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Subject: search.filters.subject.Geopolymers

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    Computational design of fly ash geopolymer mortar using experimental and attribute evaluation approaches
    (Springer, 2024-10) Lahoti, Mukund; Srivastava, Anshuman
    Geopolymer is a ceramic-like inorganic material synthesized at room temperature and is a potential sustainable replacement of Portland cement. In the present work, a comprehensive experimental program was designed to evaluate the relative importance of mix design factors controlling the strength of fly ash geopolymer mortar. Restrained factors, namely, temperature of curing; alkaline solution to fly ash (L/FA) ratio; sodium silicate to sodium hydroxide (SS/SH) ratio; sodium hydroxide molarity; and fly ash to sand (FA/Sand) ratio, and unrestrained factors, namely, H2O/Na2O; SiO2/Al2O3; SiO2/Na2O; and Al2O3/Na2O molar ratios, were considered for evaluation. Feature subset selection and multivariate adaptive regression splines (MARS) techniques were used to determine the significance of these factors. Results show that temperature of curing is the most significant factor. FA/Sand and L/FA are found to affect compressive strength more significantly than sodium hydroxide molarity and SS/SH. Except for H2O/Na2O molar ratio, other molar ratios were observed to be very less significant. It is noted that mix design of geopolymer mortar should not be based on the molar ratios, instead mix design must be prepared by controlling the restrained factors. The findings of this study should be helpful in optimization of design factors leading to a robust geopolymer mix.
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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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    Experimental investigation on paver blocks of fly ash-based geopolymer concrete containing silica fume
    (Taylor & Francis, 2021-12) Srivastava, Anshuman
    Utilisation of geopolymer may reduce the global warming potential of concrete. This study examines geopolymer concrete as interlocking paver blocks. Three concretes are compared: conventional cement, fly ash-geopolymer and fly ash–silica fume geopolymer. Sodium hydroxide solution is used in both geopolymer concretes, and sodium silicate solution is used in fly ash-based geopolymer concrete only. Rectangle and uni shape blocks are tested for compressive strength, flexural strength, abrasion resistance and freeze–thaw resistance. Dynamic drop loading test is conducted on block pavement with herringbone laying pattern . Results revealed that resistance to abrasion and water absorption of geopolymeris improved by adding silica fume . Freeze–thaw resistance is the lowest for cement concrete paver blocks. Lowest deflection occurred in block pavement of uni shape. Geopolymer concrete provides uniform load distribution than cement concrete. Cement concrete is slightly costlier than geopolymer concrete. This study concluded the geopolymer as suitable option for paver block applications
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    Tailoring Properties of Electric Arc Furnace Slag Based Geopolymer Through Fly Ash Incorporation
    (Springer, 2023-02) Lahoti, Mukund
    Geopolymers are novel binders and are sustainable alternatives for conventional Portland cement. Geopolymers have emerged as a phenomenon of exceptional interest for the construction industry due to their excellent mechanical properties and sustainability in the past few years. A significant factor in producing geopolymers is the selection of the precursors. In this study, electric arc furnace slag (EAFS) obtained as waste from the steel industry is used as the precursor, and the influence of fly ash (FA) on the properties of the developed geopolymer is investigated. Scanning electron microscopy (SEM), X-Ray diffraction (XRD), and X-ray fluorescence (XRF) are used for material characterization and for analysing the microstructural development.
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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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    Utilization of Metakaolin-Based Geopolymers for Stabilization of Sulfate-Rich Expansive Soils
    (ASCE, 2022) Chakraborty, Sayantan
    The durability and performance of pavements and other lightweight structures constructed over expansive soils are persistent causes of concern due to moisture-induced volumetric fluctuations. Typically, traditional calcium (Ca)-based stabilizers, especially lime, effectively mitigate the problems associated with such problematic soils by reducing their swell-shrink potential and improving their strength properties. However, the treatment of sulfate-rich expansive soils using the Ca-based stabilizers results in detrimental heave due to the formation of a highly deleterious mineral, ettringite. This research study was performed to investigate the efficacy of utilizing an eco-friendly metakaolin-based geopolymer (MKG) stabilizer for treating sulfate-rich expansive soils. A comparative study was conducted by performing engineering tests such as free swell tests and unconfined compressive strength (UCS) tests on untreated, lime-treated, and geopolymer-treated soils for different curing periods. The effects of geopolymer dosage, curing period, and moisture intrusion on swelling characteristics and strength properties of treated soils were investigated. In addition, microstructural analyses were performed to study the changes in the soil after chemical treatment with geopolymer and lime. The results of engineering tests and microstructural studies indicate that geopolymer can effectively stabilize sulfate-rich expansive soils and could be used as a sustainable and eco-friendly alternative to traditional Ca-based stabilizers.
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    Thermal Performance of Metakaolin-Based Geopolymers: Volume Stability and Residual Mechanical Properties
    (Wiley, 2017-01) Lahoti, Mukund
    This chapter describes how a series of metakaolin (MK)-based geopolymer specimens measuring 50 mm cubes with different Si/Al ratios were prepared and exposed to different heating profiles in an electric furnace. The crumbling of cement paste into small pieces while geopolymer specimens retained satisfactory compressive strengths points towards the potential of geopolymers to perform soundly as a fire resistant material and also the need to impart sufficient volume stability and strengths when subjected to high temperatures. On exposure to elevated temperatures, geopolymers either retain their amorphous condition or transform to a crystalline microstructure in an experiment. The general agreement based on previous research is that geopolymers possess a stable inorganic framework subject to elevated temperatures unlike OPC which suffers breakdown of its hydration products. The dissolution of fumed silica into sodium hydroxide solution was done to obtain a clear solution. Solutions were stored for about 24 hours before use to allow them to cool down to room temperature and to achieve equilibrium.