Research On Characteristics And Development Prediction Of Opening-mode Reflective Cracks In Asphalt Overlay Of Cement Pavement

Directly adding asphalt overlay is one of the methods for repairing and strengthening cement pavement with minor damage.Reflection cracks are prone to occur at the joint(crack)of old cement panels,directly or indirectly leading to further cracking of the composite structure of asphalt overlay on old cement pavement,while open reflection cracks dominate the initiation and early development of reflection cracks.Monitoring the development of reflective cracks can scientifically maintain the road surface and avoid road surface diseases.Therefore,it is necessary to study the characteristics and development prediction of open reflective cracks in the asphalt overlay of old cement pavement.In this paper,focusing on the reflection cracks of the cement concrete face slab with cracks directly paved with asphalt overlay,theoretical analysis,indoor tests,numerical simulation and other research methods are used to carry out the evolution characteristics analysis of acoustic emission technology and image matrix,and the development prediction research based on the Stationary-action principle and neural network.The main research content and conclusions are as follows:(1)Analyzed the relationship between acoustic emission characteristic parameters and image features of open reflection cracking in composite structures.Firstly,conduct threepoint bending fracture tests on asphalt overlay composite structures,monitor the evolution of acoustic emission characteristic parameters during the damage process,and collect digital images of the structure.Secondly,explore the evolution law of acoustic emission characteristic parameters,extract the image matrix of digital images of reflection cracks,and optimize the imaging through matrix theory and algorithm.Finally,by introducing directional energy counting and combining reflection crack feature matrix imaging,the interaction between acoustic emission features and apparent features is demonstrated.The research results indicate that the acoustic emission characteristic parameters of the composite structure under three-point bending loading fit well with the load deflection curve;On the macro level,the apparent characteristics of open reflection cracks are mainly characterized by continuous vertical upward development of cracks;The apparent characteristics of open reflection cracks can to some extent characterize the entire process of open reflection cracking behavior in asphalt overlay.(2)Revealed the mapping relationship between the feature matrix of asphalt overlay and the apparent reflection crack feature matrix.First,based on the Stationary-action principle,the extreme value characteristics of open reflective cracking of asphalt overlay are studied,and the action Equations of motion is constructed.Secondly,extract the image matrix of the digital image of the asphalt overlay,assign its values based on matrix theory and algorithms,and establish the asphalt overlay feature matrix.Finally,the action Equations of motion is simplified according to the mechanical properties of the characteristic matrix and the plane geometric relationship.The research results show that the development of reflection cracks is the difference between the two time functions from the crack initiation point to the crack tip,which is the macroscopic solution of the Equations of motion of the action;The action Equations of motion includes the mapping relationship between the asphalt overlay characteristic matrix and the apparent reflection crack characteristic matrix.(3)A neural network for predicting the development of reflection cracks was established by fitting the characteristic matrix of the green overlay layer-the reflection crack characteristic matrix.Firstly,based on the mapping relationship between the asphalt overlay feature matrix and the apparent reflection crack feature matrix,an L-M algorithm optimized BP neural network model with a 5-16-1 structure was constructed;Secondly,input the asphalt overlay feature matrix and predict all possible paths for crack development through the model.Finally,overlay the true and possible paths of crack development to evaluate the predictive effect of the model.The research results indicate that when the reflection crack develops to 0.1mm and 0.2mm,the overall prediction level of the model is above 0.75;The prediction model can effectively predict the development path of reflection cracks during the germination stage,but the prediction effect of potential development paths decreases with the failure of the composite structure.