pervious concrete when it rains, it drains! - · pdf filepervious concrete – when it...
TRANSCRIPT
Overview
• What is Pervious Concrete?
• Where can it be used?
• Why is Pervious effective?
• What are the cost advantages?
• Common Questions-
• Do I joint it?
• Will it freeze?
• Will it clog?
• Where can I get more information?
• A No-Fines Concrete Mix
• Coarse Aggregate
• Portland Cement
• Water
• Intended for use as an open-graded drainage material
What is Pervious Concrete?
• 15% to 30% air void content
• Field studies show 20-25% average
• 100 to 120 lbs/ft3 unit weight
• 2500 to 3500 psi strength*
• Introduction of small amounts of fine aggregate can increase strengths
• Compressive strength not used as acceptance criteria. Air void structure and unit weight are used instead.
Pervious Concrete Properties
Pervious Concrete
Hydrological Properties
• Drainage rate = 3 to 5 gal/min/ft2
• Equivalent of 275” to 450” of rain per hour!
• Water drains through pavement and stone bed and infiltrates slowly into underlying soil mantle• 0.1 – 0.5 in/hr preferred
• System design may be customized for unique soil conditions
Applications-Parking Lots & Pavements:
Potential Environmental Disasters
• Almost Total Runoff
• Public Water Needed for Vegetation
• Valuable Water Resources are Wasted
• Runoff Has Chemical Pollutants, Requiring Treatment
• Runoff is Hotter, Damaging Ecosystems
• Rapid, High Volume Runoff Requires Larger Public Drainage Facilities
• Hot Parking Lots Add to Urban Heat Island Effects
First Flush
• First 1” of rain
• Contains contaminants
• EPA requires collection and treatment prior to release
• USGS study – Austin, TX 2005
• High concentration of polycyclic aromatic hydrocarbons
(PAH)
• Attributed to asphalt parking lot runoff
• Runoff from asphalt-based sealants 10 times higher
• Runoff from coal-tar based sealants 65 times higher
• Source:
• http://water.usgs.gov/nawqa/asphalt_sealers.html
First Flush
• Pervious concrete pavement reduces runoff
• Eliminates first flush
• Captured by void structure
• Minimization of PAH
• Soil chemistry and biology will naturally treat water
• Oil drips and other automotive pollutants are “attacked”
by naturally occurring soil microbes
Cost Advantages
• Savings to Owners/Developers
• Reduces or Eliminates need for retention ponds & other
costly stormwater management practices
• Provides for more efficient use of land development
• Shelter Systems, Inc. Westminster, MD
• 7 ½ Acre parking lot
• Saved $400,000 in underdrain construction
• Eliminated 1 ½ Acre retention pond
• Roughly ½ the shrinkage
of normal concrete
• Joints are typically placed
every 15’ - 20’
• Best practice is to tool
joints
• Sawing can cause
raveling
Jointing
7-day moist cure is mandatory due to the
porosity and low W/C ratio
Curing pervious concrete is more important than
curing conventional concrete
Freeze-Thaw Resistance
• Depends on saturation level
• Avoid critical saturation
• Design
• Infiltration System
• Maintenance
• Clean as necessary in
severe climates
• Secret of success is to
provide the water a place
to go
What About Clogging?
• Even if 100% clogged
with dirt, pervious
concrete will still be
permeable
• For maintenance, clean
pervious pavement with
power washer and/or
street sweeper/vacuum
• Pervious Concrete is less susceptible to clogging than other porous materials
• Due to heat and pressure from continual use, porous asphalt undergoes internal compression, reducing porosity of system
What About Clogging?
Porous Asphalt
Pervious Concrete
Pervious Concrete Resources
• ACI 522 Guide Document
• PCA/NRMCA Pervious
Concrete Pavements
• PCA/NRMCA Hydrologic
Software
• NRMCA Pervious Concrete
Contractor Certification
www.PerviousPavement.org
• Benefits
• Applications
• Performance
• Design Guidelines
• Construction
• Inspection &
maintenance
• Resources
Questions?????
• Bob James
• Director of Marketing and Technical Standards
• Texas Aggregates and Concrete Association (TACA)
• 817-253-6299