Pervious Concrete –

When it Rains, it Drains!

A Concrete Solution to Storm

Water Runoff

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

Pervious Concrete Placement

Photo ©Copyright 2004, PCI Systems, LLC

• 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

University of CA,

Berkeley

Architectural Applications

Bomanite Offices,

Fresno, CA

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)

• bobjames@tx-taca.org

• 817-253-6299