March/April 2005 * Vol. 68 * No. 5

One Way to a Better Road

by Blair Barnhardt

To save time and money, a growing Georgia community in the metropolitan
Atlanta area reclaims busy roadways using foamed asphalt base
stabilization.

Today’s highway engineers and professionals are called upon to champion
innovations that are technically sound, economically feasible, and
fundamentally safe. In an editorial in the May/June 2004 issue of PUBLIC
ROADS, Federal Highway Administrator Mary E. Peters encouraged the
transportation industry to act on this challenge: Moving away from
simply building highways the same way the transportation community has
built them for decades can be done by using innovative practices and
processes, and involving nontraditional partners from outside the
highway community…How we, as individuals, as agencies, and as a
collective highway community respond to the call for a new way of
looking at transportation and highway projects can mean all the
difference.

Practicing innovation can mean working with unfamiliar technologies,
materials, or equipment. Construction Supervisor John Indrunas for the
city of Roswell, GA, in the metropolitan Atlanta area, accepted the
challenge when he tested a relatively unconventional technology; the use
of foamed asphalt base stabilization for the reclamation of four highly
traveled roads in and around Roswell. Over a period of 4 years, the
Roswell Department of Transportation (DOT) reconstructed Houze Way,
Jones Road, Hardscrabble Road, and Riverside Road. But first, some
historical background to put the Roswell story in context.

Mixing Oil with Water
The potential of foamed (or expanded) asphalt as a binder was developed
in the mid-1950s in Iowa. By injecting a small amount of cold water into
hot, liquid, petroleum-based asphalt, the resultant foaming action
expands the surface area of the asphalt. The binding process is used
with reclaimed asphalt pavement (RAP). Other countries adopted the
technology relatively quickly and developed supportive technologies and
expertise for foamed asphalt with both virgin materials and RAP.
In the 1980s, highway experts in the United States began experimenting
with the technology and building on the lessons learned up to that time.
The primary motivating factor for the U.S. interest in foamed asphalt
was the potential cost savings to agencies that use recycled pavement.
“Some agencies use recycling because that approach generally is less
expensive than complete reconstruction, conserves natural resources, and
reduces energy consumption in the construction process,” says Steve
Mueller, pavement and materials engineer with the FHWA Resource Center.
The object of all flexible pavement technology is to “glue”aggregates
together using asphalt while still providing sufficient air voids in the
mixture. Conventional hot-mix asphalt (HMA) plants completely coat
aggregates with liquid asphalt, which can be done only at temperatures
hot enough to liquefy the asphalt. To create a well-formed bond, the
asphalt must cover the entire surface of the aggregate. In HMA plants,
asphalt and aggregate are mixed in large drums under extremely high
temperatures to ensure uniform coating of the hot asphalt over the
aggregate. The mixture then is trucked to the construction site, placed
on the prepared subgrade, and rolled to obtain the proper amount of air
voids. As the temperature of the liquid asphalt falls during this
process, the material becomes stiffer and glue-like. At the completed
stage, a smooth and durable HMA layer is achieved. This proven practice
has served our national highway system well,î says Mueller.
Foamed asphalt base stabilization, on the other hand, involves using
hot, foamed asphalt cement in combination with damp RAP and/or base
course aggregates in situ. As a result, the foamed asphalt cement coats
the finer particles and creates a cold-recycled, mortar-type mix, thus
“spot-welding” the stones together. At a seminar sponsored by the
Georgia Local Technical Assistance Program, Dr. John Emery, president of
John Emery Geotechnical Engineering Limited, Toronto, Ontario, recently
pointed out that the resultant mastic (pasty material) that forms during
compaction of the recycled base courses is one of the main reasons why
foamed asphalt flexible pavement bases have high rut resistance and
excellent Marshall stabilities, especially at higher ambient
temperatures.
Due to the higher air void contents (compared to HMA) in the
cold-recycled mixes, Emery recommends HMA wearing surfaces for high
traffic counts. Farm-to-market roads, on the other hand, may be well
suited for a 150-millimeter (6-inch) foamed asphalt base course and a
double or triple surface treatment. Emery adds that layer coefficients
for properly designed and constructed (particularly compacted) foamed
asphalt bases can be as high as 0.40, thus the thickness of wearing
courses often can be reduced to keep project costs on budget.
Specially designed equipment takes up and pulverizes the old base. Once
crushed, the mixture of RAP and aggregate is laid down again, and the
road graded to near final condition to ensure the correct amount of
material is prepared. The pulverizer makes a final pass, picks up the
aggregate/RAP mixture, and this time binds it with foamed asphalt.
“Using these existing materials is a significant cost savings on many
jobs,” says Mueller. “And many times, the older existing aggregates are
higher quality than those being mined today.”
By injecting only a small (and precise) amount of water into liquid
asphalt binder heated to 170 degrees Celsius (320 degrees Fahrenheit),
millions of bubbles are formed, enhancing the take up of the binder by
the fine particles of aggregate and coating them. The asphalt-coated
finer particles in turn glue the larger aggregate particles together
much like a mortar mix. The water evaporates, and the machine returns
the new “old” asphalt to the roadway to be compacted initially by a
pneumatic roller and then later by a smooth drum vibratory roller.
The Pathway to Accepting New Practices
Back to the Roswell, GA, story. In the spring of 2000, after Indrunas
had exhausted Internet searches on the process of using foamed asphalt
to build road bases, he went in search of more information during a
meeting held in Atlanta and sponsored by the Asphalt Recycling and
Reclaiming Association (ARRA). He was joined by then-director of
transportation John “Jack” W. Seibert, III, P.E. “I knew if I could get
my manager involved with the training, it would be easier to sell to our
city council when the time came to utilize this technology,” Indrunas
says, reflecting on the initial steps he took when considering a change
in the city’s traditional approach to reclamation projects.
In 2001, Roswell became possibly the first city in the Southeast to
perform foamed asphalt base stabilization. Indrunas’ agency accepted a
bid from a local contractor for Houze Way, a major shortcut around the
Highway 9 corridor. The agency chose the roadway for a trial run using
RAP and a foamed asphalt base because the segment was short about 1.2
kilometers (0.75 mile) and was heavily traveled both in the volume of
cars and the weight of trucks taking products to the commercial
businesses in the area. According to Indrunas, approximately 16,000 cars
per day traverse many of Roswell’s main roads as commuters pass through
the city to access Georgia’s State Highway 400 to Atlanta. To manage the
flow of traffic on Houze Way, the contractor carried out the work with
vehicles passing on a single lane running one direction in the morning
and reversing in the afternoon.
The reconstruction went better than expected and afforded the
opportunity to match not only the existing curb elevations on one side
of the road, but also to widen the eastbound lane an additional 0.9
meters (3 feet) at the same time. “Even with the success of Houze Way,”
said Indrunas, “it was still important to become more fully informed
about the process.” So Indrunas attended a seminar on full depth
reclamation at the Georgia Department of Transportation (GDOT) Materials
and Research Lab in September 2001.

Cost Savings Changes Project Direction
Still not fully satisfied that reclamation was the answer to Roswell’s
overcrowded and under designed roads, Indrunas let a project for
conventional construction in the fall of 2001 for the reconstruction of
Jones Road. Initial bids came in at more than $1.5 million to complete
the work well over the project’s budget. The plan had included removing
40.6 centimeters (16 inches) of base, which meant additional costs to
relocate the affected water, gas, and phone utilities that lay beneath
the roadbed. The city’s transportation staff decided to take a different
approach the following spring and rebid Jones Road as a reclamation
project.
“We were shocked when the successful low bidder was awarded the work at
just over $270,000,” Indrunas says. With the new contract, Roswell saw a
potential cost savings of more than $1.2 million.
The new bid involved time savings as well. Using reclamation, the
roadway was scheduled to reopen after 7 or 8 working days instead of 6
months, because the Roswell DOT did not have to relocate the utilities
to accommodate the 30.5 to 35.5 centimeters (12 or 14 inches) of new
stone base that would be required if conventional reconstruction
techniques were used.
Due to the absence of freeze-thaw conditions in the Southeast, it is not
uncommon to encounter utilities at very shallow depths. With
reclamation, only 18 centimeters (7 inches) of surface was to be taken
up. “We got the strength of a brand new road for a fifth of the cost
[in] substantially less time than conventional reconstruction,” says
Indrunas.
Although the use of the full-depth reclamation process has nothing to do
with utility replacement, the decision to use one form of construction
over another did include the costs of each alternative.

        Change of Heart
By 2003, Roswell’s budget planners for street construction accepted
reclamation as an option. Based on cost savings alone, the question now
was where to use the process rather than whether to use it.
The Roswell DOT made plans in 2003 to reclaim Hardscrabble Road with a
combination of 3.9 kilometers (2.4 miles) of foamed asphalt base
stabilization and 0.8 kilometers (0.5 mile) of milling and resurfacing.
Mix designs were set, and work began to prepare a 125-millimeter
(5-inch) stabilized base under 50 millimeters (2 inches) of asphalt
overlay. With the road closed to local traffic only, reclamation crews
expedited the work in record timeó10 days versus 6 to 7 months with
conventional reconstruction.
“On a road with a traffic load of 16,000 cars a day, the difference in
time is priceless,” says Indrunas. Part of the problem with asphalt
patching, overlay techniques, and conventional reconstruction in general
is the cost to the public for detours, user delays, and road closures.
In addition, with patching and overlay methods that may appear to be
quicker and less expensive at the onset, reflective cracking into the
new asphalt overlay could occur year after year because the base course
asphalt and subgrade problems were not fully addressed in the process.
Conversely, recycling the base with foamed asphalt or another full-depth
reclamation technique provides an opportunity to complete a homogenous
base course from curb to curb and, at the same time, replace or repair
weak spots while the base is being redone. For example, certain areas of
weak subgrade on these projects were strengthened with the addition of
quick lime (other projects might use portland cement powder instead of
quick lime, depending on soil properties) up to 45.7 centimeters (18
inches) deep using a pulverizer. As a result of this all-encompassing
approach with full-depth reclamation as opposed to patching and overlay,
the agency expects to achieve a longer pavement life cycle.

Growing Confidence
In 2004 with three successful foamed asphalt base stabilizations
completed, the Roswell DOT let a bid for reconstruction of scenic
Riverside Road along the Chattahoochee River. This road is more highly
traveled than the first three reclamation projects, and part of it
includes a lane expressly for bicyclists and joggers. Originally, the
5.6-kilometer (3.5-mile) project was to take place in four phases over 1
year to limit disruptions to traffic flow. However, phase 1 went so
fast, the city decided to complete the other three phases all at once.
The engineers realized, however, that several thousand tons of new
material would be required to stabilize and build new shoulders in phase
4 of the project. Indrunas explains: “I knew that the surplus reclaimed
material in phases 1 and 2 could be utilized in lieu of new material on
phase 4, so I was delighted with the city’s decision to do all four
phases at once.”
The engineers added a shoulder to the road where formerly there was none
and, though not exclusively for biking and jogging enthusiasts, it
provided a “share the road” aspect. For taxpayers and road users alike,
the good news was that the project came in $400,000 under budget and a
month ahead of schedule.
Saving time and money are helpful factors when it comes to accepting an
innovative process, but at what cost in quality? To answer that
question, a third party contractor provided quality assurance on the
Roswell projects. Comparing the new subbase against international
standards of density and mix designs, the contractor determined that
Roswellís projects were reaching a target density between 95 and 98
percent. This density resulted not only from the binding of foamed
asphalt to the fine particulates, but also the use of a 27-metric ton
(30-ton) rubber tire roller, one of the heaviest available to the
highway construction industry today.

Increased confidence in an innovation also comes when the engineers have
a grasp of conditions that are unique to their situation and find the
appropriate adjustments that ensure success for their locale. For
example, many of Georgia’s roads are built on semiplastic soils with
minimal aggregate base, according to Ron Adderley, Roswell’s
construction and maintenance supervisor. “We found that using quicklime
stabilized the subbase and prevented the clay from becoming slippery,”
he says. (One percent quicklime is also added in conjunction with the
foamed asphalt base to increase the Marshall stability of the mix.)
Knowing that the subbase failures are properly addressed and that the
foamed asphalt base has a long life cycle when properly installed gave
Indrunas the confidence to tell city officials that the new approach to
reclamation would meet the 20-year life cycle expected for a road base.
With reclamation, the city has an affordable approach to both replacing
stretches of roads and completing needed repairs. Roswell experienced
unprecedented growth in the last 15 years, with access roads to many
subdivisions added to the original highway systems. Development
companies did not always connect their access roads to existing roads
using optimal highway construction designs. “We can adjust and correct
the resultant drainage deficiencies,î said Adderley. ” Now with proper
drainage, cross slope, width and uniformity, we are giving our taxpayers
roads that are new for a third or more of the cost of conventional
reconstruction. We can use environmentally sound processes to complete a
road in record time under traffic and at a lower cost. That is
invaluable.î
On October 18, 2004, the Asphalt Institute presented Director of
Transportation Steven D. Acenbrak and the Roswell DOT staff with an
award in recognition of their achievements using foamed asphalt base
stabilization. Peter Grass, president of the Asphalt Institute,
remarked, “All too often, we are reluctant to try newer technologies in
our public works projects for a variety of reasons, and in doing so,
fail to take advantage of effective techniques that can save both time
and money for the taxpayer.” By using this new technique, Roswell
reclaimed the four roads in a total of 45 construction days at a cost of
just under $1.4 million. Had the Roswell DOT used traditional methods,
the roadwork was estimated to have required 345 construction days with a
cost of approximately $6.5 million.

Blair Barnhardt was the operations engineer with Blount Construction Co. Inc. at the time of writing this article.  He has been involved with foamed asphalt     reclamation for 19 years in North America. Working in conjunction with instructors from the Asphalt Institute, he has taught the National Highway Institute course “AsphaltPavement Recycling Technologies” (NHI Course #131050A).For more information on this 2-day course, visit http://www.nhi.fhwa.dot.gov.

And Now He Has Published The Book on Better Roads;  Get your FREE Copy today!

The author would like to thank John Indrunas for sharing his experiences
with foamed asphalt base reclamation. For more information on foamed
asphalt base stabilization, contact steve.mueller@fhwa.dot.gov.