Void Distribution Characteristics And Acoustic Behavior Of Porous Asphalt Concrete

Traffic noise has become the main source of urban noise pollution.The original design of porous asphalt pavement is to speed up pavement drainage during heavy rain,reduce road surface water film,improve pavement skid resistance and ensure driving safety.Porous asphalt pavement also has good noise reduction performance,which largely depend on the connectivity of the internal void structure.As one kind of pavement paving material,porous asphalt concrete(PAC)can effectively reduce traffic noise.According to the meso structure characteristics of PAC mixtures,its physical model of mineral aggregate void ratio is established in this thesis.The internal void structure information of asphalt mixtures with different gradation composition is obtained using CT scanning and image processing technology.The void distribution characteristics,vibration damping properties and acoustic performance of PAC mixtures are analyzed and studied in depth.The major research contents and conclusions are as follows:(1)The physical model of mineral aggregate void ratio(VAM)is constructedAccording to the meso structure characteristics of PAC mixtures,all the aggregates are divided into four types: larger particle size aggregate(LSA),dominant aggregate size range(DASR),potential disruption aggregate(PDA)and interstitial component aggregate(ICA).The main skeleton void structure of PAC mixture is formed by DASR.Based on the analysis of the effect of the occupation and substitution of LSA,the potential interference of PDA and the filling of ICA on the main skeleton void structure,the calculation method of the main skeleton void ratio and the determination method of the particle size limit of the above four types of aggregates are proposed.Finally,the physical model of VAM is constructed on the basis of the volume method,whose rationality of the model is verified by 60 groups of Marshall compacted specimens.It is very convenient to determine the optimal gradation using this model,which greatly reduces the experimental workload for PAC mixture design.(2)Void distribution characteristics of porous asphalt mixtureUsing CT scanning and image processing technology,the internal void structure information of asphalt mixtures with different aggregate gradation composition and molding methods are obtained.The effect of molding method and aggregate gradation composition on distribution law of internal void ratio,connected void ratio,void equivalent diameter and void quantity are analyzed in depth.The concept of void size gradation of PAC mixture and its probability distribution model are proposed.The mathematical relationship is established between the void size gradation distribution model parameters(including size and shape parameters)and fractal dimension of aggregate gradation composition.The molding method has little effect on the void distribution variation along the height direction of the asphalt mixture specimens.Along the radial direction of the specimen,the internal voids of the Marshall specimen and the rutting plate specimen are evenly distributed,while the inner part void ratio and diameter of the specimen molded by system gyratory compactor(SGC)are significantly smaller than the external part.(3)Vibration damping properties of porous asphalt mixtureThe dynamic modulus test and vibration test are carried out for asphalt mixtures with different gradation composition.Based on the time-temperature equivalence principle,the relationship expression between displacement factor and temperature is proposed,and the main curves of dynamic modulus and phase angle of different mixtures are deduced by using Sigmoidal model and its differential form.Finally,a unified prediction model of dynamic modulus of asphalt mixture is established.When the nominal maximum particle size is the same,the greater the void ratio,the smaller the vibration acceleration and amplitude of PAC mixture,and the faster the vibration attenuation.When the void ratio closely for different PAC mixtures,the larger the nominal maximum particle size,the similar effect law on the vibration characteristics.Based on the principle of vibration acoustics,the relationship between dynamic modulus,phase angle and vibration damping characteristics is deeply analyzed.The critical damping ratio is half of the tangent value of phase angle,the phase angle of asphalt mixture is generally between 6°～ 40°,and the corresponding critical damping ratio is between 0.053 ～ 0.42.(4)Evaluation of sound absorption performance of porous asphalt mixtureThe sound absorption spectrum of different graded asphalt mixtures is obtained by using the standing wave tube at one-third octave frequencies.Compared with AC-13 and SMA-13 mixtures,PAC mixture has good sound absorption and noise reduction performance.The influences of gradation type,void ratio,connection void ratio and specimen thickness on the acoustic behavior of PAC mixture are studied and analyzed in depth,and the mathematical relationships between PAC noise reduction level and void fraction,connected void fraction and void size gradation composition is established.The void ratio of PAC mixture should be controlled at 20%～23%,and the reasonable paving thickness range is 4.0cm～7.0cm.The field tests indicate that PAC-13 asphalt pavement can reduce noise by 5.9～8.1dB and 2.7～4.5dB respectively compared with cement pavement and SMA-13 asphalt pavement under dry condition.Compared with SAC-13 asphalt pavement,PAC-13 asphalt pavement can reduce noise by 3.1 ～ 5.2dB in rainstorm weather.Finally,the variations of noise level with vehicle are obtained for different vehicles driving on different structure pavement in different weather.(5)Sound absorption model of porous asphalt mixtureAccording to the internal void structure characteristics of PAC mixtures,the void structure of the mixture is simplified after the a series of void structure unit body parallel and series connection.The geometric size of void structure unit body is determined according to the probability distribution model of void size gradation.Based on the acoustic-electric analogy theory,considering the influence of void distribution and vibration damping characteristics,the expression of sound impedance of the mixture is proposed.Finally,a mathematical model for describing the sound absorption behavior of PAC mixture is established,and the rationality of the sound absorption model is verified throng comparing with the experimental results.