21 research outputs found
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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
Recommended from our members
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
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State of the Practice in 2006 for Open-Graded Asphalt Mix Design
This document presents a survey performed in 2006 of the materials and procedures used to produce asphalt mixes with an open aggregate structure in the United States and in Europe. In the U.S. these types of materials are known as “open-graded mixes” and they are utilized mostly to improve permeability and, consequently, wet-weather friction, which is related to the frequency of traffic accidents. In Europe, these materials are known as “porous asphalt mixes” and they are used for the same reasons as in the U.S., as well as to lessen tire/pavement noise. In general, European porous mixes have higher air-void contents than those in the U.S., ranging between 20 and 25 percent; open-graded mixes in the U.S. generally have air-void contents of less than 20 percent. European countries have specifications for horizontal and vertical permeabilities, while there are no permeability specifications in the U.S. However in both Europe and the U.S., a maximum particle loss of 50 percent from the LA abrasion test is specified. In Europe, the tensile strength ratio for porous mixes is specified as at least 50 percent; in the U.S. however, only a few states specify a tensile strength ratio. The required value is usually above 80 percent for those states that have a tensile strength ratio specification