The Pennsylvania Turnpike is one of the older limited-access
highways in America, with its first four-lane, 160-mile stretch opened to the
public in 1940. Over the years, the highway has been lengthened to its present
size of 515 miles. Most of the later-built highway sections are in good
condition. However, the 1940 vintage roadway is in need of reconstruction
because the surface-water drainage system is inadequate and the reinforced
concrete pavement is beginning to fatigue beyond making cost-effective repairs.
The inadequate surface-water drainage system has exacerbated roadway problems
because of freeze-thaw conditions.
In Part I of this story, published last month in Roads &
Bridges, it was reported that 100 of the 160 miles would be rebuilt over the
next 10 years for an estimated cost of $1.44 billion. It was further pointed
out that a major reconstruction problem for the Turnpike Commission was in
dealing with the poor subgrade conditions (clay) encountered. This problem is
being resolved by incorporating lime/pozzolan or lime/pozzolan/portland cement
into the upper 15 in. of the subgrade for stabilization and strength. style="mso-spacerun: yes">
A well-stabilized subgrade with acceptable strength
characteristics is necessary because the new highway features Superpave
(flexible pavement) instead of the concrete pavement (rigid pavement) it is
replacing. Superpave was selected by the Turnpike Commission for a host of
reasons, but the two most compelling are: Asphalt paving is readily maintained
at any time and even overlays in the future can be made in the wee hours of the
night when traffic flow is at a minimum; and it carries an affordable
life-cycle cost. Since the motorists pay tolls for the use of the highway, the
Turnpike Commission is sensitive to their wants. The commission sees the
motorists as its customers. Understandably, encountering long lines of
bumper-to-bumper traffic, due to daytime road maintenance activities, is
The first contract let for rebuilding the 100-mile highway
was designated 76/85. It is a 9-mile section and calls for rebuilding the two
eastbound lanes and the two westbound lanes between the New Stanton Interchange
and the Donegal Interchange. The paving contractor for this contract is Lindy
Paving, a Trumbull Corp. company located in Newcastle, Pa.
Better Materials, good paving
Quality control of the paving process is Lindy Paving's
first consideration when each new paving project starts. Top-performing paving
equipment is paramount for getting high-quality paving results. Equipment to be
considered includes the plant for producing hot-mix asphalt (HMA), special
equipment for delivering the HMA directly into the paver, the paver and the
rollers used for compaction. Equally important, said Lindy Paving's Joe Conti,
is the paving crew's performance, especially the operators of the equipment.
Good equipment and poor operators or poor equipment and good operators are not
formulas for achieving good paving results, he said.
As for this project, the HMA supplier is Better Materials
Corp., Connellsville, Pa. The company bought a used Astec Turbo 400 Six Pack
portable asphalt plant from this project's prime contractor, Angelo Iafrate
Construction Co. Originally, Iafrate bought the plant new specifically for this
project. Iafrate did the paving the first season, but for the final season the
contractor decided to subcontract both the HMA production (Better Materials)
and the paving of it (Lindy Paving).
One of the main reasons for choosing the Six Pack is its
portability. Iafrate projected it might take on other contracts, yet to be let,
that are associated with this $1.44 billion, 100-mile project. Most of these
future contracts will include about 10 miles of roadway reconstruction. Since
the plant might be relocated every 18 months to a new turnpike project,
efficient plant portability was considered very important by Iafrate. style="mso-spacerun: yes">
The plant includes a Turbo 400 Double Barrel drum mixer,
cold feed, scalping screen, baghouse, cyclone, surge bin, drag conveyor and
control house. Options supplied include a RAP bin, fuel tank and an AC holding
tank. This plant's rated throughput capacity is 400 tph.
Dan Skovira said he planned to use the new plant just as
Iafrate intended to, as a portable plant. Skovira is the asphalt products
services manager for Better Materials and is responsible for 10 different
asphalt plants including the Astec Six Pack. This is the only company-owned
plant he calls "a 100% portable plant."
"I can haul this complete plant to another location in
10 truck loads even though there are many options added to it. Despite its
portable design, this plant is built rugged. It also is very reliable. We are
producing HMA at a rate of 400 tph and are experiencing near 100% plant
availability," he added.
With this plant, Iafrate produced over 250,000 tons of HMA
in the first season, and this season Better Materials produced another 160,000
tons. The base course for this project is made with BCBC 64-22 and 20% RAP
added. The Superpave is a polymer 76-22 mix with 15% RAP added. style="mso-spacerun: yes">
Stick to static
The turnpike has certain equipment-usage specifications to
which the contractor must adhere. One is the use of a material transfer vehicle
(MTV) for loading the HMA into the paver. An MTV is purposely specified by the
turnpike for reducing aggregate segregation within the mix, which is
commonplace while loading the mix into the paver, and to ensure a more even
temperature throughout the mix. In turn, this mix uniformity enables the mat to
be compacted to a uniform density.
Lindy Paving owns two Roadtec SB-2500B Shuttle Buggy MTVs
that are being used on the project. Conti said the Roadtec Shuttle Buggy is an
important link in the paving train for assuring a high-quality pavement.
Accordingly, the company uses the Shuttle Buggy on many other paving projects
even when the project does not specify its use.
Here are some quick facts about the Roadtec SB-2500: it
weighs 79,000 lb, it is powered by a 275-hp diesel engine and it is 4wd. The
main hopper surge capacity is 25 tons, and the truck unloading conveyor rate is
1,000 tph. Functionally, the HMA is remixed in the hopper with a triple-pitch
anti-segregation auger that reduces aggregate segregation and helps maintain an
even temperature throughout the mix.
Unlike many DOT agencies, the Turnpike Committee will not
allow paving contractors to use vibratory rollers in the vibratory mode on any
asphalt paving if the mat-lift is 3 in. or less.
"We have tried compacting asphalt paving in the past
using vibratory rollers in the vibratory mode with little success. While
vibratory rollers are fine for compacting the base course we find it creates a
bumpy road when compacting a binder or wear course. I realize that some newer
model compactors have very high frequency modes but we have not tried them yet.
It is possible these new compactors have corrected the problems we encountered
with older technology rollers," explained Gene Mattson.
Indeed, some make roller technology is advanced, according
to Conti. The high-frequency feature is one reason Lindy Paving bought new
Sakai vibratory rollers. Sakai rollers feature selectable vibration frequency
modes for producing 2,400, 3,200 and 4,000 vpm.
Another Turnpike Commission specification relevant to
rolling Superpave is the use of a static three-wheel roller for the breakdown.
Not having such a roller in the fleet, Lindy Paving turned to the Sakai dealer,
Highway Equipment Co., Zelienople, Pa., for selecting the best roller. The
model selected was the R2H, which has a gross weight of 30,920 lb, including
added water for ballast. An important attribute of this roller is its full 83-in.
coverage even when turning the machine because of an articulated center-design
Mattson said the turnpike gets superior results using a
three-wheel roller as the breakdown (lead) roller. "On some Superpave
projects we eliminated the three-wheel roller, and the results were very
disappointing. I am convinced that for superior pavement smoothness, a
three-wheel roller should be used. Such a roller eliminates the shoving and
scuffing that is associated with other roller designs. The pavement smoothness
results that Lindy is getting on the project speak for themselves."
Lindy is indeed achieving ideal smoothness results on this
project. The specifications call for 28 in. deviation per mile. The actual results
being recorded average 12 in. For achieving these results, the paving train
configuration includes a Roadtec SB 2500, a Blaw-Knox paver, the Sakai R2H
3-roller and two Sakai vibratory rollers that include models SW800 and SW850. style="mso-spacerun: yes">
The rollers are not operated, of course, in the vibratory
mode when compacting the 2-in.-thick, 25-mm binder course and the 2-in.-thick,
19-mm wear course. Nevertheless, even in the static mode, these rollers perform
well because of their oversized roller diameters. The SW800 has an effective
width of 67 in. and the SW850, 79 in., and weigh 23,930 lb and 27,560 lb,
Here, the same rollers are used in the vibratory mode when
compacting the base. It should be pointed out, however, that while Lindy is
meeting with extraordinary success with the smoothness of this roadway, the
company has had many other successes on paving projects in Pennsylvania and
West Virginia. Besides the NAPA award, the company has earned six other awards
for excellence in paving. All of the awards were received on projects where the
rollers were used in the vibratory mode and a three-wheel roller was not
Every piece of equipment used for mixing the HMA,
transferring it to the paver, laying the mat and compacting it, were pivotal for
realizing the excellent paving results experienced by Lindy.
Of course, as Conti stressed, the equipment performances
depend on good operators who can optimize each machine's potential.