Recommended Specifications for

Dual-Use, Infiltration Basin and Pervious Concrete Pavements

Forward

This specification is provided as a guideline only. Specific projects may have conditions that would require modifications to this document. These specifications and guidelines are derived from other on-line documents to include: The new EPA - Green Infrastructure  "Statement of Intent" and the NIBS - Federal Green Construction Guide for Specifiers and the EPA Web Site "Porous Pavement".

The dual-use system is unique in that it utilizes a layer of clean-gravel/crushed-stone for on-site stormwater storage and treatment, in conjunction with a rigid permeable pavement to provide a dual-use parking lot. Pervious concrete is recommended for this system because it is a rigid pavement, and typically has a perk rate of more than 200-inches per hour.

Developers and Engineers are encouraged to use the (non-proprietary) dual-use system, in areas where these items need to be addressed:

•         High pollution removal requirements

•         Limited land space

•         Stormwater infiltration & aquifer recharge

•         Depth of treatment system above water table

•         Low-Impact Development (LID) or Sustainable/Green-Building Development

•         LEED credits

•         Site safety & environmental concerns

•         Cost of development

•         Non-proprietary system

This section shows the typical arrangement of the pervious concrete pavement in place over a clean layer of gravel or crushed-stone (infiltration-basin). In general, rainfall flows very quickly through the pavement, and is held temporarily within the layer of clean gravel until it has had time to soak into the native soil.

Part 1 – General

1.01  Scope of Work:

        A.    The work to be completed under this contract includes the furnishing of all labor, materials and equipment necessary for the construction of the dual-use system in accordance with the plans and these specifications.

1.02  References:

        A.    Environmental Protection Agency (EPA)

                1.    Green Infrastructure - Statement of Intent

        B.     National Institute of Building Sciences (NIBS)

                1.    Federal Green Construction Guide for Specifiers

        C.   American Concrete Institute (ACI)

                1.    ACI 305  "Hot Weather Concreting"

                2.    ACI 306  "Cold Weather Concreting"

                3.     ACI Flatwork Finisher Certification Program

                4.     ACI Field Technician Certification Program

        D.    American Society for Testing and Materials

                1.    ASTM C33  "Specification for Concrete Aggregates"

                2.    ASTM C94  "Specification for Ready-Mixed Concrete"

                3.    ASTM C150  "Specification for Portland Cement"

                4.    ASTM C494  "Specification for Chemical Admixtures for Concrete"

                5.    ASTM C595  "Specification for Blended Hydraulic Cements"

                6.    ASTM D3385  "Test Method for Infiltration Rate of Soils Using Double-Ring Infiltrometer"

        E.    National Ready Mixed Concrete Association

                1.     Pervious Concrete Contractor Certification Manual

1.03 Quality Assurance:

        A.    Prospective Contractors shall attend a pre-bid meeting where the scope of work will be discussed. The Owner's Representative should make the decision if the material supplier(s), and additional sub-contractors, should also be present at the meeting(s).

        B.    Prior to the award of contract, the proposed contractor must submit evidence of having the appropriate tools, and experience, to accomplish the work. Experience will be based on at least one person, in charge of the crew, being NRMCA Certified as a Pervious Concrete "Craftsman", plus two crew members being Certified by the NRMCA as Pervious Concrete "Technicians". This requirement can be waived if the Contractor can produce evidence of having at least three persons on the crew being NRMCA Certified as "Technicians", and, in addition, the Contractor can show evidence of having completed at least five successful pervious concrete pavement projects totaling more than 250,000 square feet.

1.04 Special Equipment:

        A.    Contractor must show evidence of having the specialized equipment required for the installation of Pervious Concrete Pavements. Pervious Concrete is finished and jointed using three classes of specialized rollers. These rollers consists of form-to-form, steel-pipe rollers which are 8-inches to 12-inches in diameter, and smaller cross-rollers, with tapered edges. A special flanged-roller is used to place control joints in the pervious concrete before the pavement is covered to moist-cure.

        B.     Larger projects may require the use of vibratory screeds. These screeds must provide an adjustment for the frequency of vibration.

        C.    Some projects may require the use of a power-sprayer with a "fogging-nozzle" attachment.

1.05 Submittals: All submittals shall be approved prior to construction.

        A.    Plans shall be submitted to the Owner's Representative, by the Contractor, indicating:

•       Proposed Start Date, sequence of construction, and time of completion, for the scope of work.

•       Proposed locations for all construction-joints, and control joints, in the pavement.

•       Sections and Details showing depths, and types of materials, for all locations in the scope of work. (See the PC-2 Section above.)

        B.    A one-square-foot section of the proposed filter fabric shall be submitted to the Owner's Representative. Information regarding the properties of the material, manufacturer, suggested method of placement and guarantees shall also be submitted with the fabric.

        C.    A one-quarter-cubic-foot sample of the proposed washed, crushed-stone/gravel-fill for the infiltration basin (pavement base) shall be submitted to the Owner's Representative.

        D.    A Mix-Design, showing the weights of all materials, for the proposed pervious concrete pavement shall be submitted to the Owner's Representative. It shall be the Contractor's responsibility to become familiar with the properties, and workability, of the proposed mix-design.

        E.    Evidence of qualifications of the Contractor, as per the "Quality Assurance" section shall be submitted to the Owner's Representative.

1.06 Test Panels: If the Contractor does not meet the primary "Quality Assurance" of having a NRMCA Certified Pervious Concrete Craftsman in charge of the pavement installation, then a test panel shall be constructed by the Contractor, and approved by the Owner's Representative. The test panel then becomes the "standard" by which the Contractor's work is judged for completion of work and payment schedules.

        A.     The test panel shall be constructed in accordance with the plans and specifications, and shall be a minimum of 225 square-feet. Construction of the test panel shall be accomplished by the same crew, equipment and materials as submitted for approval. The depth of all materials shall be the same as shown on the plans.

        B.     The cost of constructing, and removing (if necessary), the test panel shall be included as a separate line-item in the proposal and contract.

Part 2 - Materials

2.01 Filter Fabric: The filter fabric shall be a non-woven geotextile fabric suitable for the application, and installed as per the manufacturer's directions.

2.02 Infiltration Basin Gravel-Fill: The Infiltration Basin shall be filled with clean (washed) gravel or crushed stone. The stone material shall be a single-size, and have a diameter of from 3/4-inch to 2-inches, and shall comply with ASTM C33. The total depth of the gravel-fill shall be indicated on the plans. (See the Section above.)

2.03 Pervious Concrete: The permeable pavement section of the dual-use system shall consist of portland-cement based pervious concrete. pervious concrete has no ACI or ASTM Specifications. It is therefore recommended that the guidelines for Ready-Mixed Concrete, ASTM C94, be used as a general guideline for the manufacturing and delivery of the pervious concrete. Each locality will generally create a unique mix design that will contain locally available materials. It is the responsibility of the Contractor to work with the local Ready-Mix suppliers to finalize a mix-design that will be acceptable for each project. If the mix-design is new to the local supplier, then at least three trial-batches shall be made before the decision is made to use that particular mix design. Both the Contractor, and the Supplier, must agree on any particular mix design before it is submitted to the Owner's Representative.

Part 3 - Execution

3.01 Subgrade: The subgrade is defined as the native soil, or finished grade, of any cut-and-fill operation that may be required to bring the soil elevation to proper grade. The top of subgrade is also the bottom of the clean-gravel. Tests for the permeability, or infiltration rates, of the native soil shall be conducted at the owners expense, and be completed before the final stormwater design is completed. The final grade of the top of subgrade shall be flat (no slope), and at the proper elevation to allow for the thickness of the layer of gravel and the pervious concrete pavement (typically one-foot). (See the Section above.) Final compaction of the subgrade shall take into effect the type of soil and permeability requirements, and requirements for pavement support. Typically, compaction should be uniform, and not greater than 95%

3.02 Filter Fabric: The filter fabric shall be placed on top of the final grade by the Contractor following the Manufacturer's directions.

3.03 Infiltration Basin Gravel-Fill: Generally, the placement of the gravel should be done to minimize destruction of the filter fabric, and over-compaction of the subgrade. Compaction of the gravel is unnecessary.

3.04 Pervious Concrete: The Pervious Concrete, including any formwork requirements, placement, jointing and curing, shall be done in accordance with the NRMCA "Pervious Concrete Contractor Certification" guidelines. It is the responsibility of the Contractor to become familiar with the NRMCA document to gain the knowledge required to properly place and finish pervious concrete pavements. The inclusion of the requirements, as set forth in the NRMCA document, becomes an integral part of these specifications.

3.05 Testing: The testing requirements for pervious concrete are generally for permeability and durability. Testing of the fresh pervious concrete is a visual test. The Contractor must have the basic knowledge of what constitutes a proper mix by a visual inspection when the material arrives on the jobsite. Traditional tests for fresh concrete, such as slump and air content, and making cylinders & beams for strength tests are not applicable for pervious concrete. Testing for long term permeability and durability are the Owner's responsibility.

3.06 Maintenance: Maintenance of the dual-use system is the Owner's responsibility. The pervious concrete pavement should be checked periodically for buildup of trash and debris. Trash and debris should be removed from the pavement by hard-vacuum systems as required. At least once every year, the pavement should be pressure-washed with the residue being removed by wet-vacuuming (similar to steam-cleaning a carpet).

End of Specifications

This specification is intended solely for the use by professional personnel who are competent to evaluate the significance and limitations of the information provided, and who will accept responsibility for the application of this information. Magruder Construction disclaims any responsibility and liability for the application of any of this information beyond our control.