The ITZ in concrete with natural and recycled aggregates : Study of microstructures based on image and SEM analysis (original) (raw)
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Measurement of microstructural gradients at the aggregate/cement paste interfacial transition zone (ITZ) in 8 hardened mortar and concrete is commonly performed via quantitative image analysis of multiple micrographs of 9 specimen surfaces, using a scanning electron microscope. However, due to the random orientation of interfaces 10 sectioned by the specimen surface, measurements of the microstructural gradients at the interface have an unknown 11 angular component, and thus have an unknown error. We present a method for the identification of interfaces that are 12 perpendicular to the specimen surface, and therefore, are more suitable for accurate ITZ analysis. This method employs 13 simple optical and electron imaging techniques on petrographic thin-sections. Use of 3D laser scanning confocal 14 microscopy helped to validate the method. Quantitative 2D image analysis of backscattered electron micrographs, 15 captured over three angular classes of interface gives an indication of this error in the determination of interfacial 16 porosity and anhydrous cement content. 17 Keywords: Backscattered electron imaging (B); image analysis (B); interfacial transition zone (B); microstructure (B); SEM (B) 18
Cement and Concrete Research, 1999
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Journal of Wuhan University of Technology-Mater. Sci. Ed., 2017
Backscattered electron images (BSE) obtained by scanning electron microscope was used to quantitatively characterize the microstructure of interfacial transition zone (ITZ) in concrete. Influences of aggregate size (5, 10, 20, and 30 mm), water to cement ratio (0.23, 0.35 and 0.53) and curing time (from 3d to 90d) on the microstructure of interfacial transition zone between coarse aggregate and bulk cement matrix were investigated. The volume percentage of detectable porosity and unhydrated cement in ITZ was quantitatively analyzed and compared with that in the matrix of various concretes. Nanoindentation technology was applied to obtain the elastic properties of ITZ and matrix, and the elastic modulus of concrete was then calculated based on the Lu & Torquato model and self-consistence scheme by using the ITZ thickness and elastic modulus obtained from this investigation. The experimental results demonstrated that the microstructure and thickness of ITZ in concrete vary with a variety of factors, like aggregate size, water to cement ratio and curing time. The relative low elastic properties of ITZ should be paid attention to, especially for early age concrete.
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Backscattered Electron Imaging to Determine Water-to-Cement Ratio of Hardened Concrete
Transportation Research Record: Journal of the Transportation Research Board, 2001
A methodology has been developed for the determination of the water-to-cement (w/c) ratio in hardened concrete using backscattered electron imaging (BEI) within a scanning electron microscope. Reproducible quantitative data are obtained by using standards from polished sections as well as by controlling brightness and contrast on the instrumentation. The method is based on concrete sections that have been vacuum impregnated with epoxy and polished to a flat surface. During impregnation, epoxy fills capillary porosity as well as cracks, voids, and other defects. The w/c ratio is directly related to the capillary porosity and degree of hydration and therefore can be measured. The epoxy-impregnated porosity appears black in BEI, whereas other phases such as calcium silicate hydrate, ferrite phases, and aggregate appear as brighter phases. Signal production, brightness, contrast, sample preparation, general methodology, and resolution are discussed.