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On some nights, Ballenger was able to replace more than
half a mile of pavement per night, says Wouter Gulden, director of
engineering and training, Southeast Chapter, American Concrete Pavement
Association. In fact, the contractor removed and replaced the 20.1 lane
miles of concrete pavement in just 16 weeks time. The actual paving took the
equivalent of 11 weeks and was done during the months of January through
April 2004.
Drama at night
Beginning at 8:00 p.m. every night, the contractor
closed down the two outside lanes, while the inside lane remained open, says
Ronnie Ashmore, a vice president with Ballenger Paving Division, APAC
Southeast. Work zone barrels came first, followed by sawing and removal of
the old concrete. A wheel loader with forks removed 6- by 10-foot blocks of
pavement. Next was smoothing and compaction of the existing base. Then
Ballenger placed dowel baskets, chairs, and reinforcing mats.
Paving began about 10:30 or 11:00 p.m. Concrete was
hauled from a central mixing plant to the site in Maxon side-dumps on
Autocar trucks. The side-dumps emptied the concrete into a Maxon spreader,
and a Gomaco 2800 slipform paver did the rest. Finishers used 16-foot
straightedges to correct any minor deficiencies.
The contractor would stop paving each morning at about
4:00 to 4:30 a.m. The middle lane — used during construction as a safety
buffer and haul road — had to reopen to traffic at 6:00 a.m. By 10:00 a.m.,
Ballenger could open the new pavement to traffic. The Georgia Department of
Transportation specifies a minimum cure requirement time of four hours.
“This all required close coordination between the
sawing and removal crews, the concrete plant, and the paving crew,” said
Ashmore. “We at the Ballenger Paving Division had a work force of 75 people
and the removal contractor had 25 people at the worksite. During a good
portion of the night, all of the activities were taking place at once, from
sawing the old slabs to paving the new concrete.”
High early strength
“Most fast-tracked concrete pavements are done during
weekends,” says Gulden. “I don’t know of one done each night in concrete.
It’s an equal production speed to deep milling of asphalt and repaving. The
concept came out of the Georgia DOT’s Maintenance Office.
“Conventional wisdom says you need the 400-psi flexural
strength or 2,500-psi compressive to hold up to trucks,” says Gulden. “But
Georgia found in the late ‘70s that you can open it up sooner. And that was
by trial and error. The Georgia DOT tried eight hours, and that worked, and
then they tried six hours, and that worked okay. They get about 1,200 to
1,500 psi in five and a half to six hours.”
To achieve that strength, the Georgia DOT designed a
high-early-strength mix with 750 pounds of Type 1 Portland Cement per cubic
yard. It’s an eight-bag mix. “They added a non-chloride accelerator,” says
Gulden. “It’s a standard paving mix except for the higher cement content and
the non-chloride accelerator.
“The DOT’s challenge was to design a pavement system
that had to be 10 inches in thickness to replace the existing slab,” says
Gulden. “The existing slab was originally designed to carry 6 million
Equivalent Single Axle Loadings, while future ESALs were estimated to be
about 115 million over the next 20 years. High-strength concrete (800-psi
flexural), dowels, short joint spacing of 15 feet, and reinforcing steel
were used in the design. The reinforcing steel mats were added to enhance
strength and provide for a margin of safety, even though design formulas do
not account for this feature.” Diamond grinding was specified as the final
finish.
APAC-Southeast’s Ballenger Paving Division received two
Southeast Concrete Alliance Network awards for this project. SCAN is
composed of state DOTs, the Federal Highway Administration, the Southeast
Chapter of the American Concrete Pavement Association, concrete paving
contractors, and equipment manufacturers and material suppliers. Awards are
presented to all concrete paving and rehabilitation projects that meet the
quality or innovation standards established by the SCAN Award Committee.
Ballenger received the following awards for this project: the 2005 SCAN
Quality Award in the Concrete Pavement Construction category; and the 2005
SCAN Innovation Award for advancing the knowledge and practice in concrete
pavements. |
