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Example of Pervious Concrete Application |
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Pioneering Pervious Pavement at Stratford
Place
Task Force assists City of Sultan and Developer
City of Sultan, has pioneered
pervious pavement in Snohomish County. This groundbreaking
project paves the way for pervious pavement as a proven
technology to provide an alternative to traditional
stormwater management on public streets.
Only one other public road in Washington has been paved with
pervious pavement, an engineered pavement product that
allows stormwater to percolate through to recharge
groundwater and keep stormwater on site.
The Stratford Place residential demonstration project
included 32,000 sf (square feet) of previous pavement laid
in place of concrete for one road, connecting driveways, and
associated sidewalks on the 700 block of Fir Street. Builder
/ developer, Craig Morrison of CMI Inc. worked with
the SDTF (Sustainable Development Task Force) members to
pioneer the project. Morrison said it took three months to
fully research the new paving alternative and to understand
the engineering involved, including developing the right
pavement mix, laying the materials, and how to incorporate
pervious pavement into the stormwater management site plan.
The builder worked with Bruce Chattin from Washington
Aggregates & Concrete Association to learn about the
technology and engineers at the City of Sultan to design the
project.
Stratford Place was the last vacant parcel remaining in the
area, so stormwater migrated to the site already, making
stormwater management a crucial challenge. Morrison reports
that although there was a significant learning curve
involved with using pervious pavement, he plans to use this
technology in future projects. In fact, he has formed a new
company, Pervious Concrete, Inc., to provide expert design
and installation services. The trick, he said, was
“formulating the right mix and using the right equipment,”
in which his new company has invested, and which offer
greater efficiencies for laying pavement, compared to
traditional flatwork methods.
CMI worked with Smokey Point Concrete to develop the mix,
which includes fly ash, a waste by-product. Fly ash comes
from coal-burning power plants and used to be dumped in
landfills; but now, it serves as a superior substitute for
Portland Cement in concrete mixes. The right mix is crucial
to a successful pervious pavement project.
The next step was learning how to lay the material. Morrison
reports that the “chance of failure can be high if (the
pervious pavement) is not laid correctly.” He continues,
“Hot sun and breezes can be unforgiving.” The traditional
method to overcoming these obstacles in the field is to add
water, but with pervious pavement, this strategy makes the
pavement cream over, making it impervious. Here is where the
months of research and the right equipment led to success.
CMI learned how to work the material in changing temperature
and weather conditions using a different approach to
traditional flatwork (term used for laying concrete roads as
opposed to foundations). Morrison said the pervious pavement
comes out like “sticky pea gravel” and the trick is to use
rakes to lay it in order to work with the short set time.
Once CMI figured out the intricacies of working with the new
material, they were able to increase their efficiencies from
laying 20 trucks of material per day up to an estimated 35
trucks per day. Traditional flat work lays 3 to 5 trucks per
day, although traditional methods cannot be directly
compared to pervious pavement efficiencies in terms of
truckloads, since pervious pavement product needs to be
thicker to meet the same performance goals of traditional
concrete. Morrison does estimate that using pervious
pavement yields a double increase in efficiency compared to
traditional concrete, which takes a lot of work and time.
The Bottom Line
The proof is in the pudding. The proof here is that during
the hard rains of November and December, “no water left the
site,” according to Morrison and Rick Cisar, Sultan City
Engineer. No traditional stormwater management system in
this state can lay that claim, according to Morrison. Cisar
was so impressed with the Stratford Place demonstration
project that he is looking to try pervious pavement in a
public street in town. He expects other projects to be in
place sometime next year. He is particularly interested in a
road section between wetlands and stream corridors. Cisar
says pervious pavement resolves drainage problems, protects
critical areas and stream corridors, and helps to protect
adjacent properties from encroaching stormwater.
As for CMI builder Craig Morrison and his new company,
Pervious Concrete Inc., pervious pavement “is golden.”
Besides the stormwater benefits, using pervious pavement
allowed Stratford Place to save two lots, which would have
been lost with traditional methods for use as catch basins
and vaults. Finally, the other winner with pervious pavement
is the environment. Recharging groundwater through onsite
percolation adds air to the water, which helps improve
groundwater quality.
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