U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
|Accelerating Infrastructure Innovations|
Publication Number: FHWA-SA-98-019
Date: February 1998
To many people, thinking about the future means making plans for celebrating the millennium. But to a growing number of highway agencies, thinking about the future means designing and building bridges that will last for up to a century. That's more than twice as long as the life of a typical bridge-and it's made possible by a technology known as high-performance concrete (HPC).
HPC is an innovative approach to designing portland cement concrete mixes to make them more durable and, if necessary, stronger than is possible with conventional concrete. HPC is made using the same basic materials and techniques as conventional concrete, but the proportions and curing conditions are engineered to produce concrete mixes that meet the requirements of specific bridge projects.
HPC allows engineers to design a concrete mix with the durability required for conditions at a project site. For example, a bridge in a cold, snowy region would use a concrete mix with low permeability to reduce the chance of damage from freeze-thaw cycles and corrosion caused by salt in deicing materials. The improved durability means that HPC bridges will require less maintenance and fewer repairs and last longer than other bridges.
HPC can also be much stronger and stiffer than conventional concrete. This allows bridges to be designed with smaller or fewer structural components or longer spans, which in some cases reduces construction costs. Highway agencies can also save money by using HPC mixes that are designed to be easy to work with or to gain strength more quickly, thus speeding construction.
HPC is not a new material-high-strength concrete has been used in buildings for more than 20 years. But HPC that meets the durability and construction requirements for bridges has taken longer to develop, making HPC bridges extremely rare until only recently. But the pace of building HPC bridges is picking up fast. At least one dozen State highway agencies and several foreign countries have built or are building bridges using HPC, and more projects are being added every year.
Two years ago, the New York State Department of Transportation (DOT) began requiring that all new bridge decks be constructed of HPC. More than 100 HPC bridge decks have been built in the State so far. The change to HPC, which was adopted as part of a broader program to improve bridge decks, is expected to result in less cracking and reduced permeability. The result will be much more durable bridges.
"We're expecting, based on our permeability specifications, that decks will last double what they last now," says Don Streeter of New York State DOT. Streeter says bridges with HPC decks are predicted to serve 60 to 65 years before needing rehabilitation, and to ultimately last for 100 years.
HPC's attributes make it an excellent choice for bridges in harsh environments. In Canada, HPC was used in the Confederation Bridge, a 12.9-km (8-mi) structure linking Prince Edward Island to New Brunswick that was completed in 1997. During its 100-year design life, the bridge must withstand high winds, the battering of ice floes, and the corrosive effects of seawater. To hold up under these conditions, the bridge was built with high-strength, low-permeability concrete.
Many contractors are making an extra effort to learn about HPC. In Washington State, the construction specifications for the Lacey V. Murrow floating bridge on Interstate 90 outside of Seattle called for the use of watertight HPC in the structure's 20 concrete pontoons. Part way through construction, the contractor asked to be able to use HPC in other parts of the bridge as well, at no extra cost to the State, in order to gain more experience with the concrete mix. According to Myint Lwin of Washington State DOT, the contractor's costs for materials increased, but "the improved workability and higher early strength of the mix offset the higher initial costs by speeding construction."
Using HPC doesn't necessarily increase overall bridge construction costs. New York State's Streeter says that "The switch to HPC has increased materials costs, but bridge deck construction costs have stabilized at levels comparable to those for conventional concrete decks." In Washington State, the highway agency is making HPC girders standard practice. These girders cost slightly more to make than conventional concrete girders, but their increased strength means fewer girders and other structural components are needed, thereby reducing the costs of hauling components to the project site and of construction.
Much of the momentum behind HPC is due to the work of the Federal Highway Administration's (FHWA) HPC for Highway Bridges Technology Delivery Team (see sidebar) and the Lead States team for HPC bridge implementation (see sidebar). The two teams are providing States with technical support, assistance in building pilot projects, and other help. The teams have an ambitious goal: at least one HPC bridge project built in every State by 2002.
Highway agencies have no reason not to build high-performance concrete bridges, says Suneel Vanikar of FHWA. Using familiar materials and curing techniques, States can easily make incremental improvements to the strength and durability of the concrete they specify for bridge projects. "HPC is not difficult to adopt, and it's a proven technology," he says. "It's not only on a piece of paper or in the laboratory-it is being used in the field under real traffic and climate conditions."
FHWA and the Lead States are involved with several projects to educate highway agency and industry staff. One example is the HPC Showcase Workshops. The workshops include presentations on the benefits of HPC and on how HPC has been used in specific bridge projects. Presentations also summarize how to design HPC mixes and how standard test procedures can be used to determine the durability and strength of these mixes. More than 200 people turned out for a workshop in Waterville Valley, New Hampshire, last fall. Workshops will be held in Denver, Colorado, this month and in Ohio and Alabama later this year. In addition to sponsoring, FHWA and the Lead States team are developing generic presentations that States can then customize for their own workshops.
Research on HPC, its use in bridges and other highway structures, and its benefits were the subject of presentations at the PCI/FHWA International Conference on HPC in New Orleans in fall 1997. The conference, held in conjunction with the Precast/Prestressed Concrete Institute (PCI) and co-sponsored by FHWA, brought together more than 1,200 people from 22 countries. During the conference, FHWA Executive Director Tony Kane presented an award to PCI President Thomas Battles for the organization's work on the conference. In turn, PCI recognized FHWA's contributions to the promotion of HPC technology.
Education will also be a big part of a new cooperative agreement between the National Concrete Bridge Council and FHWA. The two organizations will publish a newsletter on HPC bridges geared to high-level staff in State highway agencies and FHWA. They will also assemble a team of experts who will be on call to assist States that are developing HPC mixes or building HPC bridges.
Vanikar predicts a bright future for HPC. "HPC is farther reaching than any other technology. It can be used for pavements, airports, port facilities, buildings, and parking garages. With HPC, anything built using concrete can be made more durable, require less maintenance, and take advantage of higher strengths."
For more information on HPC, contact Terry Halkyard at FHWA (phone: 202-366-6765; fax: 202-366-7909; email: firstname.lastname@example.org) or James Moore of New Hampshire DOT, head of the Lead States team for HPC bridges (phone: 603-271-2731; fax: 603-271-2759). Information is also available from FHWA's HPC Web site (hpc.fhwa.dot.gov) and from the structures section of the Turner-Fairbank Highway Research Center Web site (tfhrc.gov/structur/hpc).
Technology Delivery Team
FHWA's projects to help States become familiar with the use of high-performance concrete in bridges are coordinated by the High-Performance Concrete for Highway Bridges Technology Delivery Team. The team was established in 1997, but its members had been working together informally for several years before then. The team's members are:
Lead States Team
The Lead States team for HPC bridges was established by the American Association of State Highway and Transportation Officials (AASHTO) Task Force for SHRP Implementation in 1996 to help other States more quickly implement HPC technology. The team is made up of the Lead States-Missouri, Nebraska, New Hampshire, Texas, Virginia, and Washington-and their partners in industry and FHWA. The team's members are:
New York State DOT has built more than 100 HPC bridge decks during the past 2 years. The DOT expects HPC bridge decks to last twice as long as conventional concrete bridge decks.
Crews install the final pontoons on the Lacey V. Murrow floating bridge near Seattle. The contractor on the job asked to use HPC in much of the bridge in order to gain experience with the material.
At least one dozen state highway agencies have built or are building bridges using HPC.