Mark A. Palmer, P.E., LEED AP
City Engineer, City of Puyallup
POROUS ASPHALT:
DESIGN AND CONSTRUCTION
POROUS ASPHALT: DESIGN AND CONSTRUCTION
• Materials and Specifications
• Performance of Permeable Asphalt
• Emerging Green Technologies for Asphalt
• Questions
October 20, 2014
Department of Ecology Statewide LID Training Program
POROUS ASPHALT:
DESIGN AND PERFORMANCE GOALS
Properly integrated into site design
Permeable wearing course
Flexible Pavement Section designed for saturated subgrade conditions
Pavement designed to infiltrate 100% of rainfall
Pavement depth sufficient to eliminate frost heave
Durable, long lasting wearing course
Constructible Design (materials, sequencing)
Prevents or accounts for surface water run-on
Provides drainage redundancy (inlet, outlet)
10.
Addresses potential storm water flows in subgrade/trenches
October 20, 2014
Department of Ecology Statewide LID Training Program
6. POROUS ASPHALT IS A
GOOD PRODUCT FOR
LOCAL ROADS, PARKING
LOTS AND TRAILS.
Conclusions of Final Report for SR-87
project:
“The porous pavement test section
has performed satisfactorily for five
years. Although a slight decrease in
the infiltration rate has occurred,
both the infiltration rate and the
storage capacity are above the design
values.”
“Visual observation during rain
storm has shown that the surface of
the porous pavement section does
not include sheet flow. This provides
a marked difference in stripe
delineation and pavement glare
during night time inclement weather
driving compared to conventional
pavement.”
HMA Pavement
Porous Asphalt Pavement
POROUS ASPHALT: CONSIDERATION FOR USE
Porous asphalt is a good product for local roads, parking lots and
trails.
• Parking lots are tough test-low speed turning motions
• Resist temptation to mix porous with impermeable pavements in
same section
• Depth of section can be an issue on high volume roads-consider
pervious concrete to avoid existing utilities and for life cycle cost
advantages-Geogrid and/or porous asphalt treated base can help thin
section.
October 20, 2014
Department of Ecology Statewide LID Training Program
POROUS ASPHALT: CONSIDERATION FOR USE
• Porous Asphalt vs. Pervious Concrete
– Porous asphalt does not require certified installer-normal pavers can
complete
– Porous asphalt cannot be made in small batches
– For high volume roads, pervious concrete may be more cost effective,
both short term and life cycle cost
– Porous asphalt can be used almost immediately vs. 7 days for concrete
– Porous asphalt requires thicker section for higher volume or poor soils
October 20, 2014
Department of Ecology Statewide LID Training Program
POROUS ASPHALT MIX DESIGN
October 20, 2014
Department of Ecology Statewide LID Training Program
• Committee is working on a WSDOT format specification for
porous asphalt (Jessica Knickerbocker, City of Tacoma lead)
• Interesting developments, particularly in trying to establish
optimum compaction effort.
• Final product is not yet ready for publication
POROUS ASPHALT MIX DESIGN
October 20, 2014
Department of Ecology Statewide LID Training Program
Asphalt materials will comply with WSDOT specifications for
Class ½ HMA PG 70-22 (Polymer modified) with the following
modifications:
Asphalt cement shall be between 6.0% and 7.0% by total
weight. Test for drain down and void content at 75 gyrations at
6, 6.5 and 7.0, use highest percentage that passes both tests. Use
of fibers MAY allow for higher asphalt content.
NAPA IS-115 is good starting point for aggregate specification.
NAPA IS-155
GRADATION
Good, general purpose aggregate
specification for porous
pavement
Other aggregates can be
acceptable, both larger and
smaller.
Consider requiring two face
fracture requirement for better
binding-offsets lack of fines.
Some amount of fines is good for
absorbing asphalt (get higher
%) and thickening binder
Good spec for choker course if
being used
Sieve
Percent Passing
100
85-100
3/8”
55-75
No. 4
10-25
No. 8
5-10
No. 40
No. 200
2-4
ALTERNATE
GRADATION
Good, general purpose
aggregate specification for
porous pavement
Other aggregates can be
acceptable, both larger and
smaller.
Consider requiring two face
fracture requirement for better
binding-offsets lack of fines.
Some amount of fines is good
for absorbing asphalt (get
higher %) and thickening
binder
Supplied material smaller than spec, but met voids
ratio easily
GRADATION
MISCUES
Watch for too much aggregate
of one size (poorly graded)
Not enough fracture face
Too little voids (too much
fines)
Nearly 50% of
material between
½” and 3/8”
GRADATION
MISCUES
Result of gradation miscue
(poorly graded) on choker
course
Rutting, lack of interlocking
GRADATION
CORRECTION
Correction-added correctly
graded material to existing
poorly graded material.
Rutting greatly reduced
Subsequent areas with strictly
correct rock were even better.
AGGREGATE
SPECIFICATION-
CHART
Good way to see visually how
gradation should look
Original, poorly graded
aggregate is near vertical line
Replacement material has
curve that emulates
specification curve
POROUS ASPHALT MIX DESIGN
October 20, 2014
Department of Ecology Statewide LID Training Program
Air Voids 16-25% (ASTM D3203)
Drain Down-ASTM D6390-05, 0.3% maximum @ 15° above
design mix temperature
ODOT has alternate ODOT TM 318 Drain Down Test-subjective
Consider adding fiber to mix design
All requirements should be provided with mix design from
supplier.
ASTM D6390-05
DRAIN DOWN TEST
Constituents mixed by hand per
mix design
Placed in basket with no
compaction
Cooked in oven at prescribed
temperature
Material that drops to plate
weighed and compared to 0.3%
standard
Not necessarily representative
of field conditions
Look for asphalt in the bottom of
dump trucks during
construction
ODOT TM 318
DRAIN DOWN TEST
Process similar to ASTM test-
but places paper directly
under sample
Tester interprets between
several example percentages of
drain down pictures (see
picture this page).
Like ASTM test, not likely
representative of field
conditions, also subjective
POROUS ASPHALT MIX DESIGN
October 20, 2014
Department of Ecology Statewide LID Training Program
Anti-stripping agent should be used if supplier normally uses
anti-stripping in their HMA mixes.
Should not exceed 1% by weight of aggregates
If having difficulty meeting minimum 6% asphalt in mix design
due to drain down:
Consider increasing fines in aggregate-but watch void ratio
Consider adding fiber to mix design
Intent of minimum asphalt content, polymer modified PG 70-22
is to provide full and durable coating of aggregate (design goal
#6)
HAMBURG ANTI-
STRIPPING TEST
Replaces previous tests used
by WSDOT for HMA
Validity on PHMA yet to be
determined
Single test run by City of
Puyallup indicated failure at
6,750 passes-less than 10,000
required for HMA
Failure did not appear to be
stripping but rather shear.
HAMBURG ANTI-
STRIPPING TEST
3-D profile of test area
HAMBURG ANTI-
STRIPPING TEST
Graph of rut depth vs passes
No inflection point indicates
stripping is not failure cause
Could try to add more fines to
stiffen mix, see if that performs
better
Could do more field tests with
different compaction efforts,
take cores, compare density,
asphalt content and consistency
through core.
HMA standard varies based on
asphalt grade but is generally
10,000 passes before 12.5 mm
rutting
Ruth depth, mm
ICON Porous 0.5 Inch 70-22, A-B
-10
-11
-12
-13
-14
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Rut Depth
12.57 mm rutt
wheel passes
POROUS ASPHALT SECTION DESIGN
October 20, 2014
Department of Ecology Statewide LID Training Program
Starting from bottom of pavement section up:
Non-woven geotextile fabric-mixed opinions on this option
Non-woven geotextile fabric has been shown to provide surface for microbes
which will decompose hydrocarbons-however needs more study
Not likely to clog-Apparent Opening Size (AOS) should be similar to soils
underneath, and most particles are captured in first couple of millimeters of
pavement-dirty aggregate could be a problem though
Not a requirement for structural section-does not provide significant strength
Need structural strength or want reduced section, consider geo-grid in mid-
point or higher of reservoir section.
GEOGRID
Check manufacturer's
recommendations for
placement
Can reduce overall section
thickness
Section shown is proposed
WSU Puyallup LID Frontage
Phase 1 section
Porous asphalt treated base
also helps reduce section
thickness
GEOTEXTILE
Reference:
Section 9-33.2(1) of WSDOT
2012 Standard Specifications
POROUS ASPHALT SECTION DESIGN
October 20, 2014
Department of Ecology Statewide LID Training Program
Reservoir Section
Same as other permeable pavements
Looking for 30-40% voids-storage space for water to allow infiltration
Want readily available rock with few fines
Want rock that is angular, of varying sizes to maximize interlock-
provides a stable working surface for construction
9-03.9(2) Permeable Ballast
Permeable ballast shall meet the requirements of Section
9-03.9(1) for ballast except for the following special
requirements. The grading and quality requirements are:
Sieve Size Percent Passing
2½″
100
65-100
40-80
No. 4
5 max.
No. 100
0-2
% Fracture
75 min.
All percentages are by weight. The sand equivalent value
and dust ratio requirements do not apply. The fracture
requirement shall be at least one fractured face and will
apply the combined aggregate retained on the No. 4 sieve
in accordance with FOP for AASHTO TP 61
RESERVOIR COURSE
Reference:
Section 9-03.9(2) of WSDOT
2012 Standard Specifications
Should be clean, less than 2%
passing #100 as shown is
good.
60-100¿ between 2” to ¾”
allows for large void space.
75% fracture requirement is
good for interlock, but
requiring 2 face fracture, if
available is better.
RESERVOIR COURSE
Material in picture passed 75%
fracture requirements, but was
difficult to work with.
ALTERNATE
RESERVOIR
COURSE
October 20, 2014
Department of Ecology Statewide LID Training Program
• Mix used by City of Puyallup is blend developed by PW Streets.
Uses a standard 1-1/4” CSBC rock blended with #57 rock.
• CSBC had void content of 12.5%
• #57 rock had void content of 41.3%
• Staff mixes the rock manually at 1:1 ratio
• Used as reservoir course and for porous gravel alleys, shoulders
• Can be used as single rock under porous asphalt, no choker
course required-workable surface for pavers
CHOKER
COURSE
October 20, 2014
Department of Ecology Statewide LID Training Program
• If using larger diameter permeable ballast for reservoir course, there
is a need for another layer to provide a working surface for paving
machines.
Use 1” to 1-1/2” layer of same aggregate as in asphalt mix design
Or use porous asphalt treated base (recommended)
• Porous asphalt treated base can reduce overall pavement section
thickness for structural design
• Can also provide a more stable surface for construction than
aggregate alone.
• Standard WSDOT specification for aggregate for ATB may need to be
modified to allow more permeability.
PAVEMENT
SECTION DESIGN
October 20, 2014
Department of Ecology Statewide LID Training Program
• Pavement section thickness needs to address:
Frost heave depth-lower Puget Sound basin around 1’
Hydrology-allow water to infiltrate before next storm
Structural-design flexible pavement thick enough to distribute load over
assumed poor, saturated soils.
• Frost heave only concern if fine grained, poor soils=>hydrology
and structural will over ride in these cases
• Hydrology and Structural generally will follow each other based
on soils.
STRUCTURAL
DESIGN
WSDOT has pavement design
software which can be used for
this purpose (EverStress)-
requires some expertise to use
WSDOT also has design
guideline tables which are
functional for designing
pavement thickness
Choose the appropriate table
based on traffic levels, assume
poor subgrade condition for all
porous pavements
There are also some locally
developed pavement design
programs that may be available
STRUCTURAL
DESIGN
Higher volume roads will
require greater pavement
section thickness.
Multiple lifts of porous asphalt
can be a problem, can’t tack
coat.
WSDOT does not recommend
porous pavement for high
volume roads.
Flexible Pavement
Rigid Pavement
HMA
CSBC Base
PCC Slab
Base Type and Thickness
< 5,000,000
0.50
0.67
CSBC only
0.35
5,000,000 to
10,000,000
0.67
0.50
0.75
HMA over
CSBC
0.35 + 0.35
10,000,000 to
25,000,000
0.83
0.50
0.83
HMA over
CSBC
0.35 + 0.35
25,000,000 to
50,000,000
0.92
0.58
0.92
HMA over
CSBC
0.35 + 0.35
50,000,000 to
100,000,000
1.00
0.67
1.00
HMA over
CSBC
0.35 + 0.35
100,000,000 to
200,000,000
1.08
0.75
1.08
HMA over
CSBC
0.35 + 0.35
Table 5.1. Flexible and Rigid Pavement Layer Thicknesses for New or Reconstructed
Pavements
Design Period
ESALs
Layer Thicknesses, ft
STRUCTURAL
DESIGN
WSDOT-Permeable pavement suits new
construction of very low volume, slow speed
locations with infrequent truck traffic.
The permeable base storage layer
thicknesses shown above are based on the
minimum structural needs of the permeable
pavement application. Reference the
WSDOT Highway Runoff Manual to
determine the thicknesses based on
subgrade infiltration and the pavement
storage capacity needs. In some cases,
additional permeable base thickness may be
required for frost design purposes.
Permeable base aggregate shall consist of an
AASHTO 57 gradation or as approved by the
State Materials Laboratory.
Facility
Flexible
Rigid
• Light Vehicle
Access Areas
0.50 ft HMA
0.50 ft (permeable base)
0.75 ft PCC (undoweled)
0.50 ft (permeable base)
• Truck Parking
0.50 ft HMA
0.50 ft (permeable base)
0.75 ft PCC (undoweled)
0.50 ft (permeable base)
• Car Parking
0.35 ft HMA
0.50 ft (permeable base)
0.67 ft PCC (undoweled)
0.50 ft (permeable base)
• Pedestrian
Sidewalks and
Trails
0.25 ft HMA
0.35 ft (permeable base)
0.35 ft PCC (undoweled)
0.35 ft (permeable base)
STRUCTURAL
DESIGN
Section used at the WSU LID
Center
Note, choker course was not
used, aggregate for reservoir
course was deemed adequate
for working surface
Would not recommend
compaction of subgrade as
shown here.
CONSTRUCTION
October 20, 2014
Department of Ecology Statewide LID Training Program
• Sequencing Important:
– Plan site work to keep construction traffic off subgrade
– Example-excavate to subgrade as moving out, back fill with aggregate
from opposite end
– Once geotextile and reservoir rock is down, can compact that and allow
traffic on rock.
– For anything but asphalt treated base, will likely need rollers around to
fix/compact rock as pavers are working
CONSTRUCTION
October 20, 2014
Department of Ecology Statewide LID Training Program
• Watch materials and placement:
– Look for aggregate to be porous, no sheen or sealed off areas
– Make sure subgrade has not been compacted by construction traffic, if it
has, scarify before geotextile and rock are placed.
– Watch for asphalt in the beds of delivery trucks-indicates drain down
issue
– Make sure rollers are on the asphalt in the correct temperature range (by
mix design)
– Make sure…