1. Ph.D Theses
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Item Development of Eco-Friendly Concretes – A Step Towards Sustainable Construction(National Institute of Technology Karnataka, Surathkal., 2024) Reddy, Ramala Rakesh Kumar; Yaragal, Subhash COwing 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.Item Development and Characterization of Metal Injection Moulded Components in Improving Resistance to High Temperature Wear and Oxidation(National Institute of Technology Karnataka, Surathkal, 2019) C, Veeresh Nayak.; Ramesh, M. R.; Desai, Vijay.Metal injection moulding (MIM) is a near-net shape manufacturing technology for producing intricate parts, cost-effectively. MIM comprises combined techniques of plastic injection moulding and powder metallurgy. A wax-based binder system consisting of paraffin wax (PW), low-density polyethylene (LDPE), polyethylene glycol (PEG-600) and stearic acid is established for MIM of powder systems of Cr3C2- NiCr (30% Wt.) +NiCrSiB (70% Wt.), SS316L (70% Wt.) +WC-CrC-Ni (30% Wt.) and Tool Steel. The excellence of the MIM product depends on feedstock characteristics, process parameters of the injection moulding stage as well as debinding and sintering stage. Injection stage is most important as many defects such as phase separation, weld line, voids etc. may occur during injection stage due to improper selection of injection moulding parameters and these defects cannot be repaired in the subsequent debinding and sintering stages. The feedstock was characterized by rheological properties at different temperatures. Injection temperature was determined by the rheological investigation of the feedstock having the 56 % powder loading and 44% binder by volume. The solvent debinding temperature is optimized and defect-free MIM component is obtained at a temperature of 48°C. Sintering process was carried out with the temperature cycle in the range of 1150–1200 °C under hydrogen purged atmosphere. The sintering density achieved was 96%. The MIM components showed good and acceptable shrinkage in linear dimensions. Material behaviour at elevated temperature is becoming an increasing technological importance. Components working at higher temperatures like in land-based gas turbines, power generation boiler tubes, hot sections of aero engine, gas and steam turbine, propulsion bearings, materials processing, and internal combustion engines are subjected to surface friction, wear, oxidation conditions. Service conditions of such components in elevated temperature environments may compromise their mechanical properties resulting in a reduced life cycle. Components working in such adverse conditions demand suitable components processed through near net shape techniques. The proposed MIM compacts are investigated for their resistance to wear and oxidation under laboratory conditions.vi Three types of MIM specimens namely Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). Further, microstructure and mechanical properties were characterized to evaluate their potential for hightemperature application. Dry sliding wear behaviour of MIM specimens are evaluated using a high-temperature pin on disc tribometer. The SS316L+WC-CrC-Ni and Tool Steel MIM specimens displayed a lower coefficient of friction and wear rate in comparison with Cr3C2- NiCr+NiCrSiB. Excellent wear resistance of the MIM specimens is attributed to the solid lubricants effect. Based on the wear rate data, the relative wear resistance of the MIM specimens under dry sliding conditions is arranged in the following sequence: (Tool Steel) > (SS316L+WC-CrC-Ni) > (Cr3C2-NiCr+NiCrSiB) Higher wear resistance of MIM Tool Steel specimens is attributed to the high hardness of Cr3Ni2 phase formed during the sintering process. Thermo cyclic oxidation behaviour of MIM specimens was carried out at 700 °C for 20 cycles. Each cycle consisted of heating at 700 °C for 1 hour, followed by 20 minutes of cooling in the air. The thermogravimetric technique is used to approximate the oxidation kinetics of MIM specimens. The Cr3C2-NiCr+NiCrSiB and SS316L+WCCrC-Ni MIM specimens reported lower weight gain as compared to the Tool steel. Cr3C2-NiCr+NiCrSiB MIM specimens registered less weight gain as compared to SS316L+WC-CrC-Ni which is attributed to the excellent oxidation resistance of NiCrSiB and formation of NiCrO4 along with NiO and Cr2O3 oxides on the surface of MIM specimens. In the present study, the powders of Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are successfully metal injection moulded and sintered to achieve 96% density. Developed MIM components exhibit resistance to high-temperature wear and oxidation which is suitable for components subjected to elevated temperature service conditions.Item Studies on Elevated Temperature Tribological Behavior of Fly Ash Based Plasma Spray Coatings(National Institute of Technology Karnataka, Surathkal, 2018) Mathapati, Mahantayya; M R, Ramesh; Doddamani, MrityunjayMaterial behavior at elevated temperature is becoming an increasing technological importance. Components working at higher temperatures like in land based gas and steam turbines, power generation boiler tubes, hot sections of aero engine, propulsion bearings, materials processing and internal combustion engines are subjected to surface friction, wear, oxidation and hot corrosion conditions. Service conditions of such components in elevated temperature environments may compromise their mechanical properties resulting in the reduced life cycle. Components working in such adverse conditions demand suitable surface modification techniques like thermal spray coatings that are widely adopted in similar situations. Plasma spray coating processes belong to the family of thermal spraying techniques and are widely used in many industries to protect the components against erosion, oxidation and wear. Thermal energy is utilized in this process to deposit a wide variety of materials including finely divided metallic and non-metallic materials. Higher temperatures utilized in these processes enable the use of coating materials with very high melting points like ceramics, cermets, and refractory alloys. The present work explores the possibility of using fly ash based plasma spray coatings for high temperature applications. The proposed coatings are investigated for their resistance to erosion, oxidation and wear under laboratory conditions. Commercially available Cr3C2-25NiCr, NiCrAlY, WC-Co, fly ash cenospheres, MoS2, CaF2 and CaSO4 are used as coating feedstock in the present investigation. Six types of coatings namely Cr3C2-NiCr/Cenosphere, NiCrAlY/WC-Co/Cenosphere, Cr3C2-NiCr/Cenosphere/MoS2/CaF2, Cr3C2-NiCr/Cenosphere/MoS2/CaSO4, NiCrAlY/WC-Co /Cenosphere/MoS2/CaF2 and NiCrAlY/WC-Co /Cenosphere/MoS2/CaSO4 are deposited on MDN 321 steel substrate (Midhani Grade). Coatings are characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). Further, microstructure and mechanical properties (microhardness, adhesion strength, erosion, oxidation, and wear) have been characterized to evaluate their potential for hightemperature application. For the chosen spray parameters, seemingly dense laminar structured coatings (six types as mentioned earlier) with a thickness in the range of 350-400 m having porosity lower than 5 % has been achieved. Erosion behavior of MDN 321 steel, Cr3C2-NiCr/Cenosphere, and NiCrAlY/WCCo/Cenosphere coatings are investigated at elevated temperatures using solid particle erosion test (ASTM G76-13) set up at 200, 400, 600 °C with 30 and 90° impact angles using alumina erodent. Erosion resistance of both the coatings is observed to be higher than the substrate for the test temperatures chosen and noted to be more prominent at lower impact angle and higher temperature. Both the coatings exhibited a brittle mode of material removal through brittle cracking and chipping. NiCrAlY/WC-Co/Cenosphere coating reported better erosion resistance as compared to Cr3C2-NiCr/Cenosphere coating which may be attributed to plastic deformation of the NiCrAlY matrix due to the ductility of the matrix and hard WC-Co reinforcement to resist the matrix plow thereby reduces the erosion loss. Cyclic oxidation behavior of MDN 321 steel, Cr3C2-NiCr/Cenosphere and NiCrAlY/WC-Co/Cenosphere coatings are further carried out at 600 °C for 20 cycles. Each cycle consisted of heating at 600 °C for 1 hour, followed by 20 minutes of cooling in air. The thermogravimetric technique is used to approximate the kinetics of oxidation of substrate and coatings. Both the coatings reported lower weight gain as compared to the substrate. NiCrAlY/WC-Co/Cenosphere coating registered less weight gain as compared to Cr3C2-NiCr/Cenosphere coating which is attributed to the excellent oxidation resistance of NiCrAlY and formation of CoWO4 along with NiO and Cr2O3 oxides on the coating surface. Influence of solid lubricants on Cr3C2-NiCr/Cenosphere and NiCrAlY/WCCo/Cenosphere coatings is dealt next for tribological response. Dry sliding wear behavior of MDN 321 steel, Cr3C2-NiCr/Cenosphere/MoS2/CaF2, Cr3C2- NiCr/Cenosphere/MoS2/CaSO4, NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2 and NiCrAlY/WC-Co/Cenosphere/MoS2/CaSO4 is carried out using high temperature pin on disc tribometer as outlined in ASTM G99-05 standard. All the four coatingsdisplayed a lower coefficient of friction and wear rate in comparison with the substrate. Excellent wear resistance of the coatings is attributed to the solid lubricants effect. Based on the wear rate data, the relative wear resistance of the coatings under dry sliding conditions is arranged in the following sequence: (Cr3C2-NiCr/Cenosphere/MoS2/CaSO4) > (Cr3C2-NiCr/Cenosphere/MoS2/CaF2) > (NiCrAlY/WC-Co/Cenosphere/MoS2/CaSO4) > (NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2) Higher wear resistance of Cr3C2-NiCr/Cenosphere/solid lubricant coatings is attributed to the high hardness of Cr3C2-NiCr which is incorporated in the coatings. Developed coatings in the present study exhibit higher temperature resistance to erosion, oxidation and wear as compared to MDN321 steel making them suitable for components subjected to elevated temperature service conditions.