Permeable Interlocking Concrete Pavement:
Capitalizing on a Green Opportunity

David Pitre, Chairman-Elect, Interlocking Concrete Pavement Institute; Engineering and Sales Manager for Pavestone, LLC

Permeable interlocking concrete pavement (PICP) is made to process precipitation and runoff from even the highest intensity rainstorms. Runoff is often eliminated completely, greatly reducing chances for pollutants to reach waterways.

Contractors looking for a break from the sluggish economy should explore the prospects provided by permeable pavement. Industry surveys show that permeable use has grown by 100 percent since 2000, and could double again in the next decade.

When mass-produced automobiles became available in the 1920s, an explosion of pavement ribboned across the United States, connecting the nation with about 43,000 square miles of urban impervious cover ?EUR??,,????'?????<

PICP relies on solid, high-strength concrete units to support traffic, surrounded by small, highly permeable stone-filled joints to infiltrate stormwater. The angular-shaped joint aggregate aids interlock and load transfer between units.

The three primary technologies that promote stormwater infiltration in vehicular and pedestrian pavements are porous asphalt, pervious concrete and permeable interlocking concrete pavement (PICP). Pervious concrete and porous asphalt consist of small-sized aggregates bound with asphalt or cement, creating a porous matrix that supports vehicular traffic. In contrast, PICP is manufactured from a mix of crushed rock, sand, cement and pigment. Because there is very little water in the mix, it is moved easily on conveyor belts and compressed into a paver mold. A press is inserted into the concrete-filled mold and vibrated to create a strong bind between the aggregate particles and cement. These solid, high-strength concrete units support vehicle traffic, and are surrounded by small, highly permeable stone-filled joints that infiltrate stormwater. The angular aggregate in the joints also contributes to load transfer and interlock between units.

Permeable pavers can reduce job costs by eliminating the need for other stormwater management systems, like swales and retention ponds.

PICP is produced in a variety of shapes and sizes, and generally have joints that vary between 3/16 and 1/2 inches. The joints should be filled with small-sized aggregate (ASTM No. 8, 9, or 89 stone) that provide high surface infiltration rates. Some sites have initial infiltration tests exceeding 500 inches-per-hour, well above the most intense of rainfalls, equaling or exceeding other permeable surfaces.

This detail illustrates a common design for permeable pavers and the sub-base beneath them. The open graded aggregate receives, stores and infiltrates runoff before releasing it into the subgrade soil.

Meet Low Impact Development Objectives with PICP
Low Impact Developments (LIDs) work within nature to manage stormwater as close to its source as possible. LID goals include preserving natural landscape features, minimizing effective imperviousness, and creating functional and appealing site drainage that treats stormwater as a resource rather than a waste product.

Permeable pavement has become an integral component of LID design and regulations. Through low impact principles, water can be managed in a way that reduces the effect of built areas and promotes the natural movement of water within a watershed. LID has been characterized as a sustainable stormwater practice by the Water Environment Research Foundation and is increasingly being added to state and municipal stormwater design manuals.

Pavestone's Eco-Priora?EUR??,,????'?????????????? permeable pavers (pictured) meet or exceed ASTM C-936 requirements, with a compressive strength greater than 8,000 psi and a water absorption maximum of 5 percent. There are no structural load-bearing reductions using PICP, and the product does not need any time to cure at the job site.

PICP Advantages
In many cases, permeable pavers can eliminate runoff completely and prevent or greatly reduce any opportunity for pollutants to contaminate waterways. Permeable pavements rely on the ability of open graded aggregate in their surfaces and base to receive, store and infiltrate runoff back into the subgrade soil. By capturing stormwater and allowing it to seep into the ground, PICP is instrumental in recharging groundwater and reducing damage from runoff. In fact, by eliminating the need for other stormwater management devices, PICP gives contractors the ability to lower overall project costs on a first-cost basis

Research on permeable pavers has shown substantial reductions in total suspended solids (TSS), nutrients, metals, and can reduce surface runoff temperatures by four to six degrees compared to asphalt.

The EPA and many environmental management agencies recognize permeable pavements as a best management practice (BMP) for sustainable construction. As authorized by the Clean Water Act, the National Pollutant Discharge Elimination System also recognizes the use of permeable pavement as a BMP for stormwater control. Additionally, rating systems for sustainable construction such as Leadership in Energy and Environmental Design (LEED???????(R)????) and Green Globes offer credit to site designs that use permeable pavement. For more PICP information, visit www.icpi.org/permeable.