Conference Papers

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Author: search.filters.author.Narasimhan, M.C.

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    Performance of Geopolymer concrete mixes at elevated temperatures
    (2012) Kishanrao, M.P.; Narasimhan, M.C.
    Reducing the greenhouse gas emissions is the need of the hour. Five to eight percent of the world's man-made greenhouse gas emissions are from the Cement industry itself. It is an established fact that the green house gas emissions are reduced by 80% in Geopolymer concrete vis-a-vis the conventional Portland cement manufacturing, as it does not involve carbonate burns etc. Thus Geopolymer based Concrete is highly environment friendly and the same time it can be made a high-performance concrete. In the present study, fly ash, blast furnace slag and catalytic liquids have been used to prepare Geopolymer concrete mixes. This study is continued to investigate the behaviour of such Geopolymer concrete under high temperatures ranging from 100°C to 500°C. Cubes of size 100mm × 100mm × 100 mm are tested for their residual compressive strengths after subjecting them to these high temperatures. © 2012 IEEE.
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    High Strength Flowable Alkali Activated Slag Concrete Mixes produced using industrial wastes
    (Institute of Physics Publishing helen.craven@iop.org, 2019) Manjunath, R.; Narasimhan, M.C.
    A new class of High-Strength Flow ableAlkali activated Slag Concrete(HSFASC)mixes is developed using steel slag sand and EAF (Electric Arc Furnace) slag aggregates, respectively, as the fine and coarse aggregates. These mixes use the ground granulated blast furnace slag as the source material. Thus it is to be recognized that all the three materials used - GGBFS, slag sand and EAF slag aggregates are by-products of the Iron and Steel Industry, and are available in very large quantities demanding safe disposal. Different amounts of Sodium silicate solutions, with specified amounts of Sodium Hydroxide flakes dissolved in them, are used as alkaline solutions. Test specimens were cast using a total of nine HSFASC mixes, (based on Taguchi's Method), each of which satisfied the relevant EFNARC guidelines with respect to their rheological properties. The test results indicate higher compressive strengths values for all the mixes tested herein. Microstructure studies are conducted on samples from the fractured surfaces of test specimens of different mixes, using advanced SEM, EDX and XRD analyses and the results are discussed. © 2019 IOP Publishing Ltd. All rights reserved.
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    Effect of addition of OPC on Performance characteristics of Self-compacting Alkali activated slag concrete mixes
    (Institute of Physics Publishing helen.craven@iop.org, 2019) Manjunath, R.; Narasimhan, M.C.
    An attempt has been made in the present research to develop construction friendly, self-compacting, alkali-activated slag concrete mixes with ground granulated blast furnace slag (GGBFS) as the major source of binder material. In an effort to make the concrete mixes more eco-friendly and sustainable, by-products from Iron and Steel Industry such as steel slag sand and Electric Arc Furnace (EAF) slag aggregates, were used as the fine and coarse aggregates respectively. While the total binder content has been varied in the range of 700 - 800 kg/m3 (in increments of 50 kg/m3), all the trial mixes had a constant w/b ratio of 0.40. Different amounts of sodium silicate solutions, with specified amounts of sodium hydroxide flakes dissolved in them, are used as alkaline solutions, with the combined Na2O percentage in them varying between 6% - 8%. Test specimens were cast with mixes which showed enhanced flow-properties as per relevant EFNARC guidelines and were tested for their mechanical strength and durability characteristics. Effect of admixing of ordinary Portland cement (OPC) in smaller percentages (2.5% - 10 %, in increments of 2.5%), on the performance characteristics of this novel class of AAC mixes is evaluated. Increased cement contents are found to lead to better flow ability properties and higher strengths values with lower sorptivity values in all the Cement-Admixed, Self-compacting, Alkali-Activated Slag Concrete mixes (CASAASC mixes) tested herein. Studies with a scanning electron microscope have shown more densified morphologies developed, accounting for better performances of these mixes. © 2019 IOP Publishing Ltd. All rights reserved.
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    Experimental studies on shear strength characteristics of alkali activated slag concrete mixes
    (Elsevier Ltd, 2020) Manjunath, R.; Narasimhan, M.C.; Shashanka, M.; Vijayanand, S.D.; Vinayaka, J.
    In the present study an attempt has made to study the shear strength characteristics of alkali activated slag concrete mixes developed using steel slag sand and Electric Arc Furnace (EAF) slag aggregates, respectively, as the fine and coarse aggregates. These mixes use the ground granulated blast furnace slag (GGBFS) as the primary source material. Thus it is to be recognized that all the three materials used-GGBFS, slag sand and EAF slag aggregates are by-products of the Iron and Steel Industry, and are available in very large quantities demanding safe disposal. Different amounts of Sodium silicate solutions, with specified amounts of Sodium hydroxide flakes dissolved in them, are used as alkaline solutions. The test results indicate higher compressive strengths values for all the mixes in the range of 50-70 MPa with their shear strength values ranging between 7.5 and 12.0 MPa. Further the relationship between shear strength and compressive strength of the AASC mixes was also developed. © 2019 Elsevier Ltd. All rights reserved.
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    Effect of binder chemistry on sulphate resistance of fly-ash blended cement concrete mixes
    (Institute of Physics Publishing helen.craven@iop.org, 2020) Nazeer, M.; Narasimhan, M.C.; Rajeeva, S.V.
    The chemical durability of concretes exposed to sulphate environment largely depends on the quality and quantity of products of cement hydration. Certain hydration products are readily reactive with the sulphate ions and form expansive products such as gypsum and ettringite. On the other hand, some sulphate compounds participate in reducing the cementing property of hydration products. These reactions cause expansion and deterioration of strength of concrete. Sulphate resistance of concrete can be improved by the incorporation of Supplementary Cementitious Materials (SCMs). Reduced water-binder ratio and proper curing can make concrete more durable in sulphate environment. This paper reports the details and results of an investigation of effect of chemical composition of binder materials on the sulphate resisting property of concrete exposed to a rich MgSO4 solution. The effect of initial curing is also investigated so that it may be possible to suggest the mix compositions for typical field applications of concrete. The variables investigated in this report are the oxide composition of binder components and the initial curing conditions. A set of concrete mixes, all with a constant binder content and water-binder ratio are used in the investigation. © 2020 Published under licence by IOP Publishing Ltd.
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    Performance evaluation of steel fiber-reinforced deep beams using self-compacting concrete
    (Springer Science and Business Media Deutschland GmbH, 2021) Manjunath, R.; Narasimhan, M.C.; Janagam
    Reinforced self-compacting deep beams were developed, and their performance with varying percentages of steel fibers has been investigated in the present research. Fine aggregate being river sand along with 12.5 mm downsize jelly as coarse aggregate, and all the concrete mixes were proportioned for attaining a strength of M-30 grade concrete. Based on standard code IS: 456-2000, all the reinforced SCC deep beams were designed. As per the EFNARC guidelines, all the SCC mixes were subjected to different flowability tests for ascertaining the concrete as SCC mixes. Test results concluded that the ultimate flexural strength of the reinforced concrete deep beams increased with the increase in the percentage of steel fibers due to the better stitching actions of the steel fibers with the cementitious matrix. © Springer Nature Singapore Pte Ltd 2021.
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    Performance evaluation of deep beams using self-compacting concrete subjected to corrosion
    (Springer Science and Business Media Deutschland GmbH, 2021) Manjunath, R.; Narasimhan, M.C.; Bibesh Nambiar, C.
    Effect of corrosion on RCC–SCC deep beams subjected to three different percentages of corrosion have been investigated in the present study. These SCC mixes were designed for obtaining a cube strength of M-30 grade using river sand as finer portions of the aggregate and 12.5 mm downsize jelly as coarse aggregate. Design of SCC reinforced concrete deep beams was carried out as per IS-456:2000 and the accelerated corrosion technique has been employed for carrying out the corrosion. All the trial SCC mixes were subjected to different flow ability tests in order to evaluate their SCC property as per the EFNARC guidelines. From the obtained test results, it can be observed that for the lower percentage of corrosion decrease in ultimate flexural strength was observed due to decrease in arch action. Further with increase in percentage of corrosion showed an increased ultimate flexural strength due to increase in arch action. © Springer Nature Singapore Pte Ltd 2021.
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    One part alkali-activated materials for construction - A review
    (Elsevier Ltd, 2023) Mahendra, K.; Narasimhan, M.C.
    With the present-day call for sustainability in concrete constructions, alkali-activated materials (AAM) - both mortar and concrete mixes, are attracting immense interest owing to their enhanced strength and durability characteristics, and lower environmental impact. However, the utilization of the conventional two-part AAM's is generally restricted to precast sector, primarily due to the inherent difficulties associated with the transporting, storage, and handling of alkaline activator solutions which are generally aggressive in nature. This has led to the development of one-part type (or "Just add water"- type) geopolymers in which liquid activator solution is replaced with a solid or anhydrous activator. The performance of a one-part geopolymer is significantly influenced by the type of aluminosilicate precursors and solid activators used. Notably, in most of the studies, fly ash and/or GGBFS are used as the precursors, while any of anhydrous sodium silicate, sodium hydroxide, sodium carbonate, calcium hydroxide, and sodium metasilicate is used as the activator. This review article discusses the various studies that have focused on the production and placement, and the fresh, and hardened properties of one-part alkali-activated materials. Various issues associated with efforts to make such binder systems more amenable also to cast-in-situ applications are addressed. © 2023 Elsevier Ltd. All rights reserved.
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    Corrosion of steel rebars embedded in One-part Alkali activated concrete mixes
    (EDP Sciences, 2023) Reddy, B.K.K.; Narasimhan, M.C.
    To reduce CO2 emissions and turn a variety of industrial/agricultural wastes into valuable cementitious products, alkali-activated materials (AAM) are recognized as suitable substitutes for regular Portland cement (OPC). However, the concentrated aqueous alkali solutions used in conventional two-part alkali activated materials are highly corrosive, viscous, and are difficult to handle in direct field applications. As a result, the potential for developing so-called "just add water"type one-part AAMs, as compared to traditional two-part AAM, is being explored, particularly in cast-in-situ applications. In the present study on corrosion of reinforcing steel bars in fly ash-slag (FA-GGBS) based one-part AAC mixtures, three parametersthe total binder content, the relative proportions of GGBS and Fly-ash and the percentage of sodium oxide (Na2O) - are recognized as the key factors in determining the strength and durability performance (including corrosion of rebars embedded in it) of a given AAC mix. Accordingly, experiments were conducted on AAC mixes with three binder contents (440, 460, and 480 kg/m3), three Slag/FA ratios (80/20, 70/30 and 60/40, by volume) and three alternate Na2O percentages (5, 6, and 7%, by weight of total binder content). Prismatic cylindrical test specimens of reinforced geopolymer concrete were prepared and half-cell potential and corrosion rate measurements were made after 28-, 56-, and 90 days of continuous exposure to 3% of NaCl solution, to accelerate the corrosion process. Measured corrosion current density and corrosion rates using a Electro-chemical Corrosion Analyser have indicated that the AAC mixture having a total binder content 440 kg/m3, GGBS/FS ratio of 70/30 and 6% Na2O content, exhibits best corrosion resistance amongst the various mixes tested herein, as measured up to the end of 90-days. © ICSTCE 2023
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    Performance of Alternate Superplasticizers on Performance of Self-compacting Geopolymer Mortars—An Experimental Study
    (Springer Science and Business Media Deutschland GmbH, 2024) Prakash, G.B.; Mahendra, K.; Tanush, L.; Narasimhan, M.C.
    Geopolymer binders are the best alternatives to Ordinary Portland cement in the view of carbon impact on the environment. The effect of addition of different types of superplasticizers (SPs) on the flow and compressive strengths of a class of self-compacting geopolymeric mortar (SCGM) mixes is investigated in the present study. Three different kinds of SPs, namely modified Polycarboxylate Ether (MPCE), Polycarboxylate Ether (PCE), and Sulfonated Naphthalene Formaldehyde (SNF), were used in the production of SCGM with varying proportions at 1, 1.5, and 2% by weight of the binder. Results revealed that modified PCE-based SP showed better results in flow and compressive strength (CS) in comparison to PCE and SNF-based SPs. However, an increase in the dosage of SP had less/adverse effect on the flow properties. A maximum slump flow of 270 mm was observed for a modified PCE-based SP at 1.5% dosage, while the highest CS of 34 MPa was observed at 1.5% dosage of the same SP. Scanning electron microscope (SEM) analyses were carried out on a few selected SCGM mixes. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.