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At the very heart of research is the desire to push the limits of technology and imagination—to create new boundaries for possibility. This desire is the very essence of what College of Engineering & Technology researchers have undertaken as they strive to test the limits of how much fly ash can be used in concrete mixes to create a product that is environmentally friendly, cost-effective and structurally sound.

Professor Berryman stands next to a concrete culvert that contains 25 percent fly ash. The culvert is a product of Concrete Industries.
Samy Elias, Sherif Yehia, Charles Berryman and Maher Tadros recently received a grant from the Appalachian Transportation Institute of Marshall University to research the “Utilization of Fly Ash in Reinforced Concrete Transportation Applications.” The primary aim of the research is to identify the most promising applications of fly ash in reinforced concrete: lightweight masonry blocks, concrete pipes, concrete overlays for highway bridges, pre-cast retaining walls and pre-stressed concrete ties, in which large volumes of fly ash safely can be used. Secondly, the researchers sought to come up with the best design mix of fly ash and cement at the lowest cost for each of these applications, as well as to test the design mixes for the qualities of good concrete. “We are trying to come up with the best recipe,” Tadros said.

At the height of the Roman Empire, builders began making cement by mixing slaked lime with pozzolana, a volcanic ash from Mount Vesuvius, an extraordinary combination because it produced cement capable of hardening under water and enabled construction of the infrastructure, including roads, aquaducts, temples and palaces. As the Roman Empire declined and the Dark Ages came to pass, the use of concrete nearly disappeared. Then in 1824 Joseph Aspdin, a British stone mason, burned finely divided clay with finely divided chalk in a lime kiln until the carbon was burned off, producing “Portland cement,” the same cement used today.

The use of fly ash in concrete is an innovative junction of abundant resources. Concrete is the world’s most widely used building material with annual global production exceeding 5 billion cubic yards. Concrete, a composite material, is made up of a filler and binder. The typical concrete is a mixture of fine aggregate (sand), coarse aggregate (rock), cement and water. Concrete is, in many ways, the perfect construction material because it is durable, malleable and resistant to the elements.

Each year, power plants in the United States produce millions of tons of fly ash, a fine-grained, powdery material made up of tiny glass spheres and consisting primarily of silicon, aluminum, iron and calcium oxides. This fly ash is a byproduct of burning coal at electric utility plants. More than two-thirds of all fly ash produced has to be disposed of in landfills at great expense to power utilities. The remainder, however, is used in beneficial applications researchers continue to explore. In 2001, for example, U.S. utility plants generated about 71.2 million tons of coal fly ash, with about 25.1 million tons used productively, more than twice the average annual amount of fly ash used productively between 1985 and 1995.

When cement, fly ash and aggregates are combined, they yield a concrete that is lighter, more durable and more cost effective. Although fly ash can be used to improve the workability of concrete as a replacement for fine aggregates, it is most useful when added as a material to replace a portion of the Portland cement that normally would be used in a given batch of concrete.

Stress Test
In a before and after stress test, small cylinder concrete models are randomly tested to insure the concrete mix is correct and will withstand the stress of the actual cylinder structure they build.

Elias, associate dean for research, is focusing on using a combination of fly ash and cement to build railroad ties that are stronger and more environmentally sound. “Wood is scarce and must be treated, and that treatment is harmful to the environment,” Elias said. His research focuses on answering questions about the strength and durability of fly ash-based concrete as it relates to pre-stressed concrete railroad ties that have a higher load capacity, minimal maintenance cost and no negative impact on the environment.

Tadros, a professor in civil engineering, is researching the use of fly ash in retaining walls and concrete overlays for highway bridges. As early as 1996, Tadros and his research team participated in the construction of the first high-performance concrete bridge in the United States, in Sarpy County. “At this point, we’re continuing to refine the process,” Tadros said. “We want to use as much fly ash as possible in concrete mixes, while enhancing the mechanical properties of the resulting concrete.”

Berryman, associate professor in construction management, is focusing his research efforts on the utilization of fly ash in concrete pipes used for culverts, drainage and other similar applications. Berryman and his graduate student, Jingyi Zhu designed and tested six different mixes. After reaching optimization, they went to Concrete Industries, where fly ash is used in most products, to try their mixes in the field.

Doug Mohrman, sales and marketing manager at Concrete Industries helped coordinate the logistics. “We always try to work with the university on research,” Mohrman said. “We are interested in coming up with a better mousetrap, so to speak, so it is in our best interests to lend a hand. If the research succeeds, it will ultimately lower our costs.” And lend a helping hand, Concrete Industries has. They’ve provided the use of their pipe plant, the cement, aggregates, equipment and people, including president Bob Nordquist, production supervisor Mike Mueller, pipe division foreman Bill Shottenkirk, assistant foreman Monte Polivka and Steve Austin in pipe quality control.

“Without the help of Concrete Industries, this project would not have gotten off the ground,” Berryman said.

Once the experimental concrete was mixed, three-edge bearing tests were run, to determine the maximum load that could be applied to a piece of pipe, chosen at random, to produce a crack with a width of 0.01 inch throughout a continuous length of 1-foot pipe. The results of the tests run on the concrete yielded from Berryman’s six design mixes were compared with the results of current concrete design mixes. The experimental design mixes fared evenly, if not better.

And yet, there are obstacles in the researchers’ path. The quality of fly ash can be inconsistent because it is, after all, an industrial byproduct. However, researchers are learning to work within those limitations. “As the technology evolves, the quality of fly ash is becoming very good,” Berryman said. “And that technology offsets many of the variables faced when fly ash was first introduced to the concrete industry.” The logistics of working with fly ash also are a constraint.

“You need to worry about how to get the fly ash to the mixing plant, how to store it and how to prevent moisture from affecting it,” Tadros said.

As with anything relatively new, there are questions about the integrity of concrete made from fly ash. Are structures built with fly ash concrete safe? Are there long-term repercussions for using this type of concrete? Studies have shown that concrete made from fly ash mixes gain strength over time because the fly ash particles are smooth and round and blend together with cement and aggregates seamlessly. And while the use of fly ash is becoming increasingly widespread, there still is a segment of the industry that views fly ash as a harmful energy byproduct. “It has been a gradual process, convincing people in the industry to use fly ash,” Berryman said. “But it is being used far more than people realize.”

The biggest obstacle, nevertheless, is the fact that the American Society for Testing and Materials (ASTM) currently permits only a 25 percent Portland cement replacement maximum for fly ash, while Berryman’s research has shown that mixes of up to 65 percent fly ash replacement with Class C fly ash and 40 percent with Class F fly ash yielded concrete that met the specifications required by ASTM for Class 3 pipe. It will now be up to researchers, wielding these results, to convince ASTM and the American Association of State Highway and Transportation Officials (AASHTO) that the minimum can be dropped, opening the door for partners in the concrete industry to use a higher percentage of fly ash in their mixes. Berryman will be presenting his case this August at the annual AASHTO conference.

Despite the challenges they are facing, Berryman, Elias, Yehia and Tadros have met with a great deal of success. Cost analysis has shown that increased percentages of fly ash in concrete mixes could potentially save the industry millions of dollars each year. In the near future, researchers will continue to increase the percentage of fly ash used in concrete mixes, as well as explore different additives and manufacturing processes that may lead to more cost-effective and better performing concrete mixes. They also will explore other productive applications within the concrete industry for the ever-abundant fly ash.

“This type of research will be around for a long time to come,” Berryman said.