Measurements of basic acoustical properties of the porous pavement and their applications to the estimation of road traffic noise reduction

This paper describes measurements of basic acoustical properties of porous pavement such as sound propagation constant, acoustic characteristic impedance and acoustic impedance. As their application, it also describes estimation of their effect on road traffic noise reduction. In porous asphalt, propagation attenuation is less than typical fibrous porous material of glass wool or rock wool, and propagation speed in it is 1/2-1/3 as slow as that in the air. From the point of acoustical characteristic impedance, porous asphalt is about ten times acoustically harder than that in the air for frequencies below about 1.5 kHz, and it has high absorption peak at a frequency below 1 kHz. Noise reduction effects of porous asphalt can be estimated by using these measured properties. It was found in this study that porous pavement causes some excess attenuation of noise. It was also found that amount of A-weighted noise reduction due to tire-road interaction noise is about 2-3 dB. Total noise reduction effect of well-constructed porous pavement is probably larger than 4 dB even at a short distance.