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Solidifying the Future
VConcrete Innovations Get the Job Done
Across the country, construction teams are turning to concrete innovations to get the job done. New trends are sweeping the industry form Texas, Alabama and Georgia, where the state's DOT recently used roller-compacted concrete for the first time on a highway reconstruction job, to Chicago, Seattle and Monterrey Bay, where a school aims to be the first new educational campus to earn a LEED platinum designation using, among other things, ground granulated blast furnace slag in lieu of 100 percent Portland cement or flyash.
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A construction boom coupled with designers and contractors
looking for faster and better ways to deliver projects for
owners have created an ideal environment where concrete innovation
has thrived in recent years. Although the acceptance of new
technology in concrete has traditionally been a slow and methodical
process in the United States, market forces have converged
to drive the use of more emerging mixes and applications.
As with many building materials, increased construction activity
nationwide has spurred greater use of concrete. In 2006, consumption
of Portland cement, a main ingredient in concrete, is expected
to reach a record 124 million metrics tons - reflecting 2.3
percent growth over 2005, according to the Portland Cement
Association. Even as construction activity is predicted to
cool in 2007, the market should record another 1.3 percent
gain in 2007.
Rising costs over the past five years of other building materials,
such as steel, have helped contribute to the popularity of
concrete. Additionally, durability and speed of delivery have
been factors. With owners looking to have projects completed
faster, use of precast concrete has risen dramatically. In
2005, use of precast increased by 17.5 percent compared to
2004.
Ty Gable, president of the National Precast Concrete Association,
said precast has reached greater popularity as owners request
more fast-tracked projects and contractors struggle with labor
shortages.
"It's more and more of a challenge on the jobsite to
get the skilled labor necessary, so architects and designers
are turning to precast get jobs done faster," he said.
In many cases, they also want them to last longer. Durability
has become an increasingly important aspect of the developer's
equation on infrastructure projects, especially as more private
entities have begun to invest in roads and bridges, said Steve
Kosmatka, vice president of research and development at the
Portland Cement Association.
"Public-private partnerships create an opportunity for
people to use innovations, as opposed to the standard designs
that have been in the books for 30 years," he said. "PPPs
are willing to take risks especially if they see it reduces
maintenance. Banks that look at these projects want technology
that will allow contractors to put down a bridge or highway
that won't have to be touched for years."
The trend is promoting greater interest in use of ultra-high
performance concrete, also known as reactive powder concrete,
which is nearly five times stronger than conventional concrete.
Although it has been used abroad, researchers are testing
it here in the U.S., including a new bridge built in Iowa
that is the first in the country to use the material.
Michigan's Department of Transportation and University of
Michigan scientists are testing the use of a new fiber-reinforced
"bendable" concrete, also referred to as engineered
cement composites concrete. Because it can bend, ECC reportedly
is less likely to crack and fail. It's also nearly 40 percent
lighter than conventional concretes.
"Traditionally, DOTs have been very conservative - they
don't want to take risks," Kosmatka said. "To see
them take an interest in doing these things on their own is
very promising."
Despite early progress, the same barriers to acceptance remain
- without broadly recognized specifications and testing methods,
limited numbers of engineers will take risks on new materials.
"You can't go to the building codes and find out how
to use these materials," Kosmatka said. "The average
engineer at the average firm wouldn't know how to use them."
Despite this, the demands of developers often prevail. Pervious
concrete has gained tremendous interest among developers as
an option for storm water management. Water passes through
pervious concrete where it is filtered by the concrete matrix.
Using pervious concrete on parking lots could allow developers
to avoid dedicating a portion of their site to retention ponds,
thereby saving them money on land costs.
Dan Huffman, director of natural resources at the National
Ready Mixed Concrete Association, said he hopes that pressure
from owners will prompt the industry to embrace pervious concrete.
"Agencies and owners of sizeable companies, like WalMart,
are slobbering over this technology," he said. "We
just need to get our act together in terms of having concrete
producers who can make the material and contractors that can
put it down."
The potential of pervious concrete is one of many ways that
concrete is riding the trend toward more environmentally-friendly
developments. Use of pervious concrete, for example, can be
used to gain points toward LEED certification. In some cases,
designers are using recycled materials as aggregate in concrete
to gain LEED points.
Researchers in Italy are pushing the envelope even further.
Italian producer, Italcementi, have produced a so-called "smog-eating
concrete." The material contains titanium dioxide, which,
when triggered by sunlight, absorbs pollution and releases
it as non-toxic gas. As a result, the concrete also stays
clean.
While cutting-edge advances could have an impact in the coming
decades, many are looking for yesterday's innovations to become
the norm. Lionel Lemay, vice president of technical resources
at the National Ready Mixed Concrete Association, said he
sees self-consolidating concrete as having the greatest room
for expansion in the industry. The labor-saving qualities
represent a main reason he expects it to gain greater acceptance
in the coming years.
"Anything that reduces labor is a positive these days,"
he said. "If it saves having to put someone out in the
field to vibrate the concrete, that's a plus."
The growth in SCC has trended along with increased use of
precast concrete.
The NRMCA estimates that 40 percent of precasters use SCC.
Meanwhile, researchers continue to experiment with new applications
for SCC. A project underway at Iowa State University is tackling
one of the more challenging potential uses of SCC - paving.
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"I believe eventually all concrete could meet the self-consolidating
definition," Lemay said. "At some point there will
never be a need to vibrate concrete anymore."
By Bruce Buckley, Washington D.C. correspondent,
Engineering News-Record . The McGraw-Hill Construction publication
can be read online by visiting www.enr.construction.com
Concrete Innovation
Across the Country These Projects Use Concrete to the Fullest
Granulated Blast Furnace Slag Helps California School Go
For Platinum
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here for Concrete as Art Photo Spread >>
For a school complex to achieve a LEED platinum rating, every
conceivable sustainable technique and product has to be used
to its utmost viability. And for the Chartwell Progressive School
in Seaside, Calif. (in the Monterey Bay area), even its concrete
goes far beyond flyash in achieving green excellence.
As recommended by San Francisco-based EHDD Architects, the task
of finding a suitable concrete substitute fell in the hands
of the general contractor, Ausonio Construction, Inc., of Castroville,
Calif. President Andrew Ausonio contacted its concrete subcontractor,
Don Chapin Ready Mix Division of Salinas, which suggested ground
granulated blast furnace slag in lieu of 100 percent Portland
cement or flyash.
Slag is 99 percent byproduct of the production of iron ore,
which is usually sent to landfills. Substituting convention
cement with slag reduces 70 percent of CO2 emissions released
during the production of conventional cement.
The post-industrial, recycled product is recognized by the U.S.
Environmental Protection Agency as a "recovered" product.
Since no other company locally or regionally was mixing slag
cement, Ausonio asked his subcontractor to find a supplier.
Don Chapin also agreed to purchase an extra silo to handle the
26,000-sq.-ft. campus project.
Lehigh Cement Co. of Concord, Calif., the supplier, had the
history of environmental and sustainable efforts to make the
project successful, said Ausonio. "We provided a stronger,
less expensive material that helps Chartwell fulfill the requirements
of LEED certification," Ausonio said.
The slag mixture was used in the foundations, lots and sidewalks.
"Ground granulated blast furnace slag is lighter - around
25 percent lighter -- in color than regular cement," said
Ausonio. "This also deletes the heat island effect and
saves energy inside the building. This ambient reflection effect
also requires fewer lighting fixtures inside the buildings."
By Robert Carlsen, editor of California
Construction. www.california.construction.com
Concrete Stands Tall in Chicago
Concrete is a key element in the 92-story Trump International
Tower & Hotel under construction in Chicago in part because
it forms the building's structural support.
Indeed, 20 concrete mixes are used, and about 300 trucks full
of concrete are received every week, said Brett Szabo, senior
project manager of concrete for James McHugh Construction
Co., the concrete contractor.
The stiffness of the concrete was specified on Trump so that
the eventual residents of the condominiums and hotel do not
perceive sway in the building after it is completed. The modulus
of elasticity specification of the concrete was measured.
"It's pretty unheard of," said Bob Sinn, associate
partner of Chicago-based Skidmore, Owings & Merrill LLC,
the architect and structural engineer.
"Most concrete suppliers know about strength tests of
concrete. Modulus of elasticity is a different animal for
them."
Numerous details keep the crews busy.
For instance, the floor-slab thickness of the completed garage
is 14 in., Szabo said. The depth will be 9 in. for a typical
residential floor and 18 to 20 in. for a transfer level.
Supporting the garage are 30 6-ft.-diameter concrete columns,
and 47 thinner concrete columns will support the residential
portion.
Transfer levels are needed because setbacks at levels 16,
29 and 51 require column pressure to be transferred from some
lines to adjacent lines, Sinn said.
The transfer levels, which also hold mechanical equipment,
are on 15, 28, 50 and 90.
Usually, mammoth outrigger beams that are typically 17-ft.,
6-in. deep and 5-ft., 6-in. wide are on each transfer level.
They provide lateral stability against the city's winds.
The outrigger beams extend from the perimeter columns to the
197-ft.-long, 49-ft.-wide central core, also concrete. The
core, which is composed of four I-shaped walls and one C-shaped
wall, will hold the elevators and stairs.
More important, it provides additional lateral stability.
The care taken with the 10-ft.-thick mat slab shows how important
concrete recipes on the project are.
The building has four below-grade levels, and the 200-ft.-long,
60-ft.-wide slab, which is below Lower Level Four, was poured
over a 22-hour period between Sept. 30 and Oct. 1, 2005. The
slab serves as a juncture between the below-ground caissons
and the above-grade core.
The mix was composed of self-consolidating concrete that features
specialty additives and low-water content, said Tim Snyder,
construction manager in
Chicago for New York-based Trump, the developer.
Key benefits include strength and less labor during the pour.
Because of the chemistry, the material is poured without having
to be vibrated. And, as the name implies, the concrete has
a high slump rate.
"That concrete is so sticky and dry because it has so
little water and so much cement and other additives that within
15 to 20 minutes of striking it off, it goes hard," Snyder
said.
More important, the concrete's temperature and strength were
carefully monitored to ensure strength and solidity.
Readings were taken every minute at 36 points and downloaded
onto a computer so a curve could be plotted.
Within 24 hours, the temperatures spiked at 150 degrees because
of hydration but receded over weeks. After 10 days, the concrete
averaged around 120 to 125 degrees.
Similarly, six full-depth cores were made in the mat to measure
the concrete's strength. The concrete was poured at 10,000
psi. It measured at 7,000 psi after seven days due to heat
gain but averaged 13,000 psi after cooling.
"It was a 56-day design mix, but we were reaching design
strength in less than 28 days," Snyder said.
By Craig Barner, editor of Midwest
Construction. www.midwest.construction.com
Concrete Use Gets Cooler in Texas
Researchers at the University of Texas at Austin's Construction
Materials Research Group have been studying the effects of liquid
nitrogen on concrete since 2004. Their investigation, sponsored
by the Texas Department of Transportation, is focusing on the
safety implications of liquid nitrogen applications; its effects
on mixing equipment, cement hydration and microstructural development;
and its effects on concrete properties and performance including
fresh properties, strength, dimensional stability and durability.
"The research is being done so that TxDOT will feel comfortable
recommending more extensive use of the technique," said
Maria Juenger, assistant professor in the department of civil,
architectural, and environmental engineering at UT-Austin. The
goal is to be able to recommend optimal liquid nitrogen delivery
devices and methods with regard to human and equipment safety.
Juenger said the initial prognosis is good. "Any changes
to the concrete properties that we have seen are minimal,"
she said. "I think the technique will become much more
widespread because of the convenience of use compared to traditional
techniques such as crushed ice."
In Texas, where the summers are anything but cool, liquid nitrogen
as a cement-mix coolant to replace ice and chilled water in
the warmer months, is especially attractive.
In addition to a potential cost savings, benefits include fewer
nighttime pours and longer distances ready-mix can be transported.
And since liquid nitrogen is a waste product of the liquid oxygen
industry, it keeps the price low and carries the potential environmental
benefit of utilizing a waste product.
"It saves time, labor and often money," Juenger said.
"It also allows concrete to be cooled to a lower temperature."
Liquid nitrogen proved a cool solution on the recently completed
State Highway 45 project in Austin. General contractor Austin
Bridge & Road of Dallas opted to use liquid nitrogen extensively
to cool concrete to 75 ° Fahrenheit, which TxDOT requires
for mass placements of anything with a least dimension of 5
ft.
Joe Dan Johnson, quality control manager with Dallas-based TransitMix,
the concrete supplier for the job, said he was aware of liquid
nitrogen, and thought it was a good option for the job as opposed
to ice because of the "great deal of mass placements."
"We decided to stop fighting ice we go with liquid nitrogen,"
Johnson said.
Johnson and William Beaver of PBS&J, the project's construction
manager, went to El Paso to tour Jobe Readymix, which had a
system for liquid nitrogen installed at their plant. "They
were the only company that had been using liquid nitrogen in
ready-mix operations on a regular basis for certain jobs,"
Johnson said. "We watched what they did to get an idea
of what it took to get a system going."
Johnson said that setting up such a system can be expensive.
"The capital investment is high," he said. "So
there has to be enough yards of at a certain price to justify
a system."
"Currently it is cost effective on big projects,"
Juenger said. "The biggest investment is in the delivery
devices and storage containers - not in the nitrogen itself."
By Eileen Schwartz, editor of Texas
Construction. www.texas.construction.com
Georgia Gets Rolling With Some Concrete Changes
The Georgia Department of Transportation is expanding its use
of roller-compacted concrete pavement.
After an initial recent trial of roller-compacted concrete on
the shoulders of a section of Interstate 285 in Atlanta, the
Georgia Department of Transportation is looking to expand its
utilization of the paving material, including its possible use
on mainline pavements.
"We've had good results, so that gives us an opportunity
to see if it'll work in a different application," said
Georgene Geary, state materials and research engineer with the
Georgia DOT.
The transportation agency first used RCC for approximately 35
lane mi. of shoulders on I-285 in 2005. Contractor A.G. Peltz
of Birmingham, Ala., placed the concrete material for the 10-ft.-wide
shoulders using an asphalt paver and several 10- to 12-ton steel
drum and pneumatic tire rollers. GDOT was looking for a cost-effective
option to its previous use of asphalt for interstate shoulders.
Geary said the RCC alternative came in at a comparable price
to asphalt.
RCC contains the same ingredients as conventional concrete but
has a low water-cement ratio, creating a zero-slump mixture.
Additionally, RCC can usually be placed with just one lift -
of about 8 to 10 in. thick - whereas asphalt is typically placed
in several lifts of 2 to 3 in. each.
Essentially, RCC provides similar strength and durability characteristics
as conventional concrete, but at a lower price and increased
ease of application, said Allan Childers, Georgia state director
for the American Concrete Pavement Association.
"It's just a different way of putting it down," said
Childers, who previously worked for the Georgia DOT for more
than 30 years. "They've been pleased with it."
The initial results from that I-285 project have GDOT working
on another, second project utilizing RCC on State Route 6 in
Cobb and Douglas counties, as well as a planned upcoming shoulder
project on I-985, both near Atlanta.
On the S.R. 6 project, GDOT is reconstructing a five-lane highway
that includes a four-lane travelway and a center turning lane,
plus shoulders. The mainline pavement will consist of conventional
concrete pavement, while the center lane and shoulders are being
constructed with RCC.
Though there are no smoothness or ride specifications for the
center-lane section, Geary said the department is interested
in discovery how smooth an RCC pavement can become.
For example, Geary said the agency is "batting around the
idea" of using RCC as a mainline pavement on low-volume
roads. While the typical RCC mix is not as smooth as a conventional
concrete mix, Geary was optimistic that the industry could achieve
better ride characteristics without altering the material makeup.
"It has to do with construction techniques and the contractors
getting more comfortable with the technique," she said.
"Over time, we're going to find those little tricks in
RCC that will build smoother roads."
In addition to road projects, GDOT also is starting to use the
material for park-and-ride lots as well as for some of its own
maintenance facility lots.
By Scott Judy, editor of Southeast Construction.
www.southeast.construction.com
Concrete Domes in Birmingham
The $16.5 million activity center project at Faith Chapel
Christian Center in Birmingham, Ala., is not like most other
church expansion projects.
This one requires the construction of six monolithic concrete
domes totaling 120,000 sq. ft. across 16 of the church's 140
acres. The additions are being built next to the church's
existing 87,000-sq.-ft. domed sanctuary, the largest single
dome in the country at the time of its construction three
years ago.
The new domes - three are 144 ft. and three are 164 ft. in
diameter - will house a children's play area, entertainment
areas complete with a pair of NBA-size basketball courts,
a 12-lane bowling alley and commercial kitchen, and a connecting
lobby.
To build the domed roofs, construction manager Monumental
Contracting Services of Birmingham, Ala., and contractor South
Industries of Menan, Idaho, install a roofing membrane - called
an Airform - on top of the wall forms. Polyurethane foam is
then applied to the interior surface of the membrane, which
then acts as a base for attaching the roof's reinforcing steel.
Work is currently under way on the fourth dome, which will
be inflated this month, said William Robertson, president
of Monumental Contracting Service.
"You have to have constant air pressure to keep it inflated,
and you have to inflate it 24 hours a day," Robertson
said. "The contractor has to monitor the intake and outflow
to keep the pressure even."
To access the air structure, the contractor must enter through
a double door airlock, which keeps the air-pressure inside
at a constant level. Steel reinforcing rebar is attached to
the foam using a specially engineered layout of hoop and vertical
steel rebar.
Shotcrete - a special spray mix of concrete - is applied in
1-in. layers over the mats of reinforcing steel. Some areas
of the dome can be as much as 24 in. thick, he said. Drying
time varies, depending on the circumference of the dome, but
usually two layers can be applied each day.
Robertson said the side walls for each dome - built in the
same way with layers of shotcrete and steel mesh - range from
10 to 14 ft. high, depending on the building's use.
The monolithic layered-construction method required about
575 cu. yds. of concrete per dome, or 3,450 cu. yds. for the
project. Each dome also requires about 55 tons of steel, or
about 330 tons for the project.
Construction of a dome takes about two months from start to
finish,
Robertson said. The last one should be completed by June,
when interior finish work will start. The entire project is
scheduled for completion in December.
LPDJ Architects LLC, of Salt Lake City, Utah, is the architect
for the center.
"The uniqueness about this client is they are an all-cash
deal," Robertson said.
"There is no debt service."
By Candy McCampbell, contributor, South
Central Construction. www.southcentral.construction.com
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