The purpose of this study was to investigate the acoustic effects of two topping materials used on bridges in the Seattle area. One material was applied to the bridge on Interstate-5 which crosses the Duwamish River. It is an English product called Spray-Grip which is supposed to have very good anti-skid properties, as well as the ability to stick to the road in thin layers thus making it suitable for the repair of worn surfaces. The other material is an epoxy-asphalt mixture which was applied to some sections of the Evergreen Point Floating Bridge over Lake Washington, particularly over sections where worn grating was causing excessive noise. Hopefully, this substance will be capable of long-term sticking in relatively thin layers.
Of the two materials, it was found that the epoxy-asphalt topping on the Evergreen Point Floating Bridge was by far the quieter, and, at least as newly applied, proved to be very quiet at the road/tire interface. It is likely that this good acoustic performance is due to the smoothness of the surface rather than directly to the fact that the material contains epoxy. The role of the epoxy would be as an adhesive and to resist wear so that its original acoustic performance could be maintained for a considerable length of time. Spray-Grip, on the other hand, although slightly quieter than the rutted, worn roadway, was not as quiet as the original unworn road surface.