Fighting A Beating

Asphalt Article February 05, 2001
Printer-friendly version

Itís
the kind of challenge seldom seen in the highway construction business. Faced
with a rutting problem on some aging pavements, the Maryland State Highway
Administration (SHA) decided to compare the performances of hot-mix asphalt
(HMA) and portland cement concrete (PCC).

In
1994, the SHA gave the HMA and PCC industry one intersection each
style='font-family:Symbol;mso-ascii-font-family:"Courier New";mso-fareast-font-family:
"MS Mincho";mso-hansi-font-family:"Courier New";mso-char-type:symbol;
mso-symbol-font-family:Symbol'>æboth
along U.S. Route 40 in northeastern Maryland
æ style='mso-fareast-font-family:"MS Mincho"'>and charged them with rebuilding
the two intersections. Traffic gives Route 40 a beating. It has an average
daily traffic of 29,200, including 12% trucks. The four-lane highway has right-
and left-turn lanes, and it runs through suburbs with traffic lights every
half-mile or so. All those trucks sitting at traffic lights, especially during
Marylandís hot summers, produce a high potential for a rutted pavement. What is
more, Route 40 sees a number of freeze-thaw cycles in the winter. The estimated
equivalent axle loadings through the year 2014 is 12,744,000.

Each
industry selected its own pavement design. The HMA industry chose two Superpave
mixes to use in rebuilding its intersection, the corner of Route 40 and
Maryland Route 213 near Elkton, Md. The PCC industry rebuilt the adjacent
intersection of Route 40 and Landing Road using 61/2 in. of unreinforced
whitetopping over existing pavement.

In
1994, T.C. Simons Inc., Fallston, Md., laid 15,000 sq yd of new HMA pavement in
11 nights, working from 7:00 p.m. to 6:00 a.m. with little disruption to
traffic. The PCC contractor installed about 1,800 sq yd of pavement, working
around the clock for 12 days and nights. Without counting the cost of user
delays, the PCC pavement cost $104.25 per sq yd. In contrast, the HMA cost
$36.11.

The
performance results: the HMA pavement is still in place and performing well,
while the PCC began cracking in 1998 and had to be saw-cut and removed last
summer.

[if !supportEmptyParas] [endif]

Taking over

The
whitetopping had been placed for a distance of some 800 ft in the passing and
travel lanes of the eastbound side of Route 40.

"Cracking
in the whitetopping was first evident in 1998, and it continued to deteriorate
through 1999," said Brian Dolan, president of the Maryland Asphalt Association.

"The
concrete was spalled and cracked in many areas of the 800-ft-long section,"
added Scott Kiebler, project manager with T.C. Simons Inc. Transverse joints
were installed at 40-ft intervals in the concrete. "Almost every joint was
cracked, and there were areas where the whitetopping had failed between the
transverse joints," said Kiebler.

In the
latter part of July 2000, T.C. Simons Inc. hired East Coast Concrete Cutting,
Baltimore, Md., to saw-cut the concrete. One lane was closed at a time to allow
the sawing contractor space to work. "We sawed each 12-ft-wide lane down the
middle," said Kiebler. That made 6-ft-wide strips of concrete. Then East Coast
cut the concrete across the lanes at 8-ft intervals, making 6- x 8-ft slabs of
concrete. The total area of saw-cut concrete was 800 x 24 ft.

Then at
7:00 p.m. on Aug. 1, 2000, T.C. Simons began concrete removal. "I submitted a
traffic plan to shut down the travel and passing lanes and to shift traffic
onto the deceleration lane on the right side,î said Kiebler.

The
entire removal and repaving operation took less than 24 hours.

"We
used two Gradall XL-4100 excavators with stripping buckets," said Kiebler. "We
picked up the concrete slabs and stacked them into eight tandem-axle dump
trucks."

Concrete
removal took just six hours.

Under
the whitetopping was a 1-in.-thick course of HMA that acted as a bond breaker.

"We
milled out the bond breaker in four hours with a Caterpillar 465 milling
machine," said Kiebler. ìThen at 7:00 a.m. we started paving."

Simons'
paving operation consisted of one Barber Greene 225 paver fed by six
tandem-axle end-dumps hauling HMA.

"We
paved 12 ft wide and laid down two lifts at a 4-in. depth to make the 8 in.,"
said Kiebler.

The mix
design: a Superpave with 25 mm top size aggregate and a PG 70-22 grade of
asphalt cement. Compaction was handled with two Ingersoll-Rand rollers, a DD-90
and a DD-110. Paving took just eight hours, and by 5:00 p.m. on Aug. 2 the
pavement was opened to traffic.?

"At a
later date we topped that with a 2-in. surface course of Superpave (12.5 mm top
size aggregate) and PG 76-22 grade of asphalt cement,î said Kiebler. "That mix
was polymer-modified."

The
removal of the whitetopping and the reconstruction was part of a $4.5 million
project that included various safety improvements along U.S. Route 40. style="mso-spacerun: yes">

Today,
the estimated design loading at both intersections is between 10 million and 30
million ESALs (equivalent single axle loadings) over the 20-year design life of
the pavement, said Dolan.

[if !supportEmptyParas] [endif]

style="mso-spacerun: yes">

As good as new

Meanwhile,
the HMA at the Maryland 213 intersection has performed very well. The following
are three evaluations made at different points in time by SHA officials
addressing the performance of the Superpave intersection built in 1994.

Two
years after construction, here's what John Knight, the SHA's district
maintenance engineer, had to say: ìWith two yearsí service and close monitoring
of the pavements, we're very pleased with the performance of the HMA project.
In fact, it still looks real good, just like the day we put it down. Thereís no
noticeable rutting.

"The
HMA section has performed so well that we've just recently reconstructed
another troubled intersection along I-95 adjacent to a truck stop using the
same design considerations. We think we've found the solution to our rutting
problem while maintaining all the advantages of HMA construction," Knight
concluded.

"This
(HMA) material has been down for over five years and I really am impressed with
how well it's performed," said Mike Lewis, a Maryland state resident engineer,
in 1998. "It's been a real good solution. I haven't had to be out here in the
last five years to do any maintenance. We have done no milling to the
intersection, and if you look at the intersection today you can see there's no
evidence of rutting anywhere."

"The
HMA intersection is still out there and performing well," said Sam Miller, head
of the Materials Division, Maryland DOT.

[if !supportEmptyParas] [endif]

Early decisions

A good
deal of planning and design work went into the HMA project. With the challenge
in hand, the HMA industry formed a small task force composed of representatives
from the Maryland Asphalt Pavement Association, the National Asphalt Pavement
Association and the Asphalt Institute. The goals of the task force were to
determine how much of the existing 8 in. of HMA should be removed, the new
mixes to be used and a construction schedule.

Extensive
materials testing was conducted prior to construction. The Superpave mix
designs developed at the Asphalt Institute in Kentucky were replicated at the
Koch Materials laboratory in Pennsauken, N.J. Samples of the proposed mixes
were sent to Kochís laboratory in Terre Haute, Ind., where Hamburg Wheel
Tracking Tests confirmed that the proposed mixtures were quite rut resistant.

HMA
officials felt that it was important to know the exact depth of rutting in the
existing pavement. Existing data showed the pavement consisted of 8 in. of HMA
over 9 in. of PCC. But to learn how deep the rutting went, a 1-ft cut was taken
out of the travel lane on Route 40 and one core was taken from each of the four
eastbound lanes.

The
cores confirmed the expected pavement thickness. The cut taken from the
eastbound travel lane showed that rut depths extended to 6 in. or more. In the
eastbound lanes, rutting was evident 835 ft back from the stop bar, and
extended for an additional 435 ft through the intersection.

The
scope of the original project was reduced somewhat to meet budget. On eastbound
Route 40, total removal of 8 in. of HMA would take place only in the travel,
passing and right-turn lanes. The left-turn lane was to have 5 in. removed. The
westbound lanes, which had appreciably less rutting, had only 2 in. removed
from the travel, passing and left-turn lanes. The right-turn lane had failed
structurally, so 5 in. were removed.

Contractor
T.C. Simons Inc. replaced the milled pavement with 3-in. lift(s) of base course
and one 2-in. lift of surface course. Changes to the initial plan were agreed
upon by both the SHA and the HMA industry when the SHA agreed to use only the
eastbound travel and passing lanes when making comparisons between HMA and
PCC.

[if !supportEmptyParas] [endif]

Increasing the dosage

HMA
officials decided to use two Superpave mix designs, a base mix with 25 mm top
size aggregates and a surface mix with 19 mm top size aggregates. The task
force decided to "bump up" the Superpave-recommended grade of asphalt cement
from PG 64-22 to a PG 76-22 to correct for standing traffic.

The
selection of the coarse gradation for the base mix was an effort by the task
force to use as high a percentage of large aggregate in the mix as possible.
More large aggregate in an HMA mixture creates more stone-on-stone contact and
gives the mixture a stronger structural framework. After testing three trial
mixes in T.C. Simons Inc.ís parking lot, the project team decided to use 4.6%
asphalt cement in the base course and 4.9% in the surface course. style="mso-spacerun: yes">

Following
construction, both the HMA and PCC pavements were tested for smoothness with a
profilograph. The results: the HMA pavement had values more than twice as
smooth as the PCC test section. And more than one year after the paving was
completed, the results were the same: no rutting.

About the author: 
Brown is the owner of Technicomm, a communications business based in Des Plaines, Ill.
Files: 
Overlay Init