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October 2012
PERVIOUS CONCRETE PAVEMENT
This document serves as an introduction to the design considerations for Pervious Concrete
Pavement when it is part of a stormwater management plan.
DESIGNER NOTES:
The designer should consider the following when designing a pervious concrete pavement
system:
1. Pervious Concrete Pavement may be used to provide water quality volume (WQv)
provided it is designed and constructed in accordance with the March 16, 2012 Stand
Alone Water Quality BMP policy change letter (Insert Link Here) 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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
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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.
7. 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.
8. 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.
9. 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.
10. A minimum of 2 feet vertical clearance should be provided between the bottom of the
storage bed and seasonally high water table.
11. Placing Pervious Concrete Pavement over areas of recent fill or compacted fill is not
optimal for infiltration.
12. 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.
13. Typical porosities range from 12-25% in the pervious concrete, and 40% in the open
graded gravel storage bed portion.
14. 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
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overflow apparatus, if any, should discharge only when the storage volume is
exceeded.
15. 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.
16. 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.
17. 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.
18. The design of the finished grade of the pavement surface shall take into consideration
the Americans with Disabilities Act (ADA) and local code requirements.
19. Pervious Concrete Pavement shall be designed by a qualified Engineer to handle
projected traffic loading.
20. 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”.
21. 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.
22. 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
23. 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.
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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)
c. Aggregate
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:
Material Proportions
(lb./yd3)
Cementious Materials 575 to 625
Aggregate 2000 to 2500
Water cement ratio (by mass) shall not to exceed 0.40
Aggregate Cement ratio (by mass) 4 to 4.5:1
Fine Coarse Aggregate ratio (by mass) 0 to 1:1
PLAN NOTES:
The following notes shall be included on plans, details, and specifications for pervious concrete
pavement designs proposed for MSD plan approval:
1. 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.
2. 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.
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3. Prior to obtaining a construction permit from MSD to construct Pervious Concrete
Pavement for a given project, the Engineer providing As-Built Certification shall:
a. 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
b. Verify how the contractor will meet at least one of the following:
a. 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
b. At least three NRMCA Certified Pervious Concrete Installers will be on
site installing the concrete.
or
c. At least 2/3 of the placing crew will be NRMCA certified Pervious
Concrete Technicians.
4. 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.
5. 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.
6. 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.
7. 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.
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8. 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.
9. 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.
10. Stone should be clean and meeting ASTM C 33 standards.
11. 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.
12. 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.
13. Pervious Concrete Mix Notes
a. 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.
b. Each load of concrete shall be visually inspected for consistency and
aggregate coating.
14. Prior to placement, the subbase preparation and forms should be double-checked. Any
irregularities, rutting, or misalignment should be corrected.
15. Placement should be continuous and spreading & strikeoff should be rapid.
Consolidation should be completed within 15 minutes of placement.
16. 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.
17. Curing should be started as soon as practical (within 20 minutes is optimal) after placing,
compacting, and jointing.
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18. 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.
19. 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.
20. Once installed, the area shall be quarantined from all traffic until site is stable to prevent
mud from being deposited.
21. 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.
22. 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.
23. 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.
24. 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.
25. At completion of the project, prior to final dedication, an as-built certification, signed and
sealed by a Missouri Professional Engineer shall be provided.
CONCRETE PRODUCER’S PREQUALIFICATION:
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:
MSD BMP Committee
Metropolitan St. Louis Sewer District
2350 Market Street
St. Louis, MO 63103-2555
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.
MATERIAL CERTIFICATION AND QUALITY CONTROL:
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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.
CONTRACTOR PREQUALIFICATION:
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:
1. 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.
2. The contractor will meet at least one of the following:
a. 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
b. At least three NRMCA certified Pervious Concrete Installers will be on site
installing the concrete.
or
c. At least 2/3 of the placing crew will be NRMCA certified Pervious Concrete
Technicians.
3. A database of Certified Contractors and Technicians may be found on-line at:
http://www.nrmca.org/Education/Certifications/Pervious_DB_Disclaimer.htm
AS-BUILT CERTIFICATION
At completion of the project, prior to final dedication, an as-built certification, signed and sealed
by a Missouri Professional Engineer shall be provided certifying:
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1. The Pervious Concrete Pavement was built in accordance with the details,
dimensions, and materials as approved by MSD for this project.
2. The Pervious Concrete Pavement was installed by a qualified contractor, and has
satisfied all applicable quality control and performance tests.
3. The Pervious Concrete Pavement installation was witnessed periodically by the
certifying engineer or a representative under their direct supervision.
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PERVIOUS PAVEMENT AS-BUILT CERTIFICATION
DATE:
To: Metropolitan St. Louis Sewer District
Department of Engineering
Attn: Keith Milson
From: (Consultant Engineer’s Name)
Title:
Consulting Engineer Company Name & Address
Re: Engineering/Construction Certification for the following project:
MSD Project Name:
MSD P#:
Project Address:
For the project’s pervious pavement practice, this correspondence shall serve as a certification of
the following:
1. The Pervious Pavement was built in accordance with the details, dimensions, and
materials as approved by MSD for this project.
2. The Pervious Pavement was installed by a qualified contractor, and has satisfied
all applicable quality control and performance tests.
3. The Pervious Pavement installation was witnessed periodically by the certifying
engineer or a representative under their direct supervision.
Printed Name:
Discipline:
License No:
(P.E. seal with signature and date)