High-Performance Materials: A Step Toward Sustainable Transportation
Adapted from a paper by Susan Lane, Eric Munley, William Wright, Marcia Simon, and James D. Cooper, presented at the U.S.-European Bridge Workshop in Barcelona, Spain, July 1996.
A world where infrastructure systems have longer life cycles and are sustained through the use of recycled materials increases the quality of life for all. Over the last few decades, these wishes are quickly becoming reality; technology has aided us in our search for solutions that lead to stronger, more durable transportation systems.
Photo 1: Samples of some high-performance materials were exhibited at the 1997 annual meeting of the Transportation Reseaarch Board.
In particular, high-performance materials offer substantial hope for better systems that last a lot longer. High-performance materials are engineered products that provide specific performance advantages in comparison with the counterpart conventional materials. For example, high-performance concrete is stronger and more durable than conventional concrete, and as a result, high-performance concrete structures potentially cost less to build and maintain. While research laboratories are still exploring ways to exploit these materials, some of them are ready for use.
Currently, the role of the U.S. Department of Transportation, which includes the Federal Highway Administration (FHWA), is to promote the use of high-performance materials on the state level. Because there is little data available on the long-term results of high-performance materials and because there is frequently a relatively high initial cost, states are reluctant to take on such a venture independently. To help overcome these obstacles, a federal-state partnership with shared funding and knowledge has been developed.
The four types of materials currently being investigated are high-performance concrete, high-performance composites, aluminum, and high-performance steel.
Photo 2: The high-performance concrete bridge in Sarpy County, Nebraska, has received awards from the state chapters of the American Concrete Institute and the American Consulting Engineers Council.
High-performance concrete (HPC) is one of the most significant new materials available for new construction and for rehabilitating the infrastructure; it provides better long-term performance and reduced life-cycle costs. Many states have expressed interest in becoming partners in this program, and to date, 10 states have become active partners with FHWA by constructing or preparing to construct bridges with HPC. Several other states are participating through pooled-fund contributions.
Two articles on HPC have been published previously in Public Roads. In the Spring 1994 issue, an article entitled "Texas High-Strength Concrete Bridge Project" described the design and construction details for the Louetta Road Overpass bridges in Houston. These bridges are the first in the United States to fully use HPC in all aspects of design and construction.
An article about "The Promise of High-Performance Concrete" was published in the Autumn 1996 issue. This article discussed the advantages of HPC and the projects underway in Texas, Nebraska, Virginia, New Hampshire, and Ohio. Much of the information for this article was drawn from papers and presentations delivered at the Strategic Highway Research Program (SHRP) Texas High-Performance Concrete Bridge Showcase in Houston, March 25-27, 1996.
Another regional SHRP HPC Showcase was held in Omaha, Neb., Nov. 18-20, 1996. The featured project of this showcase was the 120th Street and Giles Road Bridge in Sarpy County, Neb. The bridge was opened to traffic in the summer of 1996. "The Nebraska HPC project was successful because there was a lot of teamwork right from the start," said Milo Cress, FHWA Nebraska Division bridge engineer. The continuous interchange of knowledge and experience in the Nebraska project gave everyone the benefit of synergy at work. More than four years ago, the University of Nebraska's Center for Infrastructure Research convened a roundtable meeting on HPC to spark interest in a demonstration project. Then, in March 1994, when FHWA began looking for partners for HPC implementation, Nebraska was ready. Nebraska Department of Roads engineers identified the Sarpy County bridge as a suitable candidate for the demonstration project. The existing bridge a three-span, 60-meter-long, steel pony truss was structurally deficient and narrow. Sarpy County officials agreed to use HPC in a replacement bridge if redesign would not delay construction of the bridge or increase their cost for the project. The Schemmer Associates Inc. redesigned the bridge using HPC for the prestressed girders and the deck. University of Nebraska professors Maher Tadros and Atorod Azizinamini teamed up with the Ready Mixed Concrete Co. on the mix design for the project. Once mix designs were selected, several trial batches were produced. In April 1995, the project was awarded to Hawkins Construction Co. The prestressed girders were fabricated by Wilson Concrete Co., and Ready Mixed Concrete Co. of Omaha supplied the concrete. The girders were cast and installed in late 1995 and early 1996. The deck was cast in May and June 1996, and in July, Nebraska Gov. Ben Nelson cut a red ribbon to open the bridge.
The Sarpy County HPC bridge uses 82.7-megapascal concrete for seven Nebraska University NU1100 girder lines placed with a spacing of 3.81 meters. The 190.5-millimeter-thick by 25.75-meter-wide cast-in-place deck has a concrete compressive strength of 55 megapascals and chloride permeability of less than 1,800 coulombs.
The project has received several awards, including the 1996 Award of Excellence from the state chapter of the American Concrete Institute, the Grand Award as the top design project from the state chapter of the American Consulting Engineers Council, and an award of appreciation from FHWA. More importantly, the success of the partnerships formed through this project will help promote cooperation and the use of this and other technologies in the future.
Future HPC bridge showcases are scheduled for Richmond, Va., in June 1997; for Seattle, Wash., in August 1997; and for New Hampshire in September 1997. An international symposium on HPC jointly sponsored by FHWA and the Precast/Prestressed Concrete Institute is scheduled for October 1997 in New Orleans, La.
FHWA's composite research program is now involved in a long-term partnership of government, universities, and private industry. The task is to answer the theoretical and practical questions that are arising from the introduction of new materials into the field of civil construction. Design and performance data for composites will be collected and will provide future researchers, material suppliers, and manufacturers with common test methods acceptable to the highway bridge design community. And while these research efforts are underway, others are using high-performance composites in the field. FHWA has partnered with California, Delaware, Georgia, and Virginia to use composites in bridge construction and rehabilitation projects. Other projects are planned or underway.
Aluminum bridge decks have a number of advantages over concrete and steel decks.
Aluminum is about 80 percent lighter than concrete. This substantial weight savings allows many bridges to be strengthened without extensive reengineering of substructures. Construction time can be accelerated through the use of aluminum because it does not require the curing time needed by concrete.
Aluminum requires fewer welds than steel, eliminating many potential failure points. Compared to steel, aluminum is less expensive, both in the short term and the long term. An aluminum deck is also more resistant to corrosion and other environmental degradation. Also, aluminum is lighter and can be installed more quickly, which is an increasingly important factor considering the public's impatience with road construction delays.
Reynolds Metals Co. has developed a new orthotropic deck system that has great potential as a retrofit option for aging bridges. FHWA is working with Reynolds and the Virginia Department of Transportation (VDOT) to test and evaluate this new system in the laboratory.
In addition, VDOT is now constructing a demonstration bridge on U.S. Route 58 over Little Buffalo Creek in Mecklenburg County. The existing bridge is a 17.7-meter simple span structure with a composite concrete deck. The aluminum deck allows the roadway to be widened without altering the steel girders or substructure. Another projected benefit is that the construction time will be reduced by not having to wait for the concrete to cure.
A second, more ambitious demonstration will be the construction of a two-span continuous structure in Montgomery County, Va. This bridge, which is part of the Virginia "Smart Road," will be built next year.
High-strength steel has been available for a long time for bridge construction. However, its use has been extremely limited because marginal weldability, toughness, and corrosion resistance have caused performance problems in many cases. Still, there have been many examples where high-strength steel has been used to make bridge designs more cost-effective. The goal of the new high-performance properties is to develop steels that possess greatly enhanced performance properties in addition to strength. These "optimized" steels will open the door for improved, cost-effective bridge designs that will be easy to construct, have good long-term durability, and provide a high degree of public safety.
FHWA's Partnership With the U.S. Navy
The U.S. Navy and its laboratories are also pursuing a program in the development of high-performance steel (HPS). They need it for the construction of warships. Although the performance requirements of the Navy are more severe than highway bridges (i.e., resistance to explosive blast), many similarities exist between high-performance ship steels and bridge steels. For this reason, FHWA has entered into an interagency agreement with the Carderock Division of the Naval Surface Warfare Center to develop new HPS grades for bridge construction. The Navy, in turn, has implemented a cooperative government-industry research program with the American Iron and Steel Institute (AISI) to perform the required research for bridge applications. This program brings together the research capabilities of the U.S. Navy laboratories and many of the major steel producers in the United States.
One aspect being investigated through the FHWA-U.S. Navy agreement is the use of thermo-mechanical controlled processing (TMCP) techniques to produce HPS. The advantage of TMCP is that it replaces the expensive alloying process currently used in steel-making. However, while used in Europe and Japan, TMCP is not currently available in the United States. Because of this uncertainty, FHWA and the Navy are also continuing to investigate different approaches to conventional alloy processing. In addition to the FHWA-Navy work, the Building and Infrastructure Research Laboratory (BIRL) at Northwestern University has recently developed a new grade of HPS that relies on copper alloying for strength and performance. The first heats of 70W and 100W HPS were produced in 1996.
Two new bridges have been designed with 70W HPS and are now under construction in Nebraska and Tennessee. The first is the state Route 79 bridge over Maple Creek in Dodge County, Neb. This project is demonstrating the fabrication efficiency that is gained by the high weldability of HPS-70W steel. The second bridge is along Tennessee Route 53 over Martin Creek in Jackson County. This is a two-span continuous structure that has a fully optimized design for the new steel grade. Preliminary cost estimates indicate that Tennessee will save 16 percent on the cost of fabricating and erecting steel for this structure.
The demands of larger, more mobile populations make it crucial for the United States and other countries to extend the life cycles of our infrastructure systems. Continuing to use the traditional, present-day materials and processes will not enhance the sustainability of our infrastructure. We all need the benefits inherent in high-performance construction materials and systems. The benefits can be accomplished by using each of these materials singularly such as in the Sarpy County, Neb., bridge or in combination such as using high-performance steel girders with high-performance concrete decks or using high-performance concrete girders and decks reinforced with FRP strands and reinforcing steel.
Through the use of high-performance materials, we can construct bridges characterized by superior strength; enhanced durability; increased resistance to abrasion, corrosion, chemicals, and fatigue; initial and life-cycle cost efficiencies; ease in manufacturing and construction; and aesthetics and environmental compatibility. FHWA believes that the infrastructure system in the United States can be dramatically improved by using high-performance materials. We can reduce delays caused by repair work, and we can be more cost-effective and efficient. It just makes good business sense!
Susan Lane, Eric Munley, and William Wright are research structural engineers in FHWA's Structures Division, Office of Engineering Research and Development (R & D), at the Turner-Fairbank Highway Research Center (TFHRC).
Marcia Simon is a research highway engineer in FHWA's Special Projects and Engineering Division, Office of Engineering R&D, at TFHRC.
James D. Cooper is the chief of the Structures Division, Office of Engineering R&D, at TFHRC.