This research report presents the results of tire/pavement noise measurements performed on concrete pavements as a part of the California Department of Transportation (Caltrans) Quieter Pavement Research (QPR) study to investigate tire/pavement noise characteristics on concrete pavements and bridge decks. The study included a total of 120 pavement sections at 47 different sites on various state highways throughout California. Most of the sites (36) were divided into three sections each for measurement and evaluation of tire/pavement noise using the On-board Sound Intensity (OBSI) method, while the other sites had one or two test sections. The evaluation included visual observation of pavement surface condition and texture type, some of which was performed from a moving vehicle, as no traffic closures were used for this research. The following five texture types were evaluated, with the number of sections shown in parentheses: burlap drag (37), diamond ground (33), diamond grooved (19), longitudinally broomed (10), and longitudinally tined (21). The report explains the data collection and data reduction procedures, data analysis, and discussion of the results. Overall, the longitudinally broomed texture type was found to be the quietest, although this texture had a small data sample, followed by diamond grooved and diamond ground. Burlap drag was as quiet as diamond ground, and longitudinally tined was the loudest. Differences in mean OBSI levels were small between all types, while differences of up to 5 dB(A) were measured within a given texture type. The range of OBSI levels across all sections during the two years was 99.4 to 107.3 dB(A). In addition to texture, the measured OBSI levels include the effects of joint slap, faulting and sealant, if they were present.

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.

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.