Pervious Concrete Pavements: How to Reduce Demand on Your Stormwater System

Transcription

1 Pervious Concrete Pavements: How to Reduce Demand on Your Stormwater System Jason Wimberly, EI, MCE Director of Technical Services Carolinas Ready Mixed Concrete Association

2 Disclaimer This presentation has been prepared solely for information purposes. It is intended solely for the use of professional personnel, competent to evaluate the significance and limitations of its content, and who will accept full responsibility for the application of the material it contains. The Carolinas Ready Mixed Concrete Association and any other organizations cooperating in the preparation of this presentation strive for accuracy but disclaim any and all responsibility for application of the stated principles or for the accuracy of the content or sources and shall not be liable for any loss or damage arising from reliance on or use of any content or principles contained in this presentation. Unless otherwise indicated, all materials in this presentation are copyrighted to the Carolinas Ready Mixed Concrete Association. All rights reserved. Therefore reproduction, modification or retransmission in any form is strictly prohibited without the prior written permission of the Carolinas Ready Mixed Concrete Association Carolinas Ready Mixed Concrete Association 2010 National Ready Mixed Concrete Association (concept)

3 1 Needs and Environmental Benefits 2 Sustainability 3 Design, Specification and Performance 4 Getting Pervious Concrete into Your LDC 5 Case Studies

4 1 Needs and Environmental Benefits Legislation Clean Water Act NPDES Phase I and II Regulations Available land suitable for development Fixed stormwater infrastructure; aging and with limited capacities Municipalities and other public entities are demanding permeable pavements like never before!

5 Parking Lots: Environmental Disasters Almost total runoff Valuable water resources are wasted Public water required for vegetation Runoff is hotter, damaging ecosystems Rapid, high-volume runoff requires larger public drainage facilities Runoff has chemical pollutants, requiring treatment Hot parking lots add to the urban heat island effect and ozone creation

6 Stormwater Regulations EPA Stormwater Phase II Regulations: Cities with population >50,000 & densities >1,000 per sq mile must manage stormwater Pervious pavements are an EPA BMP NC: DWQ provides quantity credit for coastal plains, barrier islands and sandhills and other areas where P 0.52 in/sf/hr SC: up to local jurisdiction to approve

7 What Does EPA BMP Say construction using pervious materials may not require as much treatment as other BMP approaches. (Porous pavements) may also lead to an increase in environmental benefits. Pollutant Removal (%) Study TSS TP TN COD Metals Prince William, VA Rockville, MD Table 2: Effectiveness of porous pavement pollutant removal Porous pavement can be used to provide ground water recharge and to reduce pollutants in stormwater runoff. Porous pavement is more expensive than traditional asphalt however, when used in combination with other techniques where land prices are high, the savings associated with decreased land consumption should be considered.

8 Why are Permeable Pavements a BMP? Because they use a non-condensed INFILTRATION methodology for stormwater management and treatment They minimize or eliminate the need for retention/detention ponds They reduce the impact on local gov t stormwater management systems They provide pollutant removal They reduce or eliminate sheet flow

9 Pervious Concrete Pavements: Environmental Advantages Percolation recharges groundwater Water resources are conserved Less need for irrigation Adjacent vegetation allowed more rainwater Reduced runoff Cooler surface has less impact on air temperature Does not have to be resurfaced unlike porous asphalt Is a rigid pavement

10 2 Sustainability Low Impact Development Pollution Treatment Tree Protection Cool Communities Light Pollution Reduction

11 Sustainability: Low Impact Development Pre-Development Post-Development Low-Impact Development

12 Sustainability: Pollution Treatment About 90% of the surface pollutants are carried off by the first ½ to 1 of rainfall (first flush) First flush passes through pervious concrete into storage basin then soil Soil filters and treats rainfall Rainfall is spread over the entire parking area (instead of being concentrated in a pond) Hydrocarbons treated by filtration and microbial conversion

13 Sustainability: Protects Trees Can pave within the drip line. Water & air filters to roots.

14 Sustainability: Cool Communities (Urban Heat Island Effect) Can you guess what this is? If you guessed a Concrete Parking Garage, you re right! Akers Mill Mall; Atlanta, GA

15 Sustainability: Light Pollution Reduction Maintain safe light levels while avoiding night sky pollution Using pervious & conventional concrete in parking areas can reduce lighting requirements by as much as 30%

16 3 Design, Specification and Performance Structural Design Considerations Hydrological Design Considerations Mix Design & Performance Pervious Concrete Hydrological Properties Recommended Maintenance Freeze-Thaw Resistance

17 2 feet minimum System Structure Design: Cross-section diagram Pervious Concrete Compacted Sub-base (#57/#67 Stone) Filter Fabric Compacted Sub-grade (92% max) Water Table (wet season level)

18 System Hydrological Design Soil permeability Don t be misled by empty req ts for high permeabilities Local rainfall data Porosity of pervious concrete Thickness of pervious concrete Porosity of washed stone sub-base Thickness of washed stone sub-base Adjacent areas that will drain onto pervious Vegetated Non-vegetated (building roofs, etc.) DESIGN FOR A PURPOSE

19 Pervious Concrete: Mix Design Cementitious Materials: ~500 lbs Cement, Fly Ash, Slag Coarse Aggregate: ~ 27 cf/cy Usually 78 or 89. Blends can be used to increase flexural capacity. Talk to the local producer to determine availability Fine Aggregate: normally not used Water: +/- 23 gallons (w/c ratio ~ ) Admixtures Viscosity Modifiers Water Reducers Retarders Hydration Stabilizers (helps to prolong hydration) Others

20 Pervious Concrete: Mix Performance Slump: 0 6+ inches* Void Content: 15% - 30% Common in Carolinas is ~20% Higher void content = lower strength Density (unit weight): pcf Compressive Strength: psi Common f c seen in Carolinas, 2000 psi Introduction of small amount of fine aggregate can increase strength Flexural Strength: psi Strength should not be used for acceptance criteria

21 Pervious Concrete: Hydrological Properties Drainage rate: 3-5 gal/min/sf Equivalent of 275 to 450 of rain per hour! More than ½ of all rain events are ½ water or less A 6 concrete section w/ 20% voids holds 1-1 ¼ of stormwater

22 Maintenance Regenerative air sweepers work best Tymco Model 600 Schwarze Model A7000 Eljin Model Crosswind

23 Freeze-Thaw Resistance NC & SC are considered in the Wet Freeze region Pervious concrete that is partially saturated should have sufficient voids for the movement of water and thus demonstrate good freeze-thaw resistance.

24 4 Getting Pervious Concrete into Your LDC

25 What is a Land Development Code? AKA: LDC LDR Covers: Streets and Roads Utilities Landscaping Parking Requirements Stormwater Management

26 Who Controls the LDC? Usually the City/County Planner Everybody Influences: Mayor Council Staff Citizens Developers

27 Why Pervious Concrete Credits? Drives developers/owners to look at alternate means of stormwater control Incentives drive decisions Drives engineers to look at alternative designs Allows for easy permitting If written appropriately, can provide an avenue to control quality

28 Types of Pervious Concrete Credits Stormwater credit Quantity Quality Credit for pervious area Used to offset Impervious Surface Ratios (ISR) Especially important in Watersheds Big Box Ordinances Wetlands Setback Tree Setback

29 Stormwater Credit

30 ISR Credit ISR = Impervious Surface Ratio

31 ISR Credit

32 Wetland Setback

33 Wetland Setback

34 Tree Setback - Retail

35 Tree Setback - Office

36 Tree Setback - Residential

37 5 Case Studies

38 Charlotte, NC: Wilmore Walk

39 Wilmore Walk LID Site

40 Wilmore Walk 2.8 acre Multi-Family Urban Redevelopment Over 85% of site runoff is treated

41 Preliminary Soils Survey

42 Plan Pervious Concrete Bio- Retention Bio- Retention

43 Wilmore Walk BMPs were retrofitted into an existing site design, including 6,355 sf of pervious concrete with 3,800 cf available storage in a gravel base All water quality permit requirements were satisfied using Bio-Retention BMPs

44 Wilmore Walk Existing soils were investigated Green-Ampt equations for infiltration were used for design of basin beneath the pervious concrete area Bio-retention areas were located with grading plans adjusted accordingly.

45 Infiltration in Sandy Clay Loam Site-Specific Infiltration Testing: in/hr Avg. 0.9 in/hr Field infiltration rate helps determine probable outcome and initial design parameters

46 Design Stone Infiltration Reservoir sized for the 2yr storm for respective watershed Watershed includes surrounding rooflines and any off site contributions. Seasonal ground water fluctuations important

47 Excavation for reservoir after all surrounding landscape and hardscape is finished

48 Sub-grade Prep Clay soils are highly susceptible to inadvertent compaction

49 Stone Reservoir

50 Pervious Concrete Installation May 10, 2005

51 Pervious Concrete Installation

52 Pervious Concrete Installation

53 Pervious Concrete Pavement

54 Finished Pervious Concrete

55 Infinities USA Pressure Water Level Data Logger Monitoring

56 Preliminary Monitoring Data Aug-Sept 06 Average infiltration rate of 0.9 in/hr (0.23 cm/hr) 13 in 6 days in semi-dry conditions Rawls, Brakensiek and Saxton 1982 : Sandy Clay Loam = K of 0.43 cm/hr Rawls, Brakensiek and Saxton 1982 : Clay Loam = K of 0.23 cm/hr

57 Testing New Standard Test Method for Infiltration Rate of In Place Pervious Concrete being developed by ASTM committee C09/49 4 years later rates of in/hr

58 Preliminary Monitoring Data Saturated Soils Feb. 06 Preliminary data suggests average infiltration rate of 0.6 in/hr (0.15 cm/hr) (7.5 in 5.5 days) in saturated soil Extended research in progress through UNCC. Sponsored by the City of Charlotte Engineering. Rawls, Brakensiek and Saxton 1982 : Silty Clay Loam = K of 0.15 cm/hr

59 Bio-Retention Drain System

60 Bio-Retention Drain System

61 Finished Bioretention as landscape areas Rapid infiltration rate to start. Eventually stabilized in 6 mos.

62 Bio-retention as landscape areas Overflow weir

63 Atlantic Beach, NC: City Streets Before

64 Atlantic Beach, NC: City Streets After

65 Chapel Hill, NC: Friday Center

66 Asheville, NC: Western Carolina Retinal Associates

67 Wilmington, NC: Halyburton & Ann McCrary City Parks

68 Wilmington, NC: Costco

69 Charlotte, NC: CRMCA Office

70 Columbia, SC: Wal-Mart

71 James Island, SC: Tennis Park

72 Simpsonville, SC: Car Wash Owner Savings Using Pervious Concrete: $30,000

73 McClellanville, SC: Dollar General Owner Savings Using Pervious Concrete: $15,000

74 New Jersey: Forsgate Industrial Park 4000 psi* pervious concrete mix ½-inch coarse aggregate, 15% sand, 2 lb fibers 8 thick concrete over 14 washed stone base Placed by NRMCA- Certified Pervious Concrete Contractor Owner Savings Using Pervious Concrete: $UTD

75 Future Project: Greenville, SC Projected Owner Savings Using Pervious Concrete: $120,000

76 Beijing, China: 2008 Olympics

77 How Many Cars Can You Park on Your Detention Pond?

78 How About 587? Closed existing detention pond Paved with Pervious Concrete 40% additional retail space available Prime Retail Outlets Williamsburg, VA

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80 The CRMCA isyour Source for Resources NRMCA Pervious Concrete Contractor Technician Installer Craftsman Carolinas Ready Mixed Concrete Assn

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