Journal Articles
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/19884
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Item Microstructural study of steel-concrete interface and its influence on bond strength of reinforced concrete(ASTM International, 2019) Goudar, S.K.; Das, B.B.; Arya, S.B.In this investigation, the variations in steel-concrete interface (SCI) properties, such as porous zone thickness and calcium hydroxide content around the reinforcing steel, were studied with respect to curing time. Three kinds of commercially used cements, ordinary portland cement (OPC), portland pozzolana cement (PPC), and portland slag cement (PSC), were used, and their significance regarding SCI properties was investigated. A reliable thresholding grayscale-based technique was used to determine the porous zone thickness at the SCI. The properties of SCI were found to be quite influenced by the curing period. The PSC concrete showed significant reduction in mean porous zone thickness at SCI compared with OPC and PPC concrete after 90 days of curing. The reduction in mean porous zone thickness can be considered one of the many influencing factors that resulted in increased ultimate bond strength at 90 days of curing. Also, the variation in calcium hydroxide content from the SCI toward the bulk concrete was examined with a scanning electron microscope empowered with energy-dispersive spectroscopy. The findings indicate a gradual decrease in calcium hydroxide content away from the steel surface toward the bulk concrete. The prolonged curing resulted in a slightly higher reduction of calcium hydroxide content around the SCI for PPC and PSC concrete because of the pozzolanic reactions. Higher reduction of calcium hydroxide content around the SCI for PPC and PSC concrete is predicted to be the reason for improved ultimate bond strength after prolonged curing. © 2019 by ASTM International.Item Influence of sample preparation techniques on microstructure and nano-mechanical properties of steel-concrete interface(Elsevier Ltd, 2020) Goudar, S.K.; Das, B.B.; Arya, S.B.; Shivaprasad, K.N.Interface between steel and concrete is characterized as highly porous and weakest region which influences both mechanical properties and durability of a reinforced concrete structure. The properties of the steel-concrete interface (SCI), especially the porous zone thickness are prime factors in predicting the time for corrosion initiation to corrosion cracking in service life prediction models. Measurement of porous zone thickness of reinforced concrete samples is sensitive to the sample preparation technique for microscopic observations. It is observed that there are hardly any research articles are available in the literature regarding the sample preparation technique of reinforced concrete sample for SCI analysis. In the present study, a detailed and stepwise sample preparation technique is proposed where there is minimal damage found to be observed to SCI. The major focus is on the speed of cutting tool that is being used for obtaining a relatively small size of sample from the bulk reinforced concrete member. The properties such as porous zone thickness and nano mechanical properties around the SCI were determined through scanning electron microscopy and nano-indentation, respectively. A significant variation in porous zone thickness around SCI was observed and measured value of average porous zone thickness is found to be approximately 1.8 times higher from high-speed cutting to low-speed. A similar kind of observation was noticed for nano mechanical properties. In addition to speed of cutting, there found to be other factors such as pressing force for specimen, duration of polishing and heating temperature has significant influence on interfacial properties. © 2020 Elsevier LtdItem IMPLICATION OF HIGH-VOLUME MINERAL ADMIXTURE ON MECHANICAL PROPERTIES AND MICROSTRUCTURE AT STEEL-CONCRETE INTERFACE(Associated Cement Companies Ltd., 2023) Goudar, S.K.; Sumukh, E.P.; Das, B.B.The existence of a non-homogeneous unique zone in concrete along the periphery of steel surface is being referred as steel-concrete interface (SCI). The interface between steel and concrete exhibits a porous zone, with a thickness measuring several micrometers. This porous zone thickness around SCI plays a crucial role in influencing bond strength, durability, and is a significant parameter used in service life prediction models for reinforced concrete structures. The value of porous zone thickness around SCI is being assumed and adopted without any practical studies in service life prediction models as well as in reinforced concrete mesoscale structure modelling. In the present study, porous zone thickness was experimentally measured through obtaining backscattered electron images around SCI. Gray scale-based thresholding technique was employed to ascertain the porous zone thickness (PZT) around SCI. Furthermore, the influence of incorporating ground granulated blast furnace slag (GGBS) in high-volume on the interfacial transition zone (ITZ) between steel reinforcement bars and the surrounding concrete was investigated. It was observed that porous zone thickness around SCI varies in every other point along the periphery of reinforcement bar. The pozzolanic reaction in high volume GGBS concrete resulted in a substantial decrease of porous zone thickness (PZT) and reduced the accumulation of Portlandite around SCI with the progress in curing age. The factors contributing to the enhanced ultimate bond strength of high volume GGBS concrete compared to control concrete are the decrease in the Porous Zone Thickness (PZT) along with the reduced Ca/Si ratio around the SCI. © 2023, Associated Cement Companies Ltd.. All rights reserved.