Porous Asphalt PavementsPorous Asphalt PavementsRita B Leahy, PhD, PERita B Leahy, PhD, PE

Technical Consultant - CalAPATechnical Consultant - CalAPACalAPA Fall ConferenceCalAPA Fall Conference29-30 October 201429-30 October 2014

AcknowledgementsAcknowledgements

Kent Hansen – NAPAKent Hansen – NAPA Jim Huddleston –Jim Huddleston – Asphalt Pavement Assn of OregonAsphalt Pavement Assn of Oregon Ron Cominsky –Ron Cominsky – Pennsylvania Asphalt Pavement AssnPennsylvania Asphalt Pavement Assn Margot Yapp & Jason Puccinelli –Margot Yapp & Jason Puccinelli – Nichols Consulting EngineersNichols Consulting Engineers Brandon Milar - MeadWestvacoBrandon Milar - MeadWestvaco

Presentation OverviewPresentation Overview What are they?What are they? Why use them?Why use them? Guidelines for useGuidelines for use ResourcesResources

What are porous pavements?What are porous pavements?

Open-Graded HMA ~ 2½ to 6 in

Choker Course ~ 1 to 2 in(#57 stone)

Reservoir Course ~ 10 to 36 inClean, Uniformly GradedCrushed Agg (#2 stone) ~ 40% Voids

Non-Woven Geotextile

Uncompacted Subgrade

Why should I use porous pavement?

New stormwater regulationsNew stormwater regulationsReduce volume…not just peak flowReduce volume…not just peak flowLimit impervious areaLimit impervious areaReduce runoffReduce runoff

Sustainability (pollutants, infiltration)Sustainability (pollutants, infiltration)

Pre-DevelopmentPre-Development Post-DevelopmentPost-Development

45 inches rainfall/year45 inches rainfall/year

22 inches Evaporation

8 Runoff

15 Infiltration

2 inches

43

0

Traditional Stormwater Management

Traditional Stormwater Management

Morris ArboretumMorris ArboretumPhiladelphia, PAPhiladelphia, PA

19841984Dense-Dense-GradedGradedPorousPorous

Morris Arboretum, PhilaMorris Arboretum, Phila

Dense-Dense-GradedGraded

PorousPorous

Kaiser Medical CenterKaiser Medical CenterModesto, CAModesto, CA

KaiserKaiserMedicalMedicalCenterCenter

All runoff from site diverted to either permeable All runoff from site diverted to either permeable pavement parking structure or percolation basin. pavement parking structure or percolation basin. NO Surface Runoff leaves site.NO Surface Runoff leaves site.

Placer County – Roseville, CAPlacer County – Roseville, CA Demonstration ProjectDemonstration Project Parking area for open space accessParking area for open space access

Porous Pavement UsePorous Pavement Use Primary UsePrimary Use

Parking lotsParking lots Roads w/ little cut or fillRoads w/ little cut or fill Trails/SidewalksTrails/Sidewalks DrivewaysDriveways

Roads/Highway ChallengesRoads/Highway Challenges Cuts and fillsCuts and fills SlopeSlope Variable soil conditionsVariable soil conditions UtilitiesUtilities Limited useLimited use

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15 20

Rainfall, inchesHours

Design ConsiderationsDesign Considerations

Location/Site ConditionsLocation/Site Conditions

HydrologyHydrology

StructuralStructural

HoursR

ainf

aill

(inc

hes)

Location/Site ConditionsLocation/Site Conditions Soil permeability/infiltration rateSoil permeability/infiltration rate

EPA – 0.5 in/hrEPA – 0.5 in/hr 0.1 in/hr - OK0.1 in/hr - OK

Depth toDepth to bedrock > 2ftbedrock > 2ft high water > 3fthigh water > 3ft

Fill – Fill – not recommendednot recommended

http://websoilsurvey.nrcs.usda.gov

Slope – limit surface slope to 5%Slope – limit surface slope to 5% Terrace when necessaryTerrace when necessary Conventional HMA for steeper slopesConventional HMA for steeper slopes

Location/Site ConditionsLocation/Site Conditions

Terraced

Gravel

Stone edge provides alternative path for water to enter recharge bed if pavement is sealed or plugged.

Hydrology - Stormwater DesignHydrology - Stormwater Design RainfallRainfall

Typical: 6 month/24 hr stormTypical: 6 month/24 hr storm Conservative: 25 year/24 hr stormConservative: 25 year/24 hr storm Local & State wastewater mitigation Local & State wastewater mitigation requirementsrequirements

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15 20

Rainfall, inches

Hours

Structural Design - AASHTOStructural Design - AASHTO

MaterialMaterial Layer CoefficientLayer Coefficient

Porous AsphaltPorous Asphalt 0.40 – 0.420.40 – 0.42

Asphalt Treated Permeable BaseAsphalt Treated Permeable Base 0.30 – 0.350.30 – 0.35

Porous Agg BasePorous Agg Base(Recharge Bed)(Recharge Bed)

0.10 – 0.140.10 – 0.14

Structural Design – NAPAStructural Design – NAPARecommended Minimum ThicknessRecommended Minimum Thickness

Caltrans Design GuidanceCaltrans Design GuidanceCategory Examples Loading Speed Risk

A

Landscaped areas, sidewalks and bike paths (with no vehicular access), miscellaneous pavement to accept run-on from adjacent impervious areas (e.g. roofs)

No vehicular

loadsN/A Low

B

Parking lots, park & ride areas, maintenance access roads, scenic overview areas, sidewalks and bike paths (with maintenance/vehicular access), maintenance vehicle pullout

Few heavy loads

Low speed (less than 30 mph)

Low

C Rest areas, maintenance stations Moderate

heavy loads Low speed Low

DShoulders, some low volume roads, areas in front of noise barriers (beyond the traveled way)

Moderate heavy loads High speed Medium

E Highways, weigh stationsHigh heavy

loads High speed High

California Department of TransportationDivision of Design Office of Storm Water Management 1120 N Street Sacramento, Californiahttp://www.dot.ca.gov/hq/oppd/stormwtr/

Other ConsiderationsOther Considerations

MaterialsMaterialsConstructionConstructionMaintenanceMaintenance

Porous Asphalt - OGFCPorous Asphalt - OGFC

Caltrans Standard Spec Section 39Caltrans Standard Spec Section 39 ½-inch or 1-inch gradation½-inch or 1-inch gradation

Binder: PG 70-10; PG-M (PG 76-22); Binder: PG 70-10; PG-M (PG 76-22); Asphalt RubberAsphalt Rubber

CT 368 – OBC (optimum binder content)CT 368 – OBC (optimum binder content) Method spec for compactionMethod spec for compaction

Key Mix PropertiesKey Mix Properties ““Open” gradationOpen” gradation

Increased permeabilityIncreased permeability >18% air voids>18% air voids

Binder contentBinder content Pavement durabilityPavement durability

Draindown (< 0.3%)Draindown (< 0.3%) ConstructabilityConstructability Film thicknessFilm thickness

Plan to build late in construction processPlan to build late in construction process Wait untilWait until

““dirty work is done”dirty work is done” vegetation is establishedvegetation is established

Excavate bed to about 1ft above planned Excavate bed to about 1ft above planned elevation and use for SW controlelevation and use for SW control Excavate to plan elevation when readyExcavate to plan elevation when ready

Construction SchedulingConstruction Scheduling

Bed ExcavationBed Excavation Excavate bed to Excavate bed to

plan elevation using plan elevation using equipment w/ “soft equipment w/ “soft footprint”footprint”

Don’t compact Don’t compact subgradesubgrade

Non-woven GeotextileNon-woven Geotextile

Spread geotextile Spread geotextile immediately after fine immediately after fine gradinggrading

Overlap fabric >16inOverlap fabric >16in Install drainage pipes Install drainage pipes

if usedif used Excess fabric (> 4ft) Excess fabric (> 4ft)

folded over agg laterfolded over agg later

Stone Recharge BedStone Recharge Bed

Place clean, single size, Place clean, single size, washed aggregatewashed aggregate

Don’t drive trucks on Don’t drive trucks on fabricfabric

Spread and grade with Spread and grade with tracked equipmenttracked equipment

Light compaction - staticLight compaction - static Protect pipesProtect pipes

Choker CourseChoker Course Place “Choker” course – ½-inch clean Place “Choker” course – ½-inch clean

washed aggregatewashed aggregate Purpose -lock up surface for stable Purpose -lock up surface for stable paving platformpaving platform

1 to 2-inches thick1 to 2-inches thick Grade and compactGrade and compact

StaticStaticVibratory? Vibratory?

low amplitudelow amplitudehigh frequencyhigh frequency

Mix ProductionMix Production

Watch temperatureWatch temperature Don’t store for extended Don’t store for extended

periods in silosperiods in silos Batch plant - lower productionBatch plant - lower production

PavingPaving Recommend track paverRecommend track paver Minimize truck movements Minimize truck movements

over aggregateover aggregate Stability may be issueStability may be issue Avoid disturbing agg surface Avoid disturbing agg surface

Place mix ~ 200Place mix ~ 200°°F to 250F to 250°°FF Limit handworkLimit handwork

CompactionCompaction

1 to 3 passes with 1 to 3 passes with 10-ton static steel 10-ton static steel wheelwheel

Less stable than thin Less stable than thin OGFC, may have to OGFC, may have to coolcool

Photo Courtesy of Cahill & Assoc

Photo Courtesy of Cahill & Assoc

After CompactionAfter Compaction Restrict traffic for 24 hoursRestrict traffic for 24 hours Keep sediment control in place till Keep sediment control in place till

vegetation establishedvegetation established

Photo Courtesy of Cahill & Assoc

MaintenanceMaintenance

Inspect first few months during storm events; Inspect first few months during storm events; annually thereafterannually thereafter

Repair/Patching-dense HMA if <10Repair/Patching-dense HMA if <10% of area% of area Regular cleaning – fRegular cleaning – flushed, jet washed, vacuum lushed, jet washed, vacuum

sweepingsweeping

MaintenanceMaintenance Do NOT use traditional seal coat treatmentsDo NOT use traditional seal coat treatments Do not use salt or sand for de-icingDo not use salt or sand for de-icing

Salt - contaminate groundwater infiltrationSalt - contaminate groundwater infiltration Sand - reduce permeabilitySand - reduce permeability

SandSaltAsh

Seal Coat

Cost?Cost?

Stone BedStone Bed

SW Pipes & InletsSW Pipes & Inlets

Earthwork & ExcavationsEarthwork & Excavations

Detention BasinsDetention Basins

ConclusionsConclusions Porous pavements Porous pavements ─ ─ good alternative good alternative

to conventional stormwater mitigationto conventional stormwater mitigation Site conditions criticalSite conditions critical Protect pavement from contamination Protect pavement from contamination

during and after constructionduring and after construction Properly designed, constructed and Properly designed, constructed and

maintained will last than 20+ yearsmaintained will last than 20+ years

Permeability

Recharge Bed

Questions? Comments?Questions? Comments?

ResourcesResources

http://www.asphaltpavement.org/http://www.asphaltpavement.org/

Pervious PavementDraft Design Guidance

May 2013

California Department of TransportationDivision of Design Office of Storm Water Management 1120 N Street Sacramento, Californiahttp://www.dot.ca.gov/hq/oppd/stormwtr/

ResourcesResources

ResourcesResources

http://www.unh.edu/unhsc/