Department of Civil Engineering

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Author: search.filters.author.Chakraborty, Sayantan

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    Lime stabilization of sulfate-rich soil using quarry fines as a sustainable co-admixture
    (Springer, 2025-05) Chakraborty, Sayantan
    The engineering properties of the underlying soil govern the durability and performance of civil engineering infrastructures. Chemical stabilization using lime is adopted widely to treat problematic clayey soils that do not possess acceptable engineering properties. However, the presence of sulfate salts is often counterproductive due to ettringite formation. Precompaction mellowing or the addition of amorphous silica-rich co-admixtures like fly ash or ground granulated blast furnace slag are widely used to mitigate ettringite-induced heaving. This research study investigates the potential of utilizing a crystalline silica-rich sustainable co-admixture derived from quarry dust to improve the engineering properties of sulfate-rich soil with kaolinite as the predominant clay mineral. Unconfined compressive strength tests, with and without capillary soaking, and one-dimensional (1D) free swell tests were performed on specimens treated with lime alone and lime along with quarry fines after different curing periods to assess the extent of strength reduction and swelling characteristics after moisture exposure. Mineralogical and microstructural analyses using X-ray diffraction and scanning electron microscope imaging with energy-dispersive X-ray spectroscopy were used to investigate the potential causes of the observed changes in strength and volume change characteristics. Results indicate that lime, along with quarry fines, effectively stabilized the problematic sulfate-rich soil. The improvement in engineering properties was prominent at higher dosages of quarry fines and after prolonged curing time.
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    Micro-mechanical analyses to understand the durability of chemically stabilized geomaterials against moisture-induced damage
    (ASCE, 2025) Chakraborty, Sayantan
    Chemical stabilization with calcium or Ca-based stabilizers, such as lime, has been used worldwide to enhance the engineering properties of problematic soils. Although lime treatment improves the mechanical properties of problematic soils, moisture intrusion is often detrimental to the stabilized layers. The extent of improvement and the durability of the lime-treated soils depend on several factors, including stabilizer dosage, curing period, and soil type. This research study was designed to investigate the influence of predominant clay minerals and stabilizer dosage on the durability and resiliency of lime-treated soils against moisture-induced damage. Two clayey sand groups bearing kaolinite and montmorillonite as the predominant clay minerals were treated with the Ca-based stabilizer as per existing recommended practice, and the strength and durability properties were studied after different curing periods. Besides engineering tests, mineralogical and microstructural analyses were also considered to identify the reasons responsible for the observed engineering behavior before and after moisture conditioning. Test results indicate that the extent of strength gained after lime treatment is less for soils with kaolinite as the predominant clay mineral than those containing montmorillonite. However, the percentage strength loss after capillary soaking was lower in lime-treated kaolinite-rich soils compared to that having montmorillonite when treated with optimum +2% lime dosage and cured for a longer time.
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    Ground improvement studies on problematic soils: innovative materials with sustainable applications
    (Springer, 2024-10) Chakraborty, Sayantan
    Chemical stabilization of problematic sulfate-rich soils is a considerable cause of concern even to this day for geotechnical and transportation engineering practitioners. With the advent of innovative materials and technologies, researchers have tried to incorporate them into ground stabilization practices. However, the application of novel materials is often met with apprehension when the concept of long-term durability and sustainability of construction is weighed upon. The researchers at Texas A&M University have been studying innovative stabilization methods to address some of the prevailing problems of traditional stabilization methods. Application of metakaolin-based geopolymers and novel silica-based admixtures with Ca-based treatments to improve problematic soil properties is presented in this paper. Micro-mechanical behavior of the stabilized soils was investigated using both engineering and mineralogical studies. Engineering studies included strength, stiffness, moisture-susceptible durability, and free swell strain tests. Additionally, X-ray diffraction studies and scanning electron microscope imaging were performed to understand the microstructural behavior of the treated geomaterials. Sustainability benefits of the stabilizers were assessed using a unified framework, which subsumed the effects of embodied energy for production, environmental impacts, and socio-economic impacts of the treatment. The engineering and microstructural studies showed that the new stabilization methods provided more durable geomaterials as compared to traditional treatments. Sustainability assessments showed that new stabilization methods could be considered as a potential alternative if the production cost is significantly reduced. Overall, this keynote paper provides new insights into innovative stabilization methods, which may be of enormous benefit to geotechnical and transportation engineering practitioners.
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    Optimization of sandstone processing waste, electric arc furnace slag, and fly ash-based ternary blended eco-friendly geopolymers
    (Springer, 2024-11) Bhunia, Dipendu; Chakraborty, Sayantan; Lahoti, Mukund
    Over the years, ordinary Portland cement (OPC) has been used to meet growing demands of land and housing facilities arising out of population overburdens. It is well documented that OPCs, besides their outstanding qualities as building materials, are also significant contributors to global greenhouse gases (GHG). Consequently, recent years have noticed an emerging interest in the search for alternatives to Portland cement-based binders. Geopolymers are well-suited to serve this purpose owing to their superior attributes and low CO2 emissions compared to conventional cement. Still, the industrialization of geopolymers has not reached a meaningful value due to the prevailing fundamental barriers involving the requirement of corrosive environments and intensive heat-curing regimes in post-fabrication processes. The current study investigates the viability of using synergistic mixtures based on stone residues, pulverized ash, and steel slags in fabricating geopolymer composites cured at ambient temperature with reduced ingestion of alkalis. A comprehensive assessment of the engineering, mineralogical, and microstructural characteristics was performed in terms of setting times, physico-mechanical, durability, non-destructive, and analytical tests. Further, a scaled-down approach was utilized to evaluate the feasibility of the designed composites as construction entities. The incorporation of SW (10–40%) prolonged the setting periods (~ 150 min.) and abridged the engineering properties of the ternary pastes collectively by 127% due to silica coalescences. Besides, replacements of stone residues with FA (20–30%) and EAF (30–60%) improved the blend performance due to Ca and Al assimilations. All the developed composites satisfied the acclamations for OPC grade 33, CEM V class 32.5N, and OPC Type – I suggested by IS, EN, and ASTM standards, respectively, with matrices constituting CASH-CSH-NASH-(N,C)-A-S–H type gelation complexes identified by the X-ray, infrared, and electron imaging spectroscopic analysis. In addition, a cumulative deficit of about 60–90% was observed in energy and carbon footprints relative to OPCs, indicative of the binders’ sustainability traits.
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    Role of Nano- and Crystalline Silica to Accelerate Chemical Treatment of Problematic Soil
    (ASCE, 2023-04) Chakraborty, Sayantan
    A 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.
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    Experimental Studies and Sustainability Assessments of Quarry Dust for Chemical Treatment of Expansive Soils
    (ASTM, 2023-08) Chakraborty, Sayantan
    Civil 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.
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    Micro-mechanical behavior of nanosilica-treated high-sulfate soils
    (Candian Science Publishing, 2024-05) Chakraborty, Sayantan
    The 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.
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    Alkali-Activation Potential of Sandstone Wastes with Electric Arc Furnace Slag as Co-additive
    (Springer, 2023-12) Bhunia, Dipendu; Chakraborty, Sayantan
    Electric 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.
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    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, Sayantan
    Natural 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.
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    Understanding Shallow Slope Failures on Expansive Soil Embankments in North Texas Using Unsaturated Soil Property Framework
    (ASCE, 2017) Chakraborty, Sayantan
    Slopes 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.