TechBrief Publication Number FHWA-HIF-15-007 | JANUARY 2015 Permeable Interlocking Concrete Pavement Contents Introduction Introduction Permeable interlocking concrete pavement, also Benefits referred to as PICP, consists solid concrete paving Applications and Limitations units with joints that create openings in the pavement Typical Properties & surface when assembled into a pattern. (The USEPA Characteristics has a fact sheet on PICP.) The joints are filled with Design permeable aggregates that allow water to freely Construction Considerations enter the surface. The permeable surface allows flow Maintenance rates as high as 1,000 in./hr (2,540 cm/hr) (Borst Performance 2010). The paving units are placed on a bedding Summary and Future Needs layer of permeable aggregates which rests over a References base and subbase of open-graded aggregates. The concrete pavers, bedding and base layers are typically restrained by a concrete curb in vehicular This TechBrief presents an applications. The base and subbase store water and overview of permeable inter- locking concrete pavement allow it to infiltrate into the soil subgrade. Perforated (PICP) and its use. General underdrains in the base or subbase are used to information is provided on PICP composition with a sum- remove water that does not infiltrate within a given mary of benefits, limitations, and characteristics. Important design period, typically 48 to 72 hours. considerations such as hydro- Geosynthetics such as geotextiles, geogrids or logical design, structural de- sign, construction, and main- geomembranes are applied to the subgrade tenance are also provided. depending on structural and hydrologic design objectives. Separation geotextiles are used on the sides of the base/subbase to prevent entrance of fines from adjacent soils. Figure 1. Typical permeable interlocking concrete pavement cross section. • Building code requirements. Examples • Can be installed in freezing temperatures if include CALGreen in California, the subgrade and aggregates remain unfrozen Figure 1 illustrates PICP components. The figure shows a partial infiltration design with drainage to International Green Construction Code, • Capable of wet weather (light rain) installation accommodate some water that does on enter low infiltration soils. PICP over high infiltration sub- ASHRAE Standard 189.1, or other codes that grade soils may not require an underdrain(s) and these are called are called full infiltration designs. require compliance to Leadership in Energy Reduced Runoff & Improved Water Other designs over expansive or fill soils or close to buildings may enclose the pavement structure and Environmental Design (LEED®) or similar Quality with geomembrane (impermeable liner). An outlet pipe provides temporary storage and outflow sustainable design and construction rating control. This design approach also can be used for water harvesting or for horizontal ground source systems. • 100% surface runoff reduction heat pumps. The use of a geomembrane to restrict infiltration into the soil subgrade is often called a • 100% infiltration depending on the design, no infiltration design. There are non-regulatory drivers that influence inflows, and soil subgrade infiltration rate PICP use. These include; economics that often • Capable of installation over or next to plastic make PICP a lower-cost alternative to convention- underground storage vaults or crates al drainage system designs, gaining stormwater • Can be designed with water harvesting sys- utility fee credits, and project owner preference tems for site irrigation and gray water uses for conformance to sustainable rating systems for • Reduces nutrients, metals and oils (Collins roads/transportation infrastructure. Examples of 2008) (TRCA 2007) (TRCA 2012) (Fassman rating systems include the Institute for Sustainable 2010) (Brattebo 2003) (Clausen 2007). Infrastructure’s Envision™ evaluation system, • Does not raise runoff temperature which can Greenroads, GreenPave or the Federal Highway damage aquatic life (Wardynski 2013) Administration INVEST or Infrastructure Voluntary Evaluation Sustainability Tool. Site Utilization PICP benefits are listed below (Smith 2011). • Reduces or eliminates unsightly detention/ retention ponds and related liability Construction • Increased site and building utilization • Conservation of space and reduction of im- • Paving materials require no time-sensitive site pervious cover forming • Preserves woods and open space that would • Immediately ready for traffic upon comple- have been destroyed for detention/retention tion, no time needed for curing ponds • Promotes tree survival by providing air and water to roots (roots do not heave pavement) Figure 2. Parking lot in Elmhurst, IL. Benefits pavements) and resulting runoff • Runoff volume storage and/or infiltration to PICP may help achieve compliance with many reduce overflows, especially combined sewer national, provincial, state and local regulations overflows. as well as transportation agency design require- • Meeting total maximum daily load (TMDL) ments for stormwater runoff control. These re- requirements for receiving waters. quirements may include the following: • Managing water quality volume capture and or quantity storm events, typically expressed • National Pollutant Discharge Elimination as a percentile; e.g. 85th percentile storm System (NPDES) permit compliance depth, or the 95th percentile storm depth as • Runoff volume and pollutant control for new required for U.S. federal government facilities development and redevelopment in Section 438 of the Energy Independence • Limits on impervious cover (i.e., roofs and and Security Act. TechBrief: Permeable Interlocking Concrete Pavement | Page 2 TechBrief: Permeable Interlocking Concrete Pavement | Page 3 Figure 3. Green alley in Richmond, VA. Applications and Limitations PICP is used for walkways, driveways, parking than 2 ft or 0.6 m) although it has been used in lots, alleys, low-speed roads and road shoulders. coastal areas with sandy soil subgrades in Figures 2, 3 and 4 below illustrate vehicular ap- Maryland, Virginia, South Carolina and Georgia. plications. PICP is intended for areas with posted Like all permeable pavements, PICP should not vehicle speeds no greater than 35 mph (50 be used on extremely dirty sites where there is kph). PICP is generally used in areas exposed uncon-trolled water borne sediment or wind to less than 1 million 80 kN lifetime equivalent borne dust that can rapidly clog the surface. single axle loads (ESALs) (or Caltrans Traffic Index < 9). These applications use unstabilized Typical Properties and Characteristics open-graded aggregates. Open-graded bases stabilized with cement or asphalt, or the use of pervious concrete or porous asphalt bases can Concrete paving units and jointing materi- provide higher lifetime ESALs and accommodate als – Concrete pavers conform to ASTM C936 heavier load applications. PICP has seen limited Standard Specification for Solid Interlocking use in heavy load applications with permeable Concrete Paving Units. Minimum 3 1/8 in. (80 asphalt stabilized bases (Knapton 2003, Sieglen mm) thick units are used in vehicular areas and 2004). Design guidance for heavy loads can be pedestrian areas may use 2 3/8 in. (60 mm) thick • Colored units can mark parking stalls and Drainage System found in overseas sources Knapton 2007 and units. Depending on joint widths, they are filled driving lanes Knapton 2012. Research is being conducted on with permeable, small-sized aggregates such • Reduced downstream flows and stream bank • Eliminates puddles on parking lots, walkways, the structural behavior of PICP at the University as ASTM No. 8, 89 or 9 stone per ASTM D448 erosion due to decreased peak flows and entrances, etc. of California (Davis) Pavement Research Center Standard Classification for Sizes of Aggregate volumes • Capable of plowing with municipal snow re- and specifically that of the open-graded aggre- for Road and Bridge Construction or AASHTO • Increased groundwater recharge moval equipment gate base materials. In addition, the American M-43 Sizes of Aggregate for Road and Bridge • Decreases risk of salt water incursion and • Concrete units resist freeze-thaw and degra- Society of Civil Engineers is preparing a national Construction. drinking water well pollution in coastal areas dation from deicing materials standard with guidance on design, construction • Reduced peak discharges and stress on • Reduces ice and deicing material use/costs and maintenance for release in 2015. Open-graded Bedding Course storm drainage pipes and related liability due to faster ice melt and This permeable layer is typically 2 in. (50 mm) thick • Reduces combined sanitary/storm sewer surface infiltration PICP should not be used in areas subject to and provides a level bed for the pavers. It consists overflows • Provides traffic calming loading/unloading or storage of hazardous of small-sized, open-graded aggregate, typically • Paver surface can be coated with photocata- materials. It is generally not placed in areas with ASTM No. 8 stone or similar sized material. lytic materials to reduce air pollution Reduced Operating Costs high depth to seasonal water tables (i.e. less • High solar reflectance index (SRI) surface • Reduced overall project costs due to reduc- helps reduce micro-climatic tempera- ing or eliminating storm sewers and drainage tures and contributes to urban heat island Figure 4. Main Street, Warrenville, IL. appurtenances reduction • Lower life-cycle