Soil Stabilization with Bioenergy Coproduct

The production and use of biofuel have increased under the context of sustainable development. Biofuel production from plant biomass not only produces biofuel or ethanol but also coproduces products containing lignin, modified lignin, and lignin derivatives. The use of lignin-containing biofuel coproduct in pavement soil stabilization was explored as a new application area. The primary experimental test plan encompassed the comparison of coproduct-treated soils, untreated soils, and traditional stabilizer-treated soils in terms of their strengths. The focus of the secondary experimental test plan was to investigate the effect of additive combinations on strength improvement. The laboratory test matrix in each test plan included variations in additive type, additive content, curing period, and moisture condition. Statistical analyses were performed on unconfined compression strength test results to evaluate whether the strength improvements resulting from the addition of the coproducts to soils are significant. Results indicated that the biofuel coproducts are effective in stabilizing the Iowa Class 10 soil classified as CL or A-6(8). Strengths comparable to traditional additive (fly ash) could be obtained through the use of combined additives (Coproduct A  fly ash; Coproduct A  Coproduct B). The use of biofuel coproduct as a stabilization material for soil appears to be one of many viable answers to the profitability of the biobased products and the bioenergy business. Disciplines Bioresource and Agricultural Engineering | Civil and Environmental Engineering Comments This article is from Transportation Research Record: Journal of the Transportation Research Board, 2186 (2010): 130-137, doi: 10.3141/2186-14 . Posted with permission. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ccee_pubs/22 streams to improve the economics of the bio-based products and the bioenergy business. The natural soil deposits do not always possess the requisite engineering properties to serve as qualified geotechnical materials for construction. As a result, well-established techniques of soil stabilization are often used to improve the properties of geotechnical materials through the addition of binding agents into soil (5). The soil-stabilizing additives or admixtures traditionally used include hydrated lime, portland cement, and fly ash. The standardized practical guidelines for these traditional stabilizers have been established by previous researchers including Little and coworkers (6–9), Thompson (10, 11), and many others (8). The use of waste materials and by-products in various industrial applications continues to gain attention under the concept of sustainable development, which meets the needs of the present without compromising the ability of future generations to meet their own needs (12). Various industrial by-products have been applied in soil stabilization (8). Edil et al. (13) evaluated a variety of industrial by-products for stabilization using a 1.4-km section along a Wisconsin state highway. They reported that stabilized sections provided adequate support for the construction equipment without pavement distress. The use of lignin in soil stabilization has been studied over the past decades (14–19). Adding lignin to clayey soils increases the soil stability by causing dispersion of the clay fraction (20, 21). According to Gow et al. (21), the dispersion of the clay fraction benefits stability of the soil–aggregate mix by (a) plugging voids and consequently improving water tightness and reducing frost susceptibility, (b) eliminating soft spots caused by local concentrations of binder soil, (c) filling voids with fines and thus increasing density, and (d) increasing the effective surface area of the binder fraction, which results in greater contribution to strength. Most of the previous lignin-related soil stabilization studies investigated sulfite lignins (lignosulfonates) derived from paper industry, whereas the lignins obtained from biofuel or ethanol production are sulfur free. Even though sulfur-free lignins have been known for many years, the use of sulfur-free lignin has recently gained interest as a result of diversification of biomass processing schemes (22). Little study has been conducted to examine the use of biofuel-derived sulfur-free lignins for soil stabilization. The current study aims to investigate the use of biofuel coproduct containing sulfur-free lignin in pavement soil stabilization. Increased load-bearing capacity is used as the basis of performance characterization, as indicated by unconfined compression strength (UCS). Two experimental test plans, primary and secondary, were made to evaluate the coproduct effectiveness as soil stabilizer. The primary experimental test plan encompassed the comparison of coproduct– treated soils, untreated soils, and traditional stabilizer-treated soils in terms of their strengths. The focus of the secondary experimental test plan was to investigate the effect of additive combinations on strength improvement. The laboratory test matrix in each test plan included variations in additive type, additive content, curing periods, and moisSoil Stabilization with Bioenergy Coproduct Halil Ceylan, Kasthurirangan Gopalakrishnan, and Sunghwan Kim The production and use of biofuel have increased under the context of sustainable development. Biofuel production from plant biomass not only produces biofuel or ethanol but also coproduces products containing lignin, modified lignin, and lignin derivatives. The use of lignin-containing biofuel coproduct in pavement soil stabilization was explored as a new application area. The primary experimental test plan encompassed the comparison of coproduct-treated soils, untreated soils, and traditional stabilizer-treated soils in terms of their strengths. The focus of the secondary experimental test plan was to investigate the effect of additive combinations on strength improvement. The laboratory test matrix in each test plan included variations in additive type, additive content, curing period, and moisture condition. Statistical analyses were performed on unconfined compression strength test results to evaluate whether the strength improvements resulting from the addition of the coproducts to soils are significant. Results indicated that the biofuel coproducts are effective in stabilizing the Iowa Class 10 soil classified as CL or A-6(8). Strengths comparable to traditional additive (fly ash) could be obtained through the use of combined additives (Coproduct A + fly ash; Coproduct A + Coproduct B). The use of biofuel coproduct as a stabilization material for soil appears to be one of many viable answers to the profitability of the biobased products and the bioenergy business. Sustainable use of natural resources continues to gain attention to replace fossil-based energy and reduce carbon dioxide contribution to green house gases (1). Even though various natural resources (e.g., wind, sun, water, biomass) can be recognized as alternative sustainable resources to fossil fuels, biomass, in particular, plant biomass, is considered to be one of the most economical recourses and is transformed into bio-based energy such as biofuel and ethanol (2). Biofuel production from plant biomass also produces many different coproducts that have many unexplored uses (3). The type of coproducts produced depends on the method of biofuel production and coproducts recovery method, as well as the source of biomass. Among many different coproducts is a lignin-containing coproduct, which has been considered as a waste material or a low value coproduct, with its use predominantly limited to use as a fuel in the production of octane boosters and in bio-based products and chemical productions (4). Considering that lignin represents the third largest fraction of agricultural biomass, increasing amounts of lignin as biofuel coproduct will become available with the expansion of the lignocellulosic biofuel production industry. Newer uses of biomassderived lignin need to be developed to provide additional revenue H. Ceylan, 482B Town Engineering Building; K. Gopalakrishnan, 353 Town Engineering Building; and S. Kim, 192 Town Engineering Building, Department of Civil, Construction, and Environmental Engineering, Iowa State University, Ames, IA 50011-3232. Corresponding author: S. Kim, [email protected]. Transportation Research Record: Journal of the Transportation Research Board, No. 2186, Transportation Research Board of the National Academies, Washington, D.C., 2010, pp. 130–137. DOI: 10.3141/2186-14