The Northumberland Strait became the talk of the industry when
Canada began building the 13-km (8.08 mile) Confederation
Bridge, stretching from Prince Edward Island to New Brunswick.
The new bridge, which replaces the current ferry system, carries
traffic across the strait at heights from 140 to 200 ft.
Construction began in 1993, and the bridge opened to the public
The bridge consists of two travel lanes and a
breakdown lane, and required a specially designed parapet wall
on both sides. The Constructions Materials Group of Lafarge
Canada Inc., a subsidiary of worldwide Lafarge Corp., was
responsible for slipforming all of the parapet wall on the
project. Under a separate contract, Lafarge also supplied all of
the ready mix concrete to the bridge project.
In order to
complete the job by its scheduled date, Lafarge bought a new
Commander III slipform paver for the project, and a second
machine was leased to Autoform Contracting London Ltd., who
provided an operator for the machine. Manufactured by Gomaco
Corp., Ida Grove, Iowa, the machine features additional vibrator
circuits, custom neoprene rubber tracks and special wall forms,
with hydraulic sideplates.
The bridge's parapet wall was
designed to be 9 in. wide at the top, 20 in. wide at the bottom
and 47 in. high off the bridge deck. It overhangs the deck by 7
in. on the bottom. The purpose of the overhang is to conceal the
anchor heads for the transverse post tensioning in the concrete
The overhang was poured over wooden soffit panels that
were stripped three days later and reused again ahead of the
machine. Hydraulic sideplates on the mold prevented the crew
from having to make adjustments manually from the outside of the
This time-consuming project required several steps
toward completion. The wall was poured over reinforcing steel,
which was installed by a crew working for Strait Crossing Joint
Venture, Charlottetown, Prince Edward Island, Canada, the prime
contractor on the bridge project.
Jeff Kerr, area manager,
was asked last fall to explain the slipforming process. "It's a
revolving process. The work by one crew directly affects the
work of another crew. It's a cycle. We have crews working ahead
of us, getting the reinforcing steel ready and installing the
soffit panels. So we can pour, depending on what is happening
ahead of us."
Concrete light bases were placed every 272 ft
along the bridge. Lafarge is pouring the parapet wall right over
the bulk heads for the lights, rather than stopping, then
digging out the concrete afterward.
Expansion joints were
tooled in every 20 ft. A finishing platform traveled behind the
machine to enable finishers to work from the back side of the
Approximately 17,003 cu yd of concrete was used to
pour the 85,302 ft of parapet wall. A specified mix design of
5,000-psi silica fume concrete mix was used with a slump of 0.79
to 1.18 in. Concrete trucks, varying from three to five trucks
per machine, ran to-and-from two plants on Prince Edward Island
and one plant in New Brunswick to supply the work.
number of trucks and speed of service depended on how far out
the machines were on the bridge. The plants serviced the entire
project so, according to Kerr, there were days when they had
trouble keeping up. Fortunately for the crews, during the
construction the bridge was only open to construction traffic.
Weather Rears Its Head
Weather also was a factor as the
crews worked under the demanding schedule. Winds were very
strong while working atop the bridge and the winters were
"Working approximately 43 to 61 m (140 to
200 ft) in the air over the Northumberland Strait, it can be
extremely windy. We had to shut down if the winds got too high.
It's basically a safety element. It doesn't take long for your
hard hat to go flying off in the 50 km per hour (31 mph) winds,"
The Construction Materials Group of Lafarge
Canada had little experience with slipforming a wall before the
project. Fortunately, their parent company provided access to
other Lafarge operations with more experience in the area. The
British Columbia Lafarge crew came to their aid, lending their
experience in helping to get started on the project. With the
help of the more experienced group, along with support from
Gomaco, the paver manufacturer, and the dealer, the group got
off to a good start and had successfully slipformed 32,808 ft of
wall by mid-October 1996.