- Designer Notes
- Plan Notes
- Manufacturer's Prequalification
- Material Certification
- Contractor Prequalification
- As-Built Certification
MSD has developed details illustrating typical sections for pervious concrete pavement.
The designer should consider the following when designing a pervious concrete pavement system:
- Pervious Concrete Pavement may be used to provide water quality volume (WQv) provided it is designed and constructed in accordance with Permeable Pavement Performance Criteria or is used in conjunction with a properly designed infiltration basin/trench, sand filter, or other approved BMP per the 2000 Maryland Stormwater Design Manual. The supplemental BMP shall be located downstream from the pervious concrete system, not underneath it.
- Consideration should be given to the type of traffic loads that the pervious pavement will be required to endure. Refer to ACI 330R for parking lots and ACI 325.12R for streets and roads. An engineer with expertise in pavement design should provide input on this aspect early in the design phase.
- The design engineer shall reference ACI 522.1-08, the National Ready Mixed Concrete Association joint publication EB302.02, and MSD's Provisional Use Level approval letter, dated 10-1-2008, for additional guidelines.
- Pervious Concrete Pavement will not be allowed on sites whose land use or activity generates higher concentrations of hydrocarbons, trace metals or toxicants than are found in typical stormwater runoff. Examples of such "hotspots" are listed in table 2.6 in the 2000 Maryland Stormwater Design Manual.
- A Perforated PVC underdrain system will be required. The horizontal and vertical locations shall be determined by the design engineer, depicted on the drawings, and be in general accordance with the MSD Pervious Concrete Pavement detail.
- When Pervious Concrete is used in conjunction with stormwater runoff volume reduction practices, MSD recommends the suitability and infiltration rates of the underlying soils shall be confirmed by geotechnical evaluation prior to final design. Soil boring logs and a soil survey shall accompany all test results. Designers shall also consider the depth of the Pervious Concrete system in determining the applicability of the information. If infiltration testing is not conducted prior to design, then the underlying soils shall be assumed to have an infiltration rate of 0.05 in/hr ("default" subgrade saturated hydraulic conductivity). If use of a greater design rate is desired for the purpose of estimating volume reduction capabilities, at least one infiltration test shall be provided for each on site soil type where Pervious Concrete is proposed. In no case shall the frequency of testing be less than 1 per 5000 S.F. of Pervious Concrete. All infiltration test reports shall be submitted to MSD for review prior to final project approval.
- To provide an infiltration bed, the primary underdrain system may be perched or configured as internal water storage within the subbase rock. The perched height is dependent on the infiltration characteristics of the underlying subgrade and the desired storage. The underdrain system shall not be perched if the underlying soils are plastic or plastic soils that have been stabilized with lime. Design the open graded storage bed to completely drain within 12 to 72 hours.
- Provide an overflow system or additional aggregate storage depth to prevent water in the open graded storage bed from rising into the Pervious Concrete Pavement for the 2-yr, 24-hr storm event. Any emergency overflow pipes placed within the subbase should discharge only when the storage volume is exceeded. The horizontal and vertical location of all underdrains and overflow systems shall be determined by the design engineer and shown on the plans. Emergency overflow pipes and underdrain systems shall discharge to a storm water structure or daylight to a stabilized outfall.
- Observation wells should be provided in low areas within the Pervious Concrete Pavement system, and shall extend to the bottom of the aggregate storage bed. The wells shall consist of a six inch schedule 40 PVC pipe with cast iron frame and cover, as shown on the MSD Pervious Concrete detail. The number of wells required on an installation will vary on a site specific basis, and will be determined by the design engineer.
- A minimum of 2 feet vertical clearance should be provided between the bottom of the storage bed and seasonally high water table.
- Placing Pervious Concrete Pavement over areas of recent fill or compacted fill is not optimal for infiltration.
- A typical pavement section shall be shown on the plans. Designer should reference ACI 522.1-08 and the National Ready Mixed Concrete Association joint publication EB302.02.
- Typical porosities range from 12-25% in the pervious concrete, and 40% in the open graded gravel storage bed portion.
- The volume in the voids of the storage bed shall be considered the total water storage capacity. A void ratio not greater than 40 percent will be used to calculate storage volume. No storage volume will be allowed in the pervious concrete. The emergency overflow apparatus, if any, should discharge only when the storage volume is exceeded.
- Prepared subgrade soil should be separated from the porous subbase. The prepared subgrade soil shall be dry and, where needed, covered with MSD Type 4 filter fabric (such as Mirafi 140N or approved equal) on the vertical sides of the typical section. Separation of the prepared subgrade along the bottom of the section may be provided by MSD Type 4 filter fabric or a well graded filter layer at the discretion of the design engineer.
- Subgrade should be flat, and where topography requires, terracing of the subgrade is allowed. The volume of water stored behind each terrace will be considered part of the infiltration bed.
- Subgrade should normally be compacted to a minimum density of 90% to 95% of the theoretical density per AASHTO T 180. However, the designer should be aware that increasing the subgrade density decreases its infiltration capacity. Since soil conditions, grading requirements, and end user demands are site specific, this requirement shall be considered from a case by case standpoint. A geotechnical engineer shall provide input in balancing the infiltration and load bearing demands that the Pervious Concrete Pavement must satisfy.
- The design of the finished grade of the pavement surface shall take into consideration the Americans with Disabilities Act (ADA) and local code requirements.
- Pervious Concrete Pavement shall be designed by a qualified Engineer to handle projected traffic loading.
- Typical thicknesses for the pervious concrete range from 4" to 12", depending on the traffic load and other requirements. The nominal aggregate size should not exceed 1".
- The property owner must execute a Maintenance Agreement with MSD, and the entire Pervious Concrete Pavement area shall be platted in a Reserve Area for Stormwater Management.
- A permanent sign shall be posted warning that care should be taken during snow plowing; and prohibit the following: resurfacing, the use of sand abrasives for winter tire traction, and the use of power washers
- The design engineer is encouraged to coordinate with a MSD pre-qualified pervious concrete producer in determining the proper materials for the pervious concrete mix design.
The mix utilized on a project will be ultimately controlled by the pre-qualified supplier, design engineer's judgment, and project specific conditions. The following information outlines some "typicals" regarding Pervious Concrete, and is intended for informational use only:
a. Cementious Materials
i. Portland Cements (ASTM C150, ASTM C1157)
ii. Blended Cements (ASTM C595, C1157)
b. Supplementary Cementious Materials
i. Fly Ash and Pozzolans (ASTM C 618)
ii. Ground Granulated Blast Furnace Slag (ASTM C989)
i. Low fine aggregate content, narrow gradation for course aggregate
ii. Refer to ASTM D 448 and ASTM C33.
iii. Common Gradation from ASTM C33:
1. No. 67 (3/4" to No. 4)
2. No. 8 (3/8" to No.16)
3. No. 89 (3/8" to No. 50)
d. Typical Materials Proportions. This will vary, depending on the appropriate mix design for the site:
|Cementious Materials||575 to 625|
|Aggregate||2000 to 2500|
|Water cement ratio (by mass)||shall not to exceed 0.40|
|Aggregate Cement ration (by mass)||4 to 4.5:1|
|Fine Coarse Aggregate ratio (by mass)||0 to 1:1|
The following notes shall be included on plans, details, and specifications for pervious concrete pavement designs proposed for MSD plan approval:
- All pervious concrete construction shall meet the requirements of ACI 522.1-08, The National Ready Mixed Concrete Association joint publication EB302.02, and MSD's Standard Construction Specifications for Sewers and Drainage Facilities, 2009.
- The contractor shall verify that the concrete producer that will supply the pervious concrete for this project has been prequalified by MSD and possesses a Pervious Concrete Certification (NRMCA or approved equal). The name of the producer and their facility location shall be provided to the MSD Division Inspector prior to construction.
- Prior to obtaining a construction permit from MSD to construct Pervious Concrete Pavement for a given project, the Engineer providing As-Built Certification shall:
Verify the contractor's past history to demonstrate their applicable experience and training in installing Pervious Concrete Pavement. If the contractor has insufficient experience (less than three successful jobs), the contractor shall retain an experienced consultant (such as an engineer rated as an ACI Certified Craftsman) to monitor production, handling, and placement operations
Verify how the contractor will meet at least one of the following:
At least one National Ready Mix Concrete Association (NRMCA) Certified Pervious Concrete Craftsman will be on site overseeing each placement crew during all concrete placement, or
At least three NRMCA Certified Pervious Concrete Installers will be on site installing the concrete, or
At least 2/3 of the placing crew will be NRMCA certified Pervious Concrete Technicians.
- Inspection and testing services shall be provided by a testing laboratory under the direction of a full-time employee registered as a Professional Engineer in the State of Missouri. They shall have a minimum of five years of professional engineering experience in inspection and testing of concrete construction, and the technician shall at a minimum be ACI Field Testing Technician as well as NRMCA Pervious Concrete Certified or equal.
- The inspection and testing services provider, the engineer providing as-built certification, and the contractor shall establish a quality control and testing program to ensure that the Pervious Concrete Pavement is installed in accordance with the MSD approved plans and project specifications. ACI 522.1-08 Section 1.6 provides a recommended quality control and testing protocol.
- Test panels may be constructed on-site in an area for demolition after test approval, or in an area that may be left in place and included in the completed work.
- No product or material substitutions are permitted unless previously approved by the MSD plan review engineer or by the MSD field inspector assigned to the project. All substitutions shall be presented to MSD through the engineer responsible for the design of the Pervious Concrete Pavement system.
- The subgrade shall be constructed to ensure that the required pavement thickness is obtained in all locations. The contractor shall keep all construction traffic from the subgrade area to the maximum extent possible. Regrade the subgrade as required prior to sub base and product installation.
- Measures to provide for runoff diversion are required to protect the Pervious Concrete Pavement areas from adjacent site runoff during and after construction until the tributary site is deemed stable by the MSD inspector.
- Stone should be clean and meeting ASTM C 33 standards.
- MSD Type 4 filter fabric (Mirafi 140N or approved equal) should be installed on the sides of the aggregate storage bed to prevent sediment entry. When shown on the plans, the filter fabric may be installed between the subbase and the storage bed. The filter fabric shall not be installed between layers of aggregate.
- Subbase must be moist (without free standing water) prior to placement to prevent water from being removed from the lower portion of the pavement too soon.
- Pervious Concrete Mix Notes
- Pervious Concrete mixture should be discharged completely within one hour after initial mixing. The use of retarding chemical admixtures or hydration stabilizing admixtures may extend the discharge time to one and a half hours or more.
- Each load of concrete shall be visually inspected for consistency and aggregate coating.
- Prior to placement, the subbase preparation and forms should be double-checked. Any irregularities, rutting, or misalignment should be corrected.
- Placement should be continuous and spreading & strikeoff should be rapid. Consolidation should be completed within 15 minutes of placement.
- Joints shall be placed as specified, and may be placed at the same location along adjoining pavements. Saw cutting is possible as long as slurry is blown and/or power washed immediately after cutting. The contractor shall submit a joint detail plan to the Engineer providing as-built certification prior to construction.
- Curing should be started as soon as practical (within 20 minutes is optimal) after placing, compacting, and jointing.
- Curing is accomplished by fog misting with water and/or an appropriate cure, followed by 4-6 mil minimum poly sheeting anchored to prevent sheeting from blowing off or allowing air to billow under sheeting. The sheeting should remain for at least seven days.
- Plastic sheeting shall be secured with lumber, rebar, staking or other methods. Avoid the use of sand or dirt as this will clog the pavement.
- Once installed, the area shall be quarantined from all traffic until site is stable to prevent mud from being deposited.
- Do not open the pavement to traffic until it has cured for at least seven days and is accepted by Engineer providing as-built certification.
- Avoid using areas within the Pervious Concrete Pavement as construction staging zones or stockpile locations. This fosters the opportunity for fines from soils, mulch, equipment, etc. to migrate into the new pavement and clog it.
- Do not clean the pervious concrete pavement surface with high pressure hoses or abrasives. When cleaning is necessary, combination cleaning machines that combine a wet spray and vacuum process has been found to be effective.
- A permanent sign shall be posted warning that care should be taken during snow plowing; and prohibit the following: resurfacing, the use of sand abrasives for winter tire traction, and the use of power washers.
- At completion of the project, prior to final dedication, an as-built certification, signed and sealed by a Missouri Professional Engineer shall be provided.
Prior to supplying concrete to a site that proposes Pervious Concrete Pavement to meet MSD requirements, concrete producers shall first prequalify with MSD by providing proof of current Pervious Certification (NRMCA Certification or approved equal). This documentation shall indicate the effective duration of the certification, and be submitted to:
The duration of prequalification with the District is good for the duration of the producer's certification. Producers shall renew their prequalification with the District upon renewal of their Pervious Certification. The producer shall also notify the District, in writing, of any changes to their Pervious Certification status.
Inspection and testing services shall be provided by a testing laboratory under the direction of a full-time employee registered as a Professional Engineer in the State of Missouri. They shall have a minimum of five years of professional engineering experience in inspection and testing of concrete construction, and the technician shall at a minimum be ACI Field Testing Technician as well as NRMCA Pervious Concrete Certified or equal.
The contractor shall verify that the concrete producer that will supply the pervious concrete for this project has been prequalified by MSD and possesses a Pervious Concrete Certification (NRMCA or approved equal). The name of the producer and their facility location shall be provided to the MSD Division Inspector prior to construction.
Prior to obtaining a construction permit from MSD to construct pervious concrete pavement for a given project, the engineer providing as-built certification shall verify the following:
- The contractor's past history to demonstrate their experience and training in installing Pervious Concrete Pavement. If the contractor has insufficient experience (less than three successful jobs), the contractor shall retain an experienced consultant (such as an engineer rated as an ACI Certified Craftsman) to monitor production, handling, and placement operations.
- The contractor will meet at least one of the following:
- At least three NRMCA certified Pervious Concrete Installers will be on site installing the concrete, or
- At least 2/3 of the placing crew will be NRMCA certified Pervious Concrete Technicians.
At completion of the project, prior to final dedication, anas-built certification, signed and sealed by a Missouri Professional Engineer shall be provided certifying:
- The Pervious Concrete Pavement was built in accordance with the details, dimensions, and materials as approved by MSD for this project.
- The Pervious Concrete Pavement was installed by a qualified contractor, and has satisfied all applicable quality control and performance tests.
- The Pervious Concrete Pavement installation was witnessed periodically by the certifying engineer or a representative under their direct supervision.