Paving and Asphalt
Use Pervious Concrete
What Is It?
South Dakota Ready Mixed Concrete Association
Pervious, or permeable, concrete lets water from precipitation, storms, and flooding filter through to the soil and groundwater below. This reduces susceptibility to flooding and runoff volume, and can also help filter pollutants that would otherwise run off impervious pavement. After being mixed with less sand and fine particles than conventional asphalt, the concrete is then laid above crushed stone aggregate base to allow for water infiltration. Water is able to permeate the concrete due to void spaces of 18 - 20%, which also reduces the weight of pervious concrete by 20-30% compared to conventional concrete (this can reduce transportation emissions). Rigid pavements like concrete typically do not require aggregate bases for structural stability, though deep aggregate bases are recommended for cold climates like the northeast. Suppliers are easy to find, as pervious concrete can be mixed and applied using the same equipment and methods as impervious concrete, though the lack of fine particles gives pervious concrete a coarser look than conventional concrete. Water flow rates through pervious concrete are usually around 480 in./hr (0.34 cm/s, 5 gal/ft²/ min, or 200 L/m²/min) (National Ready Mixed Concrete Association).
As with other pervious pavements, proper maintenance (primarily vacuum sweeping) is necessary to maintain high rates of infiltration. Infiltration rates are also highly dependent on the subgrade soil. Sandy soils have highest infiltration capacity and increased load bearing capacity, but lower treatment capacity. Potholes and cracks can be fixed with patching mixes unless >10% of the surface needs replacement. The maximum slope of pervious concrete exceeds porous asphalt, allowing for a slope of up to 12% while maintaining infiltration.
Permeable or pervious concrete is often confused with the similar porous asphalt. Regular concrete uses cement as the binding agent, while asphalt uses tar; this is the main difference in their respective porous options, with the result that concrete is generally more expensive but more durable. Learn more about the latter in our Use Porous Asphalt toolkit.
Benefits
- Enhances groundwater infiltration while reducing stormwater runoff volume, rate, and pollutants
- Can contribute to lower urban air temperatures when moist due to higher reflectivity and evaporative cooling; this also combats Urban Heat Island effect because the air and water exchange from the pavement to the soil beneath keeps the surface cooler.
- A more natural exchange of water flow into the ground and cooler surface temperatures promotes plant growth, which further regulates temperatures, removes CO2 from the air, and looks pleasing
- Reduces occurrence of black ice/freezing puddles in cold climates; requires less applied de-icers
Drawbacks
- Pollutants can infiltrate groundwater; —should not be installed in areas where hazardous material spills are possible
- Plowed snow piles and improper de-icing treatment can clog void spaces and reduce infiltration rate (sand should not be used); snow plow blades can damage surface
- More expensive than porous asphalt
- Coarse appearance can be aesthetically displeasing (relative to conventional concrete)
Regulatory Impacts and Requirements
Potential regulatory touchpoints in Boston and Massachusetts include:
- Boston Groundwater Trust
- Boston Water and Sewer Commission
- Local Utilities
- Boston Public Works Department
- Public Improvement Commission
- Zoning Board of Appeals
- Architectural Access Board
- MA Historical Commission/Boston Landmarks Commission
Financing Options, Incentives, and Rebates
- Mass.gov:
- Clean Water State Revolving Fund (SRF)
- Coastal Pollutant Remediation (CPR) Grant Program
- Section 319 Nonpoint Source Competitive Grant (Funding provided under federal Clean Water Act)
- 604b Water Quality Management Planning Grant (Funding provided under federal Clean Water Act)
- Drinking Water Supply Protection Grant Program
- Newton, MA: Municipal stormwater abatement service fees
Resources:
- National Ready Mixed Concrete Association: Pervious Concrete Pavement: An Overview
- Bay Area Pervious Concrete: The Basics
- California Coastal Commission: Permeable Pavement
- US EPA: See pg. 8 of the Cooling Pavements Chapter of their Heat Island Compendium
- Seattle Right of Way Manual: Permeable Pavement Comparison Guide
- University of Maryland: Permeable Pavement Fact Sheet
News:
- “This Concrete Can Absorb a Flood,” Smithsonian, October 2015
Project Examples:
- At the Stratford Place residential project, in Sultan, WA, over $260,000 in construction costs were eliminated by using pervious concrete to pave streets and sidewalks.
- Northeast Cement Shippers Association: List of projects in NJ/DE/PA involving PCA-Northeast
A Sample of Providers:
- Cape Cod Ready Mix
- Boston Sand and Gravel
- Massachusetts Concrete & Aggregate Producers Association provides a directory of concrete mix producers, many of whom supply pervious concrete. Browse through the directory here.
- National Ready Mixed Concrete Association maintains a database of certified concrete installers. Search for pervious concrete installers and concrete sustainability experts by state here.
