Over the last 20 years, many highway jurisdictions have experimented with different asphalts that include blended recycled rubber particles as a way to re-use old tires as well as to monitor the effects of rubber in possibly reducing the aging effects in asphalt pavements. Anecdotal comments following these experiments were also being received noticing a reduction in traffic noise with these rubberized mixes when compared to conventional pavements. While there have been many claims of noise reduction from different agencies over the years, there was limited conclusive documentation and testing to support the claims. In late 2003, the University of Waterloo’s Centre for Pavement and Transportation Technologies (CPATT) and the Regional Municipality of Waterloo embarked on a partnership to first design and construct noise reducing pavement test sections and then secondly to conduct controlled noise testing on four different types of asphalt mixes to accurately determine the noise-reducing characteristics of different asphalt surface course mixes. Four asphalt mixes were placed to conduct the noise testing: Rubber-modified Open Friction Course (ROFC) Rubber-modified Open Graded Course (ROGC) Stone Mastic Asphalt (SMA) Hot Mix HL-3 (standard Region of Waterloo surface course, ie. Control Section) The test site location was selected from locations already committed for pavement rehabilitation within the Region’s annual rural resurfacing program. The location chosen for the noise testing was on Regional Road 11 (William Hasting Line) between Manser Road and the western Regional boundary in the Township of Wellesley. This 5.5 km section of road was deemed conducive for use as a controlled test section because it provided a straight horizontal alignment with uniform vertical grades, consistent adjacent land use (predominantly agricultural) and little ambient noise activity. The four different surface courses were placed in lengths of 600m. The overall 2.4 km test area was closed to traffic and four different test vehicles were driven through the test area at different control speeds with noise meters recording noise levels both at the tire/pavement interface as well as at monitoring stations off the roadway. The purpose of the testing was to measure the noise characteristics of the different asphalt mixes in order to conclude whether there was a noise reduction benefit associated with the special mixes that would warrant their use in urban noise-sensitive areas to reduce or eliminate the need for other noise mitigation measures, including noise walls. Noise level test results have indicated that the special premium pavement mixes do achieve a reduction in measured noise. The reduced noise levels are attributable to a reduction in the duration of exposure to noise observed with the special open-graded mixes. The peak noise level observed with each premium pavement mix is the same as that observed with the conventional dense course mix. However, the overall noise impact over an 8 or 16 hour time period (as used in noise modeling programs) is reduced by using premium open-graded pavement mixes. The paper will elaborate on the types of materials used, the testing protocol, the measured noise results and the conclusions which will be of use by other municipalities in assessing the merits of using premium surface course asphalts to reduce noise in urban, noisesensitive environments.
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