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Written by GJ Stott
As you navigate your way around most cities, you have probably noticed many sound walls with a myriad of designs in varieties of stone, brick, split face block and formed architectural patterns. Back in time when sound walls were only used to mitigate noise, the main objectives were to construct whatever would reduce the road noise from being a nuisance to the adjoining neighborhoods and business districts while hiding the industrial areas. The older generation sound walls were generally not very attractive, constructed out of smooth concrete blocks with no design, and depressing to look at, from both sides.
In more recent years, city, state and federal DOT (Department of Transportation) engineers and planners have been specifying more sophisticated textures and designs using advanced concrete forming technology. The sound wall upgrades to the communities are, for the most part, being welcomed and have evolved from many sources such as...
having that great appearance on the highway side of the sound wall seemed to fall short with the design on the other side of the wall. This is a real let down to everyone that spends their time on the other side of the wall having to live with the depressing appearance of a wall resembling the first generation of sound walls.
For many years, precast sound walls were being precast horizontally which made it very difficult or impossible to produce formed textures and designs on both sides of the wall. AFTEC has now developed several vertical forming systems capable of producing formed panels from one foot to twenty-four feet high cast in one contiguous panel with formed textures and designs on both sides of the wall. The full sized precast panel design is a result of many fatalities being caused from automobiles leaving the highway and hitting the bottom panel of the traditional stacked panel sound wall and the driver being guillotined by the upper panels falling down.
Highway Sound Walls have various STC (Sound Transmission Class) Ratings dependent on many factors, such as materials used, thickness and density of the materials, finished surface preparation, gaps voids and seams in the construction. The next question you may ask…
Q: What are the Sound Transmission Class (STC) ratings for concrete and masonry walls?
A: The actual Sound Transmission Class (STC) for your wall will depend on the type of wall, the finish, and the weight of the wall per square foot of surface area. STC ratings for partition materials may range from 40 to more than 60 with higher values providing less sound transmission. The Federal Housing Administration (FHA) requires a minimum STC of 46 to limit sound transmission from unit to unit in multi-family dwellings.
The above question and answer, courtesy of Portland Cement Association http://www.cement.org/tech/faq_stc.asp
It is now very important to make sure that the construction of the sound wall panels do not have voids, seams or cracks the sound can pass through. The full height panel construction, as formed in AFTEC’s Highway Sound Wall Forming System eliminates the possibility of sound escaping through the seams of stacked panels.
"Even with a high STC rating, any penetration, air-gap, or 'flanking' path can seriously degrade the isolation quality of a wall. Flanking paths are the means for sound to transfer from one space to another other than through the wall. Sound can flank over, under, or around a wall. Sound can also travel through common ductwork, plumbing or corridors. Noise will travel between spaces at the weakest points. There is no reason to spend money or effort to improve the walls until all the weak points are controlled." Courtesy of stcratings.com http://www.stcratings.com
We provide concrete forming equipment, for standard and custom highway sound wall projects globally.
Please contact us for assistance on your next highway sound wall project.