Research On Noise Reduction Performance Of Porous Asphalt Concrete Based On Microstructure

Since the 21st century,China’s highway construction has developed rapidly,forming a fast,efficient and convenient transportation network.At the same time,the road noise problem is increasingly serious,porous asphalt concrete(PAC)pavement with good noise reduction performance came into being.At present,the researches on the noise reduction performance of PAC were mainly based on the macro air voids,but PAC with the same air voids often presents different performance.Therefore,this paper studied the influence of voids characteristic parameters on its noise reduction performance from the perspective of microstructure,and proposed a reasonable design scheme through Structural Optimization Design,which provides theoretical reference and support for improving the road noise and design and application of PAC pavement.In this paper,the absorption coefficient of PAC with different air voids were measured by Standing wave tube,and the influence of air voids on the absorption performance of PAC was analyzed;and the distribution characteristics of voids in PAC were analyzed through square region image segmentation technology based on CT scanning image;based on the gray relation entropy method,the influence of the equivalent diameter of voids on the absorption performance of PAC was studied.The results showed that the sound absorption spectrum of PAC shows a trend of moving up and to the right with the increase of air voids,and has a better sound absorption effect on medium and high frequency noise;most of the voids in PAC are with area below 6mm~2 and equivalent diameter of 1-3mm;the sound absorption performance of PAC is mainly affected by the gap of equivalent diameter in the range of 3-4mm in the main frequency range of traffic noise.In addition,the Zwikiker-Kosten model of porous materials was improved by combining the effect of air velocity on flow resistance of PAC,on this basis,the influence of voids characteristic parameters on the sound absorption performance of PAC were analyzed.The results show that the peak value of absorption coefficient and the corresponding frequency of peak value increase with the increase of air voids;the peak value of absorption coefficient increases with the increase of equivalent diameter of voids,but the corresponding frequency to the peak value change little;the peak value of absorption coefficient slightly increases with the increase of the length of voids,but the corresponding frequency to the peak value obviously decreases,that is,the peak value of sound absorption coefficient is mainly affected by air voids,and the corresponding frequency of peak value is mainly affected by voids length..Finally,combined with the mechanism of noise generation and the main frequency range of traffic noise,the structural optimization design is carried out by simulated annealing algorithm.Based on the optimization results,the main voids parameters that affect the sound absorption performance of PAC were analyzed.The results show that the sound absorption performance of PAC can be improved by increasing air voids and voids length in the frequency of 500-1000Hz;the air voids play an important role in the sound absorption performance of PAC in the frequency of 1000-1500Hz.Combined with the main road noise frequency range(800-1500Hz)of small vehicles,the Structural Optimization Design was carried out.The results show that when the equivalent diameter of the voids is 3 mm,the air voids is 22%,and the pavement thickness is 40 mm,the sound absorption performance of PAC is better.Based on the study of the sound absorption performance of PAC with different air voids,the equivalent diameter range of the voids affecting the sound absorption performance of PAC and the main voids parameters affecting the sound absorption performance of PAC in each noise frequency range were obtained,and the reasonable structural optimization design scheme of PAC was proposed,which provides reference for the actual project.