This experimental project is being conducted as a part of WSDOT’s effort to produce pavements that reduce the noise generated at the tire/pavement interface. Experimental sections of open-graded friction courses were built using asphalt rubber and SBS modified binders. A section of conventional Class ½ inch hot mix asphalt (HMA) serves as the control section for the two experimental sections.
Sound intensity measurements were conducted using the On Board Sound Intensity (OBSI) method immediately after construction and monthly since the end of construction. OBSI readings immediately after construction indicated that the open-graded asphalt rubber and SBS modified sections were 3.7 to 2.0 decibels, respectively, quieter than the Class ½ inch HMA control section. The most recent readings, taken in December of 2007, show the asphalt rubber section to be 3.3 dBA quieter than the ½ inch HMA control section and the SBS modified to be 2.4 dBA quieter.
Pavement wear/rutting and roughness data indicate that there has been virtually no increase in the measured rutting and only a slight increase in the roughness for both of the open-graded sections and the control section. This experimental evaluation will continue for a minimum of five years.