Degree Type


Date of Award


Degree Name

Master of Science


Civil, Construction, and Environmental Engineering


Civil Engineering (Civil Engineering Materials)

First Advisor

Halil Ceylan


Rapid advancements in bioenergy-based industry have not only reduced our dependency on fossil resources but also brought about sustainable development for human society. The production of biofuel derived from biomass also produces co-products containing lignin. Biofuel co-products (BCPs) containing sulfur-free lignin were investigated in this research study to gain further insight into their benefits in stabilizing pavement subgrade soil. Three different types of co-products were tested: (1) a liquid type with medium lignin content (BCP A), (2) a powder type with the low lignin content (BCP B), and (3) another liquid type with high lignin content (BCP C). The laboratory tests focused on engineering properties, including unconfined compressive strength (UCS), shear strength, freeze-thaw durability, and moisture sustainability of BCPs-treated soils. Four types of Iowa soil were mixed with BCPs for testing, and the results indicated that BCPs are promising additives for soil stabilization in Iowa because of their beneficial effects in improving soil engineering properties, strength properties, durability, and resistance to moisture degradation. UCS and freeze-thaw durability of BCPs-treated soils were also compared to the same qualities of traditional stabilizer (cement)-treated soil. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were also performed to identify mechanisms of BCP based soil stabilization. A microstructural analysis showed that BCP materials could coat and bind soil grains and thereby form a strong soil structure.

Based on this study’s findings, the application of BCPs in soil stabilization appears to benefit both the bioenergy industry and the pavement construction industry. Only BCP A and BCP C tests were conducted in some of the testing activity due to lack of a sufficient quantity of these two BCPs. When a sufficient quantity of these BCPs becomes available, balanced tests and field investigation is recommended to verify the effects of BCP in soil stabilization practices.


Copyright Owner

Bo Yang



File Format


File Size

271 pages