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Twelve Years and Counting
Stephenville Cement-Recycled Streets Still Going Strong
By: Robert Lopez and Jeff Hawk
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| Consulting engineer Sanford LaHue Jr stands
on a cement-recycled street he designed in 1992. The street
has experienced no base failure since then. |
City of Stephenville officials have at least a dozen reasons to
endorse using cement to rehabilitate their streets. None of Stephenville’s
cement-recycled streets have had problems or failed in the past
twelve years. “They’ve not done any re-work on any of
the bases that we’ve [cement] stabilized,” says Sanford
LaHue Jr, consulting engineer, Schrickel, Rollins and Associates,
Arlington.
LaHue designed the city’s first cement-recycled streets in
1992 and has continued consulting for the city since then. The street
reconstruction program initially included visual evaluations of
the condition of the streets to determine which streets would require
cement recycling. The recycling and a new asphalt surface course
was proposed where base failures had occurred. A standard asphalt
overlay was placed where minor cracking was observed. This evaluation
and selection procedure allowed the city to do as many streets as
possible. But over the years, LaHue observed serious deterioration
in the overlain streets while the cement recycled streets held firm.
He began to specify cement recycling for all of the streets. “From
2000 on, we stopped straight overlays and just did cement recycling,”
says LaHue.
“Recycling with cement is our preferred option,” says
Drew Wells, Stephenville’s Director of Community Services.
Surface treatments have proven “very unpredictable and unreliable.
We’ve had some differing results,” he adds. But all
the cement recycled streets have produced a “very favorable
outcome,” says Wells. “It has been the best process
for us.”
The city begins the process by taking material samples from streets
targeted for rehabilitation to determine the right amount of cement
to use. Streets with good base and surface materials require less
cement then those with marginal materials. City specifications require
contractors to pulverize the existing asphalt surface and base six
inches deep and then add 25 lbs. per sq. yd. or 5% cement by volume
of dry weight of the material.
After adding water, the streets are re-shaped, compacted and bladed
to final elevation. The newly bonded base layer is cured with moisture
before applying a prime coat. A 1.5-inch asphalt surface finishes
the street. Since the city is using existing roadway materials,
there is no need to import new aggregate base. This eliminates the
need haul the existing roadbed material off to landfills or stockyards
or to bring in new base materials. “The process of adding
cement naturally yields some additional resultant material. On most
of the streets this material is used to restore the crown on the
streets. However, if excessive crown is a problem, the excess material
will have to be hauled off”, says LaHue. The profile of the
street remains basically the same. “You’re not overlaying
the gutters and you’re not changing the drainage,” he
adds. Most street departments welcome this excess material to their
stockpiles.
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| .A reclaimer pulverizes the existing street.
One or two passes usually achieves gradation requirements. |
A motorgrader operator
reshapes the street after adding cement to the existing pulverized
material |
A steel-wheeled vibratory roller compacts
the newly cement-bond base to 95% standard proctor density. |
Recycling with cement is a process that most contractors are equipped
to perform. “It’s easy to get contractors to install,
it’s easy to inspect, and once you get your gradation, it’s
easy to control,” LaHue adds. “Quality control is not
a big issue because the mixing process and the cement just work
so well.”
Stephenville street superintendent Tony Gonzales agrees. “It’s
a simple process,” says the 17-year veteran of the city’s
street department. The process has “saved us a lot of money
that we can use to do curb and gutter work,” he adds.
Low-maintenance cement-recycled streets allow Stephenville officials
to focus their time and money on other maintenance issues. Says
Wells: “We are beginning to see relief in our maintenance
budget because our maintenance calls are a lot less. The maintenance
on streets has been reduced and this frees us up to do other maintenance
functions.”
Unlike other road construction processes, the cost of cement recycling
has not risen dramatically over the years. City of Stephenville
bid tabulations from 1992 show that contractors charged $2.60 per
sq. yd. for cement recycling. In 2003, the price rose only 80 cents
to $3.40 per sq. yd., according to records provided by LaHue.
The confidence LaHue and city officials have in the process became
evident when the city was faced with maintaining a major thoroughfare.
In 1994, TxDOT released its obligations for maintaining Harbin Street,
a major high volume collector road running through Stephenville.
LaHue decided to lower the pulverization depth to 8 inches and add
32 lbs per sq. yd of cement. A two-inch asphalt surface capped the
new road. Since its completion in 1995, the highly trafficked street
has experienced “no base failures,” says LaHue. “It
handles the traffic loads very well.”
Cement recycling’s speed of construction is also a big plus,
says Gonzales. Crews begin the process early in the morning and
finish recycling before residents come home from work. “We
never close the streets,” says Gonzales. “I’ve
become a big believer in cement.”
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| Cement recycling produces little leftover
material. Usually 5% of the total roadway materials, if any,
need hauled away. |
Compared to traditional remove and replace construction, “the
inconvenience to residents is a lot less” says Rick Brockington,
president, Brock Paving Industries, Roanoke. Brock Paving started
up as a cement recycling contractor in 1990 and won a 2004 contract
to rehabilitate Stephenville’s streets. Cement recycling is
“a lot faster” than complete reconstruction,”
says Brockington. “It’s one-step stabilization.”
Brockington says cement recycling gives cities on tight budgets
“more bang for the buck.”
The decision to recycle has not gone unnoted by Stephenville residents.
Says Wells: “Folks have been pretty appreciative that we’re
being proactive rather than reactive.”
For more information visit the Cement Council of Texas
at www.RecyclingRoads.org
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