R.J. Watson has developed a new acoustical system to mitigate bridge joint noise that is common on bridges around the world. The company sought an effective acoustical sound mitigating material to use as the principle noise barrier for this system. Acoustiblok’s patented sound mitigating material was selected and a trial testing of the material was performed at the West Waters Avenue CR 584) Bridge in Hillsborough County, Florida. The county receives complaints from pedestrians who use the nearby biking path that is within approximately 25 feet of the noise source. The cause of the loud noise is a bridge joint located directly above the bike path.
Overview of Bridge Joint Noise Issue
Expansion and contraction caused by temperature changes, shortening and creep caused by pre- stressing, deflections caused by live loads, and longitudinal forces caused by vehicular traffic all combine to produce nearly continuous motion in highway bridges. Bridge expansion joints are designed to permit the longitudinal movement and small rotations presented on bridge decks due to changes in environmental condition, live loads, and physical changes on the structural materials such as creep and shrinkage. While there are many types of bridge joint systems, they can be classified as either open or closed joint systems.
Cause of General Bridge Joint Noise
Noise events due to vehicles passing over bridge expansion joints occur when vehicle tires strike the rectangular face of the expansion joint units and traverse the discontinuous surface profile. It can also be induced by the unevenness of the surface of the expansion joint itself and of the road surface before and after the joint. In the case of the West Waters Avenue Bridge, steel armor on the joint has come loose exacerbating the problem.
Application of Acoustiblok Material
- Acoustiblok was positioned on the concrete to form an acoustic barrier at the joint. For this test, it was fastened directly to the concrete at the top and bottom using Silicoflex locking adhesive.
- All joint gaps were sealed at the noise source to create the acoustical barrier.
- Total testing time was approximately 4 hours with the majority of that determining the best positioning of the Acoustiblok material.
- The material was applied with the goal of reducing as much noise as possible, creating the most aesthetically looking noise barrier possible.
- It took approximately 1.5 hour to apply the Acoustiblok material once a design was determined.