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“We found it’s cost-effective to use full-depth
repairs,” says Mueller. “Partial depth repairs were very successful for
a few years, but not successful for 10 or more years. We try to patch
concrete pavements and maintain them as bare concrete for as long as
possible.”
Lasting 40 years-plus
Because Minnesota is building better concrete
pavements than it built in the 1960s, the new generation of pavements
will last longer before they require a major CPR treatment, says Ted
Sexton, resident engineer in the state’s northeastern district. As
improvements, Sexton cites the following:
Joint spacings now are 15 feet, not 40 feet
as in the past. So mid-panel transverse cracking has been virtually
eliminated and the entire pavement is more durable.
The water-cement
ratio in Minnesota’s paving concrete is tightly controlled at a
maximum of 0.40.
The state now tests for aggregate with
alkali-silica reactivity, so that’s not a problem.
Contractors are not over-vibrating the
concrete.
Concrete paving is done in one lift, not
two. “The two-lift practice is antiquated and built in a
delamination,” says Sexton.
The state now installs dowel bars at all
joints, even for low-volume roads. In former days, joints in
low-volume roads were not doweled.
“The need for repair now is much less,” says
Sexton. “My prediction is that we’ll need only a very minor CPR after 17
or 20 years on these newer pavements, and then somewhere in the 25- to
30-year range they’ll need a fairly significant CPR job.
“I’m not clairvoyant, but I think we’ll see 50%
of the level of repair at 30 years that we used to see at 15 to 20
years,” Sexton says. “I would expect these new pavements to last in
excess of 40 years.”
At the Delaware DOT, says research engineer
Wayne Kling, “We prefer not to overlay concrete with asphalt for a
couple of reasons. For one, if there are any defects in the concrete,
they can reflect upward and cause a problem in the overlay. Secondly,
actual cost figures would show that CPR is more cost-effective, in the
long term, than an asphalt overlay. With CPR, you don’t have to adjust
manhole heights and you’re not changing the grade of the pavement.”
Speedy work
More than ever, speed is of the essence when
repairing concrete. In New York state, contractor Kubricky Construction
recently completed a 4-mile, two-lane stretch of CPR work in less that
10 days, says Bill Cuerdon, a civil engineer with the DOT’s Materials
Bureau.
The project was located on Route 7 in the Albany
area. It was a 17-year-old pavement that takes a pounding from 80,000
vehicles per day, with 10% trucks. “The contractor had a 10-day closure
time to do all of the partial- and full-depth repairs, the grinding, and
the joint sealing on the two-lane eastbound side,” says Cuerdon. “The
grinding was done in seven days, and the full-depth repairs were all
done in seven days.” Central Atlantic Contracting, a Division of Safety
Grooving and Grinding, was the diamond grinding subcontractor.
In Illinois, one contractor placed a
rapid-setting portland cement concrete mixture to do full- and
partial-depth repairs on 3 miles of temporary lanes used in the
reconstruction of I-55 — the Stevenson Expressway into Chicago. “The air
temperature was 32 degrees F, the concrete temperature was 85 degrees,
and the one-day compressive strength of the concrete was 7,000 psi,”
says IDOT’s Mueller. “Because of the heavy traffic demands, the
temporary lanes had to be durable. And none of those patches failed
during the two-lane temporary lane use.
“In addition to the portland cement, we used
pozzolanic materials and non-chloride accelerators, and mixed it in
ready-mix trucks,” says Mueller.
In California, the state has turned to diamond
grinding to correct step faulting, restore ride, and reduce the dynamic
loading that wheel loads cause at faulted joints. In fiscal 2000-2001,
the state spent $42 million to diamond grind some 390 lane miles of
concrete pavements in four districts, says Lance Brown, Chief, Office of
Roadway Maintenance, Caltrans.
Dowel bar retrofits
The Washington state DOT has successfully
performed dowel bar retrofits since 1992, says Jeff Uhlmeyer, pavement
design engineer. “Yes, it has been a cost-effective way to extend the
pavement life of our concrete roadways,” he says. “We hope to get 15
additional years with dowel bar retrofits.”
To decide whether to retrofit with new dowels,
the state looks at the degree of slab cracking and the amount of
faulting at the joints. These are not hard-and-fast criteria, but if a
pavement shows greater than 0,125-inch faults (but less than 0.5 inch)
at the joints, and fewer than 10% of the panels are cracked, then it’s a
candidate for dowel bar retrofit. If the pavement shows more than 10%
cracked panels, and greater than 0.5-inch faults, says Uhlmeyer, “We
probably need to reconstruct it.”
Washington has received long-term service from
its concrete pavements. Following are some typical CPR jobs:
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Last summer, 3 miles of I-5 near Bellingham,
built in 1961, was retrofitted with new dowels on the outside lanes
and diamond ground on both lanes.
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S.R. 195, partly built in 1967 and part in
1961 — a 3-mile section near Spokane received a dowel bar retrofit
on the outside lanes and diamond grinding of both lanes.
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Southbound I-5 near Mt. Vernon — a 2-mile
stretch built in 1976 was retrofitted with dowel bars on the outside
lane and received some grinding on the inside lane.
“These pavements have 15-foot joint spacings,”
says Uhlmeyer. “We typically retrofit dowels at every joint. We put them
in on 1-foot centers, three in each wheel path.”
Preventive maintenance
“Our state is going more toward preventive
maintenance because we see the value of doing it,” says Steve Oakey,
district materials/pavement engineer, southwestern Minnesota. “We have a
goal that we strive to do a certain amount of preventive maintenance
every year in the whole state.
“The goal in our district has varied in the
past,” says Oakey. “It’s been $3 million to $5 million for concrete and
asphalt pavements. Techniques include CPR, diamond grinding, and dowel
bar retrofits, for concrete pavements, as well as rout and seal and seal
coats for asphalt pavements.
“We have a program that involves looking at
pavements four years in advance, and then we submit candidates for our
construction and maintenance consideration.” For example, the state is
currently considering CPR for 2008 for a 16-mile stretch of Trunk
Highway 60 in southwest Minnesota. The first stage reviews involved
inspections by the state’s Maplewood concrete office, as well as by
industry people, including those from the Concrete Pavement Association
of Minnesota. The second stage reviews involved people from the district
office in the disciplines of construction, design, programming,
maintenance, materials, and pavement management.
“We looked at different alternatives and the
costs of each alternative and repair methods,” says Oakey. “Should we
grind or not grind? How much will rehab cost per mile? It’s information
we can carry over for design.
“We think we’re getting a good bang for the buck
with CPR,” says Oakey. “It’s a wise investment.”
Georgia’s lane replacement
program
 In
addition to its CPR program, Georgia is succeeding with a technique of
single-lane replacement on its concrete Interstate pavements. Recently
the state has completed some 50 centerline miles of single lane
replacement — nearly all of it on Interstates — says Bryant Poole, state
maintenance engineer for the Georgia DOT.
Here’s how it works. “Say you’ve got a four-lane
divided Interstate, and the outside lanes have failed, so CPR won’t
work,” says Poole. “We go in and replace the outside lane only, and do
CPR on the inside lane.
“One 2.5-mile section was full-depth asphalt,”
says Poole. “We took out the old asphalt pavement and base, put back 12
inches of granite base and topped it with 12 inches of PCC pavement. The
project received an award from the American Concrete Pavement
Association. We shut the road down except for one lane in each
direction, and we had a certain number of weekends in which to do the
work.”
Poole says these full-lane replacements are
being done on concrete pavements that are 30 to 40 years old. “Up until
this point we have performed CPR multiple times,” says Poole. “We have
exceeded the design ESAL count (equivalent single axle loadings) many
years ago.”
Compared to putting in an overlay of either
asphalt or concrete, the full-lane replacement leaves the grade at the
same elevation. “We don’t have to raise bridges, extend pipes or
culverts, and we don’t get off the right-of-way,” says Poole. “There are
no other environmental impacts. When you have to jack up bridges and
build retaining walls, it’s not cost effective.
“Full lane replacement costs more than CPR, but
it’s less expensive than traditional reconstruction,” Poole says. |
