More than 70 percent of the 98,000 mi of roads in Kansas, such as this one south of White Cloud, in Doniphan County, remain unpaved. Courtesy of the Kansas Department of Transportation
A new study being conducted at Kansas State University explores the use of lignin, a waste product of biofuel and paper production, to improve the cohesion of granular soils.
January 24, 2012—A new Kansas State University research project—partially funded by the University Transportation Center—is being conducted with the hope of finding a sustainable solution to the deterioration experienced by the State of Kansas’s rural, unpaved roads. The project explores the use of lignin, a component of plant cell walls and a waste product from the production of biofuel and paper, to improve soil cohesion.
According to Wilson Smith—a master’s student in civil engineering at Kansas State University and the transportation center’s student of the year in 2011—more than 70 percent of the 98,000 mi of roads in Kansas are unpaved. As Smith notes in a video released by the university, the erosion of unpaved roads caused by wind and traffic are a well known issues within the state.
“One of the problems with unpaved roads is that they are made from loose granular soils with particles that are not bound to each other on the road surface,” Smith said in a press release issued by the university. “This limits the speed of vehicles and often generates a lot of dust, denigrating the quality of the road.”
Lignin is a sustainable solution to the problem because it “is a nontoxic alternative to such traditional soil stabilizers as fly ash or type I portland cement, which can contaminate soil,” Smith wrote in response to written questions submitted by Civil Engineering magazine online.
By exploring the use of lignin as a binding agent, Smith is seeking to understand what concentration of lignin can be used to optimize soil stability and cohesion. According to Smith, lignin is an amorphous powder that is extracted from plant biomass and is often an unused by-product of biofuel production, a characteristic that has become more significant for Kansas roads because construction of the nation’s first commercial-scale cellulosic ethanol plant has recently begun in Hugoton, located in the southwestern portion of the state.
Smith’s advisor, Dunja Peric, Ph.D., A.M.ASCE—an associate professor of civil engineering at the university—wrote in response to questions submitted by Civil Engineering magazine online that lignin is attractive as a sustainable solution because it is a waste product that is readily available. “Lignin is [a] natural and environmentally friendly material. It is nontoxic and it does not alter [the] pH of treated soils,” she says. “In addition, it is applied in small amounts, which are not likely to affect the groundwater chemistry.”
In Smith’s research, dry sand is mixed with various concentrations of powdered lignin and water. Once the water is added to the mixture it metamorphoses from loose granular material into a claylike material. The mixture is placed in a mold and compressed, then removed from the mold and left to dry. After drying, the lignin-treated sand “becomes almost like rock,” Smith says in the video.
Smith then tests the strength of the mixtures using a direct shear device that simulates the stress created by cars and heavy machinery as they drive on unpaved roads.
“This research is really like a tip of an iceberg,” Peric says. While product application methods in a lab will differ from those used in the field, “the product performance can and must be assessed on the smaller scale in the lab before larger scale field testing and applications are attempted.”
Smith’s project is the second study directed by Peric that tests lignin’s ability to stabilize cohesionless soils. Graduate student Paul Bartley, under her direction, conducted a study of the very early strength gains experienced by sand mixed with lignin and water, which he recently submitted and defended for his master’s degree.
Bartley’s early results indicate that lignin concentrations of between 6 and 9 percent show the highest strength benefits. The testing that Smith conducts this spring will explore how the strength of those, and other, mixtures develop over time.
Smith is delivering a presentation entitled “Feasibility of Using Lignin: Plant Derived Material for Stabilization of Unpaved Roads” at the Capitol Graduate Research Summit in Topeka next month, and anticipates submitting his master’s thesis this summer. The Capitol Graduate Research Summit is an annual event in Kansas designed to expose state officials, educators, and the public to current research being conducted by graduate students within the state.
The Rothschild, Wisconsin, location of Borregaard LignoTech USA, Inc. donated the lignin used the studies.