Henry G. Russell, Henry G. Russell, Inc.
In 1993, the Federal Highway Administration initiated a national program to implement the use of high performance concrete in bridges. The program included the construction of demonstration bridges in ach of the FHWA regions and the dissemination of the technology and results at showcase workshops. A total of 18 bridges in 13 states were included in the national program. Also, other states have implemented the use of HPC in various bridge elements. Articles on many of the bridges have been published in HPC Bridge Views.
The bridges were located in different climatic regions of the United States and sed different types of superstructures. The bridges demonstrated practical applications of high performance concretes. In addition, construction of these bridges provided opportunities to learn more about the placement and actual behavior of HPC in bridges. Consequently, many of the bridges were instrumented to monitor their short- and long-term performance. Additionally, concrete material properties were measured for most of the bridges.
The superstructures for the bridges, generally, consisted of precast, prestressed concrete girders with cast-in-place concrete decks. A variety of cross sections were used for the girders. Span lengths ranged from 60 to 157 ft (18.3 to 47.9 m). Specified concrete compressive strengths at release of the strands ranged from 5500 to 8800 psi (38 to 61 MPa). Specified design compressive strengths ranged from 8000 (55 MPa) at 28 days to 14,000 psi (97 MPa) at 56 days.
The primary emphasis for concrete used in the cast-in-place decks has been to produce a concrete with low chloride permeability without specifying a high-strength concrete. Achievement of low permeability values required the use of a mineral admixture such as fly ash, silica fume, or ground granulated blast-furnace slag. Specified compressive strengths generally ranged from 4000 to 6000 psi (28 to 41 MPa) at 28 days.
As part of the FHWA implementation program, a research component was included in each bridge. The research objectives varied from bridge to bridge. On some projects, the research focused on concrete material properties. Measurements were made to determine compressive strength, modulus of elasticity, tensile strength, creep, shrinkage, chloride permeability, freezethaw resistance, deicer scaling resistance, and abrasion resistance. Concrete temperatures were measured during curing to determine the heat of hydration of the prestressed concrete beams. The use of match-cured cylinders compared to conventionally-cured cylinders for measurements of concrete compressive strengths was also investigated. On other projects, the research was used to determine prestress losses, temperature gradients in the deck and girders resulting from daily and seasonal temperature changes, strand transfer length, long-term camber, and load distribution.
HPC CD Compilation
Information from the showcase bridges is being collected by the FHWA and compiled onto a compact disc (CD) for easy retrieval and viewing. An interim version of the CD will soon be issued by the FHWA. On the CD, the information is presented in two formats. The first format consists of the individual compilation for each bridge and includes a description of the bridge and information about the benefits of HPC, costs, structural design features, specified properties for HPC, approved concrete mix proportions, concrete material properties, research data measured during and after construction, sources of data, related research, and special provisions for HPC. The second format consists of ten tables that contain a summary of the primary information from the individual bridge compilations. The tables may be used to compare data from different states and different bridges. The CD also contains a search option that allows information on a specific topic to be quickly located.
Copies of the CD may be obtained from the FHWA by contacting Terry D. Halkyard by phone: 202-366-6765, fax: 202-366-3077, or email: [email protected]. The compilation can also be viewed and downloaded at www.nationalconcretebridge.org.