Better Roads November 2014 15
dollar of cost.
• Wood noise abatement walls produce a 0.38 insertion loss
per dollar of cost over their life cycle, among the lowest of
the materials tested. Wood walls are constructed with a sus-
tainable material that blends in with a natural or residential
background. But with time, the wood will warp and shrink
leaving cracks in the wall which limit noise reduction po-
tential.
• Steel noise abatement walls produce a 0.38 insertion loss
per dollar of cost, among the lowest of the materials tested.
Steel is durable and able to withstand severe temperatures
and conditions, such as sunlight, moisture, ice and salt,
with a proper coating. But they may be electrically conduc-
tive and generate heat with sun exposure which prohibits
landscaping from growing near the wall. "Based upon the
acceptable levels of noise reduction, life cycle cost analysis,
and the durability of the product, the concrete noise walls
seem to perform better than the other noise wall materials,"
they add. "The TNM, version 2.5, is an acceptable tool to
predict noise levels for planning purposes."
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Reader questions lack of auger extensions
In reviewing our September 2014 Road Science, a reader took issue with the
apparent lack of auger extensions used in California with an extended screed
shown in the cover illustration (see Rubber Expands, September 2014, pgs.
6-10, or visit www.betterroads.com).
"[The image] appears to be an example of a poor paving practice that most,
if not all, state DOTs disallow, that being the use of a screed extension without
the accompanying use of an auger extension," writes Jeff Benefield, road
construction engineer at Alabama DOT. "There's most likely no auger extension
being used [as] there's no apparent support mechanism for the extension.
"Alabama DOT specifications require the auger extension to be no further than
18 inches away from the edge of the screed," Benefield adds. "This requirement
insures that fresh mix is easily supplied to the edge of the screed rather than
rolling or tumbling its way to the edge. Many paver manufacturers even prescribe
the use of extendable tunnels when a screed is extended this far."
Thanks to Mr. Benefield for his comments. However, auger extensions are not
required by Caltrans' new (2009) performance-based specifications, which
give contractors more leeway in how they pave with asphalt.
Correction: In the same article, Dr. Paola Bandini, P.E., New Mexico
State University, is referred to using the masculine article. Instead, "he" is a
"she." We apologize for the error.
RoadScience
