Porous Asphalt Pavements for Storm Water Management

Porous Asphalt Pavements for 

Storm Water Management 

Dr. Will Rogers 

Technical Director 

Georgia Asphalt Pavement Associa=on

Porous Asphalt Pavements 

• Introduc=on 

• Applica=ons 

• Materials & Design 

• Construc=on Guidelines 

• Maintenance 

• Jobsite Pictures 

• Keys to Success








• Keys to Success

Introduc=on to Porous Pavements

Introduc=on: Benefits of Porous 

Asphalt 

• Reduce Earthwork Cut & Fill 

• GA Contractors Regularly place the OGFC used 

for Porous Asphalt 

• Treats Runoff 

• Recharges Ground Water 

• No Discharge Permit

Reference 

Prince 

William Site 

Rockville 

Site 

Univ. of 

New 

Hampshire 

Introduc=on: Water Quality 

Total 

Suspended 

Solids 

Total 

Nitrogen 

Percent Pollutant Removal 

Total 

Phosphorus 

Lead Zinc 

Petroleum Hydrocarbons 

in Diesel Range 

95 85 65 98 99 -‐-‐ 

82 80 65 -‐-‐ -‐-‐ -‐-‐ 

99 -‐-‐ 38 -‐-‐ 96 99








• Keys to Success

Applica=ons: Parking Lots

Applica=ons: Recrea=onal Facili=es

Applica=ons: Streets & Roads








• Keys to Success

Materials & Design: Subgrade Soil 

• Soil Inves=ga=on 

– Boring or Test Pits: 6 – 8’ Deep 

• Depth ≈ 2’ Below Expected Boaom of Recharge Bed 

• Number of Pits based on Pavement Use & Size 

• Soil Condi=ons Observed 

– Test Permeability 

– Depth to High Water Table 

– Depth to Bedrock 

– Soil should Drain: 

• Within 24 – 72 Hours

Materials & Design: Subgrade Soil 

Saturated Hydraulic ConducRvity of Hydrologic Soil Groups when a Water Impermeable Layer 

Exists between 20 and 40 inches 

Hydrologic Group A Hydrologic Group B Hydrologic Group C Hydraulic Group D 

A > 5.67 in/hr 1.42 

Saturated Hydraulic ConducRvity of Hydrologic Soil Groups when any Water Impermeable 

Layer exists at a Depth Greater than 40 inches 

Hydrologic Group A Hydrologic Group B Hydrologic Group C Hydraulic Group D 

A > 1.42 in/hr 0.57 

Kentucky

Materials & Design: Geotex=le 

• Non-‐Woven Geotex=le “Filter Fabric” 

Test Requirement 

Grab Tensile Strength 

(ASTM D4632) 

Mullen Burst Strength 

(ASTM D3786) 

Flow Rate 

(ASTM D4491) 

UV Resistance Aper 500 Hours 

(ASTM D4355) 

≥ 120 lbs 

≥ 225 psi 

≥ 95 gallons / minute / SF 

≥ 70%

Materials & Design: Stone Recharge 

• Typically No. 3 Stone 

– Clean, Washed 

Bed 

• Typically Between 12 and 36 inches 

• ≈ 40% Voids 

– Typically stores Between 4.8 and 14.4 inches of 

Precipita=on 

– Since this Exceeds most Storm Events, Consider using 

Recharge Bed to Treat nearby Impermeable Surfaces. 

• Pretreatment by be Required

Materials & Design: Stone Recharge 

• In Most Cases: 

Bed 

– Recharge Bed Thickness Determined By: 

• Water Quan=ty 

• Soil Infiltra=on Rate 

– Porous Asphalt Thickness Determined By: 

• Traffic Loading 

• Same Structural Strength when Dry or Wet 

• Recharge Bed Geometry

Materials & Design: Flat Recharge Bed

Materials & Design: Choker Course 

• Op=onal 

• Typically No. 57 Stone 

• Typically 1” Thick 

• Designed to Provide Smooth Surface to Pave 

On 

– NOT Designed to fill Surface Voids of Recharge 

Bed

Materials & Design of Porous Asphalt 

1. Consider Loca=on for Porous Pavement Early 

in Design Process 

2. Soil Infiltra=on Rates: 0.1 – 10 inches/hour 

work best 

3. Min. Depth to Bedrock / Seasonal High Water 

Greater than 2 p. 

4. Boaom of Infiltra=on Bed must be Flat 

5. Max. Pavement Slope = 5%. Terrace if 

Needed.

Materials & Design of Porous Asphalt


6. Route Runoff from Nearby Impervious Areas 

7. Max. Ra=o of Impervious: Pervious Area -‐ 

5:1. For Carbonate Soils – 3:1. 

8. Design Should Provide for Alternate Path for 

Stormwater to Enter Recharge Bed 

9. Include Overflow System as Required 

10. Recharge Bed should Drain within 12 – 72 

Hours


40" - 48" TO WATER TABLE 

ROOF LEADERS SHOULD BE 

EXTENDED INTO THE RETENTION 

BED WHERE POSSIBLE 

OPEN EDGE DRAIN 

DIRECT RAINFALL 

RUNOFF IF IMPERVIOUS 

SLAG RETENTION BED 

2" x 6" RECTANGULAR 

EMERGENCY OVERFLOW 

(3) 1" Ø ORIFICE(S) 

H-20 RATED CAST 

IRON GRATE 

WATER QUALITY 

SWALE

Materials & Design: Structural 

• Most Porous Asphalt Pavements are Low 

Volume 

– Design Based on rain Event & Volume of Water to 

be Retained 

– Most Porous Pavements Overdesigned 

• Stone Recharge Bed is Structural 

• If Expec=ng Trucks / Heavy Loadings 

– Design these areas Separately 

– Consider Thickness & Mixture Type

Materials & Design: Porous Asphalt 

• Open-‐Graded Fric=on Course (OGFC) 

– Same Pavement that Tops Interstates in GA 

– On Interstates, Typically: 

• Polymer-‐Modified PG76-‐22 

• Fibers 

– Controls Drain-‐Down, Scuffing 

– Also Available: 

• Crumb Rubber-‐Modified Binders 

– In Lieu of Polymer. S=ll Bumps PG Grade to PG76-‐22. 

– Allows Recycling of Crumb Rubber 

• Warm Mix Addi=ves 

– Reduces/Eliminates Draindown


• Bump Binder Grade from PG64-‐22 to PG76-‐22 

– Two Grades up from Standard Grade 

• Air Voids: Min. of 16% 

• Asphalt Content: Min. of 5.75% 

• Moisture Suscep=bility – These mixes have 

very low Stripping Poten=al 

– Rule of Thumb: If Dense-‐Graded Mix using this 

aggregate requires An=-‐Strip Agent, Use it. 

– Georgia is a Lime State, but may also consider 

WMA addi=ves like EvoTherm

Materials & Design: GDOT Sec=on 828: 

OGFC


Mix NMAS ApplicaRon Layer Thickness 

3/8” [9.5mm] 

OGFC 

1/2” [12.5mm] 

OGFC 

3/4” [19 mm] 

OGFC 

3/4” [19 mm] 

ATPB 

Parking/Recrea=on Facili=es 1.5 – 3.5 Inches 

Wearing Surface, Streets, Heavy Commercial 2.0 – 4.0 Inches 

Wearing Surface, Roads, Heavy Commercial 2.0 – 5.0 Inches 

Base Course 3.0 – 6.0 Inches

Materials & Design – Minimum 

Asphalt Thickness

Materials & Design: Structural – Heavy 

• ADOT Constructed Structural Porous 

Pavement Roadway 

– Constructed in 1986 

– 6” of 3/8” NMAS Open Graded Asphalt 

• SN = 0.40 

– 6” Asphalt Treated Permeable Base 

• SN = 0.20 

– 8” Stone Recharge Bed 

• SN = 0.11 

• Performing Well as of 2008 

– MR of Porous Asphalt ≈ 32 – 45% of Dense HMA

Materials & Design: Overflow Systems 

• In General, Used if: 

– Soil Will Not Drain in 24 – 72 Hours 

– Security Against Larger Storm Events 

• Discharge to: 

– Rain Garden 

– Storm Drain System 

– Body of Water

Materials & Design: Overflow Systems

Materials & Design: Overflow Systems 

Outflow to 

Other BMP 

Overflow 

Weir

Materials & Design: Other 

Considera=ons 

• Rou=ng Stormwater from Impervious Areas 

– Roofs, Adjacent Roadways, ect… 

– Open Pipe Directly into Recharge Bed 

– Consider Sediment Control Devices 

– Remember 5:1 Ra=o 

• Provide Alternate Path 

– Good Prac=ce to Provide Alt. Path for Runoff to 

Enter Recharge Bed 

– Extreme Storms, Clogging

Materials & Design: Other 

Considera=ons 

• Overflow Structures 

– For Soils unable to Drain w/in 72 Hours 

– For Higher-‐Level Storm Events & Slow Draining 

Soils 

• Protect from Sedimenta=on 

– Construc=on is Dirty 

– Ideas: 

• Construct Late in Schedule, if Allowed 

• Blend Impervious/Porous Pavements on-‐site 

• Cover Porous Pavement with Geotex=le to Protect 

from Clogging








• Keys to Success

Construc=on Guidelines 

• Protect Site from Excessive Heavy Equipment 

– Low Ground-‐Pressure Equipment 

• Wider Tracks or Over-‐Sized Tires 

– Prevent Compac=ng Soil & Reducing Permeability 

• When Placing the Filter Fabric: 

– Min. 16” Overlap 

– Extend Min. 4’ Outside Recharge Bed to Prevent 

Sedimenta=on from Entering Bed 

– Fold Excess Over Recharge Bed un=l Paving

Construc=on Guidelines: Bed 

Excava=on

Construc=on Guidelines: Geotex=le

Construc=on: Drain Pipes

Construc=on: Drain Pipes


• Install Drainage Pipes, if Required, Just aper 

Placing Geotex=le 

• Place Aggregate for Stone Recharge Bed 

– Dump Aggregate at Edge of Bed, where Possible 

– Place 8 – 12 Inches Using Track Equipment 

– Compact/Seat with a Single Pass from a Light 

Roller or Vibratory Plate Compactor 

• Install Choker Course, if Required

Construc=on Guidelines: Recharge Bed


• Pave ATPB (if Required) and OGFC in 2 – 4” Lips 

– Tracked Paver Recommended 

– Follow GDOT Guidelines for OGFC/PEM 

– GA Contractors place OGFC/PEM Regularly 

• Compact w/ 10 TN Sta=c Roller 

– 2 – 4 Passes 

– Remove Roller Marks w/Lighter Roller aper Cooling 

• Limit Traffic for First 24 Hours 

– Mix may be more Tender than Usual

Construc=on: Paving

Construc=on: Paving

Construc=on: Rolling








• Keys to Success

Maintenance 

• Keep Sediment Control In-‐Place un=l 

Vegeta=on is Established 

• NEVER use Sand or Ash for De-‐Icing 

– Clogging 

– Less De-‐Icer needed with OGFC 

• Consider Placing Sign to Alert Maint. 

Personnel 

• NEVER Apply Seal Coat

Maintenance

Maintenance 

• All Porous Pavements should be Inspected 

– Several Times in First Few Months 

– Annually 

– Aper Large Storms to check for Ponding/Clogging 

• Preventa=ve Maintenance VITAL 

• Cleaning: 

– Pressure Washing (Not High Pressure) 

– Vacuum Truck 

– Recommended: Vacuum Clean 2x Per Year








• Keys to Success

Clemson Porous Pavement

Porous Parking Bays

Porous Parking On Street

Porous Parking on Street








• Keys to Success

Keys to Success 

• Make Sure Site Condi=ons are Acceptable 

– Soil Infiltra=on / Permeability 

– Depth to Groundwater and/or Bedrock 

• Design 

– Boaom of Recharge Bed should be Level 

– Limit Surface Slope to < 5% 

– Runoff from Adjacent Areas will not Plug 

Pavement 

– 5:1 Impervious to Permeable Area Ra=o

Keys to Success 

• Construc=on 

– Don’t Compact Subgrade 

– Protect Pavement from Contamina=on 

• Build Porous Pavement Late 

• Stabilize Adjacent Areas Before Construc=on 

• ALWAYS PROTECT RECHARGE BED 


– Do NOT Sand or Ash Pavements 

– Install Signage to Warn Maintenance Personnel 

– Can Patch with Conven=onal Asphalt < 10%

Ques=ons?

References

Porous Asphalt Pavements for Storm Water Management

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