| The asphalt overlay on the old cement concrete pavement can effectively improve the performance of the original pavement structure and is widely used in the reconstruction of the old cement concrete pavement.Due to the joints between cement concrete pavement slabs,reflection cracks are easy to appear at the joints at the bottom of asphalt overlay under the traffic load.Setting speed bumps on asphalt pavement can effectively reduce the speed of the vehicle,but it will increase the impact damage of the pavement.If the location of speed bumps is close to the joints,the impact load will further aggravate the extension damage of reflective cracks,which greatly shortens the service life of asphalt pavement.Based on this,the numerical model of asphalt overlay on old cement concrete pavement was established by using ABAQUS finite element analysis software.The numerical model of impact load on vehicles passing through the speed bumps based on the analysis model of jumping at bridge approach load.The "two-step" principle of preventing and controlling reflection cracks in asphalt overlay under impact load is proposed,which aims at improving the structural stress of road and prolonging the service life of road.The main research contents are as follows:(1)In this paper,according to the causes and types of reflection cracks in asphalt overlay,the mechanism of reflection cracks is analyzed.The theory of material strength is derived in detail,which can be used as an evaluation index to influence the strength of reflection crack,and the mechanical response of asphalt overlay under load is analyzed.The stress concentration at the joints of asphalt overlay is the main cause of the reflection crack.Under the impact load,the mechanical noise of asphalt overlay increases by 25.39% compared with the static effect,so the impact effect cannot be ignored.(2)Due to the limited quantitative description results of impact load on road surface of speed bump,this paper studies and establishes a "half wave sinusoidal" loading model suitable for impact load on road surface of speed bump by referring to the treatment method of impact load on jumping at bridge approach and combining with specific parameters of road speed bump.Based on this,this paper established the finite element analysis model of asphalt overlay structure with joints under impact load,and studied the sensitivity of asphalt overlay structure parameters under impact load.The research results provide a basis for the prevention and treatment of reflection crack under impact load.(3)Focusing on the problem of reflection crack prevention,this paper proposes the "two-step" principle of reflection crack prevention for asphalt overlay under impact load.Step 1: analyze the mechanical response of impact load position to asphalt overlay structure,and establish the suggested relationship expression for the location of speed bump,so that the location of speed bump can reasonably avoid the joint area,and reduce or eliminate the impact load on the reflection crack.Step 2: in some special areas where the position of speed bump cannot be adjusted,it is suggested to add stress absorption interlayer to reduce the impact of impact load on the reflection crack of asphalt overlay structure.The results show that: in order to reduce the stress concentration at the joint of asphalt overlay,the location of the speed bump should meet the expression: L ?l(10)s,and the distance between the impact location and the joint l is greater than or equal to 0.5m.The addition of stress absorption interlayer can improve the crack resistance of asphalt overlay under impact load.The increase of the thickness of stress absorbing layer and the decrease of modulus can effectively improve the stress condition of asphalt overlay.The research results provide technical guidance for the research on the prevention and treatment of reflective cracks in asphalt overlay under impact load. |
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