Research On Effects Of Pore Characteristics On Noise Reduction Performance Of Drainage Pavements

With the improvement of people's living standard,the amount of vehicles keeps incresing.The construction of high-grade roads is developing rapidly in China.The impact on the environment is increasing with the expandance of road scale,in which the traffic noise is one of problems caused by traffic.Road traffic noise has gradually become one of the main sources of environmental noise pollution in urban and rural areas.The large porous structure of drainage pavement can effectively reduce the pavement noise.However,the research on the noise reduction mechanism of drainage pavement is not enough.Therefore,this paper studied the noise reduction performance of drainage pavements to search for the influence of pore characteristics on noise absorption ability and provide theoretical support and reference for reducing traffic noise.The paper took the porous asphalt concrete(PAC)mixture as the research object.The noise level and sound absorption performance of PAC mixtures with different structures and porosities were analyzed through laboratory tests and field researches.The micro structure images of PAC mixtures were obtained by CT scanning technology,and the pore characteristics were studied through the technology of image processing and 3D reconstruction.Considering the sound aborption performance of PAC mixtures,the key parameters which mostly effected the sound absorption coefficient(SAC)were found and then a prediction model was established.The results of noise test based on the tire's accelerated falling method showed that the noise level of drainage pavement was significantly lower than that of traditional asphalt cocncrete(AC)pavement by 2-5dB(A)and it decreased with the increase of porosity.Comparing different types of 10cm thick PAC specimens,it was found that the noise reduction performance of double-layered drainage pavement is the best,and its noise level is lower than that of double-layered continuously-paved drainage pavement by 1.1dB(A),and lower than that of single-layered drainage pavement by 2.1dB(A).The field survey data also showed that the noise reduction effect of double-layered drainage pavement is better than that of the single-layered drainage pavement.It could be seen from the results of SAC test that the SACs of PAC pavements were obviously higher than that of AC pavement.Comparing different types of PAC pavements,the SAC of double-layered drainage pavement is 13%higher than that of single-layered drainage pavement,and 9.8%higher than that of double-layered continuously-paved drainage pavement.When the porosity was less than 16.36%,the SAC of single-layered drainage pavement was similar to that of AC pavement.Finally,the pore characteristics of PAC mixtures were obtained through the image processing technology with Matlab and VGStudio 3D reconstruction software.The results showed that the amount of pores in PAC specimens per 1mm in height was about 250.The amount of pores which had the volume less than l mm~3 accounted for more than 85%of the total quantity of pores.The increase of void content led to the decrease of everage pore diameter and the increase of the peak sound absorption frequency.Moreover,it was found that the parameter affecting SAC most was the measured porosity.From the microscopic perspective,the average volume of pores had the largest influence on SAC.The parameters which had high correlation with SAC were selected to establish the relationship between SAC and pore geometric parameters.The prediction model of SAC was also obtained based on the research.It was proved that the model is reliable by comparing the measured SAC values with calculated ones.The results of research in this paper can reflect the change rule of noise reduction performance for drainage pavements,and provide supports and references for the theoretical research and engineering application.