Since its 1989 introduction in Japan, self-consolidating concrete (SCC) has been used worldwide for precast and cast-in-place applications. As European
Since its 1989 introduction in Japan, self-consolidating concrete (SCC) has been used worldwide for precast and cast-in-place applications. As European countries are rapidly adopting the technology for construction of bridges and structures, transportation agencies are using SCC to build bridges in New York, Virginia, Nebraska, and other states, while more such projects are in the planning stages.
Further advancing the practice, a National Cooperative Highway Research Program (NCHRP) project (No. 18-12) is 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, contends Myint Lwin, Director of the Federal Highway Administration’s (FHWA) Office of Bridge Technology.
Primary among its benefits, SCC does not require vibration to achieve full consolidation. A high degree of workability and stability both during and after placement are additional features of an SCC mix, which 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 required labor and speeds up construction, resulting in cost savings and less traffic disruption. Thereby minimized also are noise levels in concrete plants and at construction sites, plus aggregate segregation, honeycombing, and voids in the mix. Overall concrete quality is improved with the eradication of such vibration-related problems as under vibration, over vibration, and damage to the air void structure. Enhanced as well are concrete’s resistance to chloride intrusion and its ability to withstand freeze-thaw damages. In addition, a high level of flowability results in smooth surfaces, minimizing the need for additional finishing.
In the U.S., after the introduction of SCC-type admixtures for precast and cast-in-place applications, interest in using the material continues to build. People are seeing and experiencing the benefits now, including faster placement of the concrete, better quality, and noise reduction, affirms Joe Daczko of Degussa Admixtures, Inc.
We have used SCC substantially in the last year, reports Mathew Royce of the New York State Department of Transportation. Several current NYSDOT projects incorporate significant SCC elements, including prestressed, high-performance concrete bridge beams on the Brooklyn-Queens Expressway from 61st Street to Broadway in New York City; East Tremont Avenue bridge reconstruction over the Cross Bronx Expressway; and, a substantial portion of precast substructure components for the replacement of the Roslyn Viaduct bridge, outside New York City. The performance of SCC has been excellent, says Royce. We’re achieving good quality with a minimum of defects. A slightly higher cost for admixtures has been offset by savings on labor. Overall, there is generally a reduction in cost.
The Virginia Department of Transportation uses SCC for precast/prestressed and cast-in-place applications. In 2001, precast components were fabricated with SCC for an arch bridge near Fredericksburg. In 2003, VDOT subjected two prestressed SCC girders to testing at FHWA’s Turner-Fairbank Highway Research Center in McLean, Va. Results indicated that SCC developed a good bond with prestressing strands, and shear and flexural behaviors conformed to predictions. That promising evidence prompted VDOT in 2005 to use eight prestressed SCC beams for one span of Route 33 over the Pamunkey River bridge near Richmond. To compare their performance with that of regular concrete beams, two of the 22.5-m (74-ft.)-long SCC beams were instrumented. The eight beams have good strength, low permeability, and are performing well, observes Celik Ozyildirim of the Virginia Transportation Research Council. Accordingly, our goal is to make the use of SCC standard practice, so that we are producing it consistently day in and day out.
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 now on all products on every project for Nebraska, says Concrete Industries’ Mark Lafferty. Among those projects is Omaha’s Skyline Bridge, completed in 2004, featuring a full-width bridge deck constructed of SCC. We see good performance with SCC, and the work can be done faster, Lafferty adds. The time to fill forms, for example, has been reduced about 25 percent.
PROMISING PROJECT
Initiated in 2004 and scheduled for completion in 2007, NCHRP Project 18-12, Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge Elements, aims to increase the acceptance and use of SCC in highway bridge construction. The project will develop guidelines for SCC use 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. Also addressed during the course of the study will be issues of workability, strength development, creep and shrinkage properties, durability, and other factors influencing constructibility and performance. More details on the project are available at www4.trb.org/trb/crp.nsf/NCHRP+projects (choose Area 12, Bridges, and then Area 18, Concrete Materials).
Meanwhile, a research project titled Development of Self-Consolidating Concrete for Slip Form Paving is in progress at Iowa State University’s Center for Portland Cement Concrete Pavement Technology. Its objective is development of concrete mixtures that can be used for slip form paving without external consolidation.
Also providing a boost to U.S. applications of SCC, according to Director Lwin, FHWA helped to organize SCC 2005, which combined the Second North American Conference on 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. Held in Chicago late last fall, the conference featured worldwide knowledge on and experience with SCC.
Additionally, FHWA has developed in collaboration with industry professionals a one-day workshop, Introduction to Self-Consolidating Concrete, to present fundamentals of material and mechanical properties, mix design, test methods, constructibility, quality control/quality assurance, creep and shrinkage, and other factors affecting successful application of SCC. Available to state personnel upon request, the workshop also provides a forum for discussion involving questions, concerns, and lessons learned in the field. To date, workshops have been held in West Virginia and Nevada.
SCC INFORMATION
Following are industry contacts for those interested in using self consolidating concrete mixes.
John Dick, Precast/Prestressed Concrete Institute, Chicago, Ill., 312/360-3205 (e-mail: [email protected])
Joe Daczko, Degussa Admixtures, Inc., Cleveland, Ohio, 216/839-7044 (fax: 216/839-8825; e-mail: [email protected])
Philippe Jost, Sika Corp., Lyndhurst, N.J., 201/933-8800, ext. 4223 (fax: 201/933-6225; e-mail: [email protected])
Ed Mansky, Grace Construction Products, Cambridge, Mass., 800/354-5414, ext. 5449 (fax: 800/886-4155; e-mail: [email protected])
Jim Wamelink, Axim Italcementi Group, Inc., Middlebranch, Ohio, 800/899-8795, ext. 2045 (fax: 330/499-9275; e-mail: [email protected])