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Bioethanol By-product Boosts Concrete Strength
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A bale of corn stalks and husks
A doctoral candidate at Kansas State University has created a stronger, more environmentally responsible form of concrete by adding the ash that results from burning high-lignin residue to the mix. The residue is a by-product of corn stover ethanol production, a form of ethanol that is created using the fibrous material in corn stalks and husks. Warren Gretz/NREL

New research conducted by a doctoral candidate at Kansas State University has revealed a way to strengthen concrete while reducing its carbon footprint.

April 2, 2013—New research conducted by Feraidon Ataie, A.M.ASCE, a doctoral candidate in civil engineering at Kansas State University, has uncovered a way to create stronger, “greener” concrete using a bioethanol by-product: high-lignin residue.

The residue is created when such inedible organic material as wheat straw, rice straw, or corn stover is processed to create cellulosic ethanol, a biofuel. This biofuel differs from traditional biofuel in that it starts with inedible organic matter rather than with corn. (The by-product of using corn to create biofuel produces an edible by-product—distiller’s dried grains—that can be used as cattle feed.)

In Ataie’s study, the lignin residue was burned at a high temperature to create ash, which was then used as a partial replacement for portland cement in concrete. “The idea was to develop a highly reactive supplementary cementitious material using agricultural residues,” Ataie said in written responses to questions posed by Civil Engineering online. “Pretreatment methods such as dilute acid [that are] commonly used in bioethanol production improve the reactivity of agricultural residue ashes in cementitious systems,” he explained.

Working with a limited supply of high-lignin residue, Ataie found that replacing 20 percent of the portland cement in concrete with the ash produced by burning the lignin residue resulted in a 32 percent increase in concrete strength after the sample was allowed to cure for 28 days. Increased strength also was seen after only seven days of curing time.

According to Ataie, adding the ash to the concrete mixture also “could decrease concrete permeability and hence increase concrete durability.” This advantage, however, might not be desirable where permeable surfaces are desirable to help decrease water runoff into storm drains. (See “Group Seeks Sustainable, Integrated Water Projects,” on Civil Engineering online.) But it would be very good news in certain applications, for example, roadways that are often treated with deicers.

The use of lignin residue ash in concrete also decreases the so-called carbon footprint of the process of concrete production, according to Kyle Riding, Ph.D., P.E., M.ASCE, Ataie’s doctoral supervisor and an assistant professor in the civil engineering department at Kansas State, who was quoted in a press release issued by the university. The world uses nearly 7 billion m3 of concrete annually, he said, and concrete production accounts for between 3 and 8 percent of global carbon dioxide emissions because it is such a ubiquitous construction material.

“Using the high-lignin residue ash in concrete will reduce the environmental impact of concrete production as well as help [the] bioethanol industry, since the by-product gains value,” Ataie said. Researchers have shown that other additives also can decrease concrete’s carbon footprint. (See “Geopolymer Concrete Protects against Corrosion,” on Civil Engineering online.)

And there is more than one useful way to use lignin residue: early last year a student at the university discovered that, when mixed with water, powdered lignin residue can be used as a binding agent to strengthen the dry granular soils that are common on the state’s numerous unpaved roads. (See “Study Seeks to Improve Roads,” on Civil Engineering online.)

However, the different types of lignin residue are not necessarily interchangeable, according to Ataie. “Most of the lignin-based materials come from biomass, such as wood chips and agricultural residues,” he said. “The high-lignin residue that I have used was from corn stover ethanol, which contained silica.” The silica is an important component because after the lignin residue is burned to create ash, it is the remaining silica that becomes reactive when added to cementitious systems, he explained.

Ataie’s research was funded by a $210,000 grant from the National Science Foundation; the National Renewable Energy Laboratory, which has facilities in Golden, Colorado, and Washington, D.C., provided the lignin residue used in the tests. Antoine Borden, S.M.ASCE, a senior majoring in civil engineering at Kansas State, contributed to the research efforts, which were overseen by Riding.


 

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