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Testing high performance concrete in NM

Andrew Giesler, a graduate student in civil engineering, and his team at New Mexico State University are testing ultra-high performance concrete bridge girders on a large scale to aid the development of bridge

New Mexico State University civil engineering graduate student Andrew Giesler examines data from a large-scale test on a bridge girder build with ultra-high performance concrete that is stronger and has a longer life than regular concrete. (Courtesy of NMSU)

New Mexico State University civil engineering graduate student Andrew Giesler examines data from a large-scale test on a bridge girder build with ultra-high performance concrete that is stronger and has a longer life than regular concrete. (Courtesy of NMSU)

design procedures for the state of New Mexico that could lead to a variety of improvements to the state’s infrastructure.

The concrete possesses dramatically increased compressive strengths, a very dense microstructure, and steel fibers that greatly improve post-cracking strength. These properties allow for the design of bridges that can have much longer design lives compared to those constructed with normal strength concrete.

Under the direction of Brad Weldon, assistant professor of civil engineering, Giesler conducted three large-scale flexural tests on 16-foot-long, prestressed UHPC bridge girders to evaluate their flexural strength. Graduate student Mark Manning assisted Giesler with the testing and will be conducting similar tests on a full-scale UHPC girder after Giesler graduates in fall 2014.

UHPC was designed to be stronger and more durable than average concrete.

To familiarize local producers with this material, the prestressed UHPC beams were mixed, cast, and cured at Coreslab Structures in Albuquerque, a company that donated a portion of the materials as well as their equipment and labor. The unique mixture design and consistency of this UHPC required careful observation as it went through the batching process. This particular UHPC, made primarily from New Mexico materials, had never been produced on a large scale prior to the casting of these beams.

“We needed to make sure that Coreslab’s facility would be able to accommodate this new concrete. Some of the procedures were new to them, however the entire process went very smoothly and according to plan,” Giesler said.

UHPC has a longer lifespan than average concrete. Whereas normal strength concrete bridges are designed to last approximately 50 years, UHPC bridges have been estimated to have design lives of up to 150 years.

The testing was to study the flexural behavior of the UHPC at a large-scale level to evaluate design procedures that can aid in the future development of standardized design codes. Previously, tests had been done on only small-scale rectangular beams. Large-scale tests provide a more realistic representation of how full-scale UHPC beams will behave in a structure such as a bridge.

“Large-scale testing provides much more accurate data. Hopefully, these tests will help to prove that UHPC can be designed both accurately, and efficiently, using simplified methods,” Giesler said.

Right now, the specific UHPC Giesler tested is not being used in any bridges. Giesler said there are commercially available UHPC’s that are being used in a few bridges in the United States, but the UHPC he tested would need to meet specific specifications before it can be used.

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