PERVIOUS CONCRETE

Pervious concrete is made from carefully controlled amounts of water and cementitious materials used to create a paste that forms a thick coating around aggregate particles. Unlike conventional concrete, the mixture contains little or no sand, creating a substantial void content – between 15% to 25%.

Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids which drain quickly. Both the low mortar content and the high porosity reduce strength compared to conventional concrete, but sufficient strength is readily achieved for many applications.

Pervious concrete allows 3 to 8 gallons of water per minute to pass through each square foot of the material. By allowing rainwater to seep into the ground, pervious concrete can be instrumental in recharging groundwater and reducing stormwater runoff. This capability can reduce the need for retention ponds, swales, and other stormwater management devices. Pervious pavement integrates hardscape surfaces with stormwater management.

Applications for pervious concrete include:

Hardscape

Low-volume pavements

Residential roads, alleys, and driveways

Low-water crossings

Parking lots

Sidewalks and pathways

Patios

Tennis courts

Swimming pool decks

Pavement edge drains

 

Floors

Foundations/floors for greenhouses, fish hatcheries, aquatic amusement centers, and zoos

 

Walls

Load bearing and other walls

Sound barriers

Other

Subbase for conventional concrete pavement

Slope stabilization

Artificial reefs

Well linings

Hydraulic structures

Tree grates in sidewalks

Groins and seawalls

Use of pervious concrete is among the Best Management Practices (BMP) recommended by the EPA and other agencies for the management of stormwater runoff on a regional and local basis. By eliminating the need for retention ponds, swales, and other stormwater devices, pervious concrete can lower overall project costs on a first-cost basis, and makes more efficient use of the land. Pervious concrete can also reduce operational costs and allow developers to increase utilization of available property. Pervious concrete has a significantly lower life cycle cost than other alternatives and saves money in teh long run due to its superior durability, strength, and long life span. Parking lot owners who use pervious spend fewer dollars on stormwater management systems and irrigation systems may be downsized or eliminated. Pervious canhelp property owners minimize sewer system usage and avoid municipal stormwater impact fees.

Pervious concrete has many environmental benefits. See associated sustainability solutions and technical briefs (right) for more detail.

 

Stormwater Management. By allowing water to soak through and infiltrate, pervious paving reduces stormwater flow and pollutant loads. Can contribute to LEED Credit 6.

 

Minimize Site Distrubance. By integrating paving and drainage, less site area may need to be used to manage stormwater, allowing a more compact site development footprint. May contribute to LEED Credit SS 5.

Local. Materials are usually extracted and manufactured locally. May contribute to LEED Credit M 5.

Recycled content. Fly ash, slag cement, or silica fume can substitute partially for cement, and recycled aggregates can replace newly mined gravel. Recycled content can contribute to LEED Credit M 4.

Cool. The voids reduce mass reducing the heat build up associated with heat islands. Lighter colored cements can increase reflectivity. Not specifically approved for achieving LEED Credit SS 7.

The properties of pervious concrete vary with design and depend on the materials used and the compaction procedures. General guidelines for specifications are provided below.

Permeability. Typical flow rates for water through pervious concrete are 3 to 8 gallons per sq foot per minute, but can be double that amount if desired.
Compressive Strength. Pervious concretes can develop compressive strengths in the range of 500 to 4000 psi – suitable for a wide range of applications.
Flexural Strength. Flexural strength of pervious concrete ranges between 150 and 550 psi.
Shrinkage. Drying shrinkage of pervious concrete is faster but much less than that experienced with conventional concrete. Many pervious concretes are made without control joints and are allowed to crack randomly.
Freeze-Thaw Resistance. Freeze-thaw resistance depends on the saturation level of the voids in the concrete at the time of freezing. In the field, it appears that the rapid draining characteristics of pervious concrete prevent saturation from occurring. Where substantial moisture and freeze-thaw conditions are anticipated, pervious concrete should be placed on a 6 to 18-in.-thick layer of drainable rock base such as 1-in. crushed stone.
Abrasion resistance. Because of the rougher surface texture and open structure of pervious concrete, abrasion and raveling of aggregate particles can be a problem, particularly where snowplows are used to clear pavements. Surface raveling in new pervious concrete can occur when rocks loosely bound to the surface pop out under traffic loads. This raveling is considerably reduced after the first few weeks.