks of UBCO is studied,and the fatigue life limits are defined quantitatively.Finally,the influence of whether there is an interlayer or not,the thickness of the interlayer,the overlay and the the old concrete layer are studied respectively.The results show that the fatigue damage of paving layer structure is divided into four stages,the whole process is mainly the type I fatigue crack,and I-II mixed mode fatigue crack appears gradually in the pavement after unloading,until the overlay structure failure.The interlayer of nonwoven geotextile can provide higher fatigue life for UBCO,and its important structural significance is confirmed.The thickness variation of the pavement will have an impact on the fatigue life,in which the fatigue life is most dependent on the thickness of the overlay,the thickness of the old concrete layer is the second,and the thickness of the isolation layer is the least.Finally,based on the calculation results,this paper puts forward the reasonable value of the overlay thickness,and provides some suggestions for engineering design.