Prime Time For Permeable Pavements

Increasingly stringent environmental regulations and an intensifying movement have generated interest in permeable interlocking concrete pavements (PICP).

Increasingly stringent environmental regulations and an intensifying ÎgreenÌ movement have generated interest in permeable interlocking concrete pavements (PICP). A widening range of municipal and private applications for PICP is helping hardscape unit producers realize market opportunities beyond those for conventional paving stones and segmental retaining walls.

By capturing and filtering stormwater runoff, PICPs limit pollution of downstream waters. Additionally, savings in storm sewer costs and related maintenance, plus revenue generated by dedicating real estate to profitable development rather than detention ponds or catch basins, account for significant financial gains. Thus, permeable pavements offer the ideal marriage of environmental and economic interests. Following are profiles of two large installations that reflect private owners’ and public agencies’ growing recognition of PICP performance.


Reportedly the first eco-friendly permeable pavement installed by a major league sports facility, U.S. Cellular Field’s six-acre Parking Lot L was unveiled in early April by the Illinois Sports Facilities Authority Û developer, owner and operator of the stadium that is home to the Chicago White Sox baseball club. Spanning more than 265,000 sq. ft. (equal to four and a half football fields), the project is said to be the largest permeable paving parking lot in the United States.

On hand for the ribbon-cutting ceremony was 11th Ward Alderman James Balcer, who reported that the lot’s $3.5 million price tag saved the city about $400,000, a 12-15 percent markdown from traditional asphalt. He also emphasized that the installation has a 40-year service life, nearly twice that of bituminous asphalt paving. Moreover, by substantially reducing the amount of water entering Chicago’s stormwater system, permeable pavement eases the taxpayer burden.

Parking Lot L goes a long way toward establishing Chicago as one of the nation’s greenest cities, Balcer affirmed. Building on the success of the city’s Green Alleys program (note box, at right), the project meets the 2008 Chicago Stormwater Management Ordinance designed to promote programs that attenuate stormwater runoff and the erosion-control impact of new development and redevelopment. Since water is allowed to infiltrate and collect below the paving surface, stormwater runoff and localized flooding are minimized, while contaminants are filtered by the subbase as detained water is released naturally into the environment. An additional benefit is reduction of the urban heat island effect. Accordingly, permeable pavements meet both Low Impact Development (LID) and the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) guidelines.

Recycled materials also constitute a significant portion of Parking Lot L. Following 30 days dedicated to project design, excavation of the former asphalt surface launched a 45-day construction sequence. Concrete slab discovered beneath a section of the asphalt was crushed and recycled as subbase for the new pavement.

Paving stone supplier Unilock provided interlocking L-shaped Eco-Optiloc pavers from its Aurora, Ill., plant. The 100-mm-thick Eco-Optiloc units feature edge notches that create approximately half-inch voids between each stone to achieve permeability. Installed on a 1.5-in.-deep setting bed of ∫-in. chip that covers a layer of geotextile fabric and a 14-in.-deep subbase comprising 3-in.-diameter recycled concrete and Ê- to 1-in. limestone rock, the paving system is designed to hold 600,000 gallons of water, equal to a 100-year rain event, noted project architect Ernest Wong of Site Design Group, Ltd. Its drainage capacity is 154,583 cu. ft. or 1.15 million gallons. Parking Lot L brings Unilock’s permeable pavement installation log in the Chicago market to about 2.5 million sq. ft.

Delivered in two colors Û granite and charcoal Û the paving stones’ interlocking L-shaped design facilitated moving large quantities. According to Mike Shereck, site engineer for Parking Lot L contractor Rose Paving Co., a typical day saw placement of 7,000 to 8,000 ft., while 20,000 ft. (or about a half-acre) were placed peak days, the equivalent of 2.5 mechanical installers operating at a time.

Low maintenance is assured by the pavement’s durable surface and modular design, project principals observed. Although the pavers are able to withstand most street-cleaning brushes and metal snow plows, they explained, maintenance typically requires an occasional pressure spray, and any repairs to the lot would involve replacement only of single units.
Û by the editors of Concrete Products


From Abbotsford Concrete Products and Interlocking Concrete Pavement Institute ÷ Inviting customers to park on an environmentally responsible lot to shop in their favorite stores housed in architecturally appealing structures, Marine Way Market in Burnaby, B.C., features a 350,000-sq.-ft. permeable pavement encompassing drive aisles and 1,161 parking spaces. The project’s AquaPave Permeable On-Site Stormwater Source Control System, comprising patented permeable interlocking concrete pavers (PICP) fabricated by Abbotsford Concrete Products of Abbotsford, B.C., is capable of draining large volumes of stormwater while removing 98 percent of oils and other hydrocarbons, as well as 80-96 percent of heavy metals.

Selected for the hardscape was a machine-lay standard 4_- _ 9-in., 3?-in.-thick paver in a 45-degree herringbone pattern. Shadow tint Û a charcoal and natural blend Û was chosen for parking areas to camouflage oil deposits, and a Sand/Brown blend defines the drive aisles. Shrink wrapping and delivering layers in a herringbone pattern with no shifting or misalignment expedited installation using a Probst paver-laying machine specially fitted with a clamp that enabled placement of square-yard sections. Also saving time and on-site labor, the herringbone pattern eliminated removal and placement of half stones. Accordingly, Interpave Precast Systems of Surrey, B.C., installed an average of more than 6,000 sq. ft. per day, which included filling joints with ?-in. fine washed stone, sweeping and compacting the pavers.

The City of Burnaby and developer Westbank Projects Corp. collaborated to implement green technologies enabling the site to return to predevelopment permeability. Approval was granted by the city for a partial exfiltration system that allows water to percolate into the soil, yet includes piping attached to the municipal stormwater system at a higher level in the subbase, in case the exfiltration rate slows.

Besides precipitation falling directly on the pavement, stormwater is delivered to the base by store roofs shedding water on the pavers and into narrow, stone-filled joints for which spacing is achieved by the units’ side notches. The open-graded stone base and subbase detain and filter runoff prior to being released at lower rates into the drainage system. As rainfall passes into the system, 6-in.-diameter perforated pipes placed on a slope at the bottom of the open-graded subbase convey water, directing flows to a central 24-in.-diameter storm sewer. Dieter Diedericks, P. Eng., of project engineer Associated Engineering (B.C.) Ltd. in Burnaby, notes that attenuated base outflow allowed the use of smaller oil interceptors than normally required by the municipality for impervious pavements.

The combined drainage and pavement system designed by Associated Engineering required a 2-in.-thick setting bed of ASTM No. 8 stone [<? in.], covering four inches of No. 57 stone [1_-in.-minus graded aggregate] topping a minimum 12-in.-thick subbase consisting of ASTM No. 2 stone, generally ranging in size from 3 to Ê in. Thus, the intermediate No. 57 stone effects a transition between the bedding layer and the subbase, causing all stone layers to interlock, as it contributes to runoff storage capacity. In combination, the base and subbase supply a storage reservoir exceeding 30 percent of the total volume of stone, i.e., a minimum storage capacity of 128,000 cu. ft. or about 957,000 gal.

The soil subgrade was imported as engineered fill and compacted. By contrast to most permeable pavement applications, soil compaction was recommended to ensure stability, rendering the fill impervious and allowing use of perforated drain pipes to restrict and direct outflows. After filling, grading and compacting the soil, geotextile was placed prior to subbase installation. That scheme satisfied design aims to filter water slowly through the stone base, enhancing nutrient digestion and oil reduction via microbial activity.

Grey water outflow, acceptable for irrigation and flushing of lavatories, is typically delayed by 24 to 72 hours from peak discharge of the rain event. Bank erosion is thereby avoided, as salmon and other fish species are protected from contaminating pollutants. Moreover, revenue and valuable real estate need not be dedicated to catch basins and detention ponds.


Adopting an innovative solution for a long-standing problem, the City of Chicago Department of Transportation (CDOT) is installing permeable pavement in alleys to reduce combined sewer overflow, an affliction plaguing older cities where storm sewers drain into sanitary lines. Implementation of 46 ÎgreenÌ alleys was expected by the end of 2007 to relieve the massive flow of combined sewage and untreated runoff that overwhelms waste water treatment plants during rainstorms, causing environmental damage upon diversion to lakes and streams.

Permeable pavements are set on minimum 12-in.-thick, open-graded, crushed stone bases capable of storing three to four inches of water as it is drawn into the soil subgrade. The amount of runoff entering the combined sewer system thereby is minimized, reducing pollution; and, groundwater is recharged, while flooding risks are attenuated.

Chicago’s Green Alleys program regards the city’s 1,900 miles of public alleys Û equivalent to 3,500 acres of pavement Û as the key to significant reduction of stormwater runoff and pollution by converting the surfaces to permeable pavement. In addition, using recycled materials to install permeable paving consumes waste otherwise destined for landfills. Plus, greater safety results from eliminating puddles and reducing winter ice hazards. Moreover, reflective surfaces help create cooler microclimates and enhance nighttime illumination.

CDOT’s award-winning booklet, The Chicago Green Alley Handbook, affirms the city’s commitment to creating a green and more sustainable environment by using best management practices [BMP] in alley improvements and construction. Besides detailing BMPs such as improved drainage through proper alley pitching and grading, use of permeable pavement, high albedo (reflective) surfaces, and recycled construction materials, the publication provides maintenance guidelines to keep the permeable alleys free from dirt and reduce degradation from deicing salts. It is available at


Interlocking Concrete Pavement Institute’s (ICPI) newest guide examines similarities and differences among paving options Û including permeable interlocking concrete pavement, pervious concrete, and porous asphalt Û applied as stormwater and sustainable best management practices. Permeable Pavement Comparison Guide provides a side-by-side comparison of available colors, construction efficiencies, costs, winter durability, surface cleaning, repairs, water quantity reduction, water- and air-quality improvement, urban heat island reduction, and recycled content.

Presenting an overview of each system for stormwater-monitoring agencies, design professionals, contractors, and homeowners, the publication emphasizes the advantages of permeable interlocking concrete pavement over the alternatives. As municipalities review their stormwater management programs, many reportedly are looking to reduce runoff by means of permeable pavements Û a best management practice recognized by the U.S. Environmental Protection Agency and a green system credited by LEED and GreenGlobes. A copy of the Permeable Pavement Comparison Guide and additional permeable interlocking concrete pavement resources offered by ICPI can be obtained by visiting or