Faculty Publications
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Item Studies on normal strength concrete cubes subjected to elevated temperatures(2010) Yaragal, S.C.; Babu Narayan, K.S.; Venkataramana, K.; Kulkarni, K.S.; Gowda, H.C.C.; Reddy, G.R.; Sharma, A.Concrete in structures is likely to be exposed to high temperatures during fire. The probability of its exposure to elevated temperatures is high due to natural hazards, accidents and sabotages. Therefore, the performance of concrete during and after exposure to elevated temperature is a subject of great importance and interest to the designer. Popular normal strength grades of concrete produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm cubes), cured and tested by destructive method for gathering data on strength characteristics. Later, these test samples were subjected to elevated temperatures ranging from 100 C to 800 C, in steps of 100 C with a retention period of 2 hours. After exposure, weight losses and the residual compressive strength retention characteristics are studied. Test results indicated that weight and strength significantly reduces with an increase in temperature. Residual compressive strength prediction equations are proposed for normal strength concretes subjected to elevated temperatures.Item Performance appraisal of RC beams using welded wire fabrics as lateral reinforcement in seismic zones(CAFET INNOVA Technical Society 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2011) Gowda, H.C.C.; Babu Narayan, K.S.; Venkataramana, K.Ductility is the key to design earthquake resistant structures. More rigid the structure or the element, more it attracts inertia forces. Structures and elements of infinite rigidity are out of question. Codes of practice also advocate design philosophies wherein effects of small earthquakes are to be absorbed with little or no damage, medium with damage to such extents that rehabilitation is possible and large earthquake effects to be catered without collapse. To absorb the tremendous energies that are input to structures and elements unless ductility is ensured, performance levels proposed by codes and standard practices cannot be attained. Lateral ties hold longitudinal reinforcement of R.C.elements in place and also confine the concrete. The basis of the present work is the usage of welded wire fabrics as lateral reinforcement in RC beams. A series of beams were tested with lateral ties and welded wire fabric at discrete locations and welded wire fabric alone throughout the beam with different mesh opening sizes. This paper presents the encouraging results with marginal increase in strength and considerable improvement in ductility in addition to reduced crack widths as observed for specimens having welded wire fabric with smaller mesh openings as lateral reinforcement by confining concrete. © 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Characteristics of normal strength concrete with and without chemical admixtures at elevated temperatures(CAFET INNOVA Technical Society 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2011) Yaragal, S.C.; Warad, S.A.; Babu Narayan, K.S.; Venkataramana, K.Fire is one of the most destructive powers to which a building structure can be subjected. Behavior of concrete when exposed to fire in cases like nuclear plants, cooling towers or any accidental fire in industrial buildings, is a serious concern, on the strength retention property of concrete. This work reports strength retention studies on compressive and split tensile strength of normal concrete with and without the chemical admixture (Reobuild 918, BASF make) at elevated temperatures. Concrete cubes of size 100 mm have been cast as per prior mix design for M30 grade of concrete, 28 days water cured and tested by destructive method for strength before exposure. Later these specimen were subjected to elevated temperatures of 200°C, 400°C, 600°C and 800°C with a retention period of 2 hours and were allowed cool within the furnace to reach ambient temperature. Later their appearance, colour and cracks were observed and also weight losses were determined. Further, destructive tests were conducted to estimate residual compressive and residual split tensile strengths and prediction equations are proposed to ascertain splitting tensile strengths from compressive strengths. © 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Usage potential of melt processed plastic pellets as a substitute to fine aggregate in porous concretes(2012) Maneeth, P.D.; Lokesh, G.; Yaragal, S.C.; Babu Narayan, K.S.Porous concrete (PC) has been used for over 30 years. Because of its high porosity, the most common usages have been in the area of storm water management, but have been limited to use in pavements with low volume traffic, because of its low compressive strength compared to conventional concrete. Domestic and industrial plastic waste management has posed a serious challenge to engineers and scientists today. In this study an attempt is made to utilize plastic waste (melt processed) from small industries as a substitute for fine aggregate (up to 10%) in producing porous concretes. The recycled plastic (melt processed) was produced by drawing industrial and domestic waste plastic into long strands which were cut to small pieces forming granules. The plastic granules (pellets) are used as substitute to sand in this investigation. This experimental investigation reports the scope for plastic waste utilization as a substitute for fine aggregate and its influence on properties like porosity, permeability, compressive strength and tensile strength of porous concretes. © 2012 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Strength characteristics of concrete exposed to elevated temperatures and cooled under different regimes(2012) Yaragal, S.C.; Babu Narayan, K.S.; Adari, S.Concrete loses strength in the event of accidental fires. The residual strength of normal strength concrete is of vital importance for ascertaining serviceability of buildings after the event of fires. Strength loss in concrete is dependent on the temperature of exposure, its duration and the way it gets cooled. In this study concrete cubes of size 100 mm have been cast for M25 grade of concrete, 28 days water cured. The specimens were subjected to elevated temperatures of 150°C, 250°C, 350°C, 450°C and 550°C with a retention period of 1 hour. After 1 hour of exposure, specimens were allowed to cool under different cooling regimes to ambient temperature. Later their appearance, colour and cracks were observed and also weight losses were determined. Further, destructive tests were conducted to estimate residual compressive and split tensile strengths. Important performance changes have been presented and discussed. Split tensile strengths are related to compressive strengths for all the cases of cooling regimes.Item Experimental investigation of RC frames using CFRP sheets(2013) Prashanth, M.H.; Babu Narayan, K.S.; Venkataramana, K.; Sajith, M.Reinforced Concrete frames are the main load resisting systems used in practice all over the world. These frames will be subjected to sway, due to lateral loading most of the times by either earthquake or wind. Ductility and energy dissipation capacity of the frame are the key parameters for better performance under the action of the sway loading. Retrofitting using the new generation material such as carbon fiber reinforced plastic sheets (CFRP) shows much enhancement in these properties of laterally loaded frames. Frames subjected to lateral loading introduce collapse mechanism due to the formation of the plastic hinges at critical hinge locations. An experimental investigation of partially and fully CFRP wrapped reinforced concrete (RC) frames when compared to conventional(bare) frame has been carried out, to bring out the importance of critical engineered locations to be wrapped. © 2013 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Bond strength behaviour in reinforced concrete members exposed to corrosive environment - An overview(2013) Shetty, A.; Venkataramana, K.; Babu Narayan, K.S.; Kimura, Y.Bond resistance of reinforcing bars, embedded in concrete depends primarily on frictional resistance and mechanical interlock. Corrosion of rebars in concrete is one of the major problems in the durability criteria. Local bond stress slip relationship is generally adopted to determine the mechanical properties of the interface between re-bars and concrete. Therefore the attainment of satisfactory performance in bond is an important, aspect of the design and the detailing of reinforcement in structural components. In this paper an overview of factors affecting specimen geometry of bond strength and Types of bond tests were studied. © 2013 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Recuring studies on concretes subjected to elevated temperatures and suddenly cooled by water quenching(Multi-Science Publishing Co. Ltd, 2015) Yaragal, S.C.; Kittur, M.M.; Babu Narayan, K.S.Concrete is found to undergo degradation when subjected to elevated temperatures during an accidental event, such as fire and lose substantial amount of its original strength. The loss of strength in concrete is mainly attributed to the decomposition of Calcium Silicate Hydrate (C-S-H) and release of chemically bound water, which begins when the exposure temperature exceeds 500°C. When such a concrete is supplied with water and allowed to recure, it is found to recover substantial amount of its lost strength. This work is carried out to investigate the effect of recuring on strength recovery of un-blended and blended concrete specimen (100 mm cubes) subjected to elevated temperatures from 400°C to 700°C, in steps of 100°C, for a retention period of two hours at the designated temperatures. The concrete cubes immediately after exposure were subjected to thermal shock by quenching them in water, and then temperature of thermally shocked concrete is allowed to cool to room temperature. The cooled specimen were then recured in water for 1, 3, 7, 14, 21, 28, 56 days and tested for compressive strength recovery. These studies were carried out for Portland Cement (PC) based concrete and Portland & Granulated Blast Furnace Slag (70% PC + 30% GGBS) based concrete (blended concrete), and some interesting results are presented and discussed in this paper. © 2015, Multi-Science Publishing Co. Ltd. All rights reserved.Item Assessment of thermally deteriorated concrete by drilling resistance test and sound level(Maik Nauka Publishing / Springer SBM compmg@maik.ru, 2017) Kulkarni, K.S.; Yaragal, S.C.; Babu Narayan, K.S.; Vardhan, H.Concrete being the most versatile and widely used construction material finds application in varied range of structures. Many of these like chimneys, furnaces and reactors have to sustain high temperatures and perhaps all structures have to perform at elevated temperatures in the event of fire accidents. Concrete at elevated temperatures undergoes changes in its physical structure and chemical composition and loses its strength characteristics. Need for quick assessment of fire damaged concrete for strength characteristics, has motivated this work, which explores the potential of drilling resistance test on concrete as a Non Destructive Testing (NDT) tool. Drilling times, penetration depths and sound level measurement while drilling have been recorded and analysed to provide monograms that are handy as reckoners in failure forensics. © 2017, Pleiades Publishing, Ltd.Item Multi-criteria optimization of fly ash and iron ore tailing based concretes subjected to elevated temperatures(Associated Cement Companies Ltd., 2019) Yaragal, S.C.; Babu Narayan, K.S.; Kumar, B.; Francis, J.G.Due to the rapid increase in concrete utilization all over the world, there is increased consumption of Ordinary Portland Cement (OPC), natural fine aggregate (NFA), and natural coarse aggregates. Increased use of OPC, is posing a serious threat due to excess CO2 emissions, and its production is highly energy intensive. On the other hand, extraction and processing stone-based fine and coarse aggregates too, is energy intensive, and the virgin resources are fast depleting. Therefore, for sustainable development, efforts are on all over the world to look for alternative materials in place of conventional ones. In this study, it is attempted to partly replace OPC with fly ash (FA) and partly replace NFA by iron ore tailings (IOT) in concretes. The performance of such concretes at ambient and elevated temperatures is also presented. Full factorial design of experiments was adopted with two control factors under three levels of replacement, i.e., FA (0, 15, and 30% by weight of OPC) and IOT (0, 50, and 100% by volume of NFA). Total nine concrete mixes were prepared and tested for their compressive strengths at room temperature, and residual compressive strengths when subjected to various levels of elevated temperatures (200, 400, 600, and 800°C), and cost of these concretes has also been analyzed. Further, three traditional multi–criteria optimization methods, i.e., grey relational analysis (GRA), technique for order of preference by similarity to ideal solution (TOPSIS), and desirability function approach (DFA) were used to optimize concrete mixes. Results showed that TOPSIS based optimization method is more significant when compared to other two methods. Further, FA-based concrete mixes showed improved performance under multi-criteria optimization. © 2019, Associated Cement Companies Ltd. All rights reserved.