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Average production reached about 150 cubic yards per hour, which
included time spent for a number of hand pours and block-outs for local
homes and businesses. “Our mainline paving went much faster than that,”
says Berger.
The concrete itself must have a consistent slump
and air content. Actual slump on U.S. 93 was 1.2 inches and air
entrainment averaged 5.1%. “That low slump concrete was very workable,”
says Berger. “We had to be careful not to get too high of a slump
because we were pouring curb integrally with the pavement. The concrete
was 19-inches high at the back of curb.”
It also helps to have an experienced paving crew
that can monitor the paving operation, Berger says. “The crew has to be
aware of what is going on around them and react accordingly,” he says.
“Once you’re paving, there’s a feel to it.”
The crew must constantly monitor the stringline
and the paver’s sensors. If the grade is smooth and flat, you can turn
down the sensitivity because the sensors don’t have to be as sensitive,
says Berger. But if the grade has a lot of imperfections, you have to
turn the sensitivity up, so that the paver will respond quicker to
changes in elevation.
The set-up of the machine is critical to
achieving great rides. The paver’s conforming mold must be set with the
right attitude, or angle of approach, to the concrete. If the angle is
too steep, the mold will seek to float up over the concrete. But a
negative attitude will make the paver “want to dive on you,” says
Berger. “We run our mold flat to the wire, or stringline. And your paver
needs to have enough weight to hold the mold flat to the grade as the
concrete is being vibrated. Use the right size of paver for the job.”
As recognized by an ACPA Award for Excellence,
another remarkable smoothness result was achieved by Cedar Valley
Corporation on Highway 60 in Sioux County, Iowa. The contractor placed
21.5 lane miles of mainline pavement with an average smoothness of 1.4
inches per mile using Iowa’s 0.2-inch blanking band. No corrective work
was required.
Craig Hughes, project manager for Cedar Valley,
stresses the value of proper placement of stringline pins and stringline,
as well as machine setup, before paving begins. “Make sure the pins are
vertical, not canted, and are a consistent distance apart,” says Hughes.
“Variation can allow the sensors to come off line, and if the sensors
are not perfectly level, the deviation in transverse spacing of the line
can allow the paver to wander, and in the worst case, go completely off
line. Neither is conducive to smoothness. When changing a paver from one
width to another, and setting the machine up with a new attitude or
angle of approach, precise adjustment is very important.”
Iowa studies show that each operation behind the
paver can add roughness to the pavement. Less is more when it comes to
finishing work behind the paver. If you pave with a consistent,
well-graded mix and you set the paver and stringline correctly, only
minimal finishing work should be required. “Your finishers should not be
half-dead at the end of the day,” Hughes says.
In 2004, the Iowa DOT started letting concrete
paving projects using a developmental zero blanking band specification.
Because there is no blanking band, every elevation deviation in the
profile adds count to the total deviation per segment. Under Iowa’s zero
band specification, only two of the 190 segments on Cedar Valley’s
winning project would have required corrective work.
Each year, the Iowa DOT has increased the number
of projects with the zero-band specification. “We have approximately
510,000 square yards of zero-band concrete paving under contract at this
time,” says Hughes.
“Zero band smoothness requires you to reassess
your entire process,” he says. “You have to raise your level of
attention to everything — the stringline setup, machine setup,
performance of mix through the paver, the actions of finishers behind
the paver, the type of micro and macro texture required and the
cleanliness of the slab prior to testing smoothness.”
Dowel bar inserter
For the ACPA-award-winning I-95 reconstruction
in South Carolina, the state DOT designed and required 100% diamond
grinding on all travel lanes. “South Carolina has decided that smooth
roads equate to longer lasting roads, so they determined that grinding
would make the road last as long as possible,” says Dave Rankin,
district manager for The Lane Construction Corporation, contractor on
the project.
The 10-mile stretch of I-95 had a pre-grind
specification of 10 inches of deviation per mile (0.1-inch blanking
band) and a post-grind specification of less than 40 on the Mays Ride
Meter. A small amount of corrective work was required to meet the
pre-grind spec, and Lane met the Mays Meter spec with no problem.
For the first time, the state DOT allowed the
use of a dowel bar inserter with the Guntert & Zimmerman S850 paver.
Forks automatically pushed dowels down into the concrete ahead of the
mold. The inserter worked well, Rankin said.
To ensure that the dowels stayed in position in
the concrete, Lane adjusted its aggregate gradation, which gave the mix
a more uniform quality. The original aggregate blend had only a minimum
of 0.5-inch minus stone, so Lane blended in some finer aggregate to get
a uniformly graded aggregate blend.
And to assure the state that the dowels in fact
reached the proper position, the contractor used a non-destructive
testing device called an MIT Scan, from Magnetic Imaging Tools, based in
Dresden, Germany. The device rolled along tracks placed on either side
of a transverse joint. A record of the position of each dowel was
recorded on the unit’s hard drive and could be printed out. At the time,
South Carolina was reported to be the second state, behind California,
to use the MIT Scan.
The project required the placement of 635,000
square yards of 11-inch-thick jointed plain concrete pavement over 25
months. A wet fall season caused wet subbase conditions, and the
contractor had to stabilize a much greater portion of the subgrade than
was originally planned. The state agreed to pay for the additional work
in exchange for a revision to the contract’s No Excuse Incentive. The
change allowed Lane to earn the full incentive if the project was
delivered 30 days earlier than originally scheduled. And in fact, Lane
met the earlier deadline.
Having a well-stabilized subgrade, plus the
placement of a 1.5-inch asphalt base, helped achieve the smooth
pavement, Rankin said. “We placed asphalt for extra width so that the
concrete paver’s tracks were supported on that base,” he explains. “So
we had a stable area for the tracks to run on.”
The overlay winner
Duit Construction Company won ACPA’s Excellence
in Concrete Pavement award in the Overlay category for paving 51.3
lane-miles of 10.5-inch concrete over 9 inches of existing asphalt on
Interstate 40 in Oklahoma. The Interstate was originally a full-depth
asphalt pavement that had rutted considerably over time. To prepare the
base, Duit milled out about 1 inch of the existing asphalt and placed a
leveling course of new asphalt.
Using a CMI-made SF 450 paver with a dowel bar
inserter, followed by a CMI 6004 finish paver, Duit achieved an average
ride index of 0.92 inch per mile overall. The maximum allowed is 16
inches per mile before corrective work must be performed.
The concrete was made at a batch plant on-site,
and slump averaged 1.5 inches. Duit used a burlap drag on the concrete,
and tined the pavement transversely. “Eyeballing the stringline is
important — setting good stringline and looking down it to make sure
it’s flat and true,” says Mark Willy, Duit’s project manager.
He stresses the value of an experienced paving
crew. “Our superintendent, foreman, and stringline man have all been
with us 16-plus years, and I’ve been there 14 years,” says Willy.
“Practice makes perfect. Quality is standard practice for us, and we
have a wall full of awards to prove it.”
Special spec
For the ACPA award winner in the Urban Arterials
& Collectors category, Trierweiler Construction Company installed 50,311
square yards of 10-inch-thick concrete pavement on East Washington
Avenue in Madison, Wisconsin. The owner required a smooth ride of 20
inches per mile on a 0.2-inch blanking band, which Trierweiler exceeded.
Gene Mueller, Trierweiler’s project engineer,
said the Wisconsin Concrete Pavement Association has come up with a
smoothness specification for cities that excludes the areas around
manholes and similar structures. “You’ve got a certain number of feet on
each side of a manhole that are not held to the smoothness spec,” says
Mueller.
Trierweiler gauges the adjustment of its
concrete paver mold with a stringline. “We stringline our pans to make
sure they’re very straight and smooth,” he says.
The contractor trimmed the grade in Madison with
a CMI Autograde — and ran the trimmer off the same stringline that the
concrete paver used. The project was paved with a Rex Town & Country
paver working at one and two lanes wide. Trierweiler set two stringlines
when paving the first slab, then used the existing slab to guide the
paver for adjacent lanes.
Once the stringline sensors are set on the
stringline to start paving, says Mueller, they try not to change them.
“Make sure the stringline is tight,” he says, “with no dips and
doodles.”
“Every person involved in the process has to
care about ride quality,” says Cedar Valley’s Hughes. “Great employees
make the difference!”
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