Date of Defense
21-11-2024 2:00 PM
Location
F1-1117
Document Type
Thesis Defense
Degree Name
Master of Science in Civil Engineering (MSCE)
College
College of Engineering
Department
Civil and Environmental Engineering
First Advisor
Dr. Ashraf Hefny
Keywords
Saline sabkha soils, Abu Dhabi, coastal regions, geotechnical problems, soil stabilization, Granulated Blast Furnace Slag (GGBFS), sodium silicate, Unified Soil Classification System (USCS), mineral composition, sodium aluminosilicate hydrate (N-A-S-H) gel, environmental impact, sustainable land use planning.
Abstract
Saline sabkha soil is widely distributed across the Abu Dhabi coastal regions of the UAE. These soils are associated with geotechnical problems that principally emerge from the heterogeneous nature of the soil and its high soluble salt content. Upon exposure to fresh water, the soluble salt dissolves, resulting in loss of the bond that once cemented the soil particles. In addition, the volume occupied by the salt minerals becomes part of the voids between the particles. This process results in a weak and loose soil structure of lower bearing capacity that is ready to collapse upon being subjected to loads. Moreover, sabkha soil cannot also be used as an engineering fill material for the same reasons discussed above. In this research, the characteristics of sabkha soil collected from Abu Dhabi city coast were investigated. The physical, mechanical, and chemical properties of Abu Dhabi sabkha soil will be compared to those of other coastal sabkhas within the Middle East. Furthermore, a stabilization testing program was carried out on the soil to improve its properties such as compressibility, shear strength, unconfined compressive strength (UCS), and durability. Two types of chemical additives are proposed to be mixed with the soil which are Granulated Blast Furnace Slag (GGBFS) and sodium silicate. When slag was combined with sodium silicate and water, a chemical reaction occurred that initiated the geopolymerization process. The sodium silicate acted as an alkaline activator, dissolving the aluminosilicate content in the slag. This dissolution released silicates and aluminates into the solution, allowing them to interact with each other. As water was added, these dissolved components began to polymerize, forming a gel-like structure that gradually solidified into a hardened material. During curing, the geopolymer network continued to develop, enhancing its mechanical strength and durability. The resulting geopolymer exhibited high compressive strength and durability Several mixed proportions, from 0 to 40% of each agent, were used and curing durations of up to 28 days were adopted. For each mix, the amount of total dissolved salt (TDS) in the treated soil was measured and compared to that of the untreated soil. The reduction in the TDS is an important measure for the effectiveness of the treatment under the corresponding curing time. A mineralogical and microstructural analysis were performed as well on the plain soil and treated samples in order to examine the chemical and morphological changes due to the chemical reactions resulting from mixing the soil with slag and sodium silicate. That was achieved by conducting Scanning Electron Microscopy (SEM) and X-ray diffractometer (XRD) analyses. The results showed that the examined sabkha soil falls under the classification of silty sand (SM) or clayey sand (SC) according to the Unified Soil Classification System (USCS) and is additionally categorized as clayey soils (A-7) according to the AASHTO M145-91. The utilization of slag alone demonstrated effectiveness in reducing the total dissolved solids (TDS) in the sabkha, with up to a 21.4% reduction in TDS when 30% slag was added, close to the 22.4% reduction achieved with 40% slag addition. The addition of sodium silicate to the Ground Granulated Blast Furnace Slag (GGBFS) as an alkaline activator significantly influenced the TDS. The Sodium Silicate (SS) addition was in percentage of the dry weight of slag (S), and their percentages presented as S%-SS% throughout the report. The highest reductions recorded at 92.6% and 93.3% for sabkha treated with 30% slag and 40% Sodium Silicate, and 40% slag with 40% Sodium Silicate, respectively. The study also revealed a consistent increase in the maximum dry density with rising slag content in sabkha soil, while the addition of sodium silicate as a binder resulted in a reduction in the maximum dry density of the stabilized soil. The highest compressive strength, reaching 670 kPa with a 950% improvement to the plain sabkha, was achieved with the addition of 40% slag. Also, the higher sodium silicate ratios also notably increased compressive strength, with maximum average UCS of 38.04 MPa and 41.22 MPa for S40-SS30 and S40-SS40 mixtures, respectively. Moreover, the introduction of slag and sodium silicate positively impacted the soil durability, which mainly represented by mass loss after wet-thaw cycles. It was noted that the lowest mass losses recorded at 3.56% and 2.65% for S40-SS30 and S40-SS40, affirming the efficacy of the proposed stabilization agents in preserving sabkha soil integrity and strength. The mineral composition of Abu Dhabi's sabkhas is diverse, featuring notable elements like gypsum, halite (rock salt), and calcium carbonate. Mineralogical analysis identified the main reaction product of alkali-activated slag with sabkha as sodium aluminosilicate hydrate (N-A-S-H) gel, demonstrating its crucial role in influencing the strength and durability performance of the blended geopolymer. Beyond construction implications, sabkhas in Abu Dhabi play a pivotal role in local ecosystems, influencing plant life, hydrological dynamics, and ecological resilience. As these landscapes undergo continued study, their significance in the broader context of environmental science, geology, and sustainable land use planning becomes increasingly apparent. Overall, the study will assist in evaluating the geotechnical and chemical characteristics of Abu Dhabi sabkha soil. Also, the proposed stabilization technique is believed to be highly effective in improving the soil and therefore it will contribute to the futuristic sustainability visions and plans that UAE is seeking to maintain the natural and economical resources.
Included in
GEOTECHNICAL CHARACTERIZATION OF SALINE SABKHA SOIL OF ABU DHABI, UAE, AND ITS STABILIZATION USING STEEL SLAG AND SODIUM SILICATE
F1-1117
Saline sabkha soil is widely distributed across the Abu Dhabi coastal regions of the UAE. These soils are associated with geotechnical problems that principally emerge from the heterogeneous nature of the soil and its high soluble salt content. Upon exposure to fresh water, the soluble salt dissolves, resulting in loss of the bond that once cemented the soil particles. In addition, the volume occupied by the salt minerals becomes part of the voids between the particles. This process results in a weak and loose soil structure of lower bearing capacity that is ready to collapse upon being subjected to loads. Moreover, sabkha soil cannot also be used as an engineering fill material for the same reasons discussed above. In this research, the characteristics of sabkha soil collected from Abu Dhabi city coast were investigated. The physical, mechanical, and chemical properties of Abu Dhabi sabkha soil will be compared to those of other coastal sabkhas within the Middle East. Furthermore, a stabilization testing program was carried out on the soil to improve its properties such as compressibility, shear strength, unconfined compressive strength (UCS), and durability. Two types of chemical additives are proposed to be mixed with the soil which are Granulated Blast Furnace Slag (GGBFS) and sodium silicate. When slag was combined with sodium silicate and water, a chemical reaction occurred that initiated the geopolymerization process. The sodium silicate acted as an alkaline activator, dissolving the aluminosilicate content in the slag. This dissolution released silicates and aluminates into the solution, allowing them to interact with each other. As water was added, these dissolved components began to polymerize, forming a gel-like structure that gradually solidified into a hardened material. During curing, the geopolymer network continued to develop, enhancing its mechanical strength and durability. The resulting geopolymer exhibited high compressive strength and durability Several mixed proportions, from 0 to 40% of each agent, were used and curing durations of up to 28 days were adopted. For each mix, the amount of total dissolved salt (TDS) in the treated soil was measured and compared to that of the untreated soil. The reduction in the TDS is an important measure for the effectiveness of the treatment under the corresponding curing time. A mineralogical and microstructural analysis were performed as well on the plain soil and treated samples in order to examine the chemical and morphological changes due to the chemical reactions resulting from mixing the soil with slag and sodium silicate. That was achieved by conducting Scanning Electron Microscopy (SEM) and X-ray diffractometer (XRD) analyses. The results showed that the examined sabkha soil falls under the classification of silty sand (SM) or clayey sand (SC) according to the Unified Soil Classification System (USCS) and is additionally categorized as clayey soils (A-7) according to the AASHTO M145-91. The utilization of slag alone demonstrated effectiveness in reducing the total dissolved solids (TDS) in the sabkha, with up to a 21.4% reduction in TDS when 30% slag was added, close to the 22.4% reduction achieved with 40% slag addition. The addition of sodium silicate to the Ground Granulated Blast Furnace Slag (GGBFS) as an alkaline activator significantly influenced the TDS. The Sodium Silicate (SS) addition was in percentage of the dry weight of slag (S), and their percentages presented as S%-SS% throughout the report. The highest reductions recorded at 92.6% and 93.3% for sabkha treated with 30% slag and 40% Sodium Silicate, and 40% slag with 40% Sodium Silicate, respectively. The study also revealed a consistent increase in the maximum dry density with rising slag content in sabkha soil, while the addition of sodium silicate as a binder resulted in a reduction in the maximum dry density of the stabilized soil. The highest compressive strength, reaching 670 kPa with a 950% improvement to the plain sabkha, was achieved with the addition of 40% slag. Also, the higher sodium silicate ratios also notably increased compressive strength, with maximum average UCS of 38.04 MPa and 41.22 MPa for S40-SS30 and S40-SS40 mixtures, respectively. Moreover, the introduction of slag and sodium silicate positively impacted the soil durability, which mainly represented by mass loss after wet-thaw cycles. It was noted that the lowest mass losses recorded at 3.56% and 2.65% for S40-SS30 and S40-SS40, affirming the efficacy of the proposed stabilization agents in preserving sabkha soil integrity and strength. The mineral composition of Abu Dhabi's sabkhas is diverse, featuring notable elements like gypsum, halite (rock salt), and calcium carbonate. Mineralogical analysis identified the main reaction product of alkali-activated slag with sabkha as sodium aluminosilicate hydrate (N-A-S-H) gel, demonstrating its crucial role in influencing the strength and durability performance of the blended geopolymer. Beyond construction implications, sabkhas in Abu Dhabi play a pivotal role in local ecosystems, influencing plant life, hydrological dynamics, and ecological resilience. As these landscapes undergo continued study, their significance in the broader context of environmental science, geology, and sustainable land use planning becomes increasingly apparent. Overall, the study will assist in evaluating the geotechnical and chemical characteristics of Abu Dhabi sabkha soil. Also, the proposed stabilization technique is believed to be highly effective in improving the soil and therefore it will contribute to the futuristic sustainability visions and plans that UAE is seeking to maintain the natural and economical resources.