Browsing by Author "Narasimhan, M.C."

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Alkali-activated concrete systems: A state of art
(Elsevier, 2020) Manjunath, R.; Narasimhan, M.C.
Concrete is one of the most extensively used construction materials in the world. Production of ordinary Portland cement, the major constituent in the production of concrete, is leading to large-scale exploitation of the natural reserves of limestones, clays, and coal. It is estimated that there is a release of 0.8-1.0 tons of carbon dioxide to the atmosphere for the production of every ton of cement. In view of this, alternative construction materials are being developed, using industrial by-products such as fly-ash, ground granulated blast furnace slag, and metakaolin, which are generally rich in alumina and silica. The development of alkali-activated concrete systems has attracted the attention of concrete researchers in recent years. This chapter discusses the performance of alkali-activated concrete systems with different binders and alternate aggregates, in terms of their mechanical properties, durability, performance on exposure to elevated temperatures, performance on inclusion of fibers, and finally their suitability for use in structural members. © 2020 Elsevier Inc. All rights reserved.
An experimental investigation on self-compacting alkali activated slag concrete mixes
(Elsevier Ltd, 2018) Manjunath, R.; Narasimhan, M.C.
In present work, an attempt has been made to develop self-compacting, alkali activated slag concrete mixes, using steel slag sand as fine aggregate and EAF (Electric Arc Furnace) slag as coarse aggregate. The study investigates the properties such as compressive strength, splitting tensile strength and water absorption of these mixes. Development of Self-Compacting Alkali Activated Slag Concrete mixes (hereafter referred to as SCAASC mixes) was made with GGBFS (Ground Granulated Blast Furnace Slag) as the binder, with its content varying between 700 kg/m3 and 900 kg/m3 of fresh concrete. The net W/B (water to binder) ratio of the mixes was varied between a narrow 0.47 – 0.48 range. The alkaline solutions had Na2O percentages in the range 7 – 9%, but a constant activator modulus was maintained at 1.0 in all the mixes. In order to optimise the number of trial mixes to be tested, Taguchi's design of experiments methodology was adopted. A total of nine mixes were formulated using Taguchi orthogonal L9 array. Results showed the slump flow values for the mixes greater than 700 mm, with their L–Box ratios and V-Funnel values ranging between 0.90 and 0.95 and 9 – 11 s respectively, satisfying the EFNARC guidelines. Results also showed good compressive strengths (65–80 MPa), split-tensile strengths (2–4 MPa) and low water absorption values in the range of (2%–3%). The microstructural studies such as SEM, EDX and XRD analysis were also carried out, showing denser morphologies clearly indicating effective activation of slag by the alkaline solution. © 2018 Elsevier Ltd
Axial capacity of rectangular concrete-filled steel tube columns - DOE approach
(2010) Chitawadagi, M.V.; Narasimhan, M.C.; Kulkarni, S.M.
This paper presents the effect of change in wall thickness of the steel tube (t), strength of in-filled concrete (fcu), cross-sectional area of the steel tube (A) and length of the tube (L) on ultimate axial load and axial shortening at ultimate point of rectangular concrete-filled steel tubes (CFT). Taguchi's approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the ultimate axial load and the axial shortening at ultimate point. A total of 243 rectangular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC-LRFD-1994 and EC4-1994. © 2009 Elsevier Ltd. All rights reserved.
Axial strength of circular concrete-filled steel tube columns - DOE approach
(Elsevier Ltd, 2010) Chitawadagi, M.V.; Narasimhan, M.C.; Kulkarni, S.M.
This paper presents the effect of changes in diameter of the steel tube (D), wall thickness of the steel tube (t ), strength of in-fill concrete (f cu), and length of the tube (L) on ultimate axial load (P ue) and axial shortening at the ultimate point (?ue ) of circular Concrete Filled steel Tubes (CFT). Taguchi's approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the axial load and the axial shortening at the ultimate point. A total of 243 circular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC-LRFD-2005 and EC4-1994. © 2010 Elsevier Ltd. All rights reserved.
Bond strength characteristics of fly-ash admixed selfcompacting alkali activated concrete mixes
(Associated Cement Companies Ltd. priti.saldanha@acclimited.com, 2020) Manjunath, R.; Narasimhan, M.C.; Suryanarayana, L.R.
Bonding in any type of concrete plays a crucial role in the performance of reinforced concrete structures, which are profoundly determined by many factors such as concrete compressive strength, diameter, type and size of the bar along with length of embedment and confinement of concrete. Herein, an attempt has been made to develop fly-ash admixed self-compacting alkali activated slag concrete mixes cured under laboratory ambient conditions and to evaluate the bond strength characteristics using direct pull out test along with their bond stress-slip behaviour at the age of 28 and 56 days. These self-compacting alkali activated slag concrete mixes were developed using Fly-ash and GGBFS as the major principal binder. Naturally available river sand was used as the fine aggregate; 12.5 mm down size crushed granite chips (Jelly) constituted the coarse aggregate fractions in all these mixes. The alkaline solutions basically consisted of mixtures of sodium hydroxide flakes dissolved in the calculated quantity of water and mixed with the liquid sodium silicate solution. The experiments were planned based on Taguchi’s design of experiments methodology. A total of fifteen mixes were developed and evaluated for their flow ability characteristics as per the requirements of EFNARC guidelines along with compressive strength values at the age of 7, 14, 28 and 56 days. In an initial, calibration phase, bond strength characteristics of a set of nine mixes were utilized for performance evaluation purposes. Strength prediction equations were then derived on the basis of such results, whose predictive capacity was then evaluated and ascertained in the prediction phase with actual results of experiments on a set of three new mixes. Test results indicated higher flow ability characteristics for all the mixes satisfying the requirements as per the EFNARC guidelines. Higher compressive strengths values in the range of 46 – 85 MPa were obtained at the age of 56 days. Further acceptable bond strength values were obtained varying in the range of 8.0 – 14.5 MPa as compared to control OPC based reference concrete mix. © 2020, Associated Cement Companies Ltd.. All rights reserved.
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. Â© ICSTCE 2023
Durability performance of one-part alkali-activated self-compacting concrete mixes under aggressive and elevated temperature conditions
(Elsevier B.V., 2025) Mahendra, K.; Narasimhan, M.C.; Rathod, S.; Das, A.K.; Prakash, G.B.
The growing demand for sustainable, high-performance materials in modern construction has driven the development of advanced concrete technologies. This study introduces one-part alkali-activated self-compacting concrete (OPASC) as a practical, safe, and user-friendly alternative to conventional Portland cement-based concretes. Selected mixes with compressive strengths exceeding 70 MPa were evaluated for durability under aggressive conditions, including extended exposure to 5 % sulfuric acid and 5 % magnesium sulfate up to 180 days. The thermal stability of these candidate mixes was also assessed by subjecting the mixes to sustained temperatures ranging from 200 °C to 800 °C. Chloride-ion resistance of these mixes was examined under bulk diffusion tests. Key durability indicators, including water absorption, permeable voids, and sorptivity, were quantified to evaluate matrix impermeability. The results revealed compressive strength losses of 25–32 % under acid exposure, 7–15 % under sulfate exposure, and 30–42 % under thermal exposure, with chloride diffusion coefficients ranging from 0.21 × 10?12 to 0.32 × 10?12 m2/s, indicating high resistance to ionic ingress. The mixes also exhibited low water absorption (3–4.5 %), lower soptivities (0.0024–0.0013 mm/s1/2), and much reduced permeable voids (4.3–5.5 %), reflecting an impermeable, dense matrix. Microstructural analyses using SEM-EDS and XRD revealed that degradation under acid and sulfate conditions is primarily attributable to the decalcification of C/N-A-S-H gels, accompanied by the recrystallization of stable aluminosilicate phases. Finally, the environmental sustainability evaluation, which considered both embodied energy and carbon footprint, verified the superior environmental friendliness of OPASC mixes relative to conventional concrete. These findings confirm that OPASC exhibits superior chemical and thermal durability, reduced permeability, and enhanced resilience, thereby establishing it as a sustainable and practical solution for modern infrastructure applications. © 2025 Elsevier B.V.
Effect of addition of OPC on Performance characteristics of Self-compacting Alkali activated slag concrete mixes
(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.
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. Â© 2019 IOP Publishing Ltd. All rights reserved.
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. Â© 2020 Published under licence by IOP Publishing Ltd.
Effect of containment reinforcement on the seismic response of box type laterite masonry structures-an analytical evaluation
(2013) Unnikrishnan, S.; Narasimhan, M.C.; Venkataramana, K.
Laterite blocks are used for construction of masonry walls since ages in the South-western coastal areas of India. The south-west coastal areas of India lie in zone III of seismic zonation map of Indian code IS 1893-2002. In spite of the fact that laterite is the most favored masonry material in these regions of India, the structural performance of laterite masonry has not been systematically investigated. Again there are no previous studies addressing, in detail, the seismic performance of laterite masonry buildings. Now that these areas are becoming more and more important from point of view of trade and commerce, there is a need for a detailed research on the seismic response of laterite masonry structures located in these areas. The present paper reports the results of such a study of the seismic response of box-type laterite masonry structures. Time history analysis of these structures under El-Centro acceleration has been performed using commercial finite element software ANSYS. Effect of 'containment reinforcement' on the seismic response of box type laterite masonry structures has been evaluated. © 2013 Techno-Press, Ltd.
Effect of mix parameters and hydrogen loading on neutron radiation shielding characteristics of latex modified concrete mixes
(Elsevier Ltd, 2015) Malkapur, S.M.; Satdive, H.; Narasimhan, M.C.; Karkera, N.B.; Goverdhan, P.; Sathian, V.
With the tremendous surge in the usage of radioactive materials in industry, education and research, medicine and other fields, it becomes a concern to protect the working personnel and common people around, from hazardous radiation leakages that may seriously affect their health. Among the different types of radiation, gamma and neutron radiations require adequate shielding. There have been several attempts to develop newer concretes and evaluate their neutron radiation shielding characteristics. In the present study, an attempt has been made to study the effect of varying the mix parameters and hence the resulting total hydrogen content on the neutron radiation shielding characteristics of Latex Modified Concrete (LMC) mixes. The experiments are planned in such a way that the hydrogen content of the mixes is varied by controlling the mix parameters i.e., cement content, water/cement ratio and polymer/cement ratio of LMC mixes. The results are statistically analyzed. It is found that definite improvements could be achieved in neutron radiation shielding characteristics of LMC mixes as compared to ordinary concrete, with the increase in hydrogen concentration effected by changes in mix parameters. © 2015 Elsevier Ltd All rights reserved.
Effects of fiber addition on performance of high-performance alkali activated slag concrete mixes: An experimental evaluation
(Taylor and Francis Ltd., 2022) Manjunath, R.; Narasimhan, M.C.; Kumar, S.
There is an ever-increasing awareness on issues connected with emission of high amounts of greenhouse gases from various industries, including that from the concrete construction industry. Performances of alternative binder systems including geopolymers and alkali activated slag concretes are being investigated in this context. There is again a continuous drive to enhance their performances, both when green and on getting hardened and so also, simultaneous efforts are being made to take advantage of all the various fast-track, state-of-art construction technologies, leading to efficient, eco-friendly and economical infrastructure projects. The present authors have developed and evaluated a new set of such alkali activated slag concrete mixes having self-compacting property, along with higher mechanical properties (hereafter referred to as HPAASC mixes) using three industrial by-products, all obtained from iron and steel industry. While these HPAASC mixes have higher compressive strengths (in the range of 70–90 MPa), reasonable split and flexural strengths and are self-compacting, they continue to be brittle just as other high strength concrete mixes. In order to improve their cracking behaviour during failure, either under mechanical loads or on exposure to higher temperatures, addition of increasing amounts of steel fibers in HPAASC mixes is contemplated. Hence in the present study, the attempt is to study the effect of incorporation of fibers (within a small range of 0.4 ? 0.8%) in the new class of high-performance, fibre reinforced. Self-compacting alkali-activated slag concrete mixes–(referred to as HFSASC hereafter). The present study evaluates the properties such as flow ability, compressive strength and flexural toughness performances for these mixes. Results in the present study indicate that, while all the HFSASC mixes exhibit satisfactory passing and flowing abilities specified as per EFNARC standards for self-compacting mixes, they exhibit enhanced toughness characteristics too. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Experimental investigation and optimization of one-part alkali-activated self-compacting concrete mixes
(Elsevier Ltd, 2024) Mahendra, K.; Narasimhan, M.C.; Prakash, G.B.; Das, A.K.
Emphasizing the growing importance of sustainability, alkali-activated materials (AAMs) have emerged as a revolutionary alternative for cement in the construction sector. This study delves into the fresh, mechanical, and microstructural properties of One-Part Alkali-activated Self-compacting Concrete (OPASC) mixes. While mixtures of Ground Granulated Blast Furnace Slag (GGBFS) and Fly Ash (FA) were utilized as the precursors, powdered sodium metasilicate was employed to function as the activator. To streamline experimental design and reduce the economic demands of extensive testing, the Taguchi-Grey Relational Analysis (GRA) was utilized to identify optimal multi-response parameter levels. This method considered binder content (B) within a range of 700–800 kg/m³, water-to-binder (W/B) ratios between 0.38 and 0.42, and Na2O percentages from 5 % to 7 % as key input variables. Results indicated that the designed mixes recorded workability values satisfying the EFNARC guidelines, compressive strengths greater than 60 MPa, split-tensile strengths in the range of 3.5–4.6 MPa, and flexural strengths varying between 5.5 and 7.2 MPa. The mix parameters for the optimal mix, with the highest mean grey relational grade, were identified from the Taguchi-GRPA approach as B = 750 kg/m3, W/B = 0.4, and N = 6 %. Microstructural analysis revealed the formation of C/N-A-S-H type gels, which are instrumental in developing a compact matrix enhancing the mechanical properties. A good agreement between actual experimental results obtained for a different set of verification mixes with those predicted by regression-equations confirmed the potency of the Taguchi-GRA approach in optimizing the OPASC mix parameters. © 2024 The Authors
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. Â© 2019 Elsevier Ltd. All rights reserved.
Flexural and fracture performance of fiber reinforced self compacting alkali activated concrete– A DOE approach
(Elsevier B.V., 2024) Prakash, G.B.; Prashanth, M.H.; Narasimhan, M.C.; Mahendra, K.; Das, A.K.
Owing to their much-reduced carbon footprint and lower embodied energy, compared to conventional Portland Cement (OPC-based) Concrete mixes, Alkali Activated Concrete (AAC) mixes represent a pivotal advancement towards achieving sustainability goals. The fracture properties were investigated using Three-Point Bending Tests (3-PBT) under the mode I failure mechanism. This study utilises Taguchi analysis to analyse and optimise Self-Compacting Alkali-Activated Concrete (SAAC), focusing mainly on its flexural strength and fracture characteristics. An L-16 orthogonal array of experiments with three input parameters − replacement of Blast Furnace Slag (BFS) with Fly ash (FA) (0 %, 30 %, 40 %, and 50 %), Steel Fibers (SF) volume content (0 %, 0.25 %, 0.5 % and 0.75 %) and Notch to Depth (a0/d) ratio (0.2,0.3,0.4 and 0.5), at four levels each, was adopted. The Work of Fracture Method (WFM) and Double K Fracture Criterion (DKFC) were utilised to determine the Fracture Energy (GF) and fracture toughness, respectively. The results obtained from all the sixteen mixes showed that the F0-S0.75-N0.5 mix demonstrated better values in several parameters, such as flexural strength of 7.82 MPa,KICini of 0.928 MPa√m, KICuns of 6.99 MPa√m and KICini/ KICuns of 0.133. A maximum GF of 2350 N/m was obtained with F50-S0.75-N0.2 mix. However, all the inferior values of these parameters were observed with F50-S0-N0.5 mix, which recorded a flexural strength of 4.90 MPa, KICini of 0.612 MPa√m,KICuns of 1.16 MPa√m, KICini/ KICuns of 0.528 and GF of 125 N/m. Through Taguchi analysis, the optimal combination for flexural strength was identified as FA 0 %, SF 0.75 %, and a0/d 0.5 and for both Initial Fracture Toughness (KICini) and Unstable Fracture Toughness (KICuns) at FA 0 %, SF 0.75 % and a0/d 0.4. For both the ratio of initial to unstable fracture toughness (KICini/ KICuns) and fracture energy (GF), the optimum combination was FA 0 %, SF 0.75 % and a0/d 0.2. Furthermore, the results indicate that FA significantly influences KICini, while SF predominantly affects all other parameters. The predictive performance of the regression equations demonstrates good agreement with experimental outcomes. © 2024 Elsevier Ltd
Flexural behavior of reinforced high performance self-compacting alkali activated slag concrete beams
(Associated Cement Companies Ltd., 2020) Manjunath, R.; Prashanth, M.H.; Narasimhan, M.C.; Bala Bharathi, U.K.
The present manuscript discusses the results of a series of tests conducted to study, in detail, the performance of reinforced, alkali activated slag concrete beams in terms of their flexural behavior. The present authors have developed and evaluated the performance of a new class of high-performance, self-compacting, alkali-activated slag concrete (HPAASC) mixes, using three industrial by-products, all from the iron and steel industry. While these HPAASC mixes have higher compressive strengths (around 70-90 MPa), reasonable splitting and flexural strengths along with moduli of elasticity, here, in this investigation, reinforced concrete beams made of these mixes are evaluated for their flexural performances in order to promote their applicability in large-scale infrastructural applications. Twelve under-reinforced concrete beams, were cast and were tested. Their flexural behaviors were experimentally evaluated in terms of loads at first crack, ultimate loads, strain-distributions, their load-deflection characteristics along with ductility values. Results of the present study indicate that, all the reinforced beams made of HPAASC mixes exhibit comparable flexural performances, as compared to that of beams cast with a reference OPC-based concrete mix, making a strong case for the possible application of these HPAASC mixes as structural elements in large-scale infrastructure projects. © 2020, Associated Cement Companies Ltd.. All rights reserved.
Free vibration analysis of axisymmetric laminated composite circular and annular plates using Chebyshev collocation
(SpringerOpen, 2015) Powmya, A.; Narasimhan, M.C.
Solutions, based on principle of collocating the equations of motion at Chebyshev zeroes, are presented for the free vibration analysis of laminated, polar orthotropic, circular and annular plates. The analysis is restricted to axisymmetric free vibration of the plates and employs first-order shear deformation theory for the displacement field, in terms of midplane displacements, u, ? and w. The eigenvalue problem is defined in terms of three equations of motion in terms of the radial co-ordinate r, the radial variation of the displacements being represented in polynomial series, with appropriate boundary conditions. Numerical results are presented to show the validity and accuracy of the proposed method. Results of parametric studies for laminated polar orthotropic circular and annular plates with different boundary conditions, orthotropic ratios, lamination sequences, number of layers and shear deformation are also presented. © 2015, The Author(s).
Free vibration studies of box type laterite masonry structures
(2012) Unnikrishnan, S.; Narasimhan, M.C.; Venkataramana, K.
Box-type laterite masonry structures are widely seen in south-west coastal areas of India. Not many studies are available in the literature on the dynamic response of such structures. Free vibration analysis of box-type laterite masonry structures has been attempted in this study, as a preliminary to a detailed dynamic analysis. Finite element analysis has been conducted to And the natural frequencies and corresponding mode shapes of box-type laterite masonry buildings. Results of detailed parametric studies conducted to find the effect of various parameters like modulus of elasticity of laterite masonry, provision of a lintel band or a roof slab, openings in long walls and aspect ratio on the natural frequencies and their mode shapes of box-type laterite masonry buildings are presented and discussed in this paper.
Fresh and hardened properties of polymer incorporated self compacting concrete mixes for neutron radiation shielding
(Elsevier Ltd, 2017) Malkapur, S.M.; Divakar, L.; Narasimhan, M.C.; Karkera, N.B.; Goverdhan, P.; Sathian, V.; Prasad, N.K.
Several works in the past have reported that the hydrogen content in the hydrated concrete plays an important role in shielding the neutron radiation; higher the hydrogen content, better is the neutron radiation shielding. In this study, pulverised high density polyethylene (HDPE) material is used as an additional source of hydrogen within concrete to develop a novel class of Polymer-Incorporated Self-Compacting Concrete (PISCC) mixes for enhanced neutron radiation shielding. The HDPE material was incorporated as a partial replacement to river sand. It is found that the PISCC mixes have satisfactory fresh and hardened properties and enhanced neutron radiation shielding properties. © 2017 Elsevier Ltd