Handbook for Pervious Concrete Certification in Greater Kansas City
This support material is part of the of the CPG Pervious Concrete Certification Program
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Table of Contents of Contents
Preface: The CPG Pervious Certification Program
1. Pervious Concrete: What’s it all about? (Overview) 2. Brief History Brief History of Pervious of Pervious Concrete 3. Design Elements for Pervious Concrete Hydrology, Drainage, Layout, Subgrade Soil, Subbase, Thickness, Jointing 4. Basic Mix Design Information for Pervious Concrete Aggregates, Cement & SCM’s, Water, Admixtures, Proportioning 5. Testing Pervious Concrete 6. Pervious Pavement Construction Equipment and Tools Test Panel Placement and Approval Pre‐Construction Meeting Excavation, Filter Fabric, Subgrade, Base, Jointing, Curing, Hot & Cold Weather Practices 7. Maintenance ®
8. LEED Credits 9. Decorative Pervious 10. Specifiers Guide for Pervious Concrete for Stormwater Mitigation in Greater Kansas City & Pervious Construction Checklist, Pre‐Construction Checklist 11. Websites & Resources
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Table of Contents of Contents
Preface: The CPG Pervious Certification Program
1. Pervious Concrete: What’s it all about? (Overview) 2. Brief History Brief History of Pervious of Pervious Concrete 3. Design Elements for Pervious Concrete Hydrology, Drainage, Layout, Subgrade Soil, Subbase, Thickness, Jointing 4. Basic Mix Design Information for Pervious Concrete Aggregates, Cement & SCM’s, Water, Admixtures, Proportioning 5. Testing Pervious Concrete 6. Pervious Pavement Construction Equipment and Tools Test Panel Placement and Approval Pre‐Construction Meeting Excavation, Filter Fabric, Subgrade, Base, Jointing, Curing, Hot & Cold Weather Practices 7. Maintenance ®
8. LEED Credits 9. Decorative Pervious 10. Specifiers Guide for Pervious Concrete for Stormwater Mitigation in Greater Kansas City & Pervious Construction Checklist, Pre‐Construction Checklist 11. Websites & Resources
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Preface CPG Pervious Certification Program 4 L evels CP C PG Per vious Con oncre crete te C er tifi tifica cation tion (Re (Requi quired for Cont Contrac ractors tors & Ready Ready Mi M ix Produ Produce cers, rs, optional optional and recommended for inspe inspectors, designe designers, storm stormwater enginee ngineers, architects, architects, civi civill engineers) Requirements: ents: L evel 1: C PG Per vious Concrete oncrete T echnician chnician
A) Pass the CPG Pervious Concrete Written Exam with a score of 80% or higher B) Complete plete the Performa Performance Eval Evalua uation tion usually done the same day as the written written exam, demonstrating onstrating subgrade subgrade prep, form form pl placement, the proper proper use of tools, tools, place placement procedure, prope properr joi jointi nting, ng, proper curing, curing, etc. C) Pass an individual Performance Evaluation on the individual’s 1 st job or test site, set up by the individual. D) Valid for 5 yea years af after ter receiving ving the the certi certifficati cation. on. E) Re-certification is required within 90 days after the expiration date listed on the wallet card/certification certificate. F) Starting Starting J anuary 1, 2012, 2012, re-certif re-certifiication appl appliications requir require e 2 hours hours of continuing continuing education tion credi credits ts on pervious rvi ous concrete concrete. These hours can belocal ocal, reg regional or nati nationa onal seminars, demo’s o’s or workshop workshops on pervious rvi ous concrete concrete.. I t is is up to theindividua ndivi dual to keep records records of these these continuing continuing educati ucation on hours hours to turn turn in with with the the recertification application. L evel 2: C PG Per vious C oncrete oncrete I nstaller nstaller
(Upgrade option for Contractors)
Requirements: ents: A) Have a current current A CI Flatwork Finishe Fi nisher Te Techni chnicia cian Certi Certifficate cate. B) Have acurrent current CPG CPG L evel 1 Pe Pervious rvious Concrete Concrete Technici Technicia an Certifi Certif icate cate.. C) Project Experience with successful pervious construction in a minimum of 3 projects, with a total area exceeding 10,000 sq. ft. L evel 3 CPG CP G Per vious C oncrete oncrete Cr aftsm aftsman
(Upgrade option for Contractors)
Requirements: ents: A) B) C) D)
Have a current current A CI Flatwork Finishe Finisher Technicia cian Certif Certificate cate Have acurrent current CPG CPG L evel vel 1 Pervious Pervious Concrete Concrete Technici Technicia an Certifi Certif icate cate Have a CPG CPG Le L evel vel 2 Concret Concrete e I nsta nstaller Certif Certificati cation. on. Docum Document work experience experienceconstructing constructing pervi rvious pavements exceeding ding 1,500 hours (not incl i ncludi uding ng the10,000 sq. sq. ft. f t. needed to qua qualify for for the Ins Insta talller)
L evel 4 CPG CP G A dvance dvanced Pervious Pervi ous Concr ete T eam C er tifi tifica cation tion
(Optiona (Optional for Cont Contrac ractor tor and and Ready Ready Mi M ix Te T eam) Well above and beyond traditi traditional onal concrete concrete,, successful pervi rvious concrete place placements require require a dedicated cated team with with an excellen xcell ent relationship relationship between the Ready Ready Mi M ixed Concrete Produce Producer and the Concrete oncrete Contractor. The T he Concrete Promotional Promotional Group Group has assembled bled an advanced mixture desi design gn and construction construction review review for for contractor/producer teams looking to advance their pervious concrete construction knowledge. Certification will encompass one producer, producer, one contractor, one pervi rvious concrete mixture, and one one place placement techni technique que. Upon completion of the process the producer will be provided with a performance and testing certification for the final mixture design. The contractor will be provided with certification of the in-place mixture properties and 3
performance. By completing the certification process a pervious concrete team will have documentation showing the unit weight, strength, and infiltration that will be achieved. Requirements: A) Have a current ACI Flatwork Finisher Technician Certificate B) Have acurrent CPG Level 1 Pervious Concrete Technician Certificate C) Complete theTeam Review Process outlined below: Outline of the Review Pr ocess:
The certification process involves an interactive ½day series of two test placements (at a location of the team’s selection). A. Starting mixture provided by producer. The mix is proprietary so it is kept confidential. Only the ready mix producer and Dr. J ohn Kevern will discuss these details. B. Contractor will place a 4 cy sample panel. Concrete will be held 45 minutes after batching to simulate field conditions. Inverse slump, ASTM C1688 unit weight, and timed discharge values will be recorded. C. The contractor, producer, and CPG representative will discuss consistency, workability, finishability, and discharge capacity. The mixture will then be modified to better meet the desired criteria. D. The contractor will then place a second 4 cy sample panel using the modified mixture. Inverse slump, ASTM C1688 unit weight, predicted unit weight, and timed discharge will be measured on the fresh concrete. Cylinders will be created for the compaction density curves for reporting voids, unit weight, permeability, 7 day compressive strength, and 28 day compressive strength for the selected mixture. E. The contractor and/or producer is responsible for obtaining at least (3) 4” diameter cores for hardened unit weight and permeability testing at UMKC. F. Field infiltration will be performed according to ASTM C1701 on at least five (5) locations. G. The performance and testing data will be used to create mixture certification documentation and individual field evaluation documentation. Deliverables: Deliverables will include a description and summary of the certification process including all testing data for reproduction and transmittal to any interested party.
All certified individuals and companies can be found listed on the CPG Website at www.concretepromotion.com.
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Chapter 1
Pervious Concrete: What’s it all about? What is Pervious Concrete? Pervious Concrete is a specialty concrete used to allow water to intentionally pass through the surface of a pavement and allow stormwater to eventually absorb back into the surrounding soils or evaporate. This keeps runoff water from downstream urban flooding and erosion. It also breaks the cycle of water treatment plants needing to treat stormwater where municipalities have combined sewer and stormwater systems. Pervious concrete pavements are “best management practices” (BMP’s) to collect, clean and cool stormwater. This usually eliminates the need for detention/retention ponds, thus reducing construction expenses, safety issues, and maintenance costs. Why are we worried about Stormwater? The EPA NPDES Phase II requirements now mandate municipalities to implement stormwater mitigation policies. New developments, both residential and commercial, must show how stormwater leaving the property will not exceed predevelopment conditions. That includes both quantity and quality of stormwater. There are many types of stormwater mitigation techniques. Pervious concrete is one of many options available. Why choose Pervious Concrete over other BMP Methods? Pervious Concrete not only collects stormwater but it also filters and cools it economically with local materials. Low Impact Developments (LIDs) are encouraged to save space, save natural resources and promote sustainable communities. What does this mean? Developments are encouraged to build up rather than out. With a pervious concrete parking lot or pavement the detention pond could be eliminated completely, thus conserving green space.
Figure 1.1
Pre Development
Post Development
Low Impact Development
What about freeze/thaw concerns and clay soils in Kansas City Metro Area? Pervious Concrete is usually more freeze/thaw durable than “conventional” concrete. Pervious concrete pavements have not been lost to freeze/thaw conditions. The voids in the pervious concrete allow for water (which expands 9% when it turns into ice) to expand and contract within the voids which keep it from breaking up the pavement. Pervious concrete in clay soil markets becomes a “system”. It is designed with a rock base under the previous layer to temporarily hold stormwater since the clay soils prevent fast recharging of the subsoil. Pervious concrete pavements typically loose ¾ of an inch to an inch of water a day to evaporation. A three inch rain would be gone in 4 days just to evaporation. The clay soils usually allow a slow exfiltration rate of .5 to .05 in the market.
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Pervious
Rock storage
Filter fabric
Ground soils
Figure 1.2
How does Pervious Concrete fit in with Sustainability & Green Building Ideas?
Pervious Concrete Pavements:
Maximize Open Space (LEED SS 5.2), the temporary detention area is under the pavement rather than beside it, taking the system vertical rather than horizontal. Stormwater Quantity Control (LEED SS 6.1), pervious concrete can intake huge amounts of stormwater. Stormwater Design‐Quality Control (LEED SS 6.2), filters the stormwater & cleans it. Heat Island Effect (reduction) Non‐roof (LEED SS 7.1), improved solar reflective index (SRI) reflects the suns’ light rather than absorb it like dark or black pavements. Construction Waste Management (LEED MR 2), concrete is ordered as needed and can be recycled. Recycled Content (LEED MR 4), there is pre‐consumer recycled content in the concrete mix. Regional Materials (LEED MR 5), pervious concrete is delivered with local materials from a local company, typically within 20 miles of the jobsite. Water Efficient Landscaping (LEED WE 1), Eliminates using surface or subsurface water for irrigation, instead capturing rainwater or brown water for landscaping. Pervious can catch & contain rainwater and recycled for landscaping use. Water Use Reduction (LEED WE 2), the intent is to lessen the burden on municipalities for water supply and wastewater. Pervious pavements can capture stormwater divert the water to cisterns, for brown water use, in flushing toilets and watering landscaping.
More detailed information on Pervious Concrete’s role in qualifying for Leadership in Energy and Environmental Design (LEED) for Sustainable Building and Communities is available from CPG. See our website at www.concretepromotion.com and look under the pervious tab on the left side of the front page. What maintenance is needed? An occasional vacuuming or wet/vac is usually sufficient, as dirt, leaves, or fines typically sit in
the top inch under the surface. More maintenance information can also be found at www.concretepromotion.com.
The Concrete Promotional Group, 913‐341‐5800, 10707 Barkley, Suite A, Overland Park, KS
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Chapter 2
Brief History of Pervious Concrete
Pervious Concrete has been around for hundreds of years. The Europeans recognized the insulating properties in structural pervious concrete for their buildings. Europeans have also used pervious concrete for paving including on the Autobahn. Stories passed down through the years tell us that our soldiers didn’t mind walking on pervious roads during World War II because it meant their feet would be dry! Pervious was brought to the United States after World War II. It first showed up in Florida and other southern coastal states. Slowly it has migrated to the other states where it has met different successes. As with any new product, it has had to prove itself. Many well intended ready mix producers have produced the product and many well intended contractors have placed the product. Some did well, others did not. As it is true with any material and construction technique, there is a science to it and a best way to conduct the construction. Education and experience are the key to success. The coastal states have experienced pervious concrete for over 20 years. The hesitation to move into the Midwest and Northern States was mainly due to freeze/thaw concerns. Now that those concerns are no longer considered a problem, the product has moved quickly across the United States. In the 1990’s the U.S. Environmental Protection Administration (EPA) came out with the Clean Water Act (CWA), that later led to other phases of implementation to preserve the waterways from stormwater borne pollutants. EPA identifies “stormwater runoff is generated when precipitation from rain and snowmelt events flow over land or impervious surfaces and does not percolate into the ground. As the runoff flows over the land or impervious surfaces (paved streets, parking lots, and building rooftops), it accumulates debris, chemicals, sediment or other pollutants that could adversely affect water quality if the runoff is discharged untreated. The primary method to control stormwater discharges is the use of best management practices (BMPs).” (EPA.gov). Pervious concrete is one of many BMP’s recognized by the EPA as well as our local American Public Works Association (APWA) and the Mid America Regional Council (MARC). The local APWA/MARC Best Management Practices for Stormwater Mitigation Manual can be found at: http://www.marc.org/Environment/Water/bmp_manual.htm . Basically, it requires the developer/owner to keep as much stormwater on property as possible. If stormwater leaves the property it must leave cleaner and cooler than before. Pervious concrete allows for the filtering/cleaning and detainment of stormwater. Since the municipalities have been required to enforce stormwater mitigation with the implementation of EPA NPDES Phase II, many BMP’s have been placed and tested to find out which one is going to work for their area. Balancing BMP’s becomes an art of balancing placement costs, maintenance costs, aesthetics and functionality. Budgets are tight and skepticism is high, because the BMP’s are relatively new concepts and some unproven. The first pervious placement in the Kansas City Metro Area was in Sugar Creek, MO in November 2005. Since that time about 30+ pavements have been placed and many lessons learned about what makes pervious concrete “good”. Herein, are the current guidelines that have been learned and adjusted. There are some basics we know about placing a successful pervious pavement: 1)
The design of the pervious pavement has a hand in its success.
2)
The mix design delivered by the ready mix producer has a hand in its success.
3)
The contractor placing the pervious concrete has a hand in its success.
4)
The owner has a responsibility for proper maintenance to keep the system functional.
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Chapter 3 Design Elements for Pervious Concrete
Hydrology The reason pervious concrete is being considered in the first place is because of water. Stormwater runoff is a negative issue affecting the quality of our urban and suburban areas, chasing pollutants down into the typically combined stormwater/sewer systems. This ends up doing three things, 1) sending rainwater to the water treatment plants for cleaning then back out to public as fresh cleaned water.
2) Sending rainwater into the streams, creeks and waterways creating urban flooding. 3) Sending polluted
rainwater into the waterways altering the balance of nature hurting native plants and wildlife. (In Kansas City we’ve seen the latter two points in Indian Creek, Brush Creek, Tomahawk Creek and the Little Blue River.) We are all spending millions of dollars nationally cleaning rainwater in our water treatments plants, which is really unnecessary. Most municipalities identify a typical rain event they require to be mitigated on developments. Nationally the most common rain event required to be mitigated is a 25 year storm event in 24 hours. The numbers vary by geographic area depending on the kind of rain events that frequent that area and the type of soils in the area. Obviously sandy soils let water percolate back into the surrounding soils faster than fat clay soils will. In the Greater Kansas City Area’s APWA/MARC Stormwater Best Management Practices Manual, the 100 year rain event in 24 hours is required to be mitigated. Depending on which part of town you are in, the number is somewhere between 8 or 9 inches of rain in 24 hours. Our local area has a majority of clay soils/expansive clay soils. Rain water will not percolate through the clay quickly, it seeps slowly. Regulations allow some water to run off site, but that water must be cleaner and cooler than when it hit the site. In other words it needs to be filtered or cleaned. The Portland Cement Association (PCA), the National Ready Mixed Concrete Association (NRMCA) and the American Concrete Pavement Association (ACPA) have jointly produced CD #063.02, Pervious Concrete Hydrological Design & Resources, 2007 Edition, as a resource. It can be used as an aid in designing the thickness of pervious pavement systems depending on the hydrological needs. This CD is extremely easy to use and recommended for anyone designing pervious pavements. It provides the capabilities of printing several helpful charts and graphs. In the Greater Kansas City Area the APWA/MARC BMP Manual requires a minimum of a 12” clean rock base beneath the porous pavement whether it be porous asphalt, porous pavers or pervious concrete. Sidewalks are not held to the same standards, there is no minimum listed for sidewalk applications. Basically the hydrological calculations that need to be established are: 1) How much water needs to be mitigated (check municipal requirements)? 2) How much water will 12” of clean rock base hold (typically 40% voids)? 3) Is more base rock needed or will the 12” hold it satisfactorily? 4) Adjust as needed. Do not calculate the pervious concrete to hold any of the stormwater. That way you will not have water standing on the surface, thus protecting it even more from freeze/thaw expansion. Extra base may be needed if roof top guttering runs into the pavement or adjacent areas drain into the pervious area. Are overflow piping or additional water storage containers needed? If your water calculations are correct you likely will not need additional means. However, depending on the amount of water you are mitigating you may want to allow for an overflow. See figure 3.1 for an example. Overflow pipe may be placed at the top of the clean rock base. This pipe can be routed to another BMP such as a bioswale or to the storm/sewer system with a delayed and controlled release.
Some sustainable projects have used a
sump pump to reuse this “brownwater” indoor to flush toilets and outdoors for watering landscaping.
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Pervious Concrete
Overflow Pipe
Figure 3.1
Clean Rock Base
NOTE ‐ approximately ¾” to an 1” of water will evaporate a day. This has been proven on a national level and on a local level in Leawood, KS in I’Lan Park. So even in the worst clay soils possible, the water does eventually go somewhere. After a two inch rain, the rainwater can be expected to be gone in about 2‐3 days. Why would a designer or owner choose pervious concrete pavements instead of other acceptable BMP’s? First off what are the other types of acceptable BMP’s and what are their limitations?
Rain Gardens (for smaller areas, more residential, needs a lot of maintenance, pulling weeds, etc.)
Figure 3.2 Rain garden
Bioswale
Bio‐Swales (for larger areas, can look like weeds‐gone‐wild, until the public is educated on the application)
Detention Ponds (most commonly used BMP, needs land, standing water for mosquitoes, safety hazard for children, needs maintenance, costly to place in the first place)
Figure 3.3 Fenced wet detention pond
Lake Lenexa, dam and spillway
Ponds or small lakes turned into recreational areas as in Lenexa, KS (a huge investment of land and money from the municipality, would need to be turned into a Parks & Rec. main line budget item)
Many different types of proprietary systems which can include special tree/plant wells at street side or cisterns or piping below the surface (fairly costly to construct and purchase)
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Figure 3.4 Proprietary plant wells system
Porous asphalt
Porous Asphalt (At the time of publication, there are 2 in the Greater KC Area, one in a park in Lenexa, KS the other in a church parking lot in southern KCMO. This is an oil based material. Do you really want your water running through this picking up hydro‐carbons and depositing them back into the ground sources? The first one in Lenexa, KS has issues of not passing water through the surface. Some in other markets have “birdbaths” with tire imprints where cars park.)
Porous Pavers (This is typically a 6 to 8 step installation process, building the base with rock, sand, etc. Maintenance is much higher on this type of paving material choice; it is more labor intensive and takes more time to place than the other two paving options.)
Figure 3.5 Various systems
Porous pavers
Grasscrete
Grasscrete proprietary systems combine some kind of structure below the surface to hold aggregates and soil mediums for hearty grasses or plants. (These systems take a while for the plants to establish and are multi‐step construction processes to place, and can take a lot of maintenance.)
Pervious Concrete (see below)
Figure 3.6 Grounds Park parking lot expansion Blue Springs, MO
Thermo Fisher Scientific parking lot expansion Lenexa, KS
So why choose pervious concrete parking lots to solve your stormwater mitigation issue?
It helps in achieving “Low Impact Developments” (LIDS), in other words building UP, instead of OUT. By placing pervious concrete the temporary detention basin (the clean rock base) is UNDER the parking lot surface. It eliminates the need for additional land to place a detention pond next to the building or parking lot. The pervious parking lot becomes both the detention pond and the parking surface in one. Build up not out. The owners save on land cost too, as they don’t need additional land for the detention pond.
Pervious concrete is green or sustainable. Pervious concrete is placed with regionally available materials (anything within 500 miles of a jobsite to cut down on energy for transportation costs).
Pervious concrete is recyclable. If for some reason it needs to be replaced someday in the future, it can be used for base rock or possibly for aggregate in concrete.
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Pervious can have recycled pre‐consumer materials in it. The slag or fly ash found in the KC market is often in the concrete mix. By using these beneficial supplementary cementitious materials in concrete they help keep them out of landfills.
Pervious concrete is low maintenance. An occasional vacuuming or wet/vac will pull dirt, sand and debris from the surface.
Pervious concrete like regular concrete is light reflective (especially when slag is in the mix) and cooler. This helps fight the Urban Heat Island Effect. Cooler pavements mean cooler environments near buildings and homes, and this means lower air conditioning bills in the summer. Research shows that by building with light reflective and heat reflective materials for roofs and pavements, and increasing green space (trees and plants) the ambient temperatures in urban areas can be °
reduced 5 F or save up to 18% on air conditioning bills.
Figure 3.7 Asphalt pavement at night, very little light reflectance
Concrete pavement at night, much more light reflective
The water collected within the pervious pavement system can be collected and rerouted (sump pump or other means) to use for irrigating landscaping or for flushing toilets in nearby buildings. This lessens the burden on municipal water supply and lowers the need for wastewater systems.
Figure 3.8 Finley Stadium, Chattanooga, TN, built in 1997, partial pervious pavement, collects stormwater, recycles the water to water landscaping around the stadium and the football field
Impervious pavements near or next to trees and bushes drain water away from trees. Everyone has seen concrete sidewalks “tenting”. Tree roots drive upward to find air and water for nourishment. Pervious concrete allows water and air get to the tree roots. No more sidewalk tenting.
Design & Layout Lessons learned in design and layout to maximize pervious success in regards to permeability and durability:
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1.
The bottom of the clean rock base should be as flat as possible. Gravity will feed water to the lowest point. If the pavement is on a slight grade make up the difference from bottom to the grade on the surface, with the clean rock base as it is less costly than the pervious concrete.
Figure 3.9
2.
Use trenches or check dams or other means in stabilizing downhill water flow when building on a grade.
Figure 3.10
3.
Use a dual concrete design for maximum durability. Pave the drive lanes in regular concrete (where there are more turning movements) and pave the parking stalls in pervious concrete. Place the base clean rock under all of it. Make sure both the regular concrete and the pervious pavement are the same thickness for construction ease. This way the base under the entire parking lot is used efficiently for temporary storage, while utilizing regular concrete where the most traffic and stress occurs on the surface.
Figure 3.11 Dual concrete design with pervious and conventional concrete
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4.
Pay special attention to the outer edge of the pavement where pervious meets landscaping or grass. Also in the middle of the parking area where trees and landscaping islands are within the pervious surface. This is where the maximum exposure to soils occurs. Rains will wash soils, landscaping mulch, etc. into the pervious pavement. Make sure plans are in place to immediately mitigate the surrounding soils with sod (or equal) to keep dirt and mulch in place and out of the pervious pavement. The pictures in Figure 3.12 show soils and mulch carried into pervious pavements after rains. The exposed soils and mulch were not satisfactorily secured. Landscaping islands should be slightly depressed behind the curb. Erosion control needs to be in place until grass or landscaping plants are mature. This is also the reason why pervious is used for parking lots more often than sidewalks/paths. Sidewalks have so much more linear exposure to the dirt/grass. Parking areas can limit the exposure to soils to the outer perimeter.
Figure 3.12
5.
When using green practices in design it is customary to place trees and shrubs within the parking lot matrix to provide shade and evapo‐transpiration. However, for pervious parking lots, it is best to limit the trees to the outer perimeter of the parking area, where they are more easily maintained, and the dirt/mulch doesn’t contaminate the pervious surface within the parking area as in the picture in figure 3.12.
Subgrade
The existing subgrade under the stormwater detention area shall not be compacted or subject to excessive construction equipment traffic prior to coarse aggregate bed placement. The subgrade may be scarified to improve infiltration rates.
Cuts necessary to establish proper subgrade level shall not be compacted or subject to excessive construction equipment traffic prior to coarse aggregate bed placement and may be scarified to improve infiltration rates.
When fill is needed to meet proper subgrade level, some compaction may be necessary. Compaction to approximately 92% proctor is sufficient.
Base
Filter fabric, 4 oz non‐woven geotextile shall be placed on the subgrade/soil prior to placing the base material.
The filter fabric will continue up the sides to the surface to keep fines from migrating into the storage layer.
It is advisable to continue the filter fabric up and over the surrounding soils approximately 2 to 3 feet. This will “hold” the soils under the fabric acting as erosion control until the project is complete and landscaping is ready to secure the soils next to the pervious pavement. This is an optional solution to erosion control. When the soils are secured the filter fabric can be cut to the edge of the pervious pavement. See figure 3.13.
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Figure 3.13
The coarse aggregate for the base or “storage” layer shall be a minimum of 12” in the Greater Kansas City Area. (APWA/MARC Stormwater BMP Manual) This has been established to mitigate the 100 year rain event in 24 hours. A true stormwater evaluation may be required for the specific site by a qualified stormwater engineer to meet municipal requirements. The base thickness for a parking lot can vary depending on the hydrological calculations, discussed in the beginning of Chapter 3.
Sidewalks are not held to the same standard. Sidewalks tend to have 4 to 6” of clean rock base.
The material for the base shall conform to ASTM C33 standards and be capable of having minimum voids of 38% by weight measured in accordance with ASTM C29. It shall be clean washed rock with less than 2% retained on the 100 sieve. The rock shall be a maximum top size of 1 ½”. (Fines plug the system.)
The material shall be placed in 6 inch lifts and lightly compacted with equipment. Keep movement over the storage bed as minimal as possible. Install to the required grades.
Place hay bales or equivalent at the toe of slopes to prevent sediment from washing into beds during site development.
The base shall be moist at the time of pervious concrete placement to ensure no water from the pervious is drawn down into the base layer. A water source should be at the job site to spray the base immediately prior to pervious placement.
The base may have a component installed to allow for moving the collected rainwater to be used for irrigation or for brownwater use in nearby buildings.
The base material for pervious pavement is a function of the stormwater detention, not structural performance. In some areas of the country no base material is needed as the soil conditions allow water to migrate through in a timely manner. In the Kansas City market we’ve already established the minimum standards require at least 12” of clean rock for stormwater temporary detention.
Pervious Thickness
Experience has been the driving force in making decisions determining the thickness for pervious pavements. 6 inches is common for parking areas for automobile traffic and an occasional truck. 8 inches is used for residential streets and more trafficked drive lanes in parking lots. Refer to ACI 330R Guide for the Design and Construction of Concrete Parking Lots for suggestions when designing concrete parking areas. Keep in mind pervious is not meant for heavy 18 wheeler truck traffic at this time.
The thickness of the pervious layer is somewhat determined by the equipment used to place the concrete. The roller screed tends to be the most commonly used screed in the Kansas City area. Consolidation by this equipment doesn’t reach further than 6 to 8 inches down into the concrete.
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Figure 3.14 Side view of pervious concrete thickness
Cutting a joint along a string line
Cutting a joint in fresh pervious concrete
Jointing
Jointing pervious concrete should be treated much like conventional concrete. Use the same rules of thumb.
Take the thickness of the pavement multiply it by 2 to reach the maximum spacing in feet. Ex. 6” X 2 = 12’ spacing. For pavements thicker than 7 inches, the maximum joint spacing is 15’.
Isolation joints shall be used when abutting fixed structural structures such as columns, manholes, signposts, light poles, buildings etc.
Construction joints may be needed at the end of the day’s paving, or when there is a prolonged delay in the next concrete truck delivery.
Saws should not be used for jointing. The problem using saws for jointing is that saws would require uncovering the curing pavement, exposing the fresh concrete to wind, sun and heat. Early entry saws are out of the question completely, as the pavement has been put to “sleep” with the hydration stabilizer. Again the pavement would be uncovered too long during the sawing process. Regular concrete saws would adequately cut the pavement; however, waiting to saw after the pavement has cured properly for 7 days would be fruitless. The pavement would have already cracked by the 7
th
day.
Sawing prior to the 7 days again, leaves the pavement open to moisture loss and possible raveling at the surface. The slurry from sawing is problematic, as it could clog part of the system. Saw cuts are being done in other markets. It is possible that saw cuts could be entertained in this market if the curing element could be conducted satisfactorily. Contractor would submit a plan to the owner/designer for approval to use saw cuts, and implement the plan into the Test Panel Placement for acceptance. (See test panel placement in Chapter 6, Pervious Construction.)
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Chapter 4 Basic Mix Design Information for Pervious Concrete Cement & Cementitious Materials
Portland Cement Type I, II or I/II is readily available in the Kansas City market and used for pervious concrete production. (ASTM C150)
Slag Cement (Ground Granulated Blast‐Furnace Slag, aka. GGBFS) is a cementitious material available in the market and used in pervious concrete production. (ASTM C989)
Fly Ash Type C and Type F are both available in the market and used in pervious concrete production. (ASTM C618)
Slag and fly ash are supplementary cementitious materials often used to replace the amount of cement. Both products are industrial byproducts. Using them in concrete keeps them out of landfills helping to green our environment.
They both
offer good benefits to concrete and they offer strength gain. Which means they add durability in the long run. Both require longer curing times for the concrete to initially set and gain strength.
Aggregates
Aggregates can have a direct influence in the permeability, surface texture and the appearance of the pervious slab.
A uniform large aggregate size is preferable for maximum permeability. This is opposite of the optimized gradation usually wanted in a regular concrete mix.
Aggregates large and small shall conform to ASTM D448 and comply with ASTM C33.
The size of the large aggregate will have an effect on aesthetics and the top size of the “holes” in the surface.
¼” to ½” large aggregates are preferred. Most of the aggregates used in the Kansas City market have been 3/8” or 1/2”.
The specific gravity shall be >2.5 and the absorption shall be <2.5 to aid in durability and performance.
Both rounded aggregates like pea gravel and angular aggregates like granite, quartzite and limestone have been used in the market. Experience tells us that the rounded aggregates can pack tight in the placement process, limiting some of the permeability. The angular aggregates have some limited drawbacks too, such as making it a little harder to get out of the trucks and increasing water demand slightly. Both have benefits and limitations.
For the most part, sand is excluded. However, in markets like Kansas City with severe freeze/thaw cycles, research has shown up to 6% fines in the mix can provide added durability without losing porosity.
The hardness and durability of the aggregate can also have an effect on the durability of the pervious pavement. Use sound freeze/thaw durable aggregates.
The aggregates should be good quality clean aggregates. Dust and debris can add to clogging the wet pervious matrix.
The owner/contractor/designer ordering the pervious concrete may be limited to the aggregates available in the marketplace. That usually means using aggregates already available for conventional concrete.
Aggregate Saturated Surface Dry or SSD is critical in the batching/mixing pervious mix. How wet or dry the large aggregates are can make a huge difference in the consistency and slump of the concrete. This has been one of the biggest impacts on the pervious mix affecting the plastic pervious properties. It may be advantageous for the ready mix producer to set his moisture readings manually to zero!
Water
Water used for the pervious concrete mix shall be potable, drinkable water and conform to ASTM C1602.
Using hot water in winter (used by ready mix producers for conventional concrete for Cold Weather practices) should be avoided at all costs! The hot water “flash cooks” the admixtures leaving them ineffective. Only extremely experienced pervious concrete contractors with experienced inspectors should attempt using the hot water in winter months. If
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pervious must be placed in cold weather, use water diverted from the “hot water” system that is measured accurately. Otherwise, wait until the ambient temperatures have warmed up.
Figure 4.1
Keeping aggregates wet and cool in the hot summer
Admixtures
Air entraining admixtures shall conform to ASTM C260. Dose as per the manufacturer recommendation for conventional concrete in severe freeze/thaw conditions. Dosages usually start at 2 oz/cwt
NOTE – there is not an ASTM test method for testing air in pervious concrete. The convention test for concrete would not be able to differiate between the voids in the matrix or the air entrainment.
Water reducing admixtures shall conform to ASTM C494, type A, B D or F. Dosages for pervious concrete can exceed the ranges typically used for conventional concrete. Experience is the best teacher. A starting dosage rate of 6 oz/cwt is recommended.
NOTE – The polycarboxylate type of water reducers have been proven to work best for pervious concrete mix designs. They are sometimes more costly than other types of water reducers, which is why some ready mix producers avoid them when designing their mix designs. Results have shown that polycarboxylates make significant strides in the discharge and placement process to make it worth the extra cost! Don’t under estimate the long term savings in using the slightly more expensive product.
Hydration stabilizers also known as extended control admixtures, shall conform to ASTM C494, type B or D. This admixture is critical to the success of the mix.
Examples of hydration stabilizers are BASF/Delvo® or Grace/Recover®; all pervious mix design shall have these products or another equal product.
Hydration stabilizers and/or water reducers shall be available on the jobsite for re‐dosing as needed. Placing pervious in hot temperatures often requires more hydration stabilizers, which include the ability to re‐dose on the jobsite.
Viscosity modifying admixtures (VMA’s) have been used successfully in other markets. They have met limited to poor success so far in the Kansas City area. One opinion is because viscosity modifying admixtures may need more mix water to get them properly dispersed throughout the mix. Pervious concrete is typically designed with a .30 w/c ratio, such little water may be limiting the ability for the admixture to”work” properly. VMA’s can make the mix “gummy” or “sticky”. VMA’s are commonly used in self consolidating concrete mixes.
New admixtures for pervious are appearing every day. Recently admixture companies have bundled together water reducers, hydration stabilizers and viscosity modifying admixtures in one product to market for pervious mixes. These have been met with mixed reviews. Be aware and open to trying new products as the technology and education changes for pervious.
It is recommended to use fibers polypropylene or cellulose, < 1.5 in. fibrillated or micro fiber type. Fibers have been included in all locally placed pervious projects. Other markets have used macro fibers in pervious concrete also. More research needs to be done to discover the advantages and disadvantages of these fibers.
Fiber dosage shall be a minimum 1.5 lbs/yd.
Fibers are suggested to be removed from their bags and distributed in 2‐3 gallons of water before addition to the mix to prevent balling materials and promoting even distribution.
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NOTE – Fiber benefits include preventing excess raveling, preventing too dry of a mix and preventing over compaction from too wet mix.
Proportioning Pervious Concrete Mixes
The mix design shall be submitted to the designer/owner for review and approval. Proportions shall be in compliance with ASTM C1688. Trial mixtures must be tested to establish proper proportions and determine expected behavior.
Concrete ready mix producers may have mixture proportions optimized for performance with local materials.
The pervious concrete mixture void content should range between 15 to 25% per ASTM 1701 or the new ASTM standard coming out spring 2011 for measuring voids in the hardened state.
The water/cement ratio shall be between .30 and .34.
Supplementary cementitious materials (SCM’s), either fly ash or slag shall not constitute more than 25% of the cement replacement individually. If used in ternary blended cement, the SCM’s shall not exceed 50% of the mass of the Portland cement.
Yield, Density and Permeability
In conventional concrete, yield is closely related to the volume of concrete placed, as established in ASTM C94. Pervious concrete is different; the volume of concrete placed can vary depending on the level of compaction during placement.
Also note that the density (unit weight) for pervious concrete varies from the density measured in accordance with ASTM C1688 and the density of the hardened pervious concrete. So the contractor ordering the pervious concrete will need to order with care as pervious will vary more than conventional concrete.
Density of the installed pervious concrete affects the voids in the hardened state, thus affecting the permeability of the final in‐place product.
Density is also affected by the properties of the materials in the pervious mix design (aggregates, cement, water, admixtures etc.)
Infiltration of water through the voids in the hardened pervious pavement can be field tested by using ASTM C1701.
Helpful Information for the Ready Mix Producer
The average truck load of pervious concrete is 6 yards. Pervious is much harder to get out of the truck as it ages in the truck because the admixtures have been used up and lost their effectiveness. 10 yards loads will likely need to be re‐dosed on site with additional water reducers and/or more hydration stabilizers. It is much easier to dose at the plant than it is to try and guess how much concrete is in the truck half way through unloading the truck. Plus it means stopping discharge and stopping the crew while the “fix” is being conducted on site. Experience has taught us shorter loads at 6 yards saves everyone time and money in the long run, than a 10 yard load.
The ready mix truck must have good quality “paving fins” to discharge from the truck properly. Older trucks with the fins worn down or trucks with no paving fins can jeopardize getting the concrete out of the truck. These trucks have slowed down jobs significantly, turning a 15 minute discharge into a one hour discharge! We’ve established that pervious is very perishable. Taking a long time to get the mix out of the truck jeopardizes the entire load.
Every delivery of pervious should have the water reducer and/or the hydration stabilizer available at the jobsite for re‐ dosing as needed. Review the Admixture section above for more details about the admixtures.
The truck drivers need to be educated about pervious, what is it, how it looks, etc. Jobsites have had drivers jump out of the truck and add 20+ gallons trying to “fix” the load because they didn’t know what is was. Truck drivers should be trained on the restrictions pertaining to addition of water at the jobsite for pervious and re‐dosing admixtures in the field.
Ambient temperatures affect pervious concrete even more that conventional concrete (because it is at a lower water cement ratio).
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Aggregate stock piles need to be kept at the target SSD. Moisture in aggregates has a HUGE affect on the mix design. It is more noticeable in pervious concrete than with conventional concrete. Moisture readings may need to be set to zero manually to get the appropriate water in the mix. This depends on the quality control at the plant, moisture probe calibrations, etc.
nd
Spacing the trucks to the jobsite can be tricky until the crew establishes a jobsite rhythm (usually after the 2
truck). Send
the first truck, wait 30 minutes, and then send the rest every 15 ‐20 minutes depending on the feedback from the field.
Avoid stacking the trucks at the jobsite, as pervious is more perishable than conventional concrete.
It is possible to unload two trucks at a time into a conveyor belt hopper, IF the contractor can adequately keep up with the placement at the other end.
The mix design should be submitted for approval to the contractor and designer.
It is advisable to place many trial batches and test panels to adjust the plant mix design for pervious. This is under utilized by many ready mix producers.
Ready mix quality control technicians and sales personnel should all be versed in ASTM 1688, ASTM 1701, the Inverted Slump Test and any new ASTM tests that are published for pervious concrete.
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Chapter 5 Testing Pervious Concrete
There are currently 2 ASTM tests designated specifically for pervious concrete (as of April 2011). ASTM C1688, Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete and ASTM C1701, Standard Test Method for Infiltration Rate of In Place Pervious Concrete
Spring 2011 a new standard will be released to measure the voids in the hardened pervious concrete. As soon as it is released this document will be updates with the information.
ASTM and ACI are working in tandem to develop standardized tests for other pervious concrete attributes, such as flexural and compressive strengths, abrasion resistance, etc. Pervious is still relatively new so it will take some time for the standards to be developed and published.
NOTE – The ASTM Standards for conventional concrete that we are accustomed to using for flexural and compressive strengths DO NOT apply to pervious concrete.
ASTM C1688, Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete
Figure 5.1 ASTM C1688
Equipment & materials needed
Second lift compacted
A proctor hammer
Striking off the surface
First lift compacted
Weighing & final calculations
ASTM C1701, Standard Test Method for Infiltration Rate of In Place Pervious Concrete
Figure 5.2 ASTM C1701
Equipment & Materials Needed
Calibrated markings in the rim
Secure the rim with putty
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1 gallon of water into apparatus (Step 2 if needed) 5 gallons into apparatus
Final calculations
The Inverted Slump Cone Test
Inverted Slump Test Picture credit: Kevern, Schaefer, Wang
Figure 5.3 Filling the inverted slump cone
Checking workability
Workable mix
Over‐worked mix
Using ASTM 1688 and the Inverted Slump Concrete Test for jobsite acceptance: The workability and consistency of pervious concrete may be determined for each ready mixed truck to ensure quality construction. Typically workability is adjusted on‐site for the first load and then readjusted during batching for all subsequent loads. a)
Check Batch Ticket: Upon arrival at the jobsite. Check for the correct mixture and appropriate delivery and mixing time.
b)
Check Workability: Perform an inverse slump check. If workability remediation is required first add 0.5 to 1.0 gallons of water per cubic yard. If additional workability remediation is required, add up to 50% of the original dosage of water reducer if the weather is mile and up to 50%of the hydration stabilizer if the weather is hot.
c)
Adjust subsequent loads: Radio back to the batch personnel and relay water and/or admixture adjustments.
d)
Determine Consistency: Determine ASTM C1688 unit weight and compare against required values. Unit weight values greater than 10 pcf different from the desired values may indicate that an incorrect mixture may have been delivered. If the mixture was correctly batched, but the unit weight is high, hold the truck while slowly mixing for 15 minutes. If the unit weight is light, adjust workability. In most situations poor flow through the inverse slump cone will indicate potential for low unit weight values. Adjusting for workability will improve unit weight.
e)
Discharge
Using testing for final acceptance Use the new ASTM standard (spring 2011) testing voids in hardened concrete on the test panel and comparing it to the final product could be one method for acceptance, +5 pcf. Assuming the test had been performed on the test panel and established as a goal for the project.
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Chapter 6 Pervious Concrete Construction Equipment & Tools
NOTE – the equipment and tools listed herein are most familiar in the Kansas City market. New pervious equipment and tools are being developed constantly. New screeds, curing methods, new hand tools, forms, filter fabrics, etc. need to be reviewed and tested. If a contractor can show alternate methods of placement and curing to reach the desired durability and permeability, acceptance should be considered.
Figure 6.1 4 oz. nonwoven filter fabric
Soy bean curing agent
Roller screed
Securely anchor 6 ml poly
Cross Roller
Cross roller on left & joint roller on right
Conveyor belt placement
Hand tamping edges
This list herein contains the major construction materials and tools needed to successfully place pervious concrete. o 4 oz. (minimum) Non‐Woven Geotextile Filter Fabric (check to make sure water can pass through the fabric) o Roller Screed (must be able to be filled with water or sand for weight) o Cross Roller o Flanged Roller aka “Pizza Cutter” to cut joints in plastic pervious concrete o Soy Bean Oil Curing Compound (also use for bond breaker on forms etc.), Coverage 200 to 250 sq. ft. per gallon (comes in 5 gallon bucket) o 6 oz. (minimum) Poly Sheeting (Must take the time to prepare the poly & pre roll onto tubes to roll over the forms behind the screed) o Conveyor Belt (Pervious can’t be pumped, a conveyor expedites the construction process significantly even for small jobs) o Squared ended shovel o Concrete rakes o Come‐a‐longs o Hand tampers o 2 X 4’s to hold plastic sheeting in place o Sand bags or equal to hold 2 X 4’s o Water source and hose
Test Panel Placement & Approval
Test panel placement and approval approximately one month to two weeks, prior to pervious construction.
See the Specifier Guide for Pervious Concrete in Kansas City for dimensions and details.
The contractor must use the equipment, tools and crew that will be used in the actual placement.
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NOTE – The slab will need to cure for 7 days. Then the owner/designer, contractor and testing company will meet to review the slab, conduct tests and approve the slab. IF it is not acceptable, it will need to be repeated until approved. This will take another 7 days, etc. Timing of the test slab can affect the overall start date for the construction schedule.
Overall acceptance should be on surface appearance, joint details, thickness, porosity and curing procedures.
Was the mix provided by the ready mix producer workable and acceptable? If not was it adjusted or modified until acceptable during the test?
Was the contractor ready and using proper tools? Was the placement team size appropriate? Curing practices in line?
Pre‐Construction Meeting
Refer to the Pre‐Construction Checklist in the back of the Specifiers Guide for Pervious Concrete in Kansas City.
Has the Test Panel Placement & Approval be completed and approved? The mix approved?
Conduct the meeting at least one week prior to placement.
GC, pervious contractor, ready mix supplier, excavation contractor, landscape contractor, architect, engineers, etc. in attendance.
Review the plans, specifications with all parties.
Discuss testing being conducted, test methods, samples, frequency of tests, testing company familiar with ASTM standards for pervious concrete?, etc.
Discuss weather, as it has a HUGE effect on pervious. Hot or cold weather practices? Curing? Authority to cancel and reschedule if necessary?
Discuss access to the site for ready mix trucks and conveyor belt for placement.
Review subgrade, filter fabric, base aggregate, base thickness, wetting the base prior to pervious placement, pervious thickness, jointing, curing, # on crew, etc.
Is there a water source on site (for wetting the base rock immediately prior to pervious placement)?
Discuss the width of the screed, paving in strips, constructability issues.
Is everyone aware that the poly sheeting stays in place for 7 days cure period, without any traffic on it?
Has erosion control been discussed to keep soils out of the pavement once the poly is removed?
Is the landscaper aware that they cannot use the pervious pavement for their staging area for mulch, plants, etc.?
Weather
Figure 6.2 Resecuring poly after 45 mph winds
Prevent billowing in the poly sheeting from the wind
Wind? Prepare for the wind. Severe winds in the 20 to 45+ mph range can wreck havoc on pervious placement.
The Contractor shall not place pervious concrete pavement later in the year than November 1 or earlier in the year than April 1 unless otherwise permitted in writing by the Architect/Engineer.
The Contractor shall not place pervious concrete pavement when the ambient temperature is predicted by the National Weather Service Point Forecast for the jobsite to rise above 90°F (32.2ºC) during the seven days following placement, unless otherwise permitted in writing by the Architect/Engineer. These hot days can be detrimental to getting pervious out of the truck, exposed on conveyor belts, etc. There is an increased probability of raveling on the pervious surface in its
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completed state and possible durability issues. Consider alternative placement times, i.e., 3 am to 6 am, or late night placements during cooler hours of the day/night. The owner/designer and contractor may need to delay placement in hot weather.
ACI 305 Hot Weather Concrete can provide some very helpful information. But remember pervious is more sensitive to heat that conventional concrete.
Admixtures need higher dosage rates in hot weather to work properly. The ready mix producer and contractor need to be prepared to redose at the jobsite.
Hot weather shortens the time from batching the concrete to when it must be placed on site.
The Contractor shall not place pervious concrete pavement when the ambient temperature is predicted by the National Weather Service Point Forecast for the jobsite to be 40°F (4.4ºC) or lower during the seven days following placement, unless otherwise permitted in writing by the Architect/Engineer. ACI 306 Cold Weather Concrete can also provide some very helpful information, but pervious has some additional needs in cold weather. 40°F is usually the mark where ready mix producers’ start using hot water. Pervious concrete should be avoided when the ready mix producer has moved to using hot water for cold weather conventional practices. The hot water “flash cooks” the admixtures, disabling them from working properly.
Pervious concrete cannot be placed in rain or snow or on a frozen subgrade or base.
Winter months tend to have dry or very low humidity. These conditions will “dry” the pervious out, so curing is extra important, and needed to be conducted very conservatively.
Placement in severe conditions should be avoided.
Site Preparation
Verify that the site conditions match the plans.
Review the specifications.
Verify grade stakes
Remove organic materials and trash.
Verify locations for drains, piping, underground cisterns, (if applicable) etc.
Cuts necessary to establish proper subgrade level shall not be compacted or subject to excessive construction equipment traffic prior to coarse aggregate bed placement and may be scarified to improve infiltration rates.
When fill is needed to met proper subgrade level, some compaction may be necessary. Compaction to approximately 92% proctor is sufficient.
Filter Fabric Installation
Figure 6.3 Filter fabric overlaps 18 inches
Filter Fabric up sides and over edges
Refer to Chapter 3, Design Elements for Pervious Concrete, for specifics on the filter fabric and design details.
Filter fabric shall be 4 oz. non‐woven geotextile. This keeps the fines from coming up from the subgrade below and clogging the base area. It also allows for water to move through the fabric and continue into the subgrade for movement into the surrounding soils.
NOTE – Product technology is changing to adapt to pervious pavement needs. Keep abreast of new products that may work to help water exfiltration into the surrounding soils, even in clay soils.
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Run the filter fabric up the sides of the pervious pavement.
Overlap the filter fabric to the manufacturer’s recommendations (usually 18 inches).
Base Construction
Figure 6.4 Placing clean aggregate base
Placing a perforated pipe underdrain
Placing clean rock base over filter fabric
Refer to Chapter 3, Design Elements for Pervious Concrete, for specifics on the base materials and design details.
It is critical that the base aggregate be clean washed aggregates that allow the water to move freely in the base section.
AB3 is NOT acceptable in the Kansas City market for pervious base rock; this aggregate has too many fines to work effectively and efficiently.
Optional drainage systems may be required by the designer, which may or may not tie into the pervious system. Review the plans and specifications closely. This could be constructed with check dams, piping etc. See figure 3.3.
The material shall be placed in 6 inch lifts and lightly compacted with equipment. Keep movement over the storage bed as minimal as possible. Install to the required grades.
The base layer surface shall be sprayed with water immediately prior to pervious concrete placement. This keeps the base from pulling water out of the pervious mix when it is placed. This will protect the plastic pervious concrete from being jeopardized; it’s curing the pervious from the “bottom up”.
Setting Forms
Figure 6.5 Forms set ready to pave
Forms set & joint marked in blue
Concrete strips placed in advance for forms for pervious
Forms must be study enough to stand up to the heavy roller screed and placement operations. Typically wood, steel or aluminum forms are used.
Make sure stakes are 1/2” lower than the top of the forms. This will allow the roller screed to not get hung‐up on a stake as placement progresses.
The embedded stakes must be anchored well. They must hold up to the stress of the equipment and crew. They may not allow deflection during placement.
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Size of the Crew
Figure 6.6 Crew size – 9 approx.
Crew size – 12 approx.
Crew size – 12 approx.
A typical crew size for pervious concrete placement with a roller screed is 7 to 14 crewmen, depending on the job specifics: o o o o
o o
o
Crew size – 14 approx.
One person conducting oversight, managing the arrival of new trucks, coordinating with inspectors and ready mix. One in front, keeping the base rock surface wetted down with water immediately in front of the screed. One on the end of the conveyor belt. Two to four, with squared shovels, concrete rakes or come‐a‐longs to move the pervious in front of the screed, these people also fill in holes, consolidate the edges and keep a head of concrete in front of the screed. Two, one on each end of the roller screed. Two, one on each side of the pavement, they cure with both the soybean oil and roll the poly over the surface and secure the plastic tight. One to two, jointing with the pizza cutter and cross rolling the surface over the poly.
Every team member has a job, knows what it is, and knows who is behind him and in front of him in the construction process to keep in communication with.
Concrete Arrives for Placement
Be ready BEFORE the concrete truck arrives. This product is very perishable. There is no time to add water to the roller screed to weigh it down, or place forms after the concrete truck arrives.
Is the conveyor belt in place and ready?
If placing the pervious on small jobs directly from the concrete truck, think about the placement direction ahead of time. If the chute from the concrete truck is running uphill, you are going to be there a very long time getting the pervious out of the truck! Pervious is placed with one chute down. Two and three chutes will delay the time and ability to move the pervious.
The concrete truck will need easy accessibility to the site for truck placement to work.
Using buggy’s to place pervious has been done before, however, be prepared as you will lose some of your permeability. The pervious consolidates in the buggy getting to the actual site and then is consolidated again with the roller screed. It also physically takes twice as long and it becomes harder to work with quickly. This is not the best method in the high heat of summer months! Buggies may be the only method to get pervious in tight spots, where trucks and conveyors can’t reach.
The conveyor belt method works the best and is needed for the smallest of jobs.
Be sure the pre‐approved mix has been ordered and is delivered. Check the batch ticket.
Conduct an inverted slump test, to assess the workability of the pervious.
Make adjustments, if necessary, notify plant of changes made in the field.
Conduct ASTM 1688 to calculate the unit weight. Does it fall within the +5 from the test panel established mix design weight?
Remember pervious concrete is not the typical 140‐145 pcf as in conventional concrete.
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Finishing Pervious Concrete
The Basic Steps to finishing pervious concrete: o
Spreading the plastic pervious concrete
o
Consolidating/compacting/strikingoff the concrete (most often at same time)
o
Jointing
o
Curing
o
Cross Rolling
o
Extra effort to secure plastic
o
Wait minimum 7 days
o
Remove plastic and forms
Spreading Pervious Concrete
Figure 6. 7 Filling the screed with water for weight
Placing pervious concrete
Conveyor placement
Place pervious as close to the final resting spots as possible.
The less pervious is worked/touched the better it is!
Use squared shovels, concrete rakes and come‐a‐longs to move it from below the chute or below the conveyor placement in front of the screed.
Pervious is not pumpable. A conveyor belt is the best placement method.
Use a roller screed that has been weighted down with either water or sand in the roller tube. If the roller is not weighted down it will float on the top of the pervious. It must be weighted down to properly consolidate the concrete. Do not skip this step.
If approved by the owner/designer the contractor may use an alternate screed. The test panel would need to be conducted with this screed.
Technology is constantly changing as well as the availability of new screeds. Slip form pavers have been
adapted for pervious placement. Truss screeds do not consolidate pervious effectively. Some other states have used truss screeds with shims on the first pass, then taking the shims off for the second pass. This process still has some consolidation issues and leaves the surface exposed too long. It inhibits the proper cure methods to get the pervious covered before it dries out. Laser screeds do not allow for quick efficient curing.
Extra consolidation is needed at the header and along the sides where the pervious meets the forms. Hand tampers, new specially designed edge rollers or “walking” the pervious in, next to the forms is needed.
As placement proceeds away from the forms, crew will want to AVOID walking in the pervious concrete. Walking in it will reduce the permeability in its final state.
Keeping a consistent height (head) of concrete ahead of the screed for proper consolidation and uniform surface.
Placing pervious ahead of the screed should not get too far ahead of the strike off crew. This will keep the crew from walking in the fresh pervious.
A starting guideline to set for pervious truck spacing for a new job: The first truck 30 minutes ahead of the second truck. Then spacing them 15 to 20 minutes apart thereafter. Set up constant feedback between the crew lead and the ready mix company to adjust the spacing as needed. Two trucks can discharge into the hopper of the conveyor belt truck IF the crew can place it at the other end at the same rate. Discharge rates will vary with the equipment, ambient temperature, mix design flow and the experience of the crew.
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Compaction from the roller screed is important. Too much compaction will tighten the matrix making it less permeable. Not enough compaction leaves the matrix too loose and not even. This makes for a less durable pavement and more likely to surface delaminate. A balance must be achieved. Practice and familiarity with specific mix designs improves the contractor’s ability to produce a viable pervious pavement.
The desirable finish is smooth with no roller marks and no major voids with an even texture. It allows for good water permeability and providing a durable surface for car traffic.
Jointing
Figure 6.8 Cutting in a joint in during construction
Using a “pizza cutter” to roll in a joint
Joint in the hardened pervious concrete
Joints are placed in specific places to help encourage the pavement to crack where we tell it to in order to avoid ugly and unsightly random cracks.
Sometimes the pavement will still crack where it wants to and not where we’ve told it to crack.
Joints are typically spaced twice the thickness of the pavement in feet. In other words a six inch pavement wouldn’t have joints spaced further out than 12 feet (6” X 2 = 12’).
Joints should never be further than 15’ apart.
Isolation joints are needed at manholes, sign posts, columns, buildings, etc. Anywhere the pavement meets up with something fixed that will tend to expand and contract at a different level than the pervious pavement.
Jointing is conducted with a flanged roller, aka pizza cutter in the plastic pervious concrete.
Joints must be pre‐marked where the joints will be made before paving starts.
A string line can be used to mark the path of the rolled joint.
Roll the flanged roller ONE WAY over the pavement. Throw the handle of the flanged roller to a crewman on the other side and take the cutter out on the opposite side. One path in one direction.
NOTE – Do not roll the joint roller back to the original entry side. It widens the joint too wide and often cuts a second cut.
All jointing must take place immediately behind the screed and prior to curing.
Preplaced joints/preformed joint materials can be used if the contractor is familiar with its placement. The contractor would need to demonstrate the ability to place the materials in the test panel. It is up to the owner/designer to accept/decline the method after review.
Saws have been mentioned before in Chapter 3, Design Elements for Pervious Concrete. The contractor would have to be able to demonstrate the ability to place saw cuts effectively while properly curing the pervious concrete. The contractor would need to conduct the procedure on the test panel for approval.
Edging
Edging has been considered optional in the Kansas City market.
If proper consolidation has been conducted against forms it may or may not be necessary.
Edging cleans up the edge by the form or abutting curb or abutting pavement.
It can also leave a small space where vehicles roll over putting tension on the edge, potentially causing delamination at that dead space. Some feel it is important to make sure the surface is tighter at the edge to not leave any small dead space to eliminate the “edge break off”.
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Curing
Figure 6.9 Spraying water on base prior to paving
Spraying soy bean cure
Taping poly overlap
2x4’s anchor sides of poly down
“If it dries, it dies.” Most concrete industry personnel have heard this quote once or twice. Never was it truer than when working with pervious concrete.
Curing cannot be emphasized enough.
If pervious concrete is not cured it will fail, 100% guarantee!
Curing must be executed within 3 to 5 minutes behind the screed.
Pervious concrete is placed with a typical water/cement ratio of .30. That means low or no slump concrete. It has just enough water in it to hydrate the cement particles and aid in mixing the materials. Curing is done to allow the water in the mix to properly hydrate the cement, before the water has a chance to evaporate. If the pavement is not covered up completely, it will be exposed to the weather elements such as wind and heat.
Pervious concrete is cured in a two step process.
The first step is to spray the surface with soy bean oil from both sides of the pavement. The soy bean oil can also be used as a bond breaker on the forms, as a lubricant on the roller screeds, joint roller etc.
Research has shown that soy bean oil does a much better job at coving the surface hills and valleys than the typical curing agents used on conventional concrete. It is also biodegradable and a green construction product.
The second step is to cover the pavement complete with minimum 6 ml poly sheeting. The sheeting should be pre‐rolled onto long tubes that are wide enough to ride on the forms directly behind the roller screed. This is a step the contractor has to plan and have ready prior to the start of paving.
The poly sheeting can leave a mottled aesthetic look on the surface if the plastic is not pulled taught. The bunching up of the plastic can cause these stripes to be left on the surface when the plastic is removed. Since the plastic has been pre‐ rolled on tubes prior to placement, it helps to eliminate some of the mottling left with wrinkles in the plastic.
Mottling marks left by the plastic in the curing stage are NOT structural blemishes. They are acceptable and scars of good practices been being used. The contractor can help himself in eliminating as many of these scars by communicating with his crew to keep the plastic sheeting pulled tight to keep the wrinkles out as placement is occurring.
Foggers have been implemented successfully to increase the humidity directly above the pervious pavement. Be careful, spraying water from a hose over the pervious is not recommended, as it will wash the mortar off the top aggregate or jeopardize the water/cement ratio at the surface. Not all contractors have fogging equipment.
2 X 4’s placed end to end over the poly sheeting on the formwork is best to hold down the plastic. Then place sand bags every 5’ to 6’ over the 2 X 4’s to hold them in place. An occasion mud clump or brick here or there is not sufficient to hold the plastic in the potential winds and curious on lookers.
The pervious concrete shall be cured for a minimum of 7 days. All traffic will be kept off the plastic during the 7 days.
Technology is changing curing methods for pervious concrete. Be aware of new products entering the market to better cure the pervious pavements. Be open to these products, research them, and use them in test pours and experiments to prove to yourself and others that they do work or not.
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Cross Rolling
Figure 6.10 Cross rolling over poly
Cross roll perpendicular to screed
Spray water over poly prior to cross rolling
Cross rolling is done to work out the bumps and lines left in the plastic pervious concrete after the roller screed has passed over it.
Spray water over the poly sheeting then cross roll. The water holds the plastic down and makes it easier to roll.
Cross rolling is done over the poly sheeting. This ensures the pervious is covered up and cured quickly and properly.
Cross rolling is done in the direction perpendicular to the direction the roller screed. If the roller screed is moving in a north/south direction, the cross rolling is done in the east/west direction.
It also gives the surface its last consolidation.
Rolling over the jointed area is not a problem. If any aggregates were dislodged in the jointing process, the cross roller will push them back into place.
The cross roller is not meant to close the surface. If this happens, stop. Re‐evaluate why the surface is sealing. Deal with it immediately.
Re‐evaluate the poly sheeting
Is the poly sheeting securely anchored?
Will wind, over the next 7 days, potentially billow under the plastic?
Fix problem sheeting spots before leaving.
Have a representative check the poly everyday over the 7 days and fix any problems that might arise.
Wait 7 days Remove plastic sheeting and forms
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Chapter 7 Maintenance Cleaning Debris Out
Figure 7.1 There are all kinds of vacuums on the markets, walk behinds, drive behinds, some with water and some without.
Figure 7.2 Pervious surface prior to vacuuming
Pervious surface after vacuuming
Vacuuming is the most successful way of cleaning pervious concrete. The fines that accumulate usually stay within the top 1 inch or so of the surface. So pulling them out the top is easier than pushing them further into the pavement.
Wet/Vac is a combination of wetting the surface to loosen the debris and vacuuming at the same time and has been very successful.
Power washing can be helpful to loosen packed in clay and massive debris. A high psi is NOT recommended at it can loosen the aggregate on the surface. A low psi will dislodge the packed in material. A thorough vacuuming will need to follow.
Preventive Maintenance
Preventing clogging in the first place is better than dealing with it once it has occurred!
Collect leaves/pinecones etc. after they have fallen. This keeps them from decomposing into the surface.
Vacuuming the pavement once or twice a year will prevent build up below the surface that is not visible to the eye.
Manage the immediate landscaping before, during and after pervious paving to prevent soils and mulch from contaminating the pervious pavement after a rain storm.
Make sure the landscaping contractor knows to NOT use the pervious pavement as a staging area for their mulch, dirt, plants etc.
Designers need to be aware of adjacent areas to the pavement. Direct future rainwater from carrying dirt and debris into the pavement. Create berms, bioswales etc. to protect the pavement.
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Snow Removal
Figure 7.3 No refreezing of melted snow on surface Snow disappears below the surface Less than 3 inches of snow, no plowing needed
Snow Removal should be accomplished using a rotary broom. If use of a rotary broom is not possible, snow should be cleared using a plow with a lower edge made of plastic or rubber. Metal plows should be avoided; their blades tend to catch stones (particularly at joints) and cause raveling.
Snow less than 3 inches disappear quickly once they have been walked on or driven on. The snow and melt goes below the surface and out of sight.
There is no reason to use deicers since there is no standing water on the surface.
There is no refreezing of melted snow at night since the water has moved down below into the base.
The base layer is usually 8 to 10 degrees warmer than the surface. The air voids are great insulators.
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Chapter 8 ®
LEED Credits Pervious Concrete can contribute to LEED ®2009 NC in several ways:
SS Credit 5.2: Site Development –Maximize Open Space It is possible, for example, for a pervious concrete parking lot to help eliminate the need for a detention pond and allowing that real estate to be part of the “vegetated open space area adjacent to the building” or parking lot.
SS Credit 6.1: Stormwater Design‐Quantity Control Option #1 Sites with Existing Imperviousness 50% or less Option #2 Sites with Existing Imperviousness Greater than 50% Pervious Concrete can help both conditions collect, clean and cool stormwater and in many cases eliminate post development runoff and certainly reduce predevelopment runoff by more than 25% (2 year‐ 24 hr design storm).
SS Credit 6.2: Stormwater Design‐Quality Control Pervious Concrete is one of many commonly acceptable Best Management Practices (BMP’s) used to collect, clean and cool stormwater. Capable of removing 80% of the average annual post development total suspended solids (TSS). Pervious concrete is listed and recognized by KC Metro MARC/APWA Section 5600.
SS Credit 7.1: Heat Island Effect ‐Nonroof Reduce heat island effect. Option #1: 50% of the site hardscape will consist of paving materials with a solar reflective Index (SRI) of at least 29. While regular new concrete does meet the LEED SRI minimum requirement of SRI 29, pervious concrete pavements may or may not. Pervious pavements can be designed to meet the SRI 29 requirement. Pervious concrete pavements must be tested for SRI to list testing data in the LEED template for reporting. See LEED default chart for SRI info below: Material Emissivity Reflectance New Gray Concrete 0.9 0.35 Weathered Gray Concrete 0.9 0.20 Typical White Concrete 0.9 0.7 New Asphalt 0.9 0.05 Weathered Asphalt 0.9 0.10 Pervious Concrete Needs to be tested Needs to be tested (Test in accordance with ASTM E 903, ASTM E 1918 or ASTM C 1549)
SRI 38‐52 19‐32 86‐100 0 6 Test results here
MR Credit 2: Construction Waste Management It is not possible for pervious concrete to singlehandedly fulfill this category. Since concrete is batched for each specific job there is very little waste or overage (which is in itself green). It is possible that “left over” pervious concrete could potentially be recycled back at the ready mix concrete plant with 100% of the water and aggregate for reuse in concrete, thus keeping it from the landfills. This is something we will see more of in the future. The calculations for the entire job site’s waste management for all construction materials figure into this number.
MR Credit 4: Recycled Content It is not likely pervious concrete will fulfill this category by itself. However, pervious concrete can help attain this point(s). Points are awarded for 10% (1 pt) or 20% (2 pts) of recycled content based on cost of the total value of the materials in the project. Pervious concrete will likely have fly ash or slag in the makeup of the mix design. Both fly ash and slag are preconsumer recycled materials. The ready mix producer will provide a letter with the appropriate information about the recycled material in the concrete mix to the LEED AP or project coordinator.
MR Credit 5: Regional Materials “Building materials or products that have been extracted, harvested or recovered, as well as manufactured within
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500 miles of the project site for a minimum of 10% or 20% based on cost, of the total materials value” will earn 1 pt or 2 pts respectively. In the Kansas City metro area, it is likely that the cement, large aggregates, sand, water, fly ash and even recycled aggregates are all within 500 miles of our local job sites. The ready mix producer will provide a letter with the appropriate information to the LEED AP or project coordinator.
ID Credit 1: Innovation in Design Up to four additional credits can be attained in this category. This leaves the door open to innovation and creativity. It is possible for technology or sustainable ideas to be applied here to reach new levels. These must be submitted for consideration and approval.
ID Credit 2: LEED Accredited Professional “At least one principal participant of the project team shall be a LEED AP.” While it is not likely the pervious contractor or pervious ready mix supplier will be a “principal participant” on the project team; it is likely if the project is a LEED project there will be a LEED AP already on the project team. There are concrete industry personnel that are LEED AP and they are usually available for consultation.
RP Credit 1: Regional Priority “To provide an incentive for the achievement of credits that address geographically‐specific environmental priorities.” Up to 4 credits can be earned here. This is up to the decision makers in each region. Go to www.usgbc.org to find a list of regional priority credits. As the LEED system updates and changes these categories and points will reflect those changes. For up to date information on LEED® go to www.usgbc.org . The U.S. Green Building Council (USGBC) is a 501(c)(3) non‐profit that developed the LEED (Leadership in Energy and Environmental Design) Green Building Rating System.
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Chapter 9 Decorative Pervious
All decorative processes need to be tested in a pre‐placement situation for approval.
Figure 9‐1 Trailhead with decorative pervious
Colored pervious courtyard
Stamped and colored pervious concrete
Integral Colored
Pervious concrete can be attained by adding powdered color or liquid color to the mix in the batching process in the ready mix truck or central mix unit. Keep in mind this process needs to be tested and adjusted for each individual job. The water/cement ratio is very low in pervious concrete. When adding powdered color to the mix, it will use up more of the water in the mix. More water may be needed in the decorative pervious mix than in pervious without color.
Surface Color
Color can be applied to pervious concrete with a surface application.. There are coloring agents that can be applied to the surface. Color can be sprayed on the surface in the curing stage along with the soy bean oil and reapplied as needed for color intensity or maintenance. Or done as a stain/dye process. Keep in mind pervious is usually being done to achieve green building practices, so applying a stain that requires rinsing may not be the greenest practice. Be sure coloring agents are UV stable.
Stamping
Stamping pervious concrete has been done and can be done. It is not as simple as with conventional concrete. The pervious concrete has a low to no slump, which means it is very stiff. The older metal stamps tend to be used instead of the softer neoprene/rubber mats to create an impression.
Keep in mind that stamping takes time, which leaves the pervious exposed to the wind and sun. It would be difficult to cure pervious in the required 3 to 5 minutes behind the screed when stamping.
An experienced crew would need to work very quickly to stamp the surface and get it covered (cured).
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Chapter 10 Specifiers Guide to Pervious Concrete Pavements in the Greater Kansas City Area v1.2.11
Go to www.concretepromotion.com to find the current guide. It is available on the front page of the website and/or under the “pervious” tab.
“The Pervious Construction Checklist” is found in the back of the Specifiers Guide “The Pre‐Construction Conference Checklist” is also found in the back of the Specifiers Guide
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Chapter 10 Websites and Resources Websites:
CPG website www.concretepromotion.com
National Ready Mixed Concrete Association’s (NRMCA) website www.nrmca.org
NRMCA’s Pervious website www.perviouspavement.org
Portland Cement Association (PCA) website www.cement.org
PCA’s Pervious Page http://www.cement.org/tech/cct_con_design_pervious.asp
Concrete Thinking for a Sustainable World website www.concretethinker.com
NRMCA’s Pervious Concrete Contractor Certification Program http://nrmca.org/Education/Certifications/Pervious_Contractor.htm
American Society for Testing Materials (ASTM) www.astm.org
American Concrete Institute (ACI) www.concrete.org
National Pervious Concrete Pavement Association (NPCPA) www.pervious.com or www.npcpa.org
Resources:
Storm Water Phase II Final Rule: An Overview, EPA 833‐F‐00‐001, Fact Sheet 1.0, US Environmental Protection Agency, Office of Water, January 2000, 4 pages
Freeze/Thaw Resistance of Pervious Concrete, NRMCA, May 2004, Silver Spring, Maryland, 17 pages
Mix Design Development for Pervious Concrete in Cold Weather Concrete, Iowa State University , National Concrete Pavement Technology Center, February 2006
Pervious Concrete: When it Rains it Drains, NRMCA
CIP #38 Pervious Concrete, NRMCA, Concrete in Practice Series
Storm Water Technology Fact Sheet: Porous Pavement, United States Environmental Protection Agency, EPA 832‐F‐99‐023, September 1999. www.epa.gov/npdes
Pervious Concrete Promo Flip Book , NRMCA, #2PPCPB1,
Pervious Concrete Pavements, PCA, Tennis, P. D., Leming, M. L., and Akers, D. J., Skokie, Illinois & NRMCA, Silver Spring, Maryland, EB302, 25 pgs
Pervious Hydrological Software Resource CD‐ROM, NRMCA, CD063.02
Construction and Maintenance Assessment of Pervious Concrete Pavements, RMC Foundation, January 2007, www.rmc‐ foundation.org
Hydraulic Performance Assessment of Pervious Concrete Pavements for Stormwater Management Credit , RMC Foundation, January 2007, www.rmc‐foundation.org
Portland Cement Pervious Concrete Pavement: Field Performance Investigation on Parking Lot and Roadway Pavements, RMC‐Foundation, December 2007, www.rmc‐foundation.org
Pervious Concrete Research Compilation: Past, Present and Future, RMC‐Foundation,Updated June 2008 & November 2008, www.rmc‐foundation.org
Mix Design Development for Portland Cement Pervious Concrete in Cold Weather Climates, Kevern, John T., Master’s Thesis, Iowa State University, Ames, Iowa, 2006, 155 pages
The Effect of Coarse Aggregate on the Freeze‐Thaw Durability of Pervious Concrete, Kevern, John T.; Wang, Kejin, and Schaefer, Vernon R., SN3063, Portland Cement Association, Skokie, Illinois, USA, 2008, 29 pages
ASTM C 1688, Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete http://www.astm.org/Standards/C1688.htm
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