Department of Civil Engineering
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Item Role of Nano- and Crystalline Silica to Accelerate Chemical Treatment of Problematic Soil(ASCE, 2023-04) Chakraborty, SayantanA research study was conducted to accelerate engineering property improvements by using novel silica-based coadditives along with a traditional calcium (Ca)-based stabilizer. Silica-based compounds, crystalline-silica (CS) rich waste product, and laboratory-grade nanosilica (NS) were used as coadditives with dolomitic hydrated lime to treat problematic expansive soil to study their efficacy in accelerating improvements in various engineering characteristics. The optimum dosages of the CS and NS additives with dolomitic hydrated lime were first determined based on unconfined compressive strength property, before and after capillary soaking. These dosages were subsequently corroborated by performing one-parameter and multiparameter statistical analyses. Using these optimized dosages, various engineering tests were performed on the treated soils. These tests included free-swell and linear shrinkage strains, unconfined strength with and without capillary soaking, and resilient modulus studies at curing periods of 0 (6 h), three, and seven days. Supplemental microstructural analyses were performed to gain insights into the factors responsible for the observed improvements in engineering properties. Test results indicated that treatment with hydrated lime and both silica-based coadditives is effective in stabilizing problematics soil as compared with lime treatment alone. Among the two silica-based coadditives, NS treatment provided comparatively higher accelerated improvements in the soil properties after seven days of curing than CS treatment. Mineralogical studies revealed that NS is more reactive than CS as a coadditive; hence, NS has been effective in providing equivalent long-term engineering strength gains while reducing swelling- and shrinkage-related volume-change properties in a relatively short time period.Item Experimental Studies and Sustainability Assessments of Quarry Dust for Chemical Treatment of Expansive Soils(ASTM, 2023-08) Chakraborty, SayantanCivil infrastructure constructed on expansive soils undergoes distress and loss of serviceability because of damage caused by moisture-induced volumetric changes. Traditional stabilization methods that employ calcium-based stabilizers are widely used mitigate the volume change-related distresses, but they increase the carbon footprint and emission of greenhouse gases during production and construction stages, compromising the treatment’s sustainability. This research study was designed to use silica-rich waste products, such as a quarry dust admixture with a calcium-based stabilizer, to enhance the performance of problematic soils and improve the sustainability of the system. An array of engineering tests, including unconfined compressive strength tests before and after moisture conditioning, one-dimensional free swell tests, and linear shrinkage tests, were performed on untreated and treated soils. Test results showed that the utilization of quarry dust as a co-additive significantly improved the strength and durability of the soil and reduced the shrink-swell potential to a greater extent than lime treatment alone. The sustainability assessment was then performed, which showed that the application of quarry dust can be considered a sustainable alternative that helps reduce the geoenvironmental problems related to handling and stockpiling waste products in landfills. Overall, silica-rich waste products have the potential to be appropriate and sustainable additives that work well with a traditional calcium-based stabilizer to modify expansive soil.Item Micro-mechanical behavior of nanosilica-treated high-sulfate soils(Candian Science Publishing, 2024-05) Chakraborty, SayantanThe addition of calcium (Ca)-based stabilizers to sulfate-rich expansive soils is associated with the formation of ettringite, a deleterious reactant that can cause moderate-to-severe swell-related damage to overlying lightweight infrastructures. This research study was conducted to understand the effects of combining nanosilica admixtures with a traditional Ca-based stabilizer to effectively treat high-sulfate soils with an intent to suppress the ettringite formation. Engineering and microstructural studies were thus performed to gain a comprehensive understanding of the behavior of sulfate-bearing soils treated with lime in the presence of amorphous nanosilica. The engineering studies on treated and untreated soils included strength tests before and after capillary soaking, free swell strain tests, and resilient moduli studies that were performed to study and understand the macrostructural behavior of these soils at different curing periods. Supplemental studies using scanning electron microscope imaging and energy dispersive X-ray spectroscopy, thermal analyses using differential scanning calorimetry, and X-ray diffraction studies were also conducted to determine the microstructural changes that occur within these sulfate-rich soils. The results showed that additional silica phases furnished from nanosilica suppressed the precipitation of ettringite and correspondingly increased the formation of cementitious phases. This study also provided ample evidence that the application of amorphous siliceous nanomaterials positively impacts chemical treatments and reduces the precipitation of ettringite in sulfate-rich soils, thus enhancing their engineering performance.Item Alkali-Activation Potential of Sandstone Wastes with Electric Arc Furnace Slag as Co-additive(Springer, 2023-12) Bhunia, Dipendu; Chakraborty, SayantanElectric arc furnace slag (EAF) and sandstone waste (SW) are two of the most abundantly generated industrial wastes whose utilization as precursors and supplementary cementitious materials has not been exhaustively studied. The current research study comprehensively investigates the effects of incorporating varying proportions (0–90%) of re-melted EAF as a co-additive on the engineering properties of elevated (80 °C) and ambient (30 °C) cured alkali-activated SW-based binders. Extensive laboratory tests were conducted to assess the physio-mechanical and durability performance of the resulting alkali-activated materials (AAM). Detailed mineralogical and microstructural characterization of SW, EAF, and alkali-activated samples was carried out using sophisticated analytical techniques. Results advocated that irrespective of the curing temperatures, SW-based AAM showed improved setting behavior, compressive strength, water absorption, and porosity characteristics with the increment of EAF at all substitution levels due to the concomitant development of CASH-CSH-NASH gel phases. Overall, it can be inferred that EAFs as a pozzolanic material successfully augmented the properties of SW-based alkali-activated binders, providing an efficient solution for disposal and negative environmental impacts associated with industrial wastes.Item Influence of activator ratios and concentration on the physio-mechanical and microstructural characteristics of the geopolymers derived from sandstone processing waste(Springer, 2024-03) Bhunia, Dipendu; Lahoti, Mukund; Chakraborty, SayantanNatural stones have been utilized to meet various needs of human civilization since ancient times. The exploitation of any resource is associated with the production of redundant materials called wastes. Sandstone waste (SW) is one such waste obtained during the industrial processing of sandstones. Due to its siliceous composition, extensive yield, and disorganized dumping, noxious conditions related to land and human health are promoted. However, the lack of comprehensive engineering studies, mineralogical analysis, and design methodologies associated with the utilization of sandstone processing wastes restricted their applicability only to fillers or partial substitutes with pozzolans and traditional cement in meager volumes. In the past, limited efforts have been made to utilize SW as a construction entity, particularly for binding purposes. Thus, to enhance the scope of its utilization, a comprehensive investigation has been performed in this research to transform sandstone waste into a novel construction material by geopolymerization. Mix design tailoring and laboratory tests were implemented to understand the effects of sodium hydroxide concentration and sodium silicate to sodium hydroxide ratio on the dissolution and physio-mechanical characteristics of SW-based geopolymers. The activator-to-binder ratio was restricted to 0.4 to obtain pastes with sufficient workability without hindering the properties of the matrix. Besides, a high temperature-curing regime was selected based on SW's crystallographic and reactivity analysis. Subsequently, a total of 48 samples were prepared and tested at the curing age of 28 days. Detailed characterization of SW and SW-based geopolymer samples was performed using optical, X-ray, and infrared spectroscopies aided by electron imaging and thermogravimetric techniques. SW-based geopolymer samples showed compressive strengths in the range of 6-12 MPa, ~2 to 3 times higher than those obtained in previous experimentations. Phase analysis and microstructural examinations confirmed SW's participation in geopolymerization. Overall, it could be advocated that geopolymerization is an innovative approach for solving issues related to the disposal and re-utilization of SW, extending its possible application to the fields of cement mixes, wall tiles, mortars, and masonry as per the commendations of ASTM and ACI committee.Item Understanding Shallow Slope Failures on Expansive Soil Embankments in North Texas Using Unsaturated Soil Property Framework(ASCE, 2017) Chakraborty, SayantanSlopes constructed with expansive soils are prone to shallow slope failures when subjected to seasonal wetting-drying. This article presents a field experimental study and corresponding modeling analysis to understand slope failures at shallow depths, typically ranging from 1 to 5 ft (0.3–1.5 m) from the surface. Previous studies revealed that the major cause of shallow slope failures for earthen dams is due to the formation of surficial cracks due to rapid matric suction change occurring during cyclic wetting-drying from seasonal changes. The purpose of this study is to identify the influential factors such as soil matric suction on the stability of unsaturated soil slopes. In this study, soil from a test section at Joe Pool Lake dam, Texas is considered. Test soil was subjected to basic soil characterization and later studied for their engineering behavior. Unsaturated soil properties for Joe Pool Lake soil are obtained by evaluating the soil water characteristic curve (SWCC) using pressure cell and filter paper technique. Rainfall and temperature data collected at the site were utilized for modeling the unsaturated condition of the slope using VADOSE/W software. Results showed that consistent matric suction variation contributed to the reduction in the stability of the slopes. This analysis also provided valuable insight into the formation of fully softened zones at shallow depths due to the formation of desiccation cracks.Item Establishing a Threshold Sustainability Index for a Geotechnical Construction(ASCE, 2018) Chakraborty, SayantanSustainability studies in geotechnical engineering have focused on life cycle assessment (LCA) of materials and construction processes to quantify the environmental and socio-economic impacts of construction. However, in the absence of a threshold or allowable value depicting the degree of sustainability, a comprehensive assessment of the system sustainability is infructuous. This paper demonstrates a framework to establish a threshold sustainability index for a geotechnical construction. The approach is illustrated through a subgrade stabilization project for a low-volume road (LVR) in Arlington, TX, involving treatment with lime and cement. The subgrade soil was an expansive (high plasticity) clay, having a low to moderate soluble sulfate concentration. The methodology incorporates a multi-criteria assessment of resource use, environmental impact, and socio-economic consequences. The framework designates the threshold sustainability index (IT-Sus) for a particular project, besides providing a pictographic representation of the different sustainability elements.Item A Framework for Assessment of Sustainability and Resilience in Subgrade Stabilization for a High-Volume Road(National Academy of Sciences, 2018) Chakraborty, SayantanSustainability studies for civil infrastructure have primarily focused on methods and tools for quantifying resource consumption, environmental consequences, and socio-economic implications of a project. On the other hand, resilience analyses are based on the attributes of robustness and adaptiveness of the system. This study presents a multi-criteria analysis-based framework for a combined evaluation of sustainability and resilience of a civil infrastructure. The individual metrics (impact categories) are quantified, and a combined sustainability and resilience index ICSR is introduced to assess the sustainability and resilience of a high-volume road construction project in Texas. The pavement was constructed on sulfate-rich expansive clays, and the subgrade was stabilized with materials such as lime and fly ash. The framework offers flexibility to the user in attaching weights to an impact category based on its relative priority in the analysis. A pictographic representation of both sustainability and resilience elements could be effected through this framework.Item Impact of Variation of Small Strain Shear Modulus on Seismic Slope Stability Analysis of a Levee: A Sensitivity Analysis(ASCE, 2018) Chakraborty, SayantanIn this research, a sensitivity analysis was performed to study the effect of variation in maximum shear modulus (Gmax) values of different layers of a levee structure on the seismic response and stability of the levee slopes. The analysis was implemented by systematically varying the Gmax values of the different layers to simulate the effect of possible variation in estimated Gmax values obtained from in-situ/laboratory tests and correlation equations. The Gmax values of the layers were altered in two ways: variation in (1) individual layers; and (2) group of layers; thus, simulating the effect of incorrect estimation in Gmax values of a particular layer and a group of layers, respectively. The levee was subjected to the acceleration time-history data of two earthquakes with considerably different predominant frequencies. It was observed that the inaccurate estimation of Gmax values, especially for the deeper layers, significantly affects the natural frequency and peak crest acceleration. Moreover, a prominent change in the factor of safety of slopes under seismic loading conditions was observed with variation of Gmax values for the near resonance condition. The effects were pronounced when the Gmax values were varied for a group of layers, rather than individual layers.Item Predicting the Performance of Highway Embankment Slopes(EDP Sciences, 2019) Chakraborty, SayantanResilience of transportation infrastructure, such as highway embankments, is critical to avoiding commuter delays and costly repairs. The majority of highway embankments in Louisiana and Texas are in marginal condition because the high-plasticity clays that are used during construction will moisten with time to significantly lower strengths. The ring shear tests demonstrate that the Gamez and Stark [1] empirical correlations are applicable to Texas and Louisiana soils. The soil water retention curves at each site were fitted to the Van Genuchten model [2]. For example, the air entry values vary from 0.013 to 0.053 kPa-1 in Louisiana and from 0.008 to 0.01 kPa-1 in Texas. The implications of this wide range of air entry values is that the matric suction pressure required to saturate and desaturate controls the pore-water pressure build-up during a rainfall event.