Permeable Friction Course Hot Mix Asphalt

earthwhistleUrban and Civil

Nov 25, 2013 (3 years and 8 months ago)

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P
ermeable

Friction Course Hot Mix

Asphalt

On Interstate Highways I
n Texas

The Texas Asphalt Pavement Association (TxAPA) presents the following information to make the case
that Permeable Friction Course (PFC)
H
ot
M
ix
A
sphalt (HMA) should be used as the surface of choice for
overlaying interstate highways in the state of Texas.

PFC mixes have been used throughout the United States and around the world to enhance safety,
reduce pavement noise, improve ride quality, impro
ve vehicle fuel efficiency and improve the quality of
storm water runoff. No other pavement surface combines all of these attributes as well as PFC.

The
positive
feedback

regarding PFC from the public is unmatched by any other pavement surface type. The
e
xtensive use of PFC
,
also referred to as
Open
G
raded
F
riction
C
ourses (
OGFC) is a consistent factor in
states that perennially rank as having the best highways based on ride quality such as Florida, Georgia,
Tennessee,

and Arizona to name a few.

Backgrou
nd

OGFC have been around for more than 50 years. Despite their desired attributes, the first generation of
OGFC mixes diminished in popularity in the 1980s primarily due to a lack of long term durability. Over
the past 20 years a new generation of OGFC m
ixes regained popularity after improvements were made
that significantly increased the performance life. With the exception of Stone
-
Mat
rix

Asphalt (SMA)
which is arguably the most durable type of HMA, the new generation of OGFC mixes have a
performance l
ife that is considered to be equivalent to other HMA surface mixes. The new generation
of OGFC is called PFC in Texas. These mixes go by other names such as Porous European Mix (PEM) in
Georgia and Asphalt Concrete Friction Course (ACFC) in Arizona. Regar
dless of what they are called,
other states and other countries throughout the world use these mixes because they offer enhanced
safety, comfort and environmental attributes.

Enhanced Safety

The number one benefit of a PFC surface is the ability to reduce

wet weather accidents. PFC mixes
greatly reduce the risk of hydroplaning. Hydroplaning is often cited as a major factor in wet weather
accidents that result in fatalities. PFC mixes also improve the frictional characteristics of the pavement.
When compar
ed to dense graded HMA or concrete paving surfaces, PFC surfaces typically have higher
frictional numbers and lower frictional gradients (
loss of friction in wet weather
) according to studies
conducted in the United

States, Canada, and Europe.

PFC mixes

are typically designed to have air voids percentages that range from 18% to 22%. The high
volume of air voids result in interconnecting voids that provide drainage during heavy rainfall events.
Since water is drained through the surface of a PFC mix the
re is less water on the surface that could
contribute to hydroplaning or loss of friction. Even during heavy prolonged rain events the possibility of
hydroplaning is greatly reduced due to the pressure under the vehicle tire being dissipated through the
p
e
rmeable structure of the PFC.

Higher frictional numbers and lower frictional gradients along with the
reduction in hydroplaning have contributed to a dramatic reduction in wet weather accidents in studies

conducted in

France as well as the s
tates of Virg
inia and Texas.

In one case study conducted over a 7 year time span, Texas reported that by replacing a conventional
surface with a PFC, wet weather accidents were reduced by
93% and fatalities were reduced by 75%.

Another study on IH
-
35 in Texas, where
PFC was placed as an overlay on an existing concrete pavement,
resulted in more than 50%

reduction in wet weather accidents.


Additional benefits of PFC surfaces are a reduction of splash and spray from other vehicles; the
reduction of headlight glare; and

improved visibility of pavement markings. These benefits are all the
result of PFC mixes removing standing water more quickly from the roadway surface compared to all
other paving surfaces.

Reduced Pavement Noise


Tires rolling on the road cause air to

be forced away in front of, and sucked behind, the area of contact
between the tire and the road” according to a document published by
National Asphalt Pavement
Association (
NAPA
)
.
The Asphalt Pavement Association (APA) explains that t
his air pumping cre
ates a
high frequency noise. With PFC the noise is reduced since the air is pumped down into the
porous
asphalt
pavement
.

Through the use of PFC noise reductions have been m
e
asured between 3 to 10
dB(A)
.

A reduction of 3 dB(A) is equivalent to doubling

the distance from the noise source.
The
Federal
Highway Administration (
FHWA
)

conducted a comparative noise level study of PFCs, dense graded HMA,
Portland cement concrete pavement and chip seals in Arizona, California, and Nevada. The study
concluded t
hat PFC had the lowest noise level compared to all

other pavement surfaces.

TxDOT has primarily used PFC for the safety benefits; however, the attribute
the public most often
notices is

the reduction in noise. TxDOT received numerous comments on the noise

reduction when PFC
was used to overlay concrete pavement on IH 35 near San Antonio,
on US 281 in San Antonio near
Alamo Heights,
on IH 30 near Dallas and Beltway 8 near Houston. On all
four

of these projects, TxDOT
was able to document noise reductions of

3db to 8db using on board sound intensity measurements
(OBSI) and wayside measurements. Similar to the other studies, research within TxDOT concluded that
as a group PFC pavements had the lowest noise level compared to all other pavement surfaces.


The Ar
izona D
epartment of
T
ransportation (ADOT)

received favorable public comment on the reduction
in noise when they resurfaced an urban concrete highway in Tempe and Mesa. In late 2002 ADOT
announced a three year program

funded by the Arizona Legislature

to re
surface 115 miles of existing
concrete freeways in the Phoenix
metropolitan area” with PFC.

This is significant due to the fact that
wet weather accidents are not as frequent in arid regions such as Arizona, yet the Arizona DOT still
justified the use of
PFC for noise reduction based on public input.

Improved Ride Quality

Enhanced safety and noise reduction are the PFC attributes touted most often; however, it should be
pointed out that ride quality is the attribute most often used to judge pavement quali
ty.
FHWA surveys
have supported this by documenting that the traveling public considers smooth pavements their
number one priority for pavements.
In almost every pavement management information system, ride
quality carries the most weight in determining p
avement condition scores. TxDOT has documented
significant improvements in ride quality on surfaces paved with PFC. International roughness index (IRI)
values for projects with PFC typically range from 35 in./mi. to 60 in/mi. IRI values less than 60 in./mi
. are
considered to be excellent. For comparison purposes, TxDOT’s 2010 PMIS database shows the average
IRI values for interstate highway main lanes in Texas are 70.6 in./mi. for asphalt pavements, 104.4
in./mi. for continuously reinforced concrete pavemen
ts and 122.8 for jointed concrete pavements. One
could infer that increased use of PFC on interstate highways in Texas could significantly improve the
pavement condition scores especially when used to overlay concrete pavements.

The Texas Quality Pavemen
t Awards Program jointly administered by Tx
DOT and TxAPA was altered two
years ago to create a separate category for PFC pavements. This change was made to accommodate the
fact that when competing with projects paved with conventional HMA (non PFC), projec
ts with PFC
surfaces were winning the vast majority of the awards even though they comprise less than 10% of HMA
constructed in Texas. It was acknowledged by the award committee that the smoothness and
uniformity of PFC projects gave them an unfair advant
age over projects paved with conventional HMA.

Increased Fuel Efficiency

Smooth roads conserve energy and extend the life of pavements. Studies
conducted by FHWA
at
the
WesTrack

pavement test track in Nevada have shown that driving on smoother surfaces can reduce fuel
consumption in the neighborhood of 4.5 percent compared to fuel consumption on a rough pavement.
Other studies, before and after the WesTrack study, have
concluded
that vehicles traveling
on
smoother

roads
showed fuel consumption reductions up to 10


20 percent
than vehicles
traveling on rougher

roads.


Since
PFC pavements are some of the smoothest pavements that have been placed in Texas and smooth
pavements have b
een shown to equate to

better fuel efficiency then
one could infer that the increased
use of PFC could also increase vehicle fuel efficiency. Decreasing fuel use has a direct impact on reducing
the
carbon footprint associated with fuel consumption. In addi
tion to all of the other attributes PFC
offers, PFC appears to have positive environmental attributes.

Note that the positive environmental
benefits can be increased and the carbon footprint further reduced when the PFC is placed as

a

Warm
Mix PFC.

Improv
ed
Storm W
ater Quality

Porous and open graded mixes have shown to have a dramatic beneficial effect on water quality. These
pavements can be used in parking lots as part of a system that collects storm water from the porous
pavement into a stone recharge
bed which then infiltrates into the ground. While this is the most
common use for improving water quality with HMA it has recently been learned that similar effects are
gained when PFCs are used on roadways.
Porous asphalt
pavements are recognized by the

U.S. EPA as a
best management practice for storm water management that can even improve the water quality.


TxDOT funded
a
research p
roject 0
-
4605
entitled “
Storm
Water Q
uality of
R
oadside
S
houlders
B
orrow
D
itches.
” The research was conducted by Dr. Micha
el Barrett at the University of Texas at Austin. During
that study a PFC mix was placed as an overlay on the existing dense graded HMA surface. Dr. Barrett
was able to document that 9 of the 12 measured water quality constituents improved, 1 had no change
and the remaining 2 showed a negligible decrease in water quality. Most noticeably were decreases in
total suspended solids of 93 % and a decrease in chemical oxygen demand of 53 %. Among other
factors, the research attributed the improvements to the fact
s that the decrease
in

splash and spray
resulted
in

significantly less washing

of

contaminants from the undercarriage of vehicles. They also
noted that the PFC had a filtering effect on the storm water. Additional research by Dr. Barrett has
shown that the positive environmental attributes of PFC in terms of improving the quality of st
orm
water runoff are verifiable and are not just temporary.

Conclusion

Based on all the information and performance data that has been gathered, TxAPA recommends that
TxDOT adopt a uniform policy to use PFC on
interstate highways
that are structurally sound to enhance
safety, reduce pavement noise, improve ride quality, improve vehicle fuel efficiency and improve the
quality of storm water runoff.
Interstate highways, as well as, many other highways within Texas
certainly meet the
se criteria.
We respectfully submit that PFC offers more benefits than any other
pavement surface and that more of the traveling public should be exposed to the unique benefits PFC
offers.














Sources:

(1)

Design, Construction, and Maintenance of O
pen
-
Graded Asphalt Friction Courses
, National
Asphalt Pavement Association,
May
2002

(2)

Open Graded Friction Courses: Smooth, Quiet, and More Durable than Ever
, Asphalt Pavement
Alliance

(3)

Black and Green
, National Asphalt Pavement Association, September 2009

(4)

B
enefits of Asphalt
, National Asphalt Pavement Association, September 2009

(5)

Smoothness Matters
, Asphalt Pavement Alliance

(6)

Smoothness Matters: The Influence of Pavement on Fuel Consumption
, Hot Mix Asphalt
Technology, November/December 2009

(7)

2008 Journey
Toward Excellence Award Application
, Dale Rand
,

P.E., 2008

(8)

Permeable Friction Course Rewrite Draft
, Dale Rand, P.E., July 2010

(9)

Storm Water Quality of Roadside Shoulders Borrow Ditches (Project 0
-
4605)
, Michael Barrett,
Ph.D.,
P.E.,
The University of Texas
Center for Transportation Research,
October 2005

(10)


Highway Noise Control with HMA
, Wayne Jones, Asphalt Institute Field Engineer