Bridging the
Gap
Tedd Schoch, vice president of
Technical Services, Aggregate
Industries Mid Atlantic, and the rest
of the WWBP consortium are proud of
the tremendous work they’ve done
over the past several months.
Exceptional partnering and ingenuity
conquer tough concrete pours over the
Potomac.
B
for a total clearance of 70 feet at its highest point. This, according to the Woodrow
Wilson Bridge Project, will allow for 70%
fewer bridge openings. The deck will consist of 12 lanes, which accommodate eight
general-purpose lanes, high-occupancy
vehicle lanes, and merge lanes after the
interchanges are built.
Building the massive concrete foundations beneath the bridge deck is, of
course, where the project started after the
first contract to dredge 340,000 cubic
yards of material was completed on Feb.
14, 2001.
The second contract included the
majority of foundation work for the bridge.
The foundations include steel pipe piles
that have a diameter range of 48 to 72
inches for river piers and Pier V-2, the
first pier on the Virginia shore. The other
Virginia piers include 24-square-foot prestressed concrete piles. The lengths of the
piles vary from about 40 feet for the concrete piles to about 200 feet for larger
steel pipe piles. Concrete pile caps were
also included in the contract.
Concrete production and placement
logistics
Tidewater Construction Corp./Kiewit
Construction Co./Clark Construction
(TKC) won the second contract as a joint
venture. After numerous planning meetings, a joint venture consisting of TKC,
Waldorf, Md.-based Chaney Enterprises,
and Aggregate Industries Mid Atlantic
division, Greenbelt, Md., was formed.
Called Woodrow Wilson Bridge LLC, the
group set about to make the plan for concrete production and placement a functional reality. The plan consisted of conveying material from an onsite plant to
two barges, which then feed concrete to
a rough-terrain Creter Crane equipped
with a telescopic placement conveyor that
extended 75 to150 feet.
The onsite plant, a 12-cubic-yard
Con-E-Co portable central mix plant rated
at about 400 cubic yards per hour, was
purchased by the joint venture. After the
partnership ends, Aggregate Industries will
purchase the plant from the group. Permitting the plant was relatively snag-free,
EDWIN REMSBERG / GETTY IMAGES
BY BILL WELGOSS
y any measure, the construction of a
new Woodrow Wilson Memorial Bridge
to replace the older Wilson Bridge,
built in 1961, marks one of the most important transportation projects in the country. The old bridge, originally four lanes,
was designed to carry 75,000 vehicles a
day over 20 years. Today, the 71⁄2 mile
bridge carries nearly three times the traffic volume—nearly 200,000 vehicles a day
on six lanes. The six-lane bridge connects
Virginia and Maryland over the Potomac
River via Interstate 95/Interstate 495 (the
Washington, D.C., Beltway), which is an
eight-lane highway. The narrower Wilson
Bridge causes one of the worst bottlenecks
in the United States.
Goals of the new Woodrow Wilson Bridge Project, which also consists
of new surrounding interchanges, are
to ease congestion as well as to address
community and environmental concerns and to represent a fitting tribute
to President Woodrow Wilson. The final
structure will be a drawbridge that stands
20 feet higher than the existing bridge,
WOODROW WILSON BRIDGE PROJECT
Material for the bridge
was conveyed from an
onsite plant to two
barges to feed concrete
to a rough-terrain
Creter Crane. From
there a telescopic
placement conveyor
extends 75 to 150 feet.
as no building permit was required since
the plant is portable and the land has been
set aside by the state of Maryland. The environmental permitting, which included air
and water, was essentially a formality as the
plant discharged no process water.
“The plant could certainly do 300some yards per hour, and we needed at least
250 cubic yards per hour. We never had a
problem throughout the project,” says Tedd
Schoch, vice president of Technical Services, Aggregate Industries Mid Atlantic.
To stockpile cement, the group used
five blimp storage systems, which each held
as much as five loads of cement. Area around
the plant allowed for stockpiling 3500 tons
of the three necessary aggregate sizes—sand
from Chaney Enterprises’ operation and
gravel and stone from nearby Aggregate
Industries operations.
From the onsite plant, concrete is
dumped into a 20-cubic-yard hopper, which
feeds an inclined 30-foot conveyor that
drops concrete to another 50-foot inclined
conveyor to a transfer point. At the transfer point, the concrete flow changes direction nearly 45 degrees to a 100-foot conveyor, which feeds a 125-cubic-yard coneshaped hopper equipped with vibrators and
agitators located at the shoreline. “We also
set up separate backup conveyors for each
hopper in case of a breakdown,” says Schoch.
The shoreline hopper fed a 250-foot
conveyor, which fed hoppers on two barges,
which transported concrete to the pour
(about 1 mile). These transfer barges were
each equipped with 60-foot conveyors to
feed the third barge equipped with a 125cubic-yard hopper, which supplied the
crane equipped with the telescopic placement conveyor.
Concrete temperature challenge
Concrete placement was not the only
challenge requiring a unique approach. Demanding concrete specifications, such as a
placement temperature limit of 160° F, put
quality control in the forefront.
“It was very difficult to reach 160° F,
as most large pours allow temperatures up
to 170° F. Also, considering concrete can
peak at 240 to 250° F in a solid mass, the
specification required a sizeable temperature reduction,” says Schoch.
Several strategies were incorporated to
keep concrete temperature down, especially
in the summer months when ambient temperatures would reach the mid-90s or higher.
Starting at the concrete plant, Aggregate Industries tried to keep concrete temperature
at 70° F. On the hottest days, that required
as much as 1200 pounds of ice for each 10cubic-yard batch. Chillers were also installed
on the plant to keep water at 40° F.
The concrete mix also incorporated
75% Newcem slag cement to help control
temperature. Other key admixtures used
were a Type II high-range water reducer
and retarders applied in hot weather to
help to keep set times low and maintain
slump. At point of placement, specifications required the center of the concrete
placement to remain within 35° F of the
concrete at the edge of the form. Cooling
tubes were inserted to pump water through
placed concrete to control temperatures.
Insulation was also applied to the outside
of the forms to keep the placed concrete
within the 35° F range in cold weather.
Air entrainment challenge
Maintaining the specified 6% air in
the concrete at the point of placement was
another challenge given the concrete transport system.
“The number of transfer points, with
the concrete hitting a plate then falling a
few feet into a hopper, really took the air
out of the concrete,” says Schoch.
In order to achieve concrete that met
specifications at point of placement, Aggregate Industries needed to use an air entrainment admixture to add 2 to 21⁄2 times
the amount of air (14 to 16% air) at point
of production. “It was a scary ordeal because
if too much air stayed in the concrete,
strengths wouldn’t be very good,” says Schoch.
Strength requirements for concrete
were 6500 psi for the pedestal concrete,
which provided the base for precast concrete placement for the superstructure;
4000 psi for the pilecaps; and 3500 psi for
the tremies.
Continuous pour challenge
In all, 17 piers (each of consisting of
a pedestal, pile cap, and tremie) have been
built—11 in the river and six in Jones Point
Park in Virginia. Pedestal pours for the
bridge averaged 300 to 650 cubic yards as
the bridge rose to the bascule—the drawbridge section. The pilecaps beneath the
pedestals are 700 to 1500 cubic yards. The
major challenge was providing continuous
pours for the four massive foundations supporting the bascule.
“Each large foundation required about
2000 cubic yards for the tremie, about 6000
EDWIN REMSBERG / GETTY IMAGES
The Con-E-Co portable central mix plant,
rated at about 400 cubic yards per
hour, originally was purchased
by the joint venture and will
be bought by Aggregate
Industries at the
completion of
the project.
cubic yards for the pilecap, and 8000 to
8500 cubic yards of formwork,” says Schoch.
Pours for the small foundations—each
300 to 400 cubic yards—took 3–6 hours.
For the large pours, times were measured
in days. “The last big pour for a pilecap for
the bascule required almost 7000 cubic
yards. We started on a Friday and finished
Sunday morning,” says Schoch.
In all, the bascule foundations required
about 45,000 cubic yards of concrete. For
the big continuous pours, keeping a steady
supply of aggregate and cement was a concern. For the last 7000-cubic-yard pour, the
plant beefed up aggregate stockpiles on Friday. On Saturday morning an independent trucking company replenished the stockpiles, which provided enough aggregate to
complete the pour. Cement was also stockpiled as much as possible prior to the pour,
and five cement tankers also parked onsite
to replenish cement supplies in an emergency.
Weather, especially wind, was always
an unknown during the pours. A few times
during the project, operations were stopped
because of high winds. Because all the transfer hoppers were open, rain was also a concern. Pours were scheduled around weather
forecasts, and in this respect, the group was
relatively fortunate. Although the crews
faced tough, wintry weather on some days,
conditions never reached a point of compromising the large continuous pours.
About a week before the project’s end,
the onsite plant was dismantled, and the
rest of the concrete supply duties were handled from offsite sources. Along with sampling concrete quality at the plant and at
the point of placement, Aggregate Industries also periodically inspected concrete
samples at each transfer point. A certain
number of samples of hardened concrete
were taken to a lab for petrographic analysis to ensure the concrete had the proper
air entrainment.
Given the number of variables, the
number of rejected concrete loads was miniscule. “We had one barge rejected by the
state, and it wasn’t even full,” says Schoch.
“Our own group rejected other concrete
loads, and we rebatched it ourselves. Because of time delays or slump concerns, we
may have lost about 100 cubic yards of concrete throughout the whole job.”
The smoothness of the operation
prompted the project team to invite representatives from The Washington Post and
The Baltimore Sun to observe two separate
foundation pours, which resulted in positive press coverage. Attention to detail,
cooperation from all parties, and great communication were the keys to the project’s
success. Schoch is quick to say, “Everybody
did a great job.”
Meetings vital to success
Key to the smooth operations, as well
as the timely completion of the project, according to Schoch, were the continuous
meetings throughout the project. State officials from Maryland and Potomac Crossing Consultants strongly promoted regular
and frequent meetings among all parties
involved—local, state, and federal transportation and environmental agencies as
well as contractors and subcontractors.
“These partnering meetings proved to be
very valuable,” says Schoch.
Representatives of all parties met twice
at the beginning of the project, putting all
concerns and grievances on the table before the project began. Meetings were then
held every month in the early stages of the
project, then every two months.
“Before every foundation pour, a meeting was held,” says
Schoch. “Even when the first foundation pour went well, the
partnership still met to discuss issues concerning the next pour.
Issues were put on the table immediately and resolved.”
Initially the project was delayed a few months, so the partnering group expected to fall behind schedule. Now, as the job
draws to completion, it will likely finish ahead of schedule. Additionally, milestones for the completion of each foundation
were built into the contract with financial disincentives for missing these time markers. No milestones were missed throughout
the project. Open communication fostered frequent meetings
that likely played a big part in the overall efficiency of the project. For instance, the meetings, with all necessary parties in attendance, expedited blueprint approvals for each part of the
project—an aspect of any large project that is notorious for causing delays.
Success of Woodrow Wilson Bridge LLC bodes well for each
partner for the subsequent bids to complete the other phases of
this ambitious project.
—WELGOSS is a freelance writer based in Frederick, Md. He has
more than 10 years of experience covering the aggregates and construction materials supply industries.
Publication #J03G028, Copyright © 2003 Hanley-Wood, LLC. All rights reserved