Improving Soil Strength Under Roads with Ethanol Co-Products
Iowa?s soil is great for growing corn. But it?s not so great for building roads. Iowa?s soil is mostly soft clay and till deposited by glaciers. It?s hardly the bedrock engineers would like for a good, solid roadbed. Thus, it is common practice to mix soil with chemicals to stabilize the road soil properties. This improves soil strength and makes for better roads.
Due to the limitations associated with the conventional stabilization methods with respect to high initial costs, applicable to only specific soil types and require certain site conditions, civil engineers are always looking for new chemicals that can provide a better soil stabilization. They are also exploring the possibility of using the new chemicals along with cement, lime or other existing chemicals to alleviate some of the above mentioned limitations faced by the individual chemical treatments.
This has led researchers at Iowa State University (Halil Ceylan and Kasthurirangan Gopalakrishnan) to investigate whether lignin, a co-product of producing ethanol from plant fibers, could be a good soil stabilizing agent. Their research is partially supported by a $93,775 grant from the Grow Iowa Values Fund, a state program that promotes economic development. The Iowa Highway Research Board, Grain Processing Corp. of Muscatine and Iowa State’s Office of Biorenewables Programs are also supporting the project.
Various researches who have studied lignin as a soil additive have all concluded that lignin is primarily a cementing agent. The natural cementing sugars in lignin appear to perform the same fundamental function when combined with soil particles. The cementing effect helps with stabilization by increasing the true cohesion between soil particles.
Previous Iowa State studies of lignin from the paper-making industry found it to be a cementing agent that could be of value for soil stabilization. But nobody has determined if that’s also the case for lignin from ethanol production. It is expected that the lignin derived from lignocellulosic biorefineries will see similar success, if not better.
Lignin from the paper-making industry has successfully been used to treat unpaved roads in Europe, Canada, and United States since the 1920s. A large portion of U.S. road network is made up of unpaved roads that usually carry a very small volume of the nation’s vehicular traffic. The use of unpaved roads causes dust emission into the atmosphere, loss of the road surface material over time, and frequent road surface deterioration in the form of ruts, washboarding, and potholes. Influenced by the traffic volume, these problems can lead to high economic cost. To reduce the loss of road surface fines in the form of dust, chemical additives (dust suppressants) are applied to the unpaved road surface to control dust generation and to improve the road surface stability. Field observation of the lignin-treated test sections in the past have indicated that the lignin acted like cement, binding the soil particles together into a hard surface that show strength gains over time. In the future, we intend to investigate the effectiveness of lignin from ethanol production as dust suppressants on unpaved roads in Iowa.
The researchers hope they come up with a new technology that is good for road builders, good for drivers, good for the environment and good for the cellulosic ethanol industry. The research could also be a big help to the people who build and maintain Iowa’s roads, especially as ethanol plants increase truck traffic through rural areas.