TRANSFORMING WASTES AND INDUSTRIAL BYPRODUCTS INTO SUSTAINABLE CONSTRUCTION MATERIALS FOR PAVEMENT SUBGRADE LAYERS

Author

Joshua Ayobami Fayemi, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2024

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Kolay, Prabir

Abstract

Waste generation is a constant activity of daily life, encompassing a wide variety including municipal, hazardous, industrial, agricultural, medical, radioactive, and mining waste, as well as sewage sludge. The purpose of this study is to concentrate on utilizing industrial waste, which adversely affects our environment, for use in engineering construction projects. This aims to evaluate the enhancement in both the soil’s index and engineering properties. In most civil engineering projects, the underlying soils are often unsuitable for construction purposes. Some of these soils experience significant volume changes due to moisture variations, leading to damage and instability of structures and infrastructure built on them. The complete removal and replacement of such high plastic clay and expansive soils is not always a cost-effective solution. Therefore, there's a pressing need to improve their utility by stabilizing them through eco-friendly and sustainable methods.The present research employs five industrial waste materials to enhance the clayey soil available in Carbondale, Illinois. These waste materials include Lime Sludge (LS), Lime Kiln Dust (LKD), Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), and Cement Kiln Dust (CKD). Lime Sludge and Lime Kiln Dust were mixed with the soil at proportions of 2%, 4%, 6%, and 8%. In contrast, Fly Ash and Cement Kiln Dust were used at higher ratios of 8%, 16%, 24%, and 32%. Lastly, Ground Granulated Blast Furnace Slag was added at levels of 5%, 10%, 15%, and 20%, all based on the soil's dry unit weight. The samples were prepared for Unconfined Compression Strength (UCS) and Resilient Modulus (RM) based on the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) data obtained from miniature Proctor test. These specimens underwent a 14-day curing period, sealed in plastic film and Ziploc bags, and were stored in a controlled water tub at room temperature. The UCS value for the untreated Carbondale soil was 320 kN/m2. The results indicated that with higher content of Lime Kiln Dust (LKD) and Cement Kiln Dust (CKD), the UCS strength tends to increase with CKD exhibiting the most desirable strength characteristics. The UCS value for 8% LKD was 1377.70 kN/m2 i.e., 330.52% increase. While the UCS improvements for 5% GGBS is 51.32% and 6% Lime Sludge (LS) is 51.65% with no significant enhancements, these waste materials can be more effective as modifiers. Furthermore, the study revealed that the optimal quantity of Class F fly ash for soil stabilization is 8% by dry unit weight with UCS value of 486.46 kN/m2 resulting in 52.01% increase in UCS strength, exceeding this percentage might cause reduction in strength. The highest UCS strength was obtained with 24% CKD at 3263.14 kN/m2 which corresponds to 919.70% increase when compared to the untreated soil. The results of the Resilient Modulus (RM or Mr) test indicate that the incorporation of additives to untreated Carbondale soil significantly improved its stiffness characteristics and resistance to different load cycles on the subgrade. However, the soil treated with GGBS showed a decrease in stiffness. The Resilient Modulus values ranged from 2% to 70% for LS, 47% to 128% for LKD, 4% to 35% for FA, 90% to 243% for CKD, and -16% to 0.3% for GGBS for different confining pressures. The regression analysis, using the Uzan (1985) model, showed R² values of 0.910, 0.838, 0.803, 0.871, 0.773, and 0.809 for Carbondale soil, Carbondale soil mixed with 6% LS, 8% LKD, 8% FA, 5% GGBS, and 24% CKD, respectively. These results confirm the reliability of the test, as all samples except the GGBS-treated one have R² values greater than 0.800. Additionally, consolidation tests were conducted to assess the compressibility characteristics of the additives in the soil. The selected samples were those with the mix proportions that yielded the highest UCS strength for each additive. These samples were meticulously prepared based on the moisture-density relationship obtained from the miniature Proctor test and were subjected to loading and unloading in a specific sequence. The results indicated an increase in the Compression Index (Cc) for mixtures with LS, LKD, FA, and CKD. Conversely, the mix containing GGBS displayed a reduction in the Compression Index (Cc). The Carbondale soil stabilized with 6% LS can be used for subbase stabilization as the UCS strength is greater than 345 kPa. Also, 2 to 8% LKD content can be used for subbase and base course stabilization. 8% FA without any activator can be used for subbase stabilizer. GGBS can be used for subbase soil stabilization and finally CKD can be used for both subbase and base course stabilization.