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MOISTURE SUSCEPTIBILITY OF SUBGRADE SOILS STABILIZED BY LIGNIN-BASED RENEWABLE ENERGY COPRODUCT

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• Among the various natural resources is biomass, in particular, plant biomass, which is considered a renewable source of energy, such as biofuel and ethanol, and an alternative to fossil fuels.

• Plant biomass is a lingo cellulosic material consisting of cellulose, hemicellulose, and lignin.

INTRODUCTION

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• Lignin, is a large complex polymer of phenyl propane and methoxy groups, a non carbohydrate poly phenolic substance that encrusts plant cell walls and cements plant cells together.

• It is not possible to define the precise structure of lignin as a chemical molecule.

• The definition in common is, it is a dendritic network polymer of phenyl propane basic units.

4Fig: Structure of Ligninsource: http://www.ili-lignin.com/aboutlignin.php

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EXTRACTION OF LIGNIN

Lignin is extracted from biomass by

• Formic acid/acetic acid treatment• Peroxy formic acid/peroxy acetic acid (PFA/PAA) treatment• Bleaching• Isolation of lignin

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FORMIC ACID/ACETIC ACID TREATMENT:

• Known as Pulping.

• Biomass cut into small pieces placed in a conical flask.

• 85% organic acid mixture is added to the flask.

• Flask is boiled on a hot plate for 2 hours and then cooled.

• Contents are filtered in a funnel and washed with 80% formic acid followed by hot distilled water.

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PEROXY FORMIC ACID/PEROXY ACETIC ACID TREATMENT:

• Filtered matter is delignified by treating with PFA/PAA in hot water bath at 80°c for 2 hours.

• Delignified matter is filtered to separate cooking liquor from cellulose and washed with hot water.

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BLEACHING

• Delignified fibers treated with 14ml 35% H2O2 solution in hot water bath at 8°c for 2 hours.

• It is washed with distilled water to remove residual lignin.

• Process is repeated to remove lignin completely.

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ISOLATION OF LIGNIN

• After Pulping and Delignification, residue is heated at 105°c.

• Precipitated by adding distilled water and then filtered.

• Precipitated lignin is washed with distilled water and vacuum dried over P2O5.

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SOIL STABILIZATION

• Process of blending and mixing materials with soil to improve properties of geotechnical materials.

• Traditional soil stabilizing additives includes hydrated lime, Portland cement and flyash.

• Lignin also plays a positive role in soil stabilization.

• Lignin increases soil stability by causing dispersion of clay fraction.

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EXPERIMENTAL PROGRAM

MATERIALS:• Soil: Natural soils collected from a construction site in Calhoun

country.

• Additives: Two types of Biofuel co-products are taken.

Co-product A - dark brown, free flowing liquid fuel with a smoky odor formed in a process called fast pyrolysis wherein plant material are exposed to 400–500°C in oxygen free environment.

Co-product B - Powdered Alkaline-washed corn hull obtained in the process of converting corn into ethanol.

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• Co-product A contains about 25% lignin and up to 25% water with a pH value of 2.2.

• Co-product B contains about 5% lignin, 50% hemicellulose, 20% cellulose, and other components.

• Ottumwa Class C fly ash is selected as the traditional additive against which we compare biofuel co-products.

• It is a coal combustion by-product obtained from Ottumwa the Generating Station (OGS) located near Chillicothe, Iowa.

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TESTS:

• UCS tests after “dry” and “wet” conditioning

• Dry and wet specimens are subjected to UCS tests to evaluate the moisture susceptibility of additive-treated specimens.

• The stabilization effect of a soil additive is measured in terms of the increase in load bearing capacity as indicated by UCS.

• Visual observations of Soaked specimens.

• Specimens are fully soaked in water and observed to see if they fail because of moisture.

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SPECIMEN PREPARATION:

• Natural soil collected is dried and broken down to pass through 4.75mm IS sieve.

• Additives are also dried to remove initial water, making homogenous soil blend.

• The additives are Co-product A, Co-product B, Co-product A/flyash, Co-product A/Co-product B mixtures.

• From experience the amounts of additives are found to be 12% of uncombined additive, 10% Co-product A/2% flyash and 10% Co-product A/2% Co-product B to provide strong soil mixtures.

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• Untreated soil mixtures with no additives are also prepared.

• Blended soil samples are statically compacted in the cylindrical mould (51 × 51 mm).

• Compacted specimens are allowed to cure at 25°C and 40% relative humidity.

• Curing periods are 1 and 7 days after sample preparation for the UCS test.

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Unconfined Compression Strength Test:

• Compacted specimens of each mixture are subjected to dry and wet preconditioning procedures for UCS tests.

• Specimens in the dry precondition are tested without water saturation, whereas specimens in the wet precondition are tested after specified water saturation procedures.

• The wet test procedure in this research included full saturation and half-saturation of the specimen.

• Full saturation requires complete immersion of the specimen on its side in a water bath for 1 h.

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• Half-saturation is conducted because some of specimens are broken in full saturation.

• One side of the specimen is soaked in water for 5 min. A specimen subjected to full saturation or half-saturation was then removed from the water and allowed to drain for 5 minutes. The specimen was then subjected to UCS testing.

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Fig: Fly ash-treated specimen under half-saturation procedure

Source: Journal Of Transportation Engineering © Asce / November 2012 / 1283

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Experimental Treatment Group Combinations for UCS Tests:

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Soaking Test:

• Compacted specimens of each mixture after 1 day of curing are subjected to soaking tests.

• Specimens are fully soaked in water.

• Two sets of specimens are prepared for these tests.

• Test Set 1 include Untreated soil (pure soil) 12% fly ash-treated soil 12% Co-product A-treated soil and 12% Co-product B-treated soil.

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• Test Set 2 include 10% Co-product A/2% fly ash and 10% Co-product A/2% Co-product B-treated soil.

• Specimens were observed for failure for 7 days after soaking.

Fig: Soaking tests: (a) Test Set 1; (b) Test Set 2Source: Journal Of Transportation Engineering © Asce / November 2012 / 1283

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RESULTS AND DISCUSSION UCS Test Results:

Fig: Results of UCS tests

Source: Journal Of Transportation Engineering © Asce / November 2012 / 1283

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Fig: Results of UCS tests

Source: Journal Of Transportation Engineering © Asce / November 2012 / 1283

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Fig: Results of UCS tests

Source: Journal Of Transportation Engineering © Asce / November 2012 / 1283

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• Additive-treated soils are in all cases stronger than untreated soils under dry and wet conditions.

• The fly ash-treated soil test results show the most improvement in UCS under dry conditions.

• However, fly ash-treated soil specimens disintegrated in the wet precondition or are reduced in strength after the wet precondition compared with co-product-treated soil specimens.

• Duration of curing has less influence on the strength gain of soil specimens treated with Co-product B than on other soil specimens.

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• Quantitative assessments of the degree to which additives improve strength and moisture resistance are made using the following equations.

SI(%) =

• SI - percentage strength improvement under dry condition • SAD - average strength of additive-treated soil specimen under dry

condition• SCD - average strength of control (pure soil).

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MR(%) = x100

• MR = percentage moisture resistance• SW = average strength of specimen under dry condition• SD = average strength of specimen under wet condition.

• For this experiment, significant strength improvement was defined as a SI value >100%

• Effective moisture resistance was defined as a MR value <50%.

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Moisture Resistance values

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Soaking Test Results:

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• The specimens that did not deteriorate at the conclusion of the soaking tests are then subjected to UCS testing.

• The UCS values of these specimens are as shown in Fig.

Fig UCS test results of un deteriorated specimens

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CONCLUSION

• Co-product A with higher lignin content is more effective in providing moisture resistance than Co-product B with lower lignin content and fly ash.

• Additive combinations of 10% Co-products A+2% fly ash and 10% Co-products A+2% Co-product B provide moisture resistance comparable to that provided by Co-product A alone.

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• Productive utilization of biofuel co-product as a stabilization material for soil have considerable benefits for sustainable development.

• These products could be used to improve the moisture resistance of existing subgrade materials, thereby arresting the deterioration of pavement systems.

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REFERENCES

• Kim,Sunghwan.,Gopalakrishnan, Kasthurirangan and Ceylan ,Halil.,2012, Moisture Susceptibility of Subgrade Soils Stabilized by Lignin-Based Renewable Energy Co-product, Journal Of Transportation Engineering © ASCE, 138(11),1283-1290.

• Demirbas,M.F.,and Balat,M.(2006).“Recent advances on the production and utilization trends of bio-fuels: A global perspective.” Energy Conversion and Management, 47(15/16), 2371–2381.

• http://www.ili-lignin.com/aboutlignin.php Accessed on July.31,2016.  

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