A Chemical Image Analysis Method for Portland Cements
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A CHEMICAL IMAGE ANALYSIS METHOD FOR PORTLAND CEMENTS SIDNEY DIAMOND AND DAVID BONEN Center for Advanced Cement Based Materials, School of Civil Engineering, Purdue University, West Lafayette, IN 47907 ABSTRACT A method is described for carrying out image analysis on portland cements in which the differing chemical compositions of the particles are specifically recognized. Representative fields of ca. 100 individual particles are imaged by a backscatter detector in an SEM, then ported to the attached image analyzer. After preliminary procedures, the image analyzer takes control of the SEM and individually rasters over each particle in turn to acquire both chemical (EDX) and geometrical information. The recorded EDX spectra are used to automatically assign each particle to its predominant mineralogical phase At the same time, conventional feature analysis parameters are acquired for each particle, including measurements of area, length, width, perimeter, shape, etc. The results of the analysis of a given cement constitutes a data base of all of the particles analyzed. It can be used to provide global characterization, or features can be broken out by size class, mineralogical type, shape, or various combinations of parameters. Illustrations are provided of the results of such analysis for a cement, and possible applications to clinker, cement paste, and concrete are considered. INTRODUCTION Portland cements are interground mixtures of ground portland cement clinker and gypsum, and as such can be looked on as classical particulate systems. Modem image analysis instrumentation ordinarily provides means for what is usually terned "feature analysis" for such particulate systems, the features analyzed usually including area, diameter, aspect ratio, perimeter, and shape factor, as determined from two dimensional images. However, such entirely geometrical particle analyses leave out essential information when dealing with portland cement particles, i.e. the mineralogical nature of the individual particles. Feature analysis can also be applied to masses of fused crystals, such as are found in portland cement clinker prior to grinding. In such cases the individual crystals constitute the features, and valuable information concerning crystal size and shape can be obtained. However, the behavior of portland cement in cement hydration depends on how the cement is ground, and analysis of the ground portland cement is normally of more direct concern. In image analysis, the determination of the mineralogy of individual particles in ground cement may be attempted by gray level segmentation of backscattered images, for example as reported by Scrivener [1]. She was, however, unable to distinguish between C3S and C2S, and confined her analyses to distinguishing between particles composed of the silicate phases and those composed of the interstitial phases. With current equipment the distinction between the two silicates by gray level can now readily be made, but unfortunately C2S and C3A still cannot be unambiguously distinguished fro
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