Publication Number: FHWA-HRT-06-020
Date: November 2005

Advances in Self-Consolidating Concrete

Since self-consolidating concrete (SCC) was first introduced to the concrete industry in Japan in 1989, it has been used worldwide for precast and cast-in-place construction applications (see December 2003 Focus). Many European countries are rapidly adopting the technology for the construction of bridges and structures. In the United States, applications by transportation agencies have included bridges built in New York, Virginia, Nebraska, and other States, with more to come. A National Cooperative Highway Research Program (NCHRP) project (No. 18-12) is also underway to develop SCC mixes, structural design parameters, and construction specifications for precast, prestressed concrete elements. "Whatever conventional concrete can do, SCC can do better, faster, and cheaper, especially for concrete elements with special textures, complex shapes, and congested reinforcements," says Myint Lwin, Director of the Federal Highway Administration's (FHWA) Office of Bridge Technology.

SCC does not require vibration to achieve full consolidation. An SCC mix also has a high degree of workability and remains stable both during and after placement. The mix must meet three key 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, honeycombing, 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. The concrete's resistance to chloride intrusion and ability to withstand freeze-thaw damages are also improved. In addition, a high level of flowability results in smooth surfaces, minimizing the need for additional surface finishing.

Concrete admixture manufacturers were the first to introduce SCC in the United States for precast and cast-in-place applications, with interest in using the material continuing to rise. "People are seeing and experiencing the benefits now, including faster placement of the concrete, better quality, and noise reduction," says Joe Daczko of Degussa Admixtures, Inc.

"We have used SCC in a substantial way in the last year," says Mathew Royce of the New York State Department of Transportation (NYSDOT). Current projects include using SCC for prestressed, high-performance concrete bridge beams on the Brooklyn-Queens Expressway from 61st Street to Broadway in New York City. SCC is also being used in the reconstruction of the East Tremont Avenue bridge over the Cross Bronx Expressway. And NYSDOT will use SCC for a substantial portion of the precast substructure components for the replacement of the Roslyn Viaduct bridge, outside of New York City. "The performance of SCC has been excellent," says Royce. "We're achieving very good quality with a minimum of defects. There has been a slightly higher cost for admixtures, but we save on labor. Overall, there is generally a reduction in cost."

The Skyline Bridge in Omaha, NE, features a full-width bridge deck made of SCC.

The Virginia Department of Transportation (VDOT) is using SCC for precast, prestressed, and cast-in-place applications. In 2001, SCC was used for precast components of an arch bridge near Fredericksburg. In 2003, VDOT took two prestressed SCC girders to FHWA's Turner-Fairbank Highway Research Center in McLean, Virginia, for testing. The testing indicated that SCC developed a good bond with the prestressing strands, and that the shear and flexural behaviors were as predicted. Following the successful tests, VDOT used eight prestressed SCC beams in 2005 in one span of the new Route 33 over the Pamunkey River bridge near Richmond. Two of the 22.5-m (74-ft) long SCC beams have been instrumented, to compare their performance with that of regular concrete beams. "The eight beams have very good strength, low permeability, and are performing well," says Celik Ozyildirim of the Virginia Transportation Research Council. "Our goal is to make the use of SCC standard practice, so that we are producing it consistently day in and day out. We are going to keep working toward that."

A photo of eight prestressed SCC beams used in one span of the new Pamunkey River bridge near Richmond, VA.

In Nebraska, the Department of Roads is using SCC for applications such as long-span and short-span bridge girders, pilings, and temporary Jersey barriers. "We are using it on all products on every project we do now for Nebraska," says Mark Lafferty of Concrete Industries. These projects have included the new Skyline Bridge in Omaha, Nebraska. Completed in 2004, the project features a full-width bridge deck made of SCC. "We are seeing very good performance with SCC, and the work can be done faster. The time it takes to fill forms, for example, has been reduced about 25 percent," says Lafferty.

NCHRP Project 18-12, "Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements," began in August 2004 and is aimed at increasing the acceptance and use of SCC in highway bridge construction. Scheduled to be completed in 2007, the project will develop guidelines for the use of SCC in precast, prestressed concrete bridge elements and recommend relevant changes to the Load and Resistance Factor Design Bridge Design and Construction Specifications issued by the American Association of State Highway and Transportation Officials. The study will address the issues of workability, strength development, creep and shrinkage properties, durability, and other factors that influence constructibility and performance. For more details on the project, visit www4.trb.org/trb/crp.nsf/NCHRP+projects (choose Area 12, "Bridges," and then Area 18, "Concrete Materials").

A research project titled "Development of Self-Consolidating Concrete for Slip Form Paving," meanwhile, is being conducted at the Center for Portland Cement Concrete Pavement Technology at Iowa State University. The project's objective is to develop new concrete mixtures that can be used for slip form paving without external consolidation.

In collaboration with industry, FHWA has developed a 1-day workshop, "Introduction to Self-Consolidating Concrete." The workshop's objective is to introduce the fundamentals of material and mechanical properties, mix design, test methods, constructibility, quality control/quality assurance, creep and shrinkage, and other factors that influence the successful use of SCC. The workshop also provides a forum for discussion of questions, concerns, and lessons learned in the field. It is available to States upon request. Workshops have been held this year in West Virginia and Nevada.

SCC deck slabs for Nebraska's Skyline Bridge.	SCC beams used in Virginia's Pamunkey River bridge are shown here at the concrete plant.

FHWA also helped to organize SCC 2005, which combined the Second North American Conference on the Design and Use of Self-Consolidating Concrete and the Fourth International RILEM (International Union of Laboratories and Experts in Construction Materials, Systems, and Structures) Symposium on Self-Compacting Concrete. SCC 2005 was held October 30-November 2, 2005, in Chicago, Illinois. "The conference brought worldwide knowledge on and experience with SCC to Chicago, and is expected to provide a boost in the applications of SCC in the United States," says Lwin.

For more information on SCC , contact Myint Lwin at FHWA, 202-366-4589 (email: myint.lwin@fhwa.dot.gov). To learn more about hosting an FHWA SCC workshop, contact Jon Mullarky at FHWA, 202-366-6606 (email: jon.mullarky@fhwa.dot.gov).

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