Frequently Asked Questions (FAQ)
Engineers
Developing the Pervious Concrete Dual-Use Concept
"Think Outside the Box"
Many commercial properties currently being developed incorporate a structure (building, or "box"), a parking lot, and a separate stormwater detention/treatment system. Each of these elements take up a large portion of the available land space and add to the overall cost of development. The Dual-Use concept takes a look at the advantages of designing the parking lot area inside of the on-site stormwater detention/treatment system), thereby reducing, or eliminating, the requirements for a separate detention area (on-site pond, or underground stormwater infrastructure) and, reducing the cost of site- development. The design principles herein follow the guidelines as depicted in the Federal Green Construction Guide & the EPA web site on Porous Pavement.
This page also contains Sections on: Background Information, Stormwater, On-Site Storage & Treatment, Infiltration Systems, Pervious Pavements, First-Flush, Dual-Use Concept, Observation Wells, Pervious Concrete, Codes and Regulations, Flat-Pavement Design, Runoff Coefficients, Maintenance, Freeze-Thaw, Cost Comparisons, Details & Specifications, Bid Solicitation and Bonus Features. (Click your "back-button" to return to this list.)
Magruder Construction is turning gray concrete into green parking lots.
Eliminating the need for the extra land space, and/or, the associated underground stormwater infrastructure, can substantially reduce the cost of development. LEED Credits can also be achieved by using this system.
The picture above is of a dual-use system. It is a pervious concrete parking lot that is placed inside the stormwater detention and treatment area. (See the NIBS - Federal Green Construction Guide.) All of the stormwater from this site is stored in a 6-inch layer of clean gravel directly beneath the pavement. It was raining when this picture was taken, and no water is standing on, or running off of, the pavement surface. All of the stormwater passes directly through the pavement. The Owner/Developer also saved a substantial amount of money by using this concept. For LEED Certification, the project design should start in the Parking Lot, as a part of the "Whole-Building" concept. Many LEED Credits can be achieved by properly designing the parking lot using pervious concrete and the Dual-Use system.
In order for an Engineer to represent the "Best Interest of the Owner" they should have a thorough knowledge of stormwater requirements and pervious concrete systems. If the Engineer is unfamiliar with the properties, or testing of Pervious Concrete, it may be in their best interest to negotiate the construction contract with a Sole Source Contractor. (See the Sole Source Justification page.) This is especially true for Developers contemplating LEED Certification for their projects.
If the Engineer is not familiar with the EPA stormwater management requirements, or of the physical properties of pervious concrete, they may want to visit the General Information section of this site before reading this section on the dual-use system. The Engineer may also want to visit the section on Testing, and Criteria for Acceptance, on the Details and Specifications Page. (Engineers should also see the EPA Web Site on Porous Pavement.)
Important: Because of the lack of standardized test for quality control and acceptance of Pervious Concrete, it is critical that whoever is making the decisions for acceptance of both the fresh concrete, and the finished pavement, that they are qualified to do so. The decision-maker must have adequate knowledge and experience to recognize the essential properties of Pervious Concrete, and know how to make field-adjustments. (Note: Both the NRMCA, and the National Institute of Building Sciences, recognize that only NRMCA Certified "Craftsmen" have the 1500-3000 hours of experience necessary as a basis of qualification.)
-
Engineers, who are interested in using pervious concrete in their designs, may also want to become "certified" as Technicians through a national-level program sponsored by the National Ready Mixed Concrete Association (NRMCA). They should contact a state-level sponsoring group or visit the NRMCA Web site. This program will give the Engineer a basic background in the use of pervious concrete pavements in stormwater management.
-
The EPA site on Best Management Practices is another helpful site. See also the pages on this site dedicated to the ACI and NRMCA.
Stormwater, On-Site Storage and Treatment
The EPA has mandated all states, counties and cities to comply with their NPDES permitting requirements. (See the General Information page for a background on the rulings by the EPA.) Engineers should also review the EPA Web Site on Porous Pavement. Developers are required to comply with these rulings for all new construction, and retrofitting, typically for any site of more than one-acre. The EPA has also recently (April 19th, 2007) signed a letter of agreement to encourage stormwater authorities to adopt Green Infrastructure as a part of their stormwater design criteria.
There are several options for the storage, and treatment of on-site stormwater to meet NPDES permitting requirements. One option is stormwater ponds. Both wet and dry stormwater ponds have varying capabilities for pollution treatment. However, ponds typically take up a lot of valuable land area. Another drawback is there are some major safety and environmental concerns over having "open" ponds.
Other acceptable options, for on-site stormwater storage/treatment, are underground systems. These can take the form of holding tanks, or infiltration vaults or pipes. The native-soil perk-rates, and depth of the water table, often dictate which forms can be used. However, prefabricated underground storage systems are very expensive and are often used only if there is no available land space for open ponds.
Asphalt Pavements are not part of the solution - they are part of the problem.
A better option, which is approved by the EPA, The Federal Government, and many States, are various types of "permeable-pavement" infiltration systems. One approved system is a pervious/porous pavement in combination with a base of clean gravel/crushed-stone. (See the NIBS - Federal Green Construction Guide.) This system has high efficiencies at removing pollutants from stormwater, and recharges the aquifer at the same time. See also, the EPA Web Site on Porous Pavement.
To create the best system, use a (non-proprietary) pervious concrete pavement.
There are many types of pervious/porous pavements. Some materials are proprietary, while others, such as pervious concrete, are not. A layer of gravel can be used as a pervious pavement, but gravel is generally unstable as a surface-course, and deforms under traffic loading. Therefore, both the asphalt, and the portland-cement industries, have created material-binders (glues) to add to the gravel to form more stable surfaces, but still maintain permeability. The industry names for these glued-materials are: "porous asphalt" and "pervious concrete". There is also a third pervious pavement system that uses "precast" units such as brick, stone or blocks. All of these systems have been used successfully as pervious pavements throughout the U.S.
Some important items to consider when selecting a specific type of pervious pavement system are:
-
How permeable is the surface - how well does it drain stormwater? The purpose of permeable, or pervious pavements, is to insure adequate drainage of stormwater to reduce, or eliminate runoff. Pervious concrete offers some of the best results in actual tests. See the NRMCA video on how fast pervious concrete soaks up water. Properly constructed pervious concrete pavements have a perk-rate of over 200-inches per hour. (Considerably higher than the minimum requirements of 1-3-inches per hour.) (See the Federal Green Construction Guide.) A higher initial perk-rate gives a greater latitude for degradation over time. A minimal perk-rate of 1.1-inches per hour should be maintained for 20-years. (Only properly designed, constructed and maintained pervious concrete pavements can achieve this requirement.)
-
How durable is the surface - how long will it last? Portland-cement binders have an excellent history of endurance when exposed to the elements - such as the environments of parking-lot pavements. Portland-cement systems (concrete) can last many hundreds of years. Many asphalt systems tend to degrade in the environment. This creates a condition where asphalt pavements must be resurfaced periodically to maintain their integrity as pavements. Porous asphalt pavements are not easily resurfaced because of the liquid asphalt emulsion used to bond the old and new pavements together. Liquid asphalt plugs-up the matrix of the pavement, and defeats the concept of permeability. Pervious concrete pavements do not need to be resurfaced. In addition, pervious concrete is a rigid-pavement, and does not deform under traffic loading as would flexible pavements, or precast-paver units.
-
How much does it cost? Pervious pavements tend to cost more per square yard than non-permeable pavements. One reason is that pervious pavements are generally designed with a thicker cross-section (more material). Pervious pavements generally take longer to construct than other pavements (more labor). Then there is also the cost of the materials, which are generally higher. However, pervious pavement costs are generally offset by the duty they perform. Pervious pavements should be designed into the project when their function will reduce, or eliminate, the need for other more expensive systems (such as storm-drains, inlets, storm-sewer pipes, stormwater ponds or underground vaults). Pervious pavements are also recommended by the U.S. Green Building Council (USGBC) as a part of their approach to stormwater control and re-use. See the section on this web site on LEED. (See also the new EPA - Green Infrastructure, and the NIBS - Federal Green Construction Guide for Specifiers.)
The first 0.5 inch of rainfall, is generally defined as the "first flush", and should be stored and/or treated on site. Treatment of the first flush is through a combination of actions. (See EPA definition: Stormwater first flush pollution.)
Soil type should also be considered when choosing a stormwater storage/treatment design. Soils with high percolation rates (above 0.5-inches per hour) are generally considered as suitable for infiltration, aquifer-recharge systems. If soils do not have a high percolation rate then timed-release of the stormwater may offer the best option. Karst topography may also restrict the use of below-ground infiltration systems. However, the pervious concrete dual-use system is a surface system that matches pre-construction site conditions. As a result, it is often permitted where other infiltration systems could not be considered. It is up to the Engineer, or Local Stormwater Managers, to determine if the dual-use system is permitable in their jurisdiction.
"combine the elements of a parking lot and
on-site stormwater storage/treatment into a single unit."
According to the EPA, in order to deal effectively with the "first-flush" of rainfall (stormwater), the rainfall must be contained, and treated, on-site. This means a system (BMP) must be chosen (that is site-specific) that best meets the requirements. There are many options available, including open ponds, and underground storage systems. However, these systems are cost prohibitive, and have major drawbacks.
Asphalt Pavements are not part of the solution - they are part of the problem.
The best option is to "combine" the elements of the on-site stormwater storage/treatment pond, and the parking surface, into a single unit. The design starts by expanding the on-site pond (shallow, flat, infiltration-basin) to include the entire parking area. The parking surface is a permeable, or pervious, rigid-pavement, installed inside the pond, and placed over a layer of clean gravel. The clean gravel gives structural support for the pavement, in addition to storing the stormwater within the void-space of the gravel (about one-third the total volume of the gravel). The "footprint" of the pavement (parking lot) becomes the same as the stormwater pond, thereby offering much better infiltration rates and pollution removal - in addition to reducing development costs by reducing land-use requirements (for additional ponds), and conventional stormwater infrastructure. This design concept can also be viewed as Parking in the Pond.
In the Dual-Use System, rainfall that lands on the pavement is already considered to be in the pond, and does not require an additional pond for on-site storage. The pavement also acts as the pretreatment structure to reduce trash-loading on the storage system. Trash, sometimes referred to as Total Maximum Daily Load (TMDL), stays on top of the pavement, and can be easily removed by vacuum-sweeping (truck-mounted street-sweepers).
Because of the large area of the infiltration basin (the same size, or larger than, the parking area), the depth of the gravel layer can be reduced. This allows for installation in areas where high water tables would not allow other systems. Engineers should design a minimum of 2 to 4-feet (if possible) between the bottom of the infiltration basin, and the water table (or bedrock). This is easily achieved with the dual-use system. The total depth of pavement, and the on-site storage/treatment system is typically only one-foot. As a consequence, there is also less "impact" on the site because the ground is not disturbed in order to place other stormwater infrastructures. The dual-use system is considered a low-impact system for those developers looking for low-impact components for their projects.
As an option, where the site permeability is low, the same design can be used as a settling-pond much the same as open retention ponds (wet-pond). By changing the filter-fabric, to a layer of impermeable material, (directly below the layer of clean gravel), the system becomes a "holding-pond". The gravel-layer also acts to keep turbulence at a minimum in order for pollutants to settle. The impermeable layer can be a heavy-duty layer of plastic sheeting. In this design, proper out-flow, controlled-discharge, pipes would be required to allow the accumulated water to discharge "downstream". The water is detained over the required drawdown time between storm events (typically 24-72 hours). This system allows for dissolved pollutants to settle-out of the water before it is discharged. Both the dry-system, and the wet-system, meet, or exceed, the NPDES stormwater permitting requirements.
Observation wells should also be installed in the system to allow for a visual inspection of the depth of water in the system. An observation well is typically a capped perforated pipe inserted vertically in the system in an outlying location. If the system is flat, any location will give a true reading of the depth of water in the system at any time. The well should be checked periodically to determine if the system is functioning within the design specifications.
The Dual-Use system overcomes the drawbacks of the open ponds, and the construction costs are considerably lower than most prefabricated underground systems. The dual-use system is also more environmentally friendly, safer and offers a much wider range of storage, treatment and maintenance options than do other on-site systems. (See the April,2007 - EPA - Green Infrastructure - Statement of Intent.) See also, the EPA Web Site on Porous Pavement.
Pervious concrete offers one of the most cost-effective and environmentally friendly solutions available as a permeable pavement. In the dual-use system, six-inches of pervious concrete placed over a six-inch layer of clean gravel has proven to be one of the most innovative, yet simple, solutions available to developers today. Pervious concrete also offers the benefits of a "rigid-pavement" design, which overcome the instabilities of other permeable pavement systems such as precast pavers or asphalt systems. Pervious concrete is the only pavement material available that meets the rigid-pavement requirements of the dual-use system. Most other pavement systems require a dense (impermeable) base to support the pavement because they are not a "rigid" surface. This defeats the purpose of having a permeable pavement. Properly installed, pervious concrete pavements, also offer the smoothness requirements, and horizontal surface-profile, to meet with the Americans with Disabilities Act (ADA) approval.
Pervious concrete is a mixture of portland cement, coarse aggregates (stone), water and admixtures. Pervious concrete contains little, or no sand, and is sometimes referred to as a “no-fines” concrete. (See the General Information page.) The portland cement and water forms a paste that binds the coarse aggregates together. Only enough portland cement and water is added to the mix to glue the aggregate together at the points of contact, but not enough to fill all the space between the aggregates. A typical pervious concrete mix will contain about 15-25% void space within the concrete sample. Many of the void spaces within the mix will be interconnected, forming channels that will allow water and air to pass freely through the mix.
Pervious concrete is an excellent material to create rigid permeable pavements for parking lots. As a rigid concrete pavement, it has the structural capacity to withstand the traffic loading of automobiles and light trucks most often found in parking lots. The permeability of pervious concrete pavements often exceeds 200-inches per hour (perk rate). (See the new NRMCA Video.) Most rainfall events will not exceed 3-inches per hour. The inherent over-design of the system allows for a large degradation of pavement permeability over time before the perk-rate falls below system requirements. (See the NIBS - Federal Green Construction Guide.)
Many Cities, Counties and States have adopted codes and regulations to deal with stormwater, and property development. In order to comply with many stormwater codes, stormwater must be stored on-site for 24-72 hours. This is the time considered to be optimal for vertical infiltration, or for most pollutants to settle from stormwater when confined to a specific area. In the Dual-Use concept, the stormwater is stored in the layer of clean gravel (infiltration basin) just below the pervious concrete pavement. In addition, a concrete ribbon-curb may also be constructed around the entire parking area to "contain" the stormwater within the dual-use system. However, the ribbon-curb is optional if the soils surrounding the parking area would act to contain the stormwater to the system. Other types of impermeable barriers may also be used to confine the stormwater to the system. It is up to the Engineer to define the outlines of the Dual-Use system, and which type of edge-barriers would be appropriate considering adjacent systems. (See the NIBS - Federal Green Construction Guide and the New EPA - Green Infrastructure - Statement of Intent.)
The layer of gravel gives structural support for the (rigid) pavement, and typically has enough void space between individual stones to effectively create a “storage” volume. Six-inches of clean, single-grade gravel, or crushed stone, will typically contain about two-inches of void space. In an area the size of a parking lot, there is enough storage-volume generated, within the layer of gravel, to exceed the EPA requirements for stormwater treatment. In a one-acre parking lot, within the six-inch layer of gravel, the storage volume generated is approximately 6500 cubic feet (allowing 30% void space within the gravel). The first half-inch of rainfall (first-flush), in the same area, would generate only about 1800 cubic feet of water.
In some areas, allowance may also be given for storage-space within the pervious concrete pavement (usually 5-20% of the volume), and above the pavement (typically 0.5 feet multiplied by the square-feet area of the parking lot). However, above -the-pavement storage should only be considered if conditions exist that allow for rapid exfiltration of the water - such as, a high perk rate in the underlying soils. No Owner is going to want water ponding in their parking lot for any great length of time. Also, a 6-inch high curb must be constructed around the parking area to "contain" the stormwater above the pavement. These storage volumes are generally only considered in multi-year storm calculations. Note: A six-inch high "riser" must also be constructed at the entrance of the parking lot if the volume above the pavement is to be considered as a part of the storage area.
Additionally, stormwater storage within, or above the pavement, should not be considered in areas susceptible to heavy freeze-thaw conditions. (If standing-water freezes in a fully saturated porous/pervious pavement, then damage may result to the pavement due to ice-expansion.) Water should be allowed to drain into the gravel-layer below the pavement. The "depth" of the gravel-layer becomes an Engineering decision based on the frost-line level for the specific area. (Additional air-space, in the layer of gravel, should be provided for ice-expansion during freezing conditions.)
Additional elements of design can be incorporated into the dual-use system by the use of controlled outflow pipes, exfiltration pipes and other control devices to handle peak-flow rates. These devices should be considered when the dual-use system is designed as a "settling-pond", or wet-detention area, instead of a detention/infiltration system.
"In order to design effective stormwater storage areas,
the infiltration basin bottom should be absolutely flat - no slope."
In order to design an effective stormwater "storage" area the bottom of the layer of gravel should be absolutely flat - no slope. If the bottom is sloped the water simply flows to the lowest point and "ponds" there. This would reduce the effectiveness of the overall design. The gravel-layer should have an even infiltration across the entire area, not a concentration in just one section. If the site is severely sloped, then different areas of the pavements could be terraced in flat "cells" with a sloped connecting ramp - much the same as a parking garage design. The top of pavement can be sloped, if required, or match the flatness of the gravel layer below.
Emergency-inlets, or gravel-filled inlet strips, can be incorporated into the pavement design, (between parking areas), to allow stormwater ingress to the gravel base in case of complete failure of the pavement to allow water to pass through it. Parking-bumpers should be installed, instead of curbs, within the parking lot area. However, curbs can be used to surround the entire dual-use system if required for multi-year storm storage.
A layer of non-woven filter fabric, should be placed directly beneath the layer of gravel. This helps to keep the soils, below the gravel layer, from migrating into the voids within the volume of gravel. (See sections above.)
Specifier's Note: In the design of pervious concrete pavements, where stormwater-storage is "not" a consideration, the pavements "can" be sloped (such as around trees). However, water that passes through the pervious concrete pavement, and is not immediately absorbed into the soil, will flow downhill underneath the pavement, usually carrying the base material with it. This is also why precast concrete storm-drains should not be located within a sloped pavement area. Water would flow to the drain, under the pavement, but would not be able to flow up-and-over the lip, and into the drain. If pervious concrete pavements are sloped, the drains should be located at the sides of the pavement, and be modified to accept water from below the pavement. Filter fabrics should also be placed directly below the pavement to restrict the movement of fines in the base materials.
Runoff Coefficients - "C-Factors"
In some areas of the U.S., another element in the design for stormwater management of pavements, is the consideration of, "how much water is going to run off". The quantity of water-runoff, as it pertains to specific materials, is typically referred to as the Runoff Coefficient, or C-Factor. This factor, or number, is used to calculate the volume of storage required for most developed properties. Pervious concrete pavements typically have a c-factor assigned to them by local Code Writers and Specifiers. That value usually ranges from 0-100%, dependent on how the local authority views the material, and how it is used. However, if pervious concrete is used as a pavement in the Dual-Use concept, then there is no runoff. All of the stormwater that lands on the pavement, passes through the pavement into the gravel-base below. (See sections above.) All of the stormwater remains in the infiltration basin (on-site pond), and no additional storage systems are required. (See the NIBS - Federal Green Construction Guide.)
The dual-use system is an infiltration system and requires regular maintenance to keep it functioning properly. Even though the system is one of the best BMPs at removing pollutants from stormwater, it is also one of the easiest to malfunction because of the accumulation of pollution on the pavement. The Dual-Use system is designed to overcome many of the drawbacks of other (underground) infiltration systems, but the pavement should receive frequent cleaning. Most of the trash and sediment that would clog other systems is deposited on the surface and is easily removed. (See the "Executive Summaries" for research on the maintenance of pervious concrete pavements produced by the RMC Research Foundation and the Stormwater Academy at the University of Central Florida.)
All pervious concrete pavement projects should include a maintenance-schedule and commissioning-program in the design and project specifications.
Keeping the pavement clean to maximize the effectiveness of the system becomes the owner’s responsibility. Whole-Building Commissioning is suggested as an integral part of the Design and Construction of the project. See the NIBS Whole Building Design Guide Building Commissioning. Whole-Building Commissioning is an extension of the Building Commissioning process to also include the continued design function of the pavement/stormwater system. Commissioning is a process that should be incorporated during the design phase of the project, and last throughout the life of the project.
The owner should also check installed observation-well(s) frequently after heavy rains, or have the pavement checked periodically to insure the porosity of the pavement does not fall below design requirements – usually 1-5 inches per hour perk-rate. (New pavements will typically have over 200-inches per hour perk rate.) Many owners may want to incorporate hard-vacuum cleaning systems to clean their parking lots. (Vacuum/Sweepers are not recommended.) If pressure washers are used, the back spray should be vacuumed-up to keep the residue from settling into other areas. (See the NIBS - Federal Green Construction Guide and the EPA Web Site on Porous Pavement.)
If specific areas of the pavement become clogged to the point that the perk rate is below the design specification (typically 1-5 inches per hour), then some sections of the pavement may need to be replaced. However, replacement of the entire pavement is generally not required. Only a "qualified" Pervious-Concrete Contractor should be used to replace any specified section. See the section on Contractor Certification to get a view of how a Contractor becomes qualified.
Many northern states, such as Missouri, Illinois, Indiana and Ohio have worked with Magruder Construction to have demonstration areas placed to evaluate the freeze-thaw effects on the pervious concrete Dual-Use systems. The system works equally well in freeze-thaw areas of the Country as they do in the more southern states. The stormwater is stored below the pavement, not in, or on top of, the pavement. There is typically enough air-space in the layer of gravel, because of exfiltration, to allow for ice expansion if the system goes through a hard freeze. Additional information on "Freeze-Thaw" can be obtained from the National Ready mixed Concrete Association (NRMCA), and the Iowa State University Study.
One of the primary reasons for considering the use of the Dual-Use system is the reduced cost of the system when compared to other pavements, and their associated stormwater systems, such as open ponds, or precast underground stormwater vaults or infiltration systems. The cost of open ponds, as a stormwater containment and treatment system, are prohibitive (considering the cost of the land), and are often considered a dangerous element in a neighborhood. The cost of precast "underground" vaults, and other underground stormwater piping or infiltration systems are also cost prohibitive, and do not function as well as the Dual-Use system.
Site Development costs, using the Dual-Use System, are generally reduced to less than half of the costs of asphalt pavements and associated stormwater infrastructures and retention-pond (land costs) for commercial developments.
Cost comparisons should not be considered on a "square-foot" basis of the cost of the pavement elements alone. The pavements are only one part of the overall costs related to each site's specific stormwater maintenance requirements. It has been demonstrated, that in most cases, the Dual-Use system is much less expensive, as a pavement and stormwater management system, than any of the other systems available. It is also more economical to maintain, creates a safer environment and is more environmentally friendly than the other systems. For a bid on any specific project, or just to get an idea of overall costs of the dual-use system, contact Don Wade, Program Manager, or Bill Lynn, Estimator, with Magruder Construction.
Items that will affect the cost, and are considered in any estimate, are: dates relating to the start and finish of the pavement construction; local labor rates (union or open-shop); local cost of materials at the time of construction; number of mobilizations; size and location of the project; anticipated weather conditions at the time of construction; out-of-town expenses for crews and the general scope of work (dictated by the plans and specifications of the project). All of these factors will affect the pricing of each project, and are required information for producing any construction-cost estimate.
A separate section within this Web site has been set up to discuss specifications, sections and pavement details as would be required to properly construct pervious concrete pavements and dual-use systems. Most locations in the U.S. have unique design criteria, and specifications should be written incorporating site-specific details. Please review the "Details and Specifications" page for this information. (The details for the design and construction of the pervious concrete Dual-Use system has been derived from the NIBS - Federal Green Construction Guide for Specifiers and the EPA Web Site on Porous Pavement.
Typically, an Engineer will try to get more than one "qualified" Contractor to bid on any specific project. However, not many concrete contractors are familiar with the properties, and unique placement requirements, of pervious concrete pavements, or the dual-use system. It is in the best interest of everyone that only NRMCA Certified Pervious Concrete Craftsmen be in charge of all construction of pervious concrete pavements. Most projects will require decisions to be made that can only be done by someone with enough experience to qualify as a Craftsman. (See the Contractor's Page to learn how the NRMCA Certification process works.)
The Engineer may want to contact Magruder Construction for help in a negotiated-contract arrangement in projects involving the use of the dual-use system. Magruder Construction is available as a qualified NRMCA Certified Contractor, and can also help Developers and Engineers in the design phases of the project. Contact Don Wade, Program Manager and NRMCA Certified Craftsman.
As an added bonus, the pervious concrete dual-use system offers a “cooler-pavement' choice. The evaporation of water from the pavement structure acts to cool the pavement to temperatures considerably less than other solid impervious pavements. Color can also be added to pervious concrete to create more eye appeal. Pervious concrete pavements are rigid pavements, and are also smooth enough to meet requirements by the American’s with Disabilities Act (ADA), and do not wear out or deform under traffic loading as some other permeable precast-unit pavements. With the proper design and application, the dual-use system can offer the Developer multiple credits toward LEED Certification.