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UW Professor Creates Solid Educational Foundations

February 4, 2016
Jennifer Tanner Eisenhauer discusses concrete properties with a student.
Jennifer Tanner Eisenhauer discusses concrete properties with a student.

As Caleb Jennings stares intently at the computer screen, he carefully manipulates a hydraulic pump to send forces through a wood-framed wall positioned a few feet away. The tension–both literal and figurative–is palpable.

The wood frame groans and creaks from the force and eventually, screws begin to separate from the wall. Finally, a noticeable chasm appears across the concrete. The wall has ruptured, but this in itself is a victory. In Jennifer Tanner Eisenhauer’s lab, success is determined by failure.

Tanner is an assistant professor of civil and architectural engineering at the University of Wyoming. She spends her days supervising graduate students who build up walls or structural elements and break them down. The final deliverable is information on how well current design procedures, such as structural codes, work to predict the performance of buildings. Her teaching and research into structures will benefit people, and her students will go on to design and build safe, sustainable and efficient structures.

“I want them to understand advances in building construction and I want them to be passionate about the materials they use,” she says. “We do research on innovative uses of materials or technology, with the expectation that they become lifelong learners.”

Alkali-Silica Reactions

As one of Tanner’s graduate students, Bryce Fiore of Castle Rock, Colo., performs research in an area called alkali-silica reaction (ASR) within concrete. Aggregate (materials that provide the foundation for concrete) reacts with cement paste, forming a gel that absorbs water and expands. That leads to failure, with implications for buildings, walls and foundations. ASR was discovered in the 1940s, and “we still haven’t figured it out, so it’s a big deal,” Fiore says.

Fiore is studying the use of fly ash to mitigate the effects of ASR. He casts concrete prisms and tests aggregates over a period of time to see which fly ash is effective at reducing the harmful effects of ASR from Wyoming aggregates. Although fly ash is an effective mitigator for ASR, the most reliable test method can take up to two years—a time period not feasible for entities with large construction projects. Tanner and Fiore are exploring a method to reduce the test time to one week without sacrificing accuracy. Entities like the Wyoming Department of Transportation (WYDOT) can use results from university studies to make choices regarding material use, so roadways and new construction are directly affected from the results of these tests. Materials testing at UW can help WYDOT find best practices or alternatives to current problems related to concrete performance.

“Another goal of this research is to give WYDOT more choices,” Tanner says. “By optimizing our resources we can use the most effective fly ashes with appropriate aggregates.”

Fiore has also tested recycled aggregate, using materials from old buildings to form new ones, to improve sustainability and cost efficiency.

“There is a lot of material that’s just being thrown out,” he says. “We only have so much rock. You continue mining pits, and you have to go farther and farther away. If you demolish something in town, it’s closer so you don’t have to go as far. If you find you can use that aggregate to achieve the same strength, why not?”

Autoclaved-Aerated Concrete

Another part of Tanner’s research deals with a specialty precast concrete that is lightweight, thermally and acoustically insulating and has excellent fire resistance. It’s called autoclaved-aerated concrete, and its properties can mean more sustainable buildings with lower lifecycle costs.

Jennings of Greybull, Wyo., and Shane Wilson of Green River, Wyo., focus their efforts on AAC. Wilson performs out-of-plane load testing to replicate wind forces on AAC walls, using a vacuum seal to apply area load. He built the test setup from scratch, comparing it to building a giant puzzle.

“If you were to do this the standard way, it would cost you 10 times more,” Wilson says. “Or you can get creative and come up with something. I like those kinds of challenges, so that’s why this project was so appealing.”

Jennings uses hydraulic pressure for shear wall tests to determine in-plane shear resistance. Most buildings built with AAC include shear walls to resist lateral forces like wind and seismic. He also performs floor diaphragm tests along with a variety of material property tests.

AAC is a porous, pre-cast material. The concrete slurry is mixed with aluminum powder, causing a rising action similar to bread dough. After it expands to a set volume, it is then put into a heated autoclave, which cures it quickly. It produces a much lighter material than standard concrete, at about 20 percent of the unit weight. Although strength is sacrificed in the process, it is an effective building material for structures up to six stories. It’s resistant to mold and rot, fire, has good acoustic properties and is easy to work with because it can be easily cut with hand or power tools. However, construction is limited to that near production plants and some contractors are not familiar with construction practices.

“The U.S. has not been using AAC very much,” Jennings says. “Europe has been using it since the 1920s. There’s a market for it, especially as people are wanting to go green. What this research does is provide design values to aid in the development of an AAC building code. That’s the void we’re trying to fill.”

Hands-on Learning

While the subject material is different for undergraduates and graduates, Tanner’s teaching methods are the same, featuring hands-on, active projects. In a lab packed with juniors, she uses a uniaxial test machine to determine the compressive and tensile strength of concrete cylinders or beams. Students use these results in a technical report that is similar to a typical civil engineering report.  In a separate lab, students participate in fracturing a steel reinforcing bar. Such bars are used to carry tension in reinforced creating concrete structures. A machine slowly pulls the bar apart from both ends until an audible snap.

Concrete is the most abundant and widely used building material in the world, so these tests help engineers determine how to make it stronger and more resistant to movement. It can help make buildings safer and more durable in extreme events such as earthquakes or tornados. She teaches her classes with an emphasis on material behavior, so when changes come about in a design code, her students can accept them more easily. Under her supervision, every student that goes through the junior-level course in materials touches three out of the four main building materials: concrete, steel, masonry and timber.

Recently Tanner was named a Fellow for the American Concrete Institute.  Her involvement in ACI includes chairing committee 526, Autoclaved Aerated Concrete and co-chairing 440L, Durability of Fiber Reinforced Polymers.

Her Ph.D. dissertation was developing language for integrating AAC into the masonry code.  Over the past decade she has served on the masonry code committee that is overseen by The Masonry Society. She has been involved with several committees including flexure, axial and shear; seismic; and infills. As changes are incorporated into this code, she can integrates into her curriculum. One of her work products is a set of masonry course notes through TMS.  Currently she is working on a masonry textbook with McGraw Hill.

“One thing I think we do well is in our classes is we use the building codes so our students are used to this process,” Tanner says. “They are far more ready than students who are not exposed to structural codes in the classroom.”

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