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Pervious Concrete Pilot Project
A Case StudyCity of TulsaApril 2013Mary E. Kell, AIA, NCARB, LEED © AP
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Background
• Definition of the issue
• Building sustainably in public projects
• The case for Low Impact Development (LID)
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Why design with LID in mind…
• As cities continue to be developed, so does the increased runoff from stormwater due to increased impervious surfaces
• The runoff gets transported through pipes and sewers to streams, rivers, lakes and other bodies of water
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Why design with LID in mind
• Runoff from parking lots such as oil, fuel and, deicing salts harms water quality and aquatic life, and can cause pollution, erosion, increased flow of waterways and altered aquatic life
• Pervious concrete is a tool in the LID toolkit that can help reduce the need for larger infrastructure by limiting or reducing the amount of stormwater runoff
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What we did
• Provide a pervious concrete pilot project on City of Tulsa property
• Observe, monitor and measure a defined area of pervious concrete over a minimum 2-year time span
• Encourage participation from all interested public and private entities
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Impediments that had to be addressed
• Lack of education and experience by Oklahoma contractors
As of March of 2012, only 2 contractors in the state of Oklahoma were certified by NRMCA (National Ready Mixed Concrete Association) to be able to place pervious concrete
• Three levels of certification: • Technician• Installer• Craftsman• http://nrmca.org/Education/Certifications/Pervious_Contractor.htm
for more information on the certification levels
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More Impediments…
• Cost – lack of familiarity with pervious concrete has typically driven up costs in projects and is commonly value-engineered out or not designed in the project to start with for Oklahoma projects
• Lack of support of a “new product” from City of Tulsa Engineering – a City project cannot afford to be on the cutting edge and risk failure when using public money
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Impediments, continued
• Performance data for a time-tested project constructed in Oklahoma (not a different part of the country where climate varies and / or sustainability has been accepted on a broader level, such as Portland, OR, Chicago, IL or Austin, TX)
• Public awareness
• Technical specification development
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The Plan
• In the summer of 2011 a group started gathering and meeting at regular intervals
• The group included contractors, academia, industry concrete educators and organizations, engineers, architects, builders, inspectors and code officials from the City of Tulsa, all of whom have a common personal interest in making things greener
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How we did it
• This project was primarily put together due to the volunteer efforts of many to make it happen
• After realizing that the “impediments that had to be addressed” could actually be turned into task items, the group went to work
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Timeline
• 7/27/11 – First meeting:
• Included definition of obstacles / impediments and concerns and introductions of roles, skills and resources
• Defined the need for a test project to educate the majority of those involved
• Defined the need to educate the majority of interested attendees
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Timeline
• 8/23/11 – Second meeting:
• Included gathering information on commonly perceived issues with pervious such as freeze thaw, durability and maintenance concerns.
• Location of a project site owned by the City of Tulsa underway
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Timeline
• 10/3/11 – Site visit to Twin Cities and GCC Mid-Continent, two ready-mixed concrete plants in Tulsa with pervious slabs that had been placed in the Tulsa area for 5+ years
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GCC Mid-Continent Concrete site visit
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Twin Cities site visit
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Timeline
• 11/29/11 – City of Tulsa site chosen, percolation test results review, performance spec development.
3 bores taken - .5” to 1.42” / hour percolation rate8.5” asphalt over 6” agg base, dark gray silty sand with gravel, fill
• 1/20/12 and 2/9/12 – Meetings to coordinate upcoming certification seminar and demonstration pour
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Existing SiteCity of Tulsa West Yard
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Existing SiteCity of Tulsa West Yard
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Timeline
• 3/6/12 – PC Certification seminar by the National Ready Mixed Concrete Association (NRMCA); reduced rates offered
• 20 people certified as pervious Technicians = 1,000% increase of pervious Technicians in Oklahoma.
• Still need to get more contractors with experience in Installer and Craftsman levels
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Timeline
• 3/7/12 – Demonstration pour• Technical specifications and pervious concrete consultation by the
South Central Cement Promotion Association, OMRCA and NRMCA• 5 slabs from 5 different ready-mix companies, all placed by Cantera
Concrete• Slab materials, labor and time donated by Arrow Concrete, Dolese
Brothers Company, GCC-Mid-Continent Concrete, Twin Cities Ready Mix Concrete, and Eagle Redi-Mix
• Subbase materials donated by Greenhill Materials• Excavation of subbase and subbase placed by City of Tulsa• TV and Radio Station Media present
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Details on pour
• 100’ x 12’ total area• 2,000 SF additional draining onto pervious area• Each of the 5 slabs were 20’ wide by 12’ wide• ¾” wide HDPE resin lumber expansion joints between
each slab• ¾” wide x 1- ¾” deep tooled joint was cut at middle (10’)
of each of the 5 slabs• 18” of washed #57 rock subbase• 5- ½” thick pervious over rock subbase
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Site Plan of pour
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ORMCA Newsletter: Told our story - positive press!
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Pour
The morning of the pour – expansion joints in place between the slabs
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The area, ready for the pour
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The first slab being poured and worked into place
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Power screed following the drop from the truck
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Roller, following power screed leveling
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Working the concrete – crew of 6 to 829
Plastic wrap immediately following pour30
Sandbags on 2 x 4’s to hold down the plastic
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Detail of expansion joint spacers in-between slabs
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Close up of roller
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Pouring the last slab, covering up with plastic immediately following
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Weighing samples of each slab, each sample rodded but not compacted
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One week later - removal of plastic, variation in colors of the slabs evident
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One week later – hose showing water flow
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One week later – concrete truck flowing water on slabs
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Testing
• Infiltration testing per ASTM C1701/C170M-09 currently being conducted every quarter by Professor Jason Vogel and his graduate students with Oklahoma State University (OSU)
• Metal rings were made by OSU
• Single vs. double ring testing
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Quarterly Infiltration TestingStep One: Place metal ring on slab, put plumber’s putty around the base of the metal ring
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Step Two:Pre-wetting the area to be tested, time recorded
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Step Three:Recording the time it takes a documented amount of water to flow through the slab, keeping ½ nch of water head during pour. 42
Alternate method of testing – double ring infiltration testA non-typical pervious pavement test that was tried to compare the ASTM standard with a typical method used for soil infiltration.
By utilizing the second ring, we were attempting to ensure that the middle ring is only showing the vertical movement of the water.
In general, our results indicated that there was no detectable difference unless the flow was pretty low (less than 300 in/hr or so). Also note that we only tried this one time, so these results are very limited.
While the double-ring method measures infiltration only, the standard single ring method is meant to be used as a consistent, repeatable measure of determining if the pavement is clogged.
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Infiltration Testing - Results
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Testing
• Acceptable range is 200-1800 inches per hour
• As of the 5th quarterly test conducted in March 2013, a year after the pour, all but one slab is well within or above range!
• SUCCESS
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What’s Next?
• First City of Tulsa project to use pervious concrete starts construction April of 2013
• Tulsa Fire Department Safety Training Center, located on the Tulsa Community College (TCC) northeast campus
• Pervious planned around drill tower, class A burn unit pad and winding sidewalk connection to TCC
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The group
• Special thanks to everyone who helped make this pilot project an ongoing success!
• The group included: o Concrete contractorso Ready-mix concrete supplierso National and Oklahoma Ready Mixed Concrete Associationo South Central Cement Promotion Association – part of the
Portland Cement Associationo Oklahoma State University (OSU) staffo City of Tulsa engineers and architects
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