Maturity Meters: A Concrete Success
To speed up the reconstruction of the collapsed Interstate
40 bridge in eastern Oklahoma this past summer (see August
2002 Focus), one of the technologies that the Oklahoma Department
of Transportation and contractor Gilbert Central Corporation relied
upon was the concrete maturity meter. The maturity meter system consisted
of sacrificial sensors placed in the concrete to measure temperature
and calculate maturity, as well as handheld readers to download data
from the sensors. The sensors effectively predicted the in-place concrete
strength gain, which allowed the contractor to make decisions on concrete
form removal, thereby accelerating the construction schedule.
The maturity method contrasts with conventional testing,
which requires concrete beams or cylinders to be tested before making
decisions about the readiness of the pavement. The conventional testing
is both more expensive and time consuming. Conventional testing also
does not represent the increased strength gain of the in-place concrete
at early ages. In the case of Oklahoma, where speed was of the essence,
the maturity meter system proved to be a valuable tool that contributed
to Gilbert Central completing the reconstruction 10 days ahead of schedule.
Although the maturity concept was first proposed in the
late 1940s and early 1950s, there was limited use of it over the next
40 years. Interest in the concept significantly revived in the mid 1980s,
as the concrete industry and others began looking for ways to accelerate
pavement construction and implement high-speed inspection. Over the
past 5 years, use of the maturity method has increased dramatically
as State highway agencies and industry have become more aware of the
technology and the equipment has become more advanced. A survey conducted
by the Pennsylvania Transportation Institute in 2000 found that 32 of
the 44 States responding had conducted or were currently conducting
research on implementation of the maturity concept. Thirteen of the
States had a protocol for the use of maturity testing, with the most
common use being to predict the concrete strength so as to open the
pavement earlier to traffic.
The Iowa Department of Transportation (DOT) has been using
maturity meters for nearly 5 years and includes the technology in its
standard specifications. The State's contractors have the option of
using the maturity method, with virtually all of them adopting the technology.
Iowa has found that the method provides a more reliable measurement
of when a pavement is ready for use. "Another benefit is that maturity
meters measure temperature and thereby strength in real world conditions
instead of lab settings," says Jim Grove of Iowa DOT. "Concrete
maturity meters are an excellent technique."
Jim Cable of Iowa State University notes that the maturity
method can save 3 to 4 weeks on some projects. "Maturity meters
allow projects to move forward as soon as possible. After the pavement
has been constructed, the meters allow crews to begin work on sawing
joints and placing shoulders sooner," he says. "Maturity meters
have been one of the easiest technologies to get people to use in Iowa.
Most all of the State projects in Iowa involve the use of the maturity
method and very few contractors in Iowa perform State or county jobs
without using maturity meters."
The Texas Department of Transportation's (TxDOT) Dallas
District introduced maturity meters in 1995 and has since used them
on both structures and pavements. "Maturity meters are a time saver,"
says James Hill of TxDOT. "The typical wait of some structures
to mature has been cut 2-4 days. This allows bridges to be open sooner,
saving both money and time." Use of the meters on a project on
State Highway 66 allowed TxDOT to pour the structure's columns and then
2 days later pour the caps, rather than waiting the usual 7 days. Hill
notes, however, that the use of the meters requires strict quality control
at concrete plants.
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A maturity meter device in Iowa is read before
it is covered by concrete. |
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The maturity probe is placed in the concrete slab. |
Advances in maturity meter technology and shared State success stories
have increased the popularity of the devices. The Federal Highway Administration's
(FHWA) Mobile Concrete Laboratory (MCL) has played a major role in sharing
these success stories and working with State highway agencies to implement
the maturity method (see February 2001 Focus). The MCL has promoted
the use of the maturity concept and other nondestructive testing techniques
for over 15 years to more than 30 State highway agencies ranging from
Virginia to California.
There have been several significant changes in maturity
techniques in recent years, with options ranging from simple thermometers
placed in the concrete to microprocessor-controlled dataloggers to wireless
transmission of the data directly to construction staff. This information
can now be used to immediately alert project staff to temperature-related
events in the concrete, such as freezing or elevated curing temperatures.
Models can even be incorporated into the system to forecast the future
strength of the concrete for scheduling and decision-making purposes.
Looking to the future, the next step will involve using
maturity meters to monitor the maturity or strength of concrete in real
time, with information available 24/7 at a central office. "This
will allow decisions to be made more effectively for opening newly constructed
pavements, patches, or overlays much faster than in the past, thereby
saving the contractor construction time and reducing the traffic congestion
due to lane closures," says Gary Crawford of FHWA.
For more information on maturity meters or the MCL's services,
contact Gary Crawford at FHWA, 202-366-1286 (fax: 202-493-2070; email:
gary.crawford@fhwa.dot.gov),
or Leif Wathne at FHWA, 202-366-1335 (fax: 202-493-2070; email: leif.wathne@fhwa.dot.gov).
For a schedule of the lab's upcoming visits, see box
below.
For more information on Iowa DOT's experiences with maturity
meters, contact Jim Grove at Iowa DOT, 515-239-1848 (email: jim.grove@dot.state.ia.us)
or Jim Cable at Iowa State University, 515-294-2862 (email: jkcable@iastate.edu).
For more information on TxDOT's projects, contact James Hill at TxDOT,
469-371-0649 (fax: 972-772-4879).
2002/2003 Mobile Concrete Lab Schedule
Note: This schedule is tentative and is subject to change.
November 2002—
Bridge project in Washington, DC
December 12-13, 2002—
Texas Concrete Pavement Conference
Spring 2003—
Peformance-related specification paving project in Florida
March 2003—
National Highway Institute materials course training, location
to be determined
April 2003—
Paving project in New Mexico
April/May 2003—
Paving project in New York State
Spring/Summer 2003—
Field testing for mixture evaluations for high-performance concrete
bridges on I-99 in Pennsylvania
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Articles in this issue:
Maturity Meters: A Concrete Success
A New Approach to Highway Design
A Hydraulics How To
Foamed RAP Makes the Grade in Louisiana
Winners of LTPP Data Analysis Contest Announced
Excellence in Highway Design 2002 — Award Winners
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