Browsing by Author "Yaragal, Subhash C"

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Analytical Tools for Strength Prediction of Thermally Deteriorated HPC
(National Institute of Technology Karnataka, Surathkal, 2014) Bhygayalaxmi, Kulkarni Kishor Sitaram; Yaragal, Subhash C; Narayan, K. S. Babu
Analytical tools for strength prediction of thermally deteriorated HPC” is an experimental study on development of analytical tools for strength prediction of High Performance Concrete (HPC) exposed to elevated temperatures. The prime objective is to study the behaviour of HPC at different exposure durations and temperatures. The work also focuses on the residual strength assessment of concrete exposed to elevated temperature by non-destructive testing. Exhaustive review of literature has been done to understand the state of the art, to identify the points needing further research and then to design the experimental investigation. First phase of the study deals with properties of four types of HPC mixes that include unblended and blended mixes, with partial replacement of cement by Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS), at exposure temperature range of 100°C-800°C and exposure duration of 1, 2 and 3 hours. Colour change and crack patterns have been observed. Porosity and density determination, Ultrasonic Pulse Velocity (UPV) measurements to assess the quality of concrete, have been made. Residual compressive and splitting tensile strengths have been determined by destructive testing. Second phase explores the potential of drilling resistance test on thermally deteriorated concrete as an NDT tool. Drilling time for a designated depth of drilling and sound measurement while drilling have been recorded. Determination of residual compressive strength of plain and reinforced concrete, exposed to elevated temperature has been carried out in the third phase of experiments by core recovery tests to understand the behavioural differences. From the above investigation very interesting conclusions have been drawn that highlight the superiority of blended concrete’s fire endurance properties. The potential use of drilling time and sound levels as an NDT tool, nomographs that can be used as valid decision making tools in failure forensics and also elaborate the care and caution necessary in conducting and interpretation of core test results of fire damaged structural elements.
Development of Eco-Friendly Concretes – A Step Towards Sustainable Construction
(National Institute of Technology Karnataka, Surathkal., 2024) Reddy, Ramala Rakesh Kumar; Yaragal, Subhash C
Owing to the rapid advancements in industrialization and urbanization, the utilization of concrete has witnessed an exponential surge over the past few decades. This escalating demand for concrete necessitates a proportional increase in natural resources for both cement production and the procurement of coarse aggregates. Notably, the production of cement not only depletes limestone resources but also entails environmentally unfriendly processes. Furthermore, the surge in concrete demand is accompanied by a substantial increase in the generation of construction and demolition (C&D) waste, owing to evolving trends, economic development, and the heightened demolition of existing structures in the 21st century. This surge in C&D waste generation poses a significant environmental challenge. To render concrete production more sustainable, it is imperative to mitigate the reliance on conventional cement. This can be achieved through the incorporation of supplementary cementitious materials and the utilization of C&D waste as aggregates in concrete. Such measures not only diminish the demand for natural aggregates but also contribute to reducing landfill volumes, aligning with contemporary principles of environmental conservation and sustainable development. The present study focuses on the processing of C&D waste into the quality of Recycled Coarse Aggregates (RCA) and uses them in the production of cement-less concrete. This study proposes an alternative method for processing the demolition waste into high-quality recycled coarse aggregate using the ball mill. Taguchi’s design of experiments based on orthogonal array was used to minimize the number of trials for saving material and time. Experiments were carried out based on L25 orthogonal array with three processing parameters: charge, revolution duration, and aggregate weight with five levels. The revolution speed of the ball mill was set to 60 revolutions per minute. The Taguchi method was then combined with grey relational analysis to achieve the best combination of processing parameters for producing high-quality aggregate. Experimental studies on water absorption, specific gravity, impact value, and abrasion value were used to assess the quality of recycled coarse aggregates. The best combination for each performance characteristic was achieved by using the mean of Signal to Noise ratio graphs. The optimal combination of processing parameter levels i to generate superior quality recycled aggregates and the most significant processing parameter were identified based on the response table of means of grey relation grade. The processed RCA along with Ferrochrome Slag aggregates (FCSA) was used for the production of One-Part Alkali-Activated concrete (OPAAC) by replacing cement with Fly ash (FA), Micro silica (MS), and Ground granulated blast furnace slag (GGBS). The proportion of MS is maintained at 20% of FA, while the maximum replacement of FA with GGBS is set to 60%, varying in 20% intervals (i.e., 0%, 20%, 40%, and 60%). Moreover, the natural aggregates (NA) are substituted with RCAs, FCSAs, or a combination of both. Additionally, microstructural and mineralogical investigations are conducted to determine the formation of distinct hydration products, utilizing scanning electron microscopy (SEM) and X-ray diffractometry (XRD) techniques. In OPAAC containing FA, the primary hydration products identified are alkaline alumino silicate hydrates (CASH and NASH). As the GGBS content increases, calcium silicate hydrate (CSH) becomes the predominant hydration product. Furthermore, in order to assess the sustainability of OPAAC, an analysis of embodied CO2 emissions is performed, and the results are compared with CC and alkali-activated concrete. Notably, OPAAC comprising 40% FA replaced with GGBS, 50% RCAs, and 50% FCSAs demonstrates the most favourable mechanical properties and exhibits lower CO2 emissions. In this study, an examination of the performance of OPAAC mixes under elevated temperatures was also conducted. The mechanical properties results dictated a fixed combination of RCAs and FCSAs)at 50% each. The binder composition was identified as a critical factor influencing the performance of concrete at elevated temperatures. Consequently, OPAAC mixes were meticulously formulated using various combinations of FA, MS, and GGBS. These mixes underwent exposure to temperatures ranging from 200℃ to 800℃, with increments of 200℃. Notably, the mix comprising 60% FA and 40% GGBS exhibited superior performance compared to all other OPAAC mixes and conventional concrete under the specified elevated temperature conditions.
Performance Appraisal of Eco-Friendly Mortars and Concretes
(National Institute of Technology Karnataka, Surathkal, 2018) Prabhu, K. Rajendra; Yaragal, Subhash C; Venkataramana, Katta
Cement concrete is the major construction material largely used throughout the world for infrastructures like buildings, pavements, irrigation structures and so on. Concrete is prepared by using locally available materials. One of the important concern facing construction industry today is, the scarcity of virgin materials due to their exponential depletion and continued increase in demand. This is due to rapid growth in construction industry and stringent environmental policies to check and control harmful effects on environment, caused by production or processing methods for construction materials and chemicals. As the natural resources are fast depleting and also the production of cement and aggregates consume energy (energy intensive) which also indirectly produce carbon dioxide posing threat to the environment. Due to the above pressing needs, it is most warranted to search for alternative or promising eco-friendly materials. Huge amount of wastes generated in various fields is not utilized other than for land filling, incineration etc. These wastes can be utilized as ingredients partially or fully by embedding these wastes in either mortars or concretes without being detrimental. Experiments with Broken Mangalore Tiles (BMT) wastes in the form of Secondary Cementitious Material (SCM), Fine Aggregates (FA), and Coarse Aggregates (CA) were planned and executed to replace cement, river sand and granite CA respectively, to study the performance of both BMT based mortars and BMT based concretes. Further experiments have also been conducted to ascertain performance of BMT based mortars and BMT based concretes at elevated temperatures. Usage potential of BMT CA, in pervious concretes is studied. The scope for utilizing Iron Ore Tailings (IOT) and / or Copper Slag (CS) as replacement to River Sand (RS) is also assessed. Further Melt Processed Plastic (MPP) pellets as filler in mortar and concrete is attempted. Use of EPS packaging material as FA (as filler) and CA (as filler) is also undertaken in this investigation. Results show, with BMT waste material as fine aggregate or coarse aggregate to the extent of 100% replacement is possible without compromise on concrete strength,with 90 days of curing. It is interesting to note also that 100% FA and 100% CA could be replaced by 100% BMT FA and 100% BMT CA without loss in concrete strength with 90 days of curing. Even in the case of mortar, there is no loss in strength for mortar with 100% BMT FA, with 90 days curing. 80% addition of BMT powder or 20% replacement of cement by BMT powder with 90 days curing is possible without loss in mortar strength. 100% BMT CA, based concrete has given higher endurance to elevated temperatures as regards to strength. Loss in weight increases with both rise in temperature as well as increase in the BMT CA content. Higher BMT CA increases porosity and assists better elevated temperature endurance. Up to 600°C, the performance of concrete with BMT FA (either half or full replacement) is superior when compared to concrete with 0% BMT FA. Higher BMT FA increases porosity indirectly favouring better elevated temperature endurance up to 600°C. For BMT FA and BMT CA based concrete at elevated temperatures, residual compressive strength remains nearly constant up to 400°C. Further increase in temperature up to 800°C, strength decreases. However, the differences in strengths between various combinations reduce after 400°C. Residual strength of mortar mix BMT FA100, monotonically decreases with increase in temperature. However its performance appears to be better than mortar mix BMT FA50 for temperature levels of 600°C and 800°C. It is observed that mortar with BMT powder as addition to OPC possesses more strength than replacement to OPC at all levels of temperatures. For a given porosity, the density of pervious concrete with BMT CA is always lower than that of granite CA by around 300 kg/cu.m. BMT CA in full replacement to granite CA, performs well in pervious concretes. Compressive strength of concrete reduces by about 26% when sand is replaced from 0 to 100% by IOT. Strength values almost remain constant up to 75% replacement of sand by IOT. Copper slag replacing sand to the extent of 100% does not result in strength reduction of concrete. From mortar strength studies with IOT and CS in place of sand, it is to be noted that for both cases replacement level of 50%, result in no loss in strength with two months of curing period. MPP pellets are added as filler by volume of concrete. It isobserved that the concrete strength drops by 50% for approximately 25% filler. Strength variation of mortars containing river sand, IOT and CS as FA with MPP pellets as filler at different blending dosages is studied. For all the three cases strength drops with increase in filler content, however the rate of drop is lower for mortar containing IOT as FA and higher for CS as FA, when compared to mortar with RS as FA. For concrete, with increase in EPS CA (as filler) content, all the three strengths (compression, split tensile and flexural) decrease by about 70-80% for 100% replacement. For mortar, as EPS FA (as filler) content increase, there is decrease in strength. At 100% replacement, the strength is approximately 15% of the reference mortar strength. This study is a step towards sustainable construction practices and recommends use of these eco-friendly unconventional materials to the extent possible.
Studies on Performance Enhancement by Recuring of Thermally Deteriorated Concrete and Appraisal of Plaster Compositions as Heat Sheilds
(National Institute of Technology Karnataka, Surathkal, 2014) Prashanth, Shree Laxmi; Yaragal, Subhash C; Narayan, K. S. Babu
Concrete is the most versatile construction material which finds its applications in all the civil engineering structures. The properties of the concrete deteriorate when it is subjected to elevated temperatures. Compressive strength being the most desired property of concrete, it is essential to study the strength retention characteristics of concrete at various elevated temperature levels in order to evaluate the usefulness of concrete. Residual strength of concrete subjected to elevated temperatures depends on the temperature to which it is exposed and the duration for which it is exposed. The first objective is to evaluate quantitative evaluation of effects of exposure duration, temperature and the soaking periods at those designated temperatures. Exposure durations of ½, 1, 1½ 2, 3 and 4hr for elevated temperature levels ranging from 200°C to 800°C at 100°C interval have been considered for the study. Two heating rates (slow and fast) and cooling methods (furnace cooling and water quenching) have been adopted and investigated for their influence on strength characteristics. Concrete residual strength has been found to be affected by the temperature levels especially for the temperatures above 600°C. At each of the temperatures studied concrete retains lower strength for higher exposure duration. Slower heating signifies presence of heat for larger duration resulting into larger deterioration of strength. Cooling of concrete by quenching in water results in higher deterioration of strength owing to thermal shock. Thermally deteriorated concrete when comes in contact with moisture, rehydrates, thereby resulting into partial recovery of strength. The second objective of the study was to study the efficacy of Recuring as a means of strength recovery. To facilitate rehydration thermally deteriorated concrete specimen were subjected to water curing till 56 days and recovery in strength has been noted after 7, 14, 28 and 56 days. Encouraging results were obtained for concrete exposed to temperatures upto 600°C, for higher temperatures however recuring did not result into substantial recovery. The effectiveness of recuring depends on the rehydration capacity of the dehydrated cement paste, which decreases with the increase in exposure temperatures. Partial recovery ofstrength after recuring suggests that if situation permits, recuring can be a potential technique that helps reduce restoration costs. Plastering of concrete elements is an usual practice in order to render a smooth finish and to enhance architectural features. The mortar used for plaster, if made with materials that can resist high temperatures, can protect the structural element. Objective of the research was also to study the effectiveness of mortar as heat shield. Experimental investigations on efficacy of use of vermiculite aggregates in mortar for plastering to enhance fire endurance characteristics have been detailed. The thesis presents strength deterioration of concrete at elevated temperatures with emphasis on exposure levels, duration and rate of heating and cooling. Potential benefits of recuring in strength recovery have been appraised. Efficacy of vermiculite aggregates in mortar for plaster as heat shield has been evaluated.