The Concrete of the Future
Less construction noise and better workability. Improved quality and
durability. Faster construction and higher strength. The use of self-consolidating
concrete (SCC) in highway construction offers these benefits and more,
with the potential for broad structural applications in the United States.
SCC, which does not require vibration to achieve full compaction, was
first developed and used in Japan in the early 1990s for bridge building
and tunnel construction. An SCC mix has a high degree of workability
and remains stable both during and after placement. SCC uses common
ingredients, plus superplasticizers and viscosity modifiers. The mix
must meet three key property requirements:
- Ability to flow into and completely fill intricate and complex
forms under its own weight.
- Ability to pass through and bond to reinforcement material under
its own weight.
- High resistance to aggregate segregation.
Eliminating vibration cuts down on the labor needed and speeds up construction,
resulting in cost savings and less traffic disruption. It also reduces
the noise level in concrete plants and at construction sites and reduces
aggregate segregation, honey combing, and voids in the concrete. The
overall concrete quality is improved, as problems associated with vibration,
such as under vibration, over vibration, or damage to the air void structure,
are eliminated. Also improved is the concrete’s resistance to
chloride intrusion and ability to withstand freeze thaw damages.
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This photo shows Double-T beams constructed using SCC. |
Several European countries formed a consortium in 1996 to develop SCC
for practical applications in Europe. Over the past 5 years, SCC bridges
and structures have been constructed in such countries as the Netherlands,
Sweden, and the United Kingdom. For example, SCC has been used on the
Sodra Lanken project in Stockholm, which is the largest ongoing infrastructure
project in Sweden. The project will provide a 6-km (3.7-mi) four-lane
link from west to east in the southern part of the city. It includes
seven major junctions, with bridges, earth retention walls, tunnel entrances,
and concrete box tunnels. Begun in 1998, the project is slated to wrap
up in 2004.
SCC has primarily been used for parts of the Sodra Lanken construction
that are difficult to compact by the normal vibration method, including
rock tunnel entrances, retention walls, and underground installation
structures. For example, two of the project’s parallel tunnels
did not have a full rock cover. To stabilize the tunnels and achieve
a strong and solid structure, concrete arches were constructed with
SCC. The wall sections of the arches were 5-m (16-ft) high, 9- to 16-m
(29- to 52-ft) long, and 0.8-m (2.6-ft) thick. The concrete was pumped
through a 12.7-cm (5-in) steel pipe from a mobile concrete pump. To
ensure an almost continuous flow of concrete into the formwork, two
agitating trucks standing side by side to each other discharged the
SCC mix. In comparison with other arches cast using conventional techniques,
the SCC ones were judged to be of better quality, with good surface
evenness and finish that did not require any repairs for rock pockets
or other surface defects.
Lessons learned from SCC projects in Japan and Europe include the understanding
that the production of SCC requires more experience and care than that
of conventional vibrated concrete. Although most common concrete ingredients
and mixers can be used for producing SCC, mixes must be properly designed
and tested to assure compliance with the project specifications. All
commonly used formwork materials are suitable for SCC; However, during
cold weather placement of the concrete, it may be necessary to insulate
the formwork to maintain the temperature and normal setting time. SCC
is more sensitive to temperature during the hardening process than vibrated
concrete. SCC also tends to dry faster than conventional vibrated concrete,
as there is little or no water near the concrete surface. The concrete
should be cured as soon as practical after placement to prevent surface
shrinkage cracking.
The initial cost of SCC may be higher than that of conventional concrete
because of the admixtures used. However, when used in Japan and Europe,
material cost increases of about 4 percent were offset by labor cost
decreases of 33 percent, for a total cost decrease of about 7 percent
per project.
“SCC has high potential for greater acceptance and wider applications
in highway bridge construction,” says M. Myint Lwin, Director
of the Office of Bridge Technology at the Federal Highway Administration
(FHWA). A new National Cooperative Highway Research Program project
will focus on developing design and construction specifications for
SCC to supplement the American Association of State Highway and Transportation
Officials’ Load and Resistance Factor Design specifications. The
South Carolina Department of Transportation, meanwhile, has received
an Innovative Bridge Research and Construction (IBRC) grant from FHWA
to study the use of SCC in drilled shafts. The Kansas Department of
Transportation (KSDOT) has also received an IBRC grant to study the
use of SCC in prestressed concrete bridge girders. KSDOT will build
a three-span bridge, using SCC in all of the prestressed concrete girders
for one of the spans, with the other spans being constructed using Kansas’s
standard concrete mixes. The bridge’s performance will then be
monitored for 5 years.
More information on SCC is available in the paper, “Applications
of SCC in Japan, Europe, and the U.S.,” by Masahiro Ouchi, Sada-aki
Nakamura, Thomas Osterberg, Sven-Erik Hallberg, and M. Myint Lwin. To
obtain a copy or for additional information on SCC and how it is being
implemented, contact M. Myint Lwin at 202-366-4589 (email: myint.lwin@fhwa.dot.gov).
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These photos above show an SCC bridge railing constructed
in Spokane, Washington. |
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An SCC box segment |
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