Acoustical Absorption of Open-Graded, Gap-Graded, and Dense-Graded Asphalt Pavements

This report presents results of acoustical absorption measured on asphalt pavement samples. The tests were performed on 76 highway pavement sections and characterized the acoustical absorption at the center of the lane and under one of the wheelpaths (nontrafficked and trafficked areas of the lane, respectively). This document presents the absorption coefficients and resonance frequencies for different types of pavements, an analysis of the measured absorption coefficients, and the correlation of the absorption coefficients with measured tire/pavement noise levels. The acoustical absorption of the asphalt cores was measured with an impedance tube that allowed measurement between 200 and 1,700 Hz. The pavement in the study consists of mostly four types of asphalt concrete: dense graded, open graded, rubberized open graded, and gap graded. The study also included a limited number of sections with other asphalt mixes. The study confirmed that greater acoustical absorption is obtained from pavements with high air-void content. It showed that the open-graded mixes have higher absorption values than gap- and dense-graded mixes. For both the center and wheelpath, the open-graded mixes showed an average absorption coefficient of about 0.20; this parameter for gap- and dense-graded mixes was approximately 0.04. Average absorption is an increasingly better predictor of tire/pavement noise levels at higher frequencies, with a correlation coefficient of 66 percent at 1,600 Hz.