By: Steven M. Waalkes
The maturity method is a simple nondestructive way of determining the strength of concrete pavement so it can be opened to traffic as soon as it achieves the required strength. This story details the experiences of three states that have embraced the technology: Iowa, Indiana and Texas. Although only a limited number of agencies currently use this methodology, there is growing interest in the cost-effective method.
“The biggest problem for the concrete industry is
people thinking you have to wait seven to 14 days before putting traffic on new
pavement,” said Denny Osipowicz, engineer from Lee County, Iowa.
“Concrete really gains strength faster than we give it credit for. Now
the maturity method is speeding up the whole construction process.”
Day-old concrete
According to Todd Hanson, Iowa DOT PCC engineer, the opening
strength requirement for most projects is 500 psi center point loading flexural
for traffic and construction equipment. “I’ve heard it can be as
early as 24 hours,” said Osipowicz. “Usually it’s 30 to 40
hours depending on air temperature.”
“Basically, it’s a fail-safe so we don’t
get on the pavement too early,” said Duane McDonald, division manager for
pav- ing contractor Manatt’s Inc., Brooklyn, Iowa.
The strength of the concrete can be expressed as a function
of time and temperature, thus allowing the determination of concrete strength
without conducting physical tests.
The maturity method is a simple two-step procedure to
determine the concrete strength. The first step involves making and breaking
beams at different ages. The maturity value is calculated from a temperature
reading when the beam is tested for strength, resulting in a maturity/strength
curve.
The second step takes place in the field. The contractor
installs temperature probes in the fresh concrete—at least two probes for
each day’s placement. He measures the temperature with a thermal meter or
maturity meter at the beginning of the day and again at the end, notes the time
and is then able to determine maturity values.
Lee leads
Between 1988 and 1994, Iowa conducted three experimental
projects using the maturity method. In 1995, Osipowicz initiated its use on a
concrete paving project in Lee County.
“It’s difficult to break old habits, but in my
case it was a necessity,” he said. “Everyone knew concrete gained
strength faster than seven days. And I needed to maintain access to 150 homes
along the 7-mile project.”
The success of the Lee County project made its mark on the
concrete paving process in Iowa. The following year, Iowa contractors used the
maturity method on 28 projects. In 1997, Iowa DOT made it standard for the
contractor.
“When it first came out, we jumped on the
bandwagon,” said Mike Manatt, vice president of Manatt’s.
“We’ve been using it for three years.”
Today, the maturity method is used on almost every concrete
paving job in Iowa, at the state, county and municipal level, as well as
airports. Mark Bare, project manager for pav-ing contractor Cedar Valley Corp.,
Waterloo, Iowa, admits there are some small jobs where it may not be used.
“Maybe the contractor wouldn’t use it on a job where time
isn’t of the essence or where access isn’t important,” he
said. “But that’s rarely the case.”
“One of the first projects where we began maturity
testing was awarded the Marvin Black National Quality Initiative Award, due in
some part to the implementation of the maturity method,” said Jim E.
Hunt, P.E., director of construction for the Texas Department of
Transportation. TxDOT has been using the maturity method since 1997 and first
applied the testing on two sites on U.S. 75, the North Central Expressway
project in Dallas. Each project cost over $100 million to construct.
According to Hunt, after the completion of the award-winning
project, a statewide specification was written to allow maturity testing on any
TxDOT project. “To date, the specification has been used successfully on
several projects in Dallas and El Paso. Other districts are planning to
implement maturity testing soon.”
Maturity testing will be used in the “Dallas High
Five” project, which is the largest ever by the state of Texas at a cost
of $240 million. It is the reconstruction of Dallas’ busiest
interchange.
“We’ve had great experiences with maturity
testing because instead of getting results from a laboratory, it’s the
first time we can test in place and see how concrete is gaining strength day to
day on site.”
Hunt said TxDOT is revising its standard specification next
year and hopes to include maturity testing.
Early access
“The maturity method lets the contractor on the
pavement earlier to do shouldering and allows him to use part of the road as a
haul route,” said Hanson. “It really speeds up the project.”
Another advantage of the maturity method is improved safety.
“Any time you can shorten the time traffic is in the construction zone,
you increase safety,” said Bare.
Bare also pointed out that the maturity method helps the
contractor to determine the optimum time to saw the joints. “Now we have
the data to support the decision that we didn’t have in the past,”
he said.
Bare cites another advantage for the concrete paving
industry. “Using the maturity method to open pavement quicker makes
concrete more competitive with asphalt,” he said.
Although engineers around the country have been talking to
Iowa engineers and contractors about the maturity method, so far Indiana is the
only other state that is actually using it. Dave Andrewski, InDOT materials
engineer, estimates that roughly half of the DOT concrete paving projects use
the maturity method. “It’s the contractors option on any
project,” said Andrewski. “We don’t use the maturity method
specs for acceptance, just for opening to traffic. If it’s successful,
we’ll expand the program.”
“I hope the use of the maturity method will eventually
expand to more and more education, with contractors and DOT people sharing
information.”
About The Author: Waalkes is director of engineering and rehabilitation for the American Concrete Pavement Association, Skokie, Ill.
