Caltrans Extends PCC Pavement Life Through Use of Diamond Grinding

Concrete Roads Article December 28, 2000
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The
passage of the Intermodal Surface Transportation Efficiency Act
of 1991 (ISTEA), which allowed the use of federal funds for
highway maintenance, has enabled states such as California an
opportunity to give added attention to preventive maintenance as
part of their overall maintenance strategies. In the past few
years, seismic retrofit, however, has gobbled up a large portion
of dollars spent on highways in California. With much of the
work either completed or underway, the California DOT (Caltrans)
has undertaken an assertive campaign of maintenance and
rehabilitation of its portland cement concrete (PCC) pavements.

"With the passage of ISTEA, we were able to stress
preventive maintenance more within the department," said Kevin
Herritt, structural section and design standards specialist in
Caltrans' State and Local Project Development Program.

"After the [Loma Prieta Earthquake] in '89 and the Northridge
earthquake following soon after, we had a lot of needs to
address from a safety standpoint," he said. "Seismic retrofit
became the highest priority work within the department." As the
department meets more of its seismic retrofit needs, Herritt
said more funds have been made available for nonseismic
projects.

In 1996, the state began implementation of its
Capital Maintenance Program (CAP-M), a five-year plan that
involves the use of concrete pavement restoration techniques and
asphalt overlays on selected pavements. Through July 1996,
Caltrans had let $100 million in contract awards involving 31
projects. The objective of the CAP-M is to target projects that
do not involve a great deal of attention to off-road matters.
"The key to the program is trying to focus the funding on the
pavement itself," said Herritt.

Grinding extends life

Of
the 31 projects awarded in the first half of '96, 10 were
diamond-grinding-only projects. For the year, diamond grinding
was performed on 670 lane miles of state-owned concrete
pavement. In 1997 diamond grinding will be performed throughout
the state, but there will be fewer in number than in 1996, said
Tom Pyle, a pavement management engineer for Caltrans.

The
diamond grinding let as part of the CAP-M program is a
maintenance technique that extends the useful life of the
pavement. This is accomplished through milling off a portion of
the surface layer of PCC pavement, which provides a smoother
riding surface and corrects slab curl.

Although Caltrans has
employed diamond grinding in past years, Herritt said ISTEA has
enabled the department to re-emphasize the technique and in turn
delay the necessity of performing major reconstruction on the
pavements.

"Diamond grinding offers a definite savings over
replacing," says Caltrans' Pyle. "You spend a little bit of
money and people think it's a new pavement." Diamond grinding
provides a smooth ride that often can exceed that of new
pavement.

In California, concrete diamond grinding
candidates include pavement with 2% or fewer of the slabs having
three or more cracks and a Cox ride score below 20.

For
rehabbed PCC pavements, the department is planning to lengthen
its 10-plus year extension of surface pavement life philosophy
to 20 to 25 years before major rehabilitation becomes necessary.

Field practice

Taking part in four of the diamond-
grinding projects, totaling more than $15 million in contracts
for 1996 and 1997 is Highway Services Inc., Rogers, Minn., which
is in a joint venture with Penhall Co., a California-based
contractor. The joint venture is responsible for diamond
grinding nearly 3 million sq yd of concrete in California.

Public perception of the smoothness of highway pavements also is
an important part of the diamond grinding equation. "The public
judges the road by the seat of their pants," says Gary Aamold,
president of Highway Services.

According to Aamold, the
California program accounted for approximately one-third of the
company's volume for 1996. The company, which performs work
throughout the U.S., completed its contract work in California
in February.

The last project performed by Highway Services
involved a 905,372 sq yd job on IÐ8 near El Centro on the
California-Mexican border. The joint venture was a subcontractor
to Granite Construction on the project. "The El Centro job was
particularly challenging," said Pete Lewis, Highway Services'
vice president of operations. "The panels on job were all
curled, which made it difficult for the machines and difficult
to determine the depth of cut. The aggregates used also were
hard and abrasive."

Additional projects included work on IÐ5
near Sacramento, where the joint venture was the prime
contractor, and IÐ5 near the Oregon border.

Highway Services
used five Cushion Cut PC-5000 diamond grinding machines on its
projects. Each machine was fitted with a 4-ft cutter head
containing 245 blades.

Aside from initial adjustments to the
aggregate used in the pavements, environmental issues, such
handling grinding slurry, required the most attention in the
California work, according to Aamold. Slurry disposal was a key
issue for Pavement Specialists Inc., another diamond grinding
contractor, that restored ride on IÐ80 near Dixon, Calif., this
winter. "We are particularly pleased that the state provided a
disposal area for grinding slurry on the project," said Casey
Holloway, vice president of Pavement Specialists.

"The job
is going very well," Holloway said while the 80,000-sq-yd IÐ80
project was ongoing. The project was completed in January.
Diamond grinding on IÐ80 has areas of heavy cuts due to
additional pavement wear from truck tire chains. Typically,
diamond grinding removes less than 1/4 in. average depth of the
existing concrete surface.

Prior to the IÐ80 project,
Pavement Specialists also ground 100,000 sq yd of pavement on
IÐ8 near El Centro.

"We just haven't done grinding to such a
large extent before," Caltrans' Pyle says. "We have pavements
built in the '60s, which have had a wonderful life to them. Now
we're able to grind and spend just a little bit of money and get
a lot of [benefit]."

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