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Self-Placing
Concrete
The Need
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Certain concrete pours have areas where the
congestion of reinforcing bars make placement of concrete almost impossible. Using
conventional placing and vibration techniques, the resulting concrete can have
considerable honeycombing due to the development of voids. Not only is this undesirable
but the labor cost of placing using traditional methods is high. Methods need to be
developed to reduce labor costs, shorten construction time and produce a better finished
product. |
The Technology
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Self-placing concrete is a possible solution
to the problem. Also known as self-compactable concrete, self-consolidating concrete,
flowable concrete, and non-vibration concrete. These concretes eliminate the need for
vibration in a placement process where the reinforcement makes proper vibration difficult
or impossible. Perhaps, as important as the lack of needed vibration, is that the density
is obtained without segregation. Self-placing
concrete is obtained by the use of various admixtures. The particular admixture for a mix
is usually developed by individual companies where Japanese firms are currently leading
the way. Generally, a conventional concrete mix is used with the addition of a water
reducing agent. The water cement ratio is kept the same. This combination results in a
"flowable" concrete with usually high compressive strengths.
A product with similar characteristics was developed by
Meca Engineering Co., Ltd. in Korea. The product called MELFLOW is a high-range water
reducing admixture based on Sulfonated Melamine formaldehyde. This product prevents
segregation by eliminitating the electrostatic attraction between the positive and
negative charges on the concrete particles. An electrostatic repellency is induced
increasing the negative charge of each particle and releasing the flocculated cement. |
The Benefits
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The costs of self-placing concrete may be
slightly higher but the payback of reduced labor required for placement and improved
construction schedule must be considered to determine a benefit. Additional benefits
include the ability to use conventional batching plants and ready-mix transit trucks which
eliminates the need to invest in a new plant. MELFLOW
is a superplasticizer that optimizes the water/cement ratio of concrete improving
dramatically its workability without having to add more water. It is capable of reducing
up to 30 to 40% the mixing with water. It also provides improvements in the following:
strength, density, durability, volume stability, bond, and abrasion resistance. |
Status
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Several projects have been successfully
completed in Japan since 1993 using self-placing concrete. These include a tunnel liner in
Yokohama city, the main tower on the Kiba-Park Large Bridge, and a tubular column fill on
the Landmark tower. Work needs to be done to further refine testing and quality control
procedures. The MELFLOW product has been succesfully
used by Korean companies like Hyundai Construction in many large construction projects. |
Barriers
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Because of the limited use the costs are still
high and limited to use only in severe conditions. |
Points of Contact
- Hikaru Takeuchi, Technical Research Institute, Mitsui
Construction Co., Ltd. Tokyo, Japan.
- Antonio Nanni, Pennsylvania State University.
- MELFLOW product: MECA Engineering Co., LTD. 3rd Kum-Ho
Bldg., 123-25 Karak-Dong, Songpa-Ku, Seoul, Korea (138-160). Phone: (+82-2) 443-3497. Fax:
(+82-2) 431-2570. Email: limstone@netsgo.com
References
- MECA Engineering Co., LTD. MEL-Series Catalog Information.
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
KGM03/LHM
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