Hydraulic Performance of Pervious Concrete Pavements Manoj Chopraa, Martin Wanielistaa, Joshua Spencea, Craig Ballocka and Matt Offenbergb a
Stormwater Management Academy, University of Central Florida, 4000 Central Florida Boulevard, Orlando, FL 32816; PH (407) 823-4143; FAX (407) 823-3315; email:
[email protected]; b Rinker Materials, Orlando, Florida 32817. Abstract Pervious concrete is a mixture of coarse aggregate, portland cement, water, and admixtures. Lacking fines, this material has a void ratio that typically ranges from 1520% allowing it to store and infiltrate stormwater. Pervious concrete has been used in lower traffic areas such as parking lots, shoulders, sidewalks, streets, and local roads. Though it has garnered significant interest in the past, there is still a great deal of concern about its durability, adequate infiltration capabilities, and clogging potential. This paper focuses on the hydraulic operations of a pervious concrete system including infiltration rates, storage capacity and clogging potential. Pervious concrete allows water to infiltrate at very high rates, typically 100 to 200 inches an hour, whereas the underlying soils will infiltrate water a much lower rate, usually by 1 to 2 orders of magnitude. It is important to consider that the effects of the entire system (pavement and soil) when predicting the capacity of pervious concrete pavements. A method of testing for the in situ infiltration rate of a pervious concrete system – an embedded single ring infiltrometer – has been developed and will be presented. The study consists of detailed analyses of several pervious concrete parking lots that have been in operation for 5 or more years. Field analyses include testing for system infiltration rates, estimation of surface clogging of pavement (i.e. decrease in porosity), and subgrade/subsoil investigations. Introduction Pervious concrete is a unique cement-based product whose porous structure permits free passage of water through the concrete and into the soil without compromising the durability or integrity of the concrete. State and municipal governments as well as Water Management Districts have a great interest in finding solutions for excess stormwater runoff and the associated water quality issues. The restrictions and design requirements associated with construction of impervious surfaces are often costly with regard to development. Substitution of impervious pavement areas with pervious paving surfaces provides a desirable combination of stormwater retention properties and structural features of conventional pavement that comply with stormwater regulations. This leads to a more cost effective management of stormwater runoff while retaining a water and pollution budget for local areas. Portland cement (PC) pervious concrete has generated great interest as a pervious pavement and an ACI committee (522) was formed to develop guidelines for the use of portland cement pervious concrete. It is a discontinuous mixture of coarse aggregate, Portland cement, admixtures and water. The increased porosity due to no fines in the mix and 15-20% air voids allows for the flow of water through the material.
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The advantages of pervious concrete surfaces include increased utilization of residential and commercial land, and the direct replenishment of local aquifers. PC pervious pavements have been used in the past 20 years in areas of lower traffic loads such as parking lots, shoulders of roadways, airport taxiways and runways, street and local roads provided the subsoil conditions, drainage characteristics and groundwater location are suitable. The US EPA has published a fact sheet for Porous Pavements (EPA, 1999) which also lists the advantages and disadvantages of pervious pavements (both asphalt and concrete) as follows. The advantages include: (a) Water budget retention and pollution removal; (b) Less need for curbing and storm sewers; (c) Improved road safety because of better skid resistance; (d) Recharge to local aquifer. The disadvantages include coldweather problems, lack of construction experience and expertise and restrictive soil conditions (Pratt, 1997). Although, pervious concrete has seen growing use in Florida, there is still very limited practical and documented experience with the material. Also, pervious pavement sites have had a relatively high failure rate in the past, which has been attributed to poor design, inadequate construction techniques, low permeability soil, heavy vehicular traffic and poor maintenance (EPA, 1999). Failure is determined when the pervious pavement can no longer function as a stormwater retention material due to clogging or as conventional pavement due to structural failure. However, with regards to Florida, some of the potential shortcomings that need to be addressed include operational and maintenance issues to minimize clogging and risk of contaminating groundwater. The US EPA fact sheet provides some basic guidance on the design of pervious pavements and states that such pavement surfaces must be placed over highly permeable layers of open-graded gravel or crushed stones. The void spaces may be used as a storage reservoir. Filter fabric must be placed beneath the gravel or stone subgrade. In response to the limited practical experience with porous concrete and with new regulations pending on post equal per volume budgets for stormwater management, an updated assessment of the performance of pervious pavements has been conducted within this paper. Specifically, an investigation addressing the design cross-section profile in regards to the materials and dimensions for use in various sandy type soils with varying locations of groundwater tables has been conducted. This research will complement the research of others nationwide with more focus on Florida conditions. The Florida Concrete and Products Association has produced a “Pervious Pavement Manual” that provides guidance on the use of this type of pavement as well as some limited performance data based on several field locations. However, these data are limited and dated. There is a strong need for current and updated investigations of the long-term performance of pervious pavements which addresses issues such as design section requirements, water management district acceptance criteria, operational and maintenance plan, infiltration rates with time (clogging potential) and water quality. The water management districts (WMDs) in Florida are responsible for the design of stormwater management systems and the design implications of the use of impervious surfaces such as regular pavements. The WMD may provide credit (either partial or total) for substituting pervious surfaces for impervious ones based on the volume of the stormwater that can be stored and allowed to replenish the aquifer. However, in discussions with WMD officials, in order to gain widespread acceptance for use in the State, answers and information are needed for the following questions:
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(a) (b)
(c) (d)
What is the design cross-section profile including materials and dimensions for use in sandy type soils and the location of groundwater table? What credit can be given as far as the yearly fraction of rainfall that can be controlled through infiltration through the pervious concrete and the parent soil? How is this applied to design storms as well as to yearly water budgets? Can vacuum sweeping or some operation and maintenance program be used to improve the infiltration capacity of pervious concrete? What is the potential for water quality improvement and the rates of evaporation through the pavement?
Background and Previous Work The hydrology of a developing area is severely impacted by the increase in impervious surface areas from roofs, roads and parking areas. These structures and storm sewers increase the total volume of runoff and increase peak stream flows that lead to downstream flooding, stream instability and endanger water quality (Field & Singer, 1982). The installation of pervious concrete in parking or low traffic roadways is one of the techniques utilizing this non-generation approach. Today, probably the most extensive use of this type of stormwater management has been in Tokyo, where it is estimated that some 494,000 m2 of pervious pavement have been constructed since 1984 (Pratt, 1997). In addition to providing significant decreases in river flows, other benefits such as the raising of groundwater levels, reduction of ground settlement, conservation of urban ecology (especially trees), and moderation of temperatures in the urban districts by local evaporative cooling has been generated by adopting this stormwater management technique (Pratt, 1997). The earliest report of portland cement pervious concrete installation in the United States was during the early 1970’s in Clearwater, Ft. Myers, Naples and Sarasota, Florida. The sandy soil conditions under the pervious pavement made these locations ideally suited for its application. Multiple concrete cores and field evaluations were conducted on these sites throughout Florida to evaluate the permeability, infiltration rate and durability of the pervious concrete after years of service (FCPA, 1990). The test results of the pavement sections showed that under actual field service conditions pervious concrete continued to demonstrate its ability to function as a stormwater system while also providing a structural pavement for traffic loadings. However, these data are limited and dated and there is a strong need for current and updated investigations of the long-term performance of pervious concrete. Pervious pavement is a viable option to satisfy the stormwater quality regulations in any area with favorable soil conditions. A designer can utilize the storage and filtration capacity above the water table of the natural soil or fill materials plus the pavement as stormwater retention storage. (FCPA, 1990) This method of storage is considered a layered storage method, with each layer above the seasonal high water table elevation having a measurable storage capacity (FCPA, 1990). Similar to a conventional retention pond, the portland cement pervious pavement must provide the reservoir capacity to store the first one-half inch of runoff and recover that volume within a
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seventy-two hour time period following a storm (FCPA, 1990). Currently a consistent statewide policy has not been established in reference to credit for storage volume within the voids in the pavement and coarse aggregate base. Further analysis is needed to develop a statewide policy for credit towards pervious concrete storage volume. Pervious concrete pavement systems are typically used in low-traffic areas, such as, parking pads in parking lots, residential street parking lanes, recreational trails, golf cart and pedestrian paths and emergency vehicle and fire access lanes. Heavy vehicle traffic use must be limited to ensure raveling or structural failure does not occur in the pervious pavement surface, which will fail under constant exposure to heavy vehicle traffic due to the low structural strength of the material. The slopes of these installations should be flat or gentle to facilitate infiltration versus runoff and the EPA recommends 4foot minimum clearance from the bottom of the system to the water table if infiltration is to be relied on to remove the stored water volume (EPA, 1999). Figure 1 shows a typical pervious concrete installation, showing an optional gravel sub-base layer.
Figure 1 Typical Pervious Concrete Installation Given suitable site conditions, use of pervious concrete can reduce the need for stormwater drainage systems and retention ponds required for impermeable pavements by Florida statutes. Further benefit of substitution of pervious surfaces for impervious ones is the acquisition of credit based on the volume of the stormwater that can be stored and allowed to replenish the aquifer. Currently, in the Saint Johns River WMD, credit cannot be given for pervious concrete without current and updated investigations of the material that address the design cross-section profile including materials and dimensions for use in sandy type soils and the location of the groundwater table (Register, 2004). Due to increased interest, the need for a current evaluation of the performance of pervious pavements is evident. This paper addresses issues such as materials and dimensions for use in sandy type. In addition, a field test method for infiltration rates is developed treating the pavement as a system consisting of the pervious concrete and the sub-base soil. Lastly, a recommended design section and specifications for the pavement system for sandy soils is provided.
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System Approach to Pervious Concrete Pavement This paper focuses on the hydraulic operations of a pervious concrete system including infiltration rates, storage capacity and clogging potential. Pervious concrete allows water to infiltrate at very high rates, typically 100 to 200 inches an hour, whereas the underlying soils will infiltrate water a much lower rate, usually by 1 to 2 orders of magnitude. Therefore, it is important to consider that the effects of the entire system (pavement and soil) when predicting the infiltration capacity of pervious concrete pavements. A new test method for determining the in situ infiltration rate of the pervious concrete system, namely an embedded Single-ring Infiltrometer, is discussed in this paper. Field Testing using Single Ring Infiltrometer A review of previous literature and some initial testing in this project have indicated that a soil surface-based device such as a Double-ring Infiltrometer (ASTM D3385-03) that rests on top of the concrete will not generate accurate infiltration rates due to primarily a lateral migration of water. As a result, an embedded Single-ring Infiltrometer is developed in this research in order to determine the infiltration rates of the pavement system. It can be installed either post- or pre-construction. As described in this paper, infiltration rates are measured at several field sites and also on samples collected from these sites under controlled laboratory conditions, using this Single-ring Infiltrometer It is designed to the dimensions of the concrete cores produced when the pervious concrete surface is drilled utilizing a 12” outer diameter (OD) concrete core bit. Further details of the field testing methodology are provided in the next section. The concrete cores produced during the drilling have a diameter of 115/8”, leaving a cut of 3/16” to insert the Single-ring Infiltrometer. Figure 2 presents the cross-section and top view of the Infiltrometer showing the dimensions and the in-place configuration as it would look inserted into the pervious concrete and subsoil system. The Single Ring Infiltrometer utilizes the same testing procedure as the Doublering, as outlined in ASTM D3385-03 “Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer” with the modification of its embedment and the use of a single ring. It is postulated that this is a valid modification in order to test the infiltration rates of the entire system and avoid a lateral migration of the water in the pavement alone. The depth of penetration is an important variable and will be refined based on results from extensive field testing. Initially, a depth of penetration of 14 inches was used in all testing programs, as shown in Figure 2.
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Pervious Concrete
6”
11-5/8”
20” Subsoil
11-Guage Steel
Figure 2: Single Ring Infiltrometer In an effort to model field conditions, two pervious concrete test cells were constructed at the University of Central Florida - Stormwater Management Laboratory (SMA). These cells are each 6 foot by 6 foot squares and approximately 4-feet deep. One cell contains a 5 inch deep reservoir of 3/8 – ½ inch coarse aggregate, and both cells have a 5- inch thick pervious concrete slab. The soil used in the cells was Type A hydrologic soil with the highest infiltration potential and an average infiltration rate of 2.6 inches per hour. The soil was compacted in 8 inch lifts to a minimum of 92% of the Standard Proctor maximum unit weight of 104 lb/ft3. Both cells were sealed and fitted with under-drain systems to measure system mass balance. The results of the Single-ring Infiltrometer tests for cumulative infiltration volume with time are shown in Figure 3. All of the tests were performed using duration of 45 minutes. Core A refers to the core in test cell 1 (without the drainage layer) and core B to that in test cell 2 (with the drainage layer). The uncompacted soil infiltration rates were found to be 12-20 inches per hour. Cum ulative Infiltration vs. Tim e
Cumulative Infiltration (mL)
4000
Core A: 1/19
3500
Core B: 1/19
3000
Core A: 1/20 2500
Core B: 1/20
2000
1500
Core A: 1/21
1000
Core B: 1/21
500
Core A: 1/25
0 0
5
10
15
20
25
30
35
40
45
50
Core B: 1/25
Tim e (m in)
Figure 3: Single-ring Infiltrometer – cumulative infiltration volume with time
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A previous Double-ring Infiltrometer test performed on the compacted bare soil in the test cell prior to the placement of pervious concrete pavement resulted in an average infiltration rate of 2.6 in/hr. The infiltration rates for the pavement systems (core and soil) are summarized in Table 1. The average rate was found to be 1.67 inches per hour. Table 1: Results of the Single-ring Infiltrometer tests on Pervious Concrete Test Cell Specimens
Test Location Core A Core B Core A Core B Core A Core B Core A Core B
Test Date
Volume of Rainfall (in)
Infiltration Rate (in/hr)
1/19/05 1/19/05 1/20/05 1/20/05 1/21/05 1/21/05 1/25/05 1/25/05
1.94 1.49 0.85 0.89 0.93 1.03 1.37 1.21
2.40 2.41 1.16 1.21 1.03 1.45 1.48 1.45
Based on these tests, it is observed that the pervious concrete and subsoil system displays infiltration rates of nearly the same magnitude (2.6 compared to 1.67 in/hr) as the subsoil prior to the pervious concrete placement. In addition, the infiltration rates from the Single-Ring Infiltrometer tests performed on the pervious concrete and subsoil system decrease when the subsoil is still saturated from previous testing. Laboratory Test on Design Sections to Test Infiltration Rates The test cells at the SMA laboratory were originally planned for use in conducting system mass balance measurements. However, due to problems with sealing the chambers, leaks developed and the overall balance of water could not be determined accurately. It was then decided that a laboratory-scale chamber will be constructed to provide more control over the testing process. As a result, a laboratory control chamber (Figure 4) was designed to investigate the performance of pervious concrete core samples with time. It will be used in the future to address issues such as clogging (infiltration rates with time) and water table impacts on infiltration rates. The laboratory control chamber is filled with soil typical of the conditions found in the field investigation of this research. The soil was tested extensively and the results of the various tests are summarized in Table 2. The pervious concrete cores obtained from the field sites are placed on top of the soil to be tested for infiltration using the Single-ring Infiltrometer. A cross-section the circular laboratory control chamber with the pervious concrete core is shown in Figure 5.
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Figure 4: Photograph of the Laboratory Testing Control Chamber Pervious Concrete 12” 20”
Plastic Tank
4’
Subsoil
½” PVC Pipe Outlets @ 4, 3 & 2’ from top of tank
2’
Figure 5: Laboratory Testing Control Chamber
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Table 2: Properties for the Soil in the Laboratory Chamber Test Grain Size Analysis Constant Head Permeability Test Modified Proctor
Soil Properties USCS Soil Classification = SP, Poorly graded sand Percent Passing No. 200 Sieve = 1% Coefficient of Permeability = 5.71 in/hr Dry Unit Weight = 96.1 pcf Maximum Dry Unit Weight = 108 pcf Optimum Moisture Content = 13%
Field Test Results Several pervious concrete sites in the Central Florida area were tested to measure infiltration rates using the embedded Single-Ring Infiltrometer Test. These sites ranged from 6 to 18 service years and are located around the city of Orlando except for the Florida Department of Environmental Protection (FDEP) office located in Tallahassee, Florida. These sites are functional parking lots that are currently in operation and are in various conditions in terms of maintenance, clogging and raveling. The locations and year of construction for each field site are listed below: • Site 1: Sun Ray Store-away Storage Facility: Lake Mary, Florida [1991]. • Site 2: Strang Communication Office: Lake Mary, Florida [1992]. • Site 3: Murphy Veterinarian Clinic: Sanford, Florida [1987]. • Site 4: FDEP Office: Tallahassee, Florida [1985]. • Site 5: Florida Concrete & Products Association Office: Orlando, Florida [1999]. A standardized procedure was developed and followed in the field to determine the infiltration rates of the pervious concrete. The step-by-step procedure is outlined below: 1. The pervious concrete surface is cored in three evenly spaced locations utilizing a 12 inch OD core bit. The coring rig and the core bit are shown in Figure 6.
Figure 6: Coring Rig and Core Bit for Field Testing 9
The core samples are left in place after drilling for in situ infiltration testing. Figure 7 shows the 12 inch core placed next to the location in the pavement. It is clear that the pavement system at this site does not have a drainage layer of gravel. This configuration is typical for pavements on soils with high permeability values.
Figure 7: Pervious Concrete Pavement Core 2. Infiltration rates of the three cored locations are measured using the embedded Single-ring Infiltrometer Test as discussed in the previous section. Figure 8 shows the testing process with the infiltrometer in the embedded state.
Figure 8: Embedded Single-ring Infiltrometer test at a Field Site 3. Pervious concrete cores are then extracted and returned to the Stormwater Management Academy (SMA) laboratory to be tested individually using the Laboratory Control Chambers, for the permeability of the pervious concrete and the effect of sediment loading on its infiltration capability.
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4. The field unit weight of the subsoil is then determined using the Sand Cone Method (Figure 9) as outlined in ASTM D 1556 “Standard Test Method for Density and Unit Weight of Soil in Place by the Sand-Cone Method”. 5. A soil profile beneath the pervious concrete surface is generated utilizing a handoperated bucket auger. Soil samples are obtained at locations of soil-type change down to the depth of the water table. These soil samples are later analyzed for permeability, void ratio, and grain sizes using the methods outlined in ASTM D 2434-68 and ASTM C 136-04. 6. Water table depths are recorded for use in modeling studies planned for the pervious concrete system.
Figure 9: Performing the Sand Cone Test to determine the Unit Weight of Subsoil 7. The subsoil shall be replaced and the pervious concrete is repaired using the original specifications at the locations where it was cored (Figure 10).
Figure 10: Repair of the Cored Pavement Area At the present time, all field locations have been tested and the results from these tests are being compiled and analyzed. The concrete core samples obtained in the field will be 11
further utilized in the investigation of maintenance possibilities by artificially clogging the specimens and comparing infiltration rates before and after cleaning of the pervious concrete surface. A summary of the results obtained from the field tests performed at the five locations is presented in Table 3.
Table 3: Results for infiltration rates at different field sites
Test Location
Avg. Concrete Rate Avg. Soil Rate [in/hr] (Range) [in/hr]
Limiting Factor
Site 1 – Area 1
25.7 (19 – 32.4)
34.5
Concrete
Site 1 – Area 2
3.6 (2.8 – 4.5)
14.8
Concrete
Site 2
5.9 (5.3 – 6.6)
5.4
Soil
Site 3
14.4 (2.1 – 22.5)
21.8
Concrete
Site 4 – Area 1
2.1 (0.7 – 4.5)
15.6
Concrete
Site 4 – Area 2
2.9 (0.9 – 4.9)
15.6
Concrete
Site 5
3.7 (1.7 – 5.4)
8.8
Concrete
Based on these results, the following observations may be made about the performance of pervious concrete pavement systems: •
•
•
The pervious concrete and subsoil system displays infiltration rates of nearly the same magnitude as the subsoil in locations where the pervious concrete infiltration rate is higher than that of the subsoil. In addition, the rates are comparable to stormwater retention ponds. The design rate is typically 2 in/hr which is exceeded in all of the cases above. A significant number of the pervious concrete cores were found to have very low or no infiltrations rates and are primarily cases of improper pervious concrete construction and placement where the voids of the concrete are not present. Proper mix design and placement techniques will be presented in detailed specifications at the completion of this project. This field test may also be applied to soils with lower infiltration rates as seen in the case of Site 2.
Recommended Construction Specifications Specifications for the construction of pervious concrete pavements in the state of Florida are being developed as a result of this research. Existing methods available in the FC&PA Manual (1990) are being refined based on the performance of these pavements
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in the field and in the laboratory control chambers. The preliminary specifications are summarized below. 1.0 Contractor Qualifications Prior to award of contract, contractor shall provide proof of qualifications and experience including: ACI Concrete Finisher Certifications; Pervious Concrete Finisher Certifications (NRMCA); Sample of product (i.e., cores and/or test panels) 2.0 Materials and Mix Design Cement shall comply with the latest specifications for portland cement or blended hydraulic cements. Unless otherwise approved in writing by the Engineer, the quality of aggregates shall conform to ASTM C 33. Aggregates may be obtained from a single source or borrow pit, or may be a blend of coarse and fine aggregate. Mineral admixtures shall conform to the requirements of ASTM C 618 (fly ash), ASTM C 989 (slag) and ASTM C 1240 (silica fume). Chemical admixtures including, water reducing and retarding admixtures, shall conform to ASTM C 494 and must be approved by the Engineer prior to use. Water shall be clean, clear and free of acids, salts, alkalis or organic materials that may be injurious to the quality of the concrete. It must conform to ASTM C 1602. 3.0 Construction Subgrade Material - The top six (6) inches shall be composed of granular or gravely, predominantly sandy soil. It is desirable for the soil to contain no more than a moderate amount of silt or clay. Granular or Gravel sub-base may be placed over subgrade (see 3.3 Reservoir Option). Subgrade shall have a permeability of no less than one (1) inch per hour. Site Preparation Subgrade shall be leveled to provide a uniform construction surface with a consistent slope not more than 5 %. It is recommended that the slope be as flat as possible (as per EPA 832-F-99-023). After leveling, soils shall be compacted to a minimum density of 92% of a maximum dry density as determined by ASTM D 1557 or AASHTO T 180. Forms - Forms may be either wood or steel and shall be the depth of the pavement. Forms shall have sufficient strength and stability to support pavement and mechanical equipment without deformation. The edge of existing pavement may be used as a form. Placing and Finishing - Mixers shall be operated at the speed designated as mixing speed by the manufacturer. The portland cement aggregate mixture may be transported or mixed on site and shall be used within 45 minutes of the introduction of mix water, Concrete shall be deposited as close to its final position as practicable and such that fresh concrete enters the mass of previously placed concrete. An internal vibrator should not be used to consolidate concrete. Following strike-off, the concrete shall be compacted to form level, utilizing a steel roller made from nominal 10inch diameter steel pipe of ¼ -inch thickness. The roller shall have enough weight to provide a minimum of 10 psi vertical force. Curing - As soon as possible after placement, pervious concrete should be covered with impermeable plastic sheeting – minimum six (6) mil thick.
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The plastic shall cover all exposed concrete and overlap the edges. The edges of the plastic shall be secured by some means. Jointing - Longitudinal control joints shall be constructed at the midpoint of the travel lanes if the lane width exceeds 15 feet. Construct transverse joints at a maximum 20 feet apart in travel lanes. The joints are to be installed in the plastic concrete by a roller with a flange welded to it (roller groover). The depth of the joints shall be ¼ of the pavement thickness but is not to exceed 1.5 inches. 4.0 Post Construction After placement, construction and/or heavy vehicle traffic should be limited to ensure the structural and infiltrative integrity of the concrete. Runoff from unfinished or landscaped areas should be restricted from flowing over pervious concrete slab. An acceptable form of curbing shall be constructed to protect the edges of the pervious slab from excessive wear. Pervious concrete areas should be clearly identified with signs. The recommended design section showing the curbing, subgrade preparation and pervious concrete pavement is shown in Figure 11.
Figure 11: Design Section for Pervious Concrete Pavement System
Conclusions In this paper, the hydraulic performance of pervious concrete pavement system (pavement and soil) is presented. A new method of testing for the in situ infiltration rate of a pervious concrete system, using an embedded Single-ring infiltrometer was developed and presented. More work will be continued to investigate the repeatability of the results from this new test method. Several field analyses include testing for system
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infiltration rates were conducted. In all the field tests, the infiltration capacity of the pervious concrete exceeded the design value of 2 in/hr. A preliminary design section is detailed. Acknowledgments The authors would like to acknowledge the financial support of the Florida Department of Transportation, Rinker Materials and the RMC Research Foundation. In addition, we would like to thank the Florida Concrete and Products Association and the Florida Department of Environmental Protection. References 1. United States Environmental Protection Agency, “Storm Water Technology Fact Sheet Porous Pavement”, EPA 832-F-99-023, Washington D.C., September 1999. 2. Pratt, C.J., “Design Guidelines for Porous/Permeable Pavements”, Sustaining Water Resources in the 21st Century: ASCE Conference proceedings, Malmo, Sweden, September 1997, pp. 196-211. 3. Field, R., Masters, H. & Singer, M., “An Overview of Porous Pavement Research”, Water Resources Bulletin, Vol. 18, No. 2, 1982, pp. 265-270. 4. Florida Concrete & Products Association, Inc., “Portland Cement Pervious Pavement Manual”, www.fcpa.org, 1990. 5. Register, M., St; Johns River Water Management District, Florida, Personal Communication, 2004.
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