Self-Consolidating Concrete
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Show: Self-Consolidating Concrete Offers New Opportunities for Architectural
Concrete
Architectural concrete is a hot topic. Defined by the American
Concrete Institute as “concrete which will be permanently
exposed to view and which therefore requires special care in selection
of the concrete materials, forming, placing and finishing to obtain
the desired architectural appearance,” it’s showing
its face everywhere. Examples of applications are buildings and
transportation structures like bridges and highway sound/barrier
walls. Delivery methods include cast-in-place, precast, and tilt-up,
and in every case, good appearance is essential because the concrete
is to be left exposed. Achieving good surface characteristics requires
thorough consolidation of the fresh concrete and thoroughly filled
forms. Fortunately, this also leads to a durable material because
water, precipitation, and aggressive chemicals/ions are shed by
the surface skin.
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| Slim and accurate architectural
constructions are much easier to realize with SCC, such as this
83-m high Stockholm Airport tower, which is decorated with excerpts
from the work of Antoine de Saint-Exupéry. Reduced noise
levels made construction during nighttime hours possible.
Photo courtesy: HeidelbergCement |
Conventional concrete is placed using vibrators to fill the forms.
SCC is a big step forward in fool-proofing that procedure. SCC technology
has the potential to revolutionize the concrete industry, and architectural
concrete stands to benefit from easier construction techniques and
improved surfaces.
Self-Consolidating Concrete
The construction industry has always longed for a high-performance
concrete that can flow easily into tight and constricted spaces
without requiring vibration. The need for this technology has grown
over the years as designers specify more heavily reinforced concrete
members and ever more complex formwork. Honeycombing or exposed
reinforcement in structural walls or columns is a constant concern
in these structures.
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| Placement of white cement SCC. Photo courtesy
of Aalborg White. |
Until recently, the industry used superplasticizing admixtures (also
known as high-range water reducers) in conventional mixtures in an
attempt to achieve flowable concrete and duplicate the advantages
of a true self-consolidating concrete. This allowed the use of concrete
having an 8-in. or greater slump; however, some vibration was still
required for adequate consolidation. While high doses of superplasticizers
can create a very fluid concrete that flows readily, the concrete
will segregate if the mortar is too thin to support the weight of
the coarse aggregate. The key to creating self-consolidating concrete
(SCC), also referred to as self-compacting, self-leveling, or self-placing
concrete, is to produce a very flowable mortar that retains a viscosity
great enough to support the coarse aggregate. Today, advances in admixtures
and mix proportioning are making SCC a practical reality around the
world.
SCC Formulated with White Cement
Architectural expression in concrete means different things to
different people. Some designers appreciate concrete for its unadorned
appearance. So gray portland cement concrete can receive architectural
treatment. Some designers want to use color to express aesthetics,
and white portland cement is available to create white or colored
concrete. Much of the experimental work to date on SCC has focused
on gray cement, but there are opportunities for white cement formulations.
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Slump flow test of white SCC.
Photo courtesy of Aalborg White. |
Concrete producers know that there is quite a bit of development
associated with any mix design. When SCC is brought into the equation,
the fresh properties are the most important characteristic of the
mixture. The concrete has to flow easily (slump flow) including
passing through obstructions like rebar (measured by the J-ring
test), but has to do so without bleeding or segregating. See “Testing
SCC” below or click
here for a description of the ASTM tests for assessing fresh
SCC properties.
If a mixture is designed with gray portland cement, it can be modified
to use white portland cement, but the mixture will most likely change
somewhat. Testing done by Aalborg Portland A/S identified several
suggestions for converting a gray SCC formulation to white cement
SCC. (1, 2) They take into account the difference in
chemistry of white cement and gray cement, dosages of cement, water
and admixtures, etc. Alternately, a mixture can be initially designed
in white portland cement.
 Testing
SCC: New ASTM Standards Are Approved
Flowability, passing ability, and stability are three of the most
important characteristics of SCC. In 2001, ASTM
started development of test methods that would assess these characteristics.
In 2005, the first SCC standard was published: ASTM C1611, Test
Method for Slump Flow of Self-Consolidating Concrete, which
assesses the flowability of SCC. This was
followed in March of 2006 by ASTM C1621, Test Method for Passing
Ability of Self-Consolidating Concrete by J-Ring. Test methods
to assess static and dynamic stability are currently
under development. These standards will be used in the mix design
process of SCC as well as a quality control tool.
Click here for more information.
References
(1) Thrysøe, Jacob, and Hansen, Tommy Bæk, “Self
compacting concrete based on white portland cement,” Concrete
Plant International, #1, Concrete Plant International Worldwide,
February 2006, pages 84 to 93.
(2) Self
Compacting Concrete Based on AALBORG WHITE®
Resources
Self-Consolidating
Concrete (IS546B)
Self-Compacting
Concrete: Bibliography of Resources
(LB06)
Self-Consolidating
Concrete Takes Concrete Sustainability to a New Level
 Concrete
is inherently a sustainable material. Some of its many sustainable
properties and applications are further enhanced with the use of
self-consolidating concrete (SCC). SCC provides benefits beyond
those of conventional concrete in all three aspects of sustainable
development: economic, social, and environmental.
The most important benefit of SCC is the increase in durability.
The uniformity of an SCC mixture reduces the permeability and enhances
the overall durability of the concrete. This, in turn, enhances
the lifespan of the SCC beyond that of conventional concrete (Corinaldesi
2005); thereby reducing the environmental footprint on a unit time
basis.
The use of SCC has been adopted by a large number of precast operations.
This has been done primarily due to the economic benefit of SCC.
The self-consolidating property eliminates the need for vibration,
which reduces the labor requirement for SCC placement. In some cases,
the labor requirement can be half that for conventional concrete
(Baumgartner 2003). The energy consumption associated with vibration
is also removed. Additionally, the formwork no longer is subject
to the stresses of vibration, which can reduce formwork initial
cost, maintenance costs, or both. These benefits apply to precast
operations as well as cast-in-place operations.
Another benefit associated with the elimination of vibration is
the noise reduction. This improves the working environment and safety.
This can increase employee productivity by reducing noise-induced
and vibration-induced illnesses (Daczko 2006). Additionally, operations
located within or near residential or commercial centers may experience
less noise-based negative feedback from the neighbors.
The aesthetic quality of SCC formed surfaces allows the bare concrete
to be the finish surface. Additional material, such as paint, is
not needed. This in turn reduces maintenance requirements and improves
air quality.
Additional environmental concerns can be addressed using benefits
already highlighted for the economic and social aspects of sustainable
development. The reduction in energy consumption can be directly
translated to reduced fossil fuel usage. On top of the reduction
in energy due to elimination of vibration, the rapid discharge rate
of SCC allows for shorter dwell times of trucks at the job site.
Again, this directly translates to a reduction of fossil fuel usage.
Glavind (2005) states that the industry “has suffered from
an image of being dirty, noisy, and environmentally unfriendly.”
SCC in combination with the sustainable principles of concrete in
general can be used to refute this image and show that concrete
is the choice for sustainable development.
References
Baumgartner, J., “Application of the Zero Energy System: Self-Compacting
Concrete in the Swiss Precast Concrete Industry,” Betonwerk-
und Fertigteil-Technik (Concrete Plant and Precast Technology),
Vol. 69, No. 9, 2003, pages 58-66.
Corinaldesi, V. and G. Moriconi, “Rheological Study of Blended
Cement Concrete,” Cement Combinations for Durable Concrete,
Thomas Telford, London, 2005, pages 211-218.
Daczko, J. A., and M. Vachon, "Self-Consolidating Concrete
(SCC)," Significance of Tests and Properties of Concrete
and Concrete-Making Materials, STP169D, ASTM International,
West Conshohocken, Pennsylvania, 2006, pages 637-645.
Glavind, M., D. Mathiesen, and C.V. Nielsen, “Sustainable
Concrete Structures: A Win-Win Situation for Industry and Society,”
Achieving Sustainability in Construction, Thomas Telford,
London, 2005, pages 1-14.
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