Just east of Jefferson City, Mo., sits a construction site that will soon be home to one of the nation’s first bridges to incorporate an unusual concrete mix in its girders and support structure. The three-span bridge, which is scheduled to be completed this fall on Highway 50, will also be outfitted with various sensors and instrumentation to collect data on how well the bridge performs over time.
It’s another milestone for Dr. John J. Myers, a professor of civil, architectural and environmental engineering at Missouri University of Science and Technology working with the Missouri Department of Transportation and Missouri S&T’s National University Transportation Center. Myers has spent the past decade studying and testing high-strength concrete and other innovative concrete systems for implementation.
“In 2012, we completed a two-year study that examined overall behavior of self-consolidating concrete, or SCC, using locally available materials including natural river sands, dolomitic limestone aggregates and river gravels,” Myers says. The study examined the concrete and steel reinforcing material’s shear strength, transfer and development length, creep and shrinkage as well as key durability attributes.
Myers and his team found that using high-strength self-consolidating concrete, or HS-SCC, can either extend the span length of the HS-SCC girders, a structure’s main support member, or reduce the number of girder lines needed in a given span.
“That’s because this material can allow for additional prestressing tendons, which can increase the girder’s load-carrying capacity,” says Myers.
Myers says they also expected the material to have reduced maintenance costs and an extended service life compared to conventional concrete due to the HS-SCC’s improved durability behavior.
Concrete typically has four key components: portland cement, water, fine aggregate like sand and course aggregate or rock. In HS-SCC, the course aggregate is finer and chemical mixtures are added to increase its flow rate. That allows it to flow into every corner of a form work, by its own weight, eliminating the need for vibration or other types of compacting effort that requires more labor at the precast plant or job-site.
“It’s a more efficient use of the material,” Myers says. “With its increased strength, it can extend a span’s length by 20 percent or more.”
The new bridge will combine three different types of concrete grades in the girders. The first 100-foot span will use traditional concrete. The second, 120-foot span, will use high-strength, self-consolidating concrete. The final span will use self-consolidating concrete. Using sensors embedded in the material, researchers will monitor to see any differences as they occur. The bridge also includes instrumentation that will allow the research team to collect important data during load testing and normal in-service conditions.
“The advantage of having one bridge demonstrating four to five types of concrete throughout the entire bridge is that you know the exposure conditions, salts, temperatures, weather conditions are all identical,” Myers explains.
In addition, one intermediate support will use concrete with a high-replacement level of fly ash, fine particles from coal are the by-product of a power plant’s combustion process. During the manufacture of traditional cement, limestone and other materials are heated to extreme temperatures, releasing of CO2 from both chemical reactions and the heating process. By replacing half of the cement with fly ash, the mix not only reduces the amount of fly ash that ends up in landfills but will cut CO2 emissions as well. It also will make for a more cost-effective concrete mix, which will reduce construction costs.
The state’s first bridge to use high-strength, self-consolidating concrete was constructed in 2009 in Rolla and led by Myers’ research group. The bridge, designed for rapid construction, was one of two built to demonstrate the mechanical and material properties of high-strength concrete and high-strength, self-consolidating concrete.
Dr. Jeffery Volz, a former Missouri S&T assistant professor of civil, architectural and environmental engineering, is working with Myers on the research.