Study On The Multi-parameter Improved IFI Model And Its Application In Long-term Skid Resistance Performance Evaluation Of Asphalt Pavement

The skid resistance of the pavement is of great significance to fast,safe,economical and comfortable traffic.Due to the insufficient skid resistance ability of the pavement,traffic accidents often occur,such as slippage in rain,rollover on a curve,and rear-end collision on long downhills.The classic IFI(International Friction Index)model can predict the skid resistance performance of the pavement in the speed domain through the parameters of speed number(S_P)and the standard friction coefficient(F60).The S_P parameter is calculated from the macrotexture of the pavement,that ignores the contribution of the pavement microtexture to the coupling effect of the tire and pavement.The F60 parameter and the Chinese Standard of pavement skid resistance only consider the friction coefficient under the high-speed state of 60km/h,but the low-speed friction coefficient plays an important position in the diagnosis and evaluation of the skid resistance diseases.Moreover,there is a difference between the test principle of the existing low-speed skid resistance tester of BPT(British Pendulum Tester)and the actual movement mode of the tire/road,So the test result is indirect.Therefore,this paper conducted in-depth research on the pavement texture evaluation method and low-speed skid resistance evaluation method,and then optimized the IFI model.Based on these above,the evolution principle of the long-term skid resistance performance of asphalt pavements under complex conditions was revealed.Firstly,the LTS(Laser Texture Scanner)was used to obtain the surface profile information of the asphalt mixture.Through the tire static ground pressure distribution test,the effective contact profile of the tire/mixture surface was intercepted and reproduced.Then,the robust Gaussian filter was designed,and the macrotexture waves and microtexture waves were extracted from the pavement profile.Based on these above,the geometric statistical indexes of pavement macrotexture and microtexture were calculated.Fractal dimension indexes of pavement macrotexture and microtexture were calculated by the piecewise variable dimension fractal function.The octave indexes of pavement macrotexture and microtexture were calculated through pavement texture wave spectrum analysis.Then,the correlation analysis of the effective contact macrotexture and microtexture indexes and the friction coefficient was carried out,and it was demonstrated that compared with the original texture indicators,the pavement texture indexes that had undergone effective contact interception and texture filtering processing of macrotexture and microtexture were more reliable in the skid resistance performance evaluation.Using cluster analysis and principal component analysis,the horizontal,vertical,and shape texture indexes of pavement macrotexture and microtexture were selected that were highly correlated with the skid resistance performance of the road surface,which were macro horizontal texture index(Hma),macro vertical texture index(Vma),macro shape texture index(Fma),micro horizontal texture index(Hmi),micro vertical texture index(Vmi)and micro shape texture index(Fmi)respectively.Finally,the accurate and multi-perspective evaluation method of macrotexture and microtexture on the pavement contact profile were put forward.Aiming at the limitations of the pavement low-speed skid resistance evaluation method,based on the tire/road surface mechanism,the HFT(Handy Friction Tester)was improved in terms of the test system,sprinkler system,and calibration method.Then a new pavement low-speed friction coefficient tester and its testing method of WFT(Walking Friction Tester)were developed,which is with variable slip rate and tire/road longitudinal continuous rolling contact.The evaluation index of WFT was walking friction coefficient(WFC).The key parameters of WFT test were studied and the standard WFT test method were formulated through a large number of experiments.Namely,water film thickness is 0.5mm,indoor speed is 20±2m/min;outdoor speed is 45±2m/min;slip rate is 10%.By comparing the test results of WFT and BPT on specimens with different texture,the reliability,applicability and test efficiency of WFT were analyzed,and the feasibility of WFT(WFC)for low-speed skid resistance test(evaluation)of the pavement was demonstrated.The evaluation indexes of the geometric characteristics of the aggregate surface were calculated by stereo microscope and digital image processing technology,and the influence of material design parameters on the skid resistance performance of the pavement was studied on the basis of the pavement texture index and friction coefficient(WFC),such as the type and amount of asphalt,geometric characteristics of the aggregate,the type and gradation of the asphalt mixture,and the maximum nominal size of the aggregate.Through quantifying the influence of material design parameters on the surface macrotexture,microtexture and WFC of the asphalt mixture,the influence of asphalt mixture design on pavement skid resistance was further revealed,which providing a basis for optimizing asphalt mixture design.Aiming at the parameters(S_P and F60)limitations and application range problems of the IFI model,the importance of microtexture in the pavement skid resistance model was demonstrated and the influence of each texture index on skid resistance of AC,SMA,and OGFC pavements were quantified by analyzing the multiple linear regression relationship between the skid resistance attenuation rate of 20km/h?80km/h and pavement macrotexture and microtexture.The texture indexes of asphalt pavement in the skid resistance model were optimized.According to the mixture type or MPD classification,the multi-scale pavement texture(T_p)and friction coefficient(WFC)were introduced,and the pavement multi-parameter IIFI model(Improved International Friction Index)was established respectively.Through the verification of typical road sections,it was proved that the IIFI model effectively improved the accuracy of pavement skid resistance prediction in the speed domain,especially for the OGFC pavement.In order to meet requirements of the long-term skid resistance performance research and test of skid resistance under variable working conditions,the multivariable accelerated abrasion machine(MAAM)was improved in the terms of the wear wheel,pressure device,the intelligent operation mode,the determination of the polishing agents and the number of abrasion passes,and the environment simulation equipment.On this basis,the indoor accelerated abrasion tests were carried out,and it was found that material design parameters and complex environmental factors(high temperature,high salt,high humidity,ultraviolet rays)would affect the wear characteristics of the IIFI,macrotexture,microtextures and the WFC.Therefore,the decay law of skid resistance performance of asphalt mixture surface under variable working conditions was revealed.