Study On Wet Skid Resistance Of Dense Graded Asphalt Pavement Based On Texture Evolution Mechanism

The skid resistance of asphalt pavement in wet conditions is one of the most critical factors affecting driving safety.In order to ensure the safety of the large-scale built and new highways in China,the highway operation management department needs to detect the pavement skid resistance efficiently and accurately.The three most widely used anti-skid performance evaluation indicators in my country are the structural depth of the pavement,the pendulum value BPN and the side-way force coefficient SFC.Among them,the texture depth is used to evaluate the anti-skid and drainage capacity of the pavement and is usually expressed as the average structural depth MTD.The sand patch method is a fixed-point measurement method with limited representativeness and low efficiency;the laser method can obtain the profile of the pavement section and calculate the average section depth MPD,reflecting the two-dimensional characteristics of the pavement surface.The BPN value measured by the pendulum tribometer is a standard index for evaluating the anti-skid performance of the road surface in wet conditions,which has the disadvantages of being cumbersome,inefficient and interfering with traffic.The side-way force coefficient routine investigation machine（SCRIM）obtains the road surface’s SFC value to evaluate the lateral skid resistance.Therefore,several current pavement anti-skid testing methods are gradually challenging to adapt to the growing demand for normalized anti-skid testing in China regarding technology,economy,efficiency,and environmental protection.Pavement 3D laser scanning is a high-efficiency pavement 3D data acquisition technology.It has broad application prospects in evaluating anti-skid performance,which can obtain high-resolution pavement surface texture data and be used to reconstruct the actual image of pavement 3D texture.At present,the research on the relationship between the skid resistance of asphalt pavement and the three-dimensional texture of asphalt pavement is not in-depth.There is a lack of in-depth theoretical and experimental research on the influence of texture evolution on anti-skid performance under the action of traffic wear.This paper aims at the relationship between the anti-skid performance and three-dimensional texture of asphalt pavement,as well as the evolution law of the anti-skid capacity and texture of the pavement under the action of actual wear,taking the densely graded asphalt pavement as the research object,the following work is carried out:（1）The skid resistance test method of asphalt pavement in China’s current standards is investigated,and the test conditions and feasibility of the research group are considered comprehensively.The three-dimensional texture parameter system of asphalt pavement is studied,the three-dimensional texture height,space,hybrid,function and feature parameters are established as the characteristics of the pavement surface,and the calculation programs of various parameters are written based on Matlab software.（2）The portable 3D laser scanner LS-40 has been used to collect high-resolution 3D texture data for four consecutive years since 2018 on the project road,and the self-written program was used to calculate the three-dimensional areal texture height,space,hybrid,function and feature parameters.The changing laws of pavement micro-and macro-texture parameters under wearing are summarized.The results show that for the macrotexture evolution:the negative texture structure and horizontal spatial characteristics change little with the surface wear;the steepness and the interface expansion area decrease with the pavement wear yearly;the pavement wear increases the peak volume and height but does not change the core layer,which reduces valley filling,volume and height;the wear effect tends to reduce its peak density and peak curvature.For pavement microtexture evolution:the positive texture and peak structure are significantly reduced;the spatial characteristics evolve from isotropic to anisotropic;the surface steepness and interface expansion area decrease year by year;the peak material,core material and voids,valley bottom voids’height and volume decrease year by year;the wear effect increases peak density but reduces peak curvature.（3）Four years of measurement data are used to verify the highly linear correlation between the construction depth parameters MTD and MPD,and an optimal correlation model for MTD and MPD is proposed.The relationship between the texture depth parameter and the macrotexture height parameter is analyzed,and the linear regression equations of the MTD and MPD based on the macrotexture height parameter S_a are proposed,respectively.Further,the collinearity between the three-dimensional macro-and micro-texture height,space,hybridization,function and morphological parameters was studied,and the redundant,highly linearly correlated parameters were removed.The optimized macro texture parameter group contains 13 parameters,micro-texture parameter group contains seven parameters.（4）Combining 3D texture data and Persson friction theory,a numerical calculation method is proposed for calculating Persson friction based on real surface power spectral density.This method analyses the action mechanism of macro-and micro-texture to skid resistance.The micro-texture contribution to anti-skid performance is over 63%at a low speed of 5m/s,and the macro-texture contribution to the anti-skid performance is more than 60%when the speed reaches 25m/s.On this basis,the law that the friction coefficient increases first and then decreases with micro-texture evolution and the friction coefficient decreases with macro-texture evolution is summarized.（5）A four-year skid resistance testing was carried out along the driving direction with a British pendulum meter on the engineering road section.The study obtained the change rule of the pavement longitudinal anti-skid performance,which first increased and then decreased under the action of wear.The skid resistance difference along the longitudinal and transverse directions of the vehicle is because of the appearance of wear streaks on the microtexture.At the same time,the pendulum value and 3D texture data of the same test points were analyzed,and the linear relationship between BPN₂₀ and the single texture parameter was ruled out.The multiple linear regression model and neural network prediction model of BPN₂₀ based on macro,micro and macro-micro texture are compared,and the results show that the effect of the neural network model is significantly better than that of the multiple linear regression model,indicating that there is a nonlinear relationship between BPN₂₀ and 3D texture parameters.The neural network prediction model of macro-micro parameters reaches R² at a level of 0.9.In addition,comparing the neural network models of macro-texture and micro-texture,it is found that the influence of micro-texture is more remarkable,which is consistent with the numerical calculation results of Persson’s theory.（6）A cross-test with speed and water film thickness as variables was designed using the SCRIM system.The influence of speed and water film thickness on the skid resistance was obtained,and the linear regression equations between the SFC value and water film thickness under different speed standards was established.The results show that the side-way force coefficient decreases linearly with increasing the water film thickness at a constant speed,but the decreasing rate increases with the speed increases.The multiple linear regression and neural network prediction model of SFC20 based on macro,micro and macro-micro texture are compared.The results show that the neural network model of macro-and micro-texture parameters has a better result.The micro-texture contributes to the SFC20 the same as the macro-texture,consistent with the theoretical analysis results.