Anybody involved with the introduction of new technology into the construction industry knows that it is a slow and laborious process. This edition of Technical Talk discusses some of the activities that are underway to remove barriers to the use of high performance concrete (HPC) in construction.

Technology transfer

One of the biggest challenges in the construction industry is transferring knowledge from those who have it to those who need it. When high-strength concrete was first used in the building industry, knowledge of the means to produce and test it resided within the companies involved in developing the technology. With the publication of state-of-the-art reports and recommended practices by the American Concrete Institute (ACI), this information came into the public domain, enabling others to learn. This process continues today with the additional ACI policy that their documents not inhibit or preclude the use of HPC.

When the Federal Highway Administration (FHWA) initiated a more widespread use of HPC in bridge structures, the method of implementation consisted of sponsoring HPC bridge demonstration projects in combination with showcase workshops in the different FHWA regions. Information presented in these workshops has now been combined into seven training modules that are available from the Transportation Industrial Alliance at the University of Florida, Gainesville (see sidebar).

As part of the FHWA program, partnerships were formed with state highway departments, industry, and academia to assist the local industry with HPC bridge construction while providing academia an opportunity for further research. Now available on a compact disc from FHWA is a compilation of information on the HPC projects and the results achieved.

Data gathered on HPC projects is also available in a bimonthly newsletter called HPC Bridge Views. This newsletter is published jointly by the FHWA and the National Concrete Bridge Council (NCBC). Free subscriptions are available by contacting NCBC. The FHWA, in cooperation with the Precast/Prestressed Concrete Institute, has sponsored symposia on High Performance Concrete in 1997 and 2000. A third symposium is scheduled for October 2003.

Structural design

Many of the design provisions contained in documents such as the ACI Building Code Requirements for Structural Concrete (ACI 318) and AASHTO Bridge Design Specifications are based on empirical relationships that include the concrete compressive strength. Most of these provisions were developed on the basis of concrete with compressive strengths less than about 6,000 psi (41 MPa). With the publication of the 1989 version of ACI 318, restrictions were placed on the maximum concrete compressive strengths that could be used in design for shear strength, development length, and splices of reinforcement. These restrictions were necessary because sufficient information was not available to demonstrate the applicability of the provisions to higher strength concretes.

Subsequently, ACI formed a subcommittee on High Performance Concrete to provide leadership and technical guidance on high performance concrete for all ACI activities. The subcommittee in cooperation with the National Institute of Standards and Technology undertook a review of ACI 318 to identify provisions that are impacted by the use of HPC. This review culminated in several high-priority recommendations presented to Committee 318. Changes resulting from several of the recommendations are expected to appear in the 2002 edition of ACI 318. In the meantime, work is still underway on other modifications.

A similar review to that performed on ACI 318 has recently been completed for the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing, the AASHTO Standard Specifications for Highway Bridges, and the AASHTO LRFD Bridge Design Specifications. It is expected that the results from the review will be published by FHWA in the near future. The review will also result in a series of recommendations for changes in these documents to facilitate the use of both high-strength concrete and high performance concrete.

Research

The limitations on concrete compressive strength in ACI 318 were introduced due to a lack of information demonstrating the applicability of the provisions to high-strength concrete. The AASHTO Standard Specifications for Highway Bridges contain a barrier to the use of high-strength concrete when the design of precast/prestressed members is specified as ordinarily based on a compressive strength of 5,000 psi (34 MPa). “An increase to 6,000 psi is permissible where, in the Engineer's judgment, it is reasonable to expect that this strength will be obtained consistently. Still higher concrete strengths may be considered on an individual area basis. In such cases, the Engineer shall satisfy himself completely that the controls over materials and fabrication procedures will provide the required strengths.”

The more recent AASHTO LRFD Bridge Design Specifications limit the applicability of the design provisions to a maximum concrete strength of 10,000 psi (69 MPa), unless physical tests are made to establish the relationships between concrete strength and other properties.

For the barriers in the specifications to be removed, additional research with higher compressive strength concretes is needed. Fortunately, the National Cooperative Highway Research Program (NCHRP) of the Transportation Research Board is sponsoring research on high-strength concrete in the following areas:

• NCHRP Project No. 18-07, “Prestress Losses in Pretensioned High-Strength Concrete Bridge Girders” at the University of Nebraska — Lincoln with Dr. Maher K. Tadros as the principal investigator.

• NCHRP Project No. 12-56, “Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions” at the University of Illinois — Urbana-Champaign with Dr. Neil M. Hawkins as the principal investigator.

• NCHRP Project No. 12-60, “Transfer, Development, and Splice Length for Strand/Reinforcement in High-Strength Concrete” expected to be awarded in Spring 2002.

In addition to the NCHRP program, research on other aspects of HPC is being performed at many universities and other research facilities around the country.

NCBC strategic plan

In November 2000, representatives from FHWA, state highway agencies, consulting engineering firms, academia, and industry met in a focus group to brainstorm over the advantages, weaknesses, opportunities, and threats to HPC bridges. According to Portland Cement Association's Dr. Basile Rabbat, chairman of NCBC, the group identified critical issues that needed to be addressed, namely, a lack of understanding on the use of HPC, a lack of technology transfer mechanisms, inadequate training of engineers, and little training in the life-cycle cost methods for bridges.

Consequently, NCBC is developing a white paper that will outline a strategy to tackle these problems. Development of a detailed action plan with participation of all stakeholders will follow publication of the white paper. Implementation of this plan will be a big step to remove additional barriers to HPC bridges.

Henry Russell is an engineering consultant based in Glenview, Ill. He is a member of American Concrete Institute, American Society for Testing and Materials, Precast/Prestressed Concrete Institute, and American Segmental Bridge Institute. He is currently the chairman of ACI's subcommittee on High-Performance Concrete.

HPC information sources

HPC Training Modules from Transportation Industrial Alliance
Gib Peaslee, 352/392-2371, ext. 245 (phone); gib@ce.ufl.edu (E-mail)

HPC Compilation from FHWA
Terry D. Halkyard, 202/366-6765 (phone); terry.halkyard@fhwa.dot.gov (E-mail)

HPC Bridge Views from NCBC
Shri Bhide, 847/966-6200 (phone); or ncbc@portcement.org (E-mail); or www.portcement.org/br/newsletters.asp (Web site)

HPC Symposium Proceedings from PCI
Precast/Prestressed Concrete Institute, 312/786-0300 (phone); info@pci.org (E-mail)

NCHRP Projects
www4.nas.edu/trb/crp.nsf/nchrp+projects (Web site)

Strategic Plan from NCBC
Basile G. Rabbat, 847/966-6200 (phone); brabbat@portcement.org (E-mail)

Slag group charts course

In a follow up to August (page 6) Scope coverage …The Slag Cement Association (SCA) was formed earlier this year to promote increased use of slag cement and portland-slag cement blends. The Association is seeking to position itself as the leading source of knowledge on blast furnace slag-based cementitious products — educating customers, specifiers and other end-users on the varied attributes, benefits and uses in construction.

SCA's board of directors recently named Jan Prusinksi, P.E., its executive director. With more than 20 years experience in engineering, marketing and finance, Prusinski has particular expertise in product and market development for cementitious materials. He was formerly the Portland Cement Association's program manager for Soil-Cement and Roller Compacted Concrete Pavements. He holds a B.S. in civil engineering from the University of Michigan, an M.B.A. from the University of Houston and is a registered professional engineer.

“The use of slag cement in concrete has significantly increased over the last five years due to heightened awareness of improved concrete performance with slag and expanded slag grinding capacity,” notes Prusinksi. “The formation of the SCA ensures that engineers, specifiers and contractors can turn to a knowledgeable resource whenever questions arise about slag cement use in concrete and other construction applications.”

SCA President Randy Dunlap, of Holnam Inc., concurs, “Our member companies are committed to fostering awareness and use of slag cement. SCA provides consistent, accurate information about the benefits of slag cement, with the highest level of service.”

Slag is produced during the reduction of iron ore to iron. Molten non-iron minerals are separated, rapidly quenched, then ground to a fine powder, called slag cement. It typically replaces, pound-for-pound, a portion of portland cement in a concrete mixture. Using slag cement provides significant benefits to concrete:

• Reduced carbon dioxide generated in producing concrete raw materials

• Better workability and finishability

• Lower permeability

• Lower life-cycle costs

• Enhanced resistance to chemical attack

• Higher compressive, flexural strengths

Joining Holnam in SCA membership are Essroc Cement Corp.; Lafarge North America.; Lehigh Portland Cement; Lone Star Industries; and St. Lawrence Cement Co. These companies account for the majority of U.S. slag cement shipments. SCA is headquartered just outside Houston: P.O. Box 2615, Sugar Land, Texas 77487-2615; 281/494-0782 (phone); 281/494-0784 (fax).