Date of Award
5-1-2026
Degree Name
Master of Science
Department
Civil Engineering
First Advisor
Kolay, Prabir
Abstract
Soil Stabilization is a common practice in geotechnical engineering and is used for wide range of applications. The concept is thousands of years old and the traditional method of soil stabilization using lime and cement is indeed effective. However, this method is not sustainable for the environment because of the major carbon footprint it leaves behind during its manufacturing and use. This study investigates the use of three industrial by-products e.g., Ground Granulated Blast-furnace Slag (GGBS), Fly Ash (FA), and Cement Kiln Dust (CKD) obtained as byproduct from iron manufacturing, coal burning, and cement manufacturing process, respectively. The primary goal of this study was to investigate the strength and resilience behavior of the soil treated with unison of these three industrial by-products. The target was to take advantage of high alkalinity of CKD to activate the dormant GGBS and FA in order to achieve both short- and long-term development in strength. Varying concentrations of GGBS (i.e., 5%, 10%, 15%, 20%, and 25% by dry weight of soil) and fixed concentration of FA and CKD (15% each) with different curing period (7, 14, and 28 days) were used to study the effectiveness of stabilization using the ternary mix.
Laboratory tests including Specific Gravity, Atterberg’s limits, Miniature Proctor Test, Particle Size Distribution, Ultrasonic Pulse Velocity (UPV), Unconfined Compressive Strength test (UCS), Resilient Modulus (RM), and Scanning Electron Microscopy (SEM) were conducted to assess the index properties, strength characteristics and resilience behavior of the treated soil samples. The results indicated significant improvement in soil characteristics with reduction in soil plasticity index and significant increase in UCS and RM.
The Liquid Limit (LL) of soil was 62 and Plasticity Index (PI) was 38 which classified the soil as high plastic clay (CH). The liquid limit and plasticity index decreased sharply for treated soil of all mixes. The maximum dry density (MDD) and optimum moisture content (OMC) of untreated soil were 1.49 g/cm3 and 26.95%, respectively. For soil treated with GGBS (5, 10, 15, 20, 25%), 15% FA and 15% CKD, the MDD showed an increasing trend whereas the OMC displayed a decreasing trend with the increase in GGBS content.
The maximum UCS achieved at 28 days curing period for soil stabilized with 25% GGBS + 15% FA + 15% CKD was 4637.776 kPa which is a significant 1883.84 % increase in strength from 233.778 kPa for natural untreated soil. The average UPV for soil stabilized with 25% GGBS + 15% FA + 15% CKD was 2193 m/s which is a 206.28% increase from 716 m/s for untreated soil. Strong correlation of 0.9633 between UPV and UCS indicated increased UPV velocities corresponded significantly to higher UCS strength.
Resilient modulus (RM) of all the treated soil showed better results as compared to untreated soil. This signifies that the treated soil displayed better stiffness and resilience properties under repeated loading. Soil stabilized with 25% GGBS + 15% FA + 15% CKD also displayed better performance than other proportional mix for all curing periods. For curing period of 14 days the RM value reached 250.59 MPa, 330.68 MPa and 381.08 MPa for 13.8 kPa, 27.6 kPa and 41.4 kPa of confining stress respectively, corresponding to the increase of 202.129%, 338.493% and 330.107%. This is significant improvement which is critical for pavement design. The regression analysis between experimental and calculated RM values showed a positive correlation ranging from R2 = 0.7726 to 0.9888, indicating a reliable predictive model for RM based on the material coefficient parameters obtained from the test.
Microstructural analysis was performed through Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX) to study the microstructure characteristics of treated and untreated soil. SEM images of the treated soil show dense and compact microstructures which is potentially due to the formation of Calcium Silicate/Aluminate Hydrates (C-S-H, C-A-H, C-A-S-H) gels. The EDX validates the images obtained in the SEM by identifying the elemental composition of calcium, silica, alumina and oxygen in the treated soil samples.
In conclusion, this study provides a promising, sustainable, environmentally friendly alternative to soil stabilization displaying improvements in strength, resilience stiffness and microstructural properties.
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