Quantitative Backscattered Electron Analysis Techniques for Cement-Based Materials

Abstract

Backscattered electron imaging and x-ray microanalysis are used to identify phases within polished epoxy impregnated cement paste sections. A silicon-magnesium standard is applied and an objective procedure is developed for the calibration of the scanning electron microscope and the image analysis system, so that the L;tensity of individual phases in cement paste appears within reproducible ranges when using backscattered electron imaging, The techniques allow for consistency in quantitative analysis of cement microstructure. Image analysis of cement phases is carried out and a statistical basis is established for the number of frames that must be analyzed to obtain a satisfactory level of confidence in the data. Backscattered electron imaging of polished surfaces of cement paste can be used to distinguish the phases within unhydrated cement particles and the phases of cement I hydration products. The existence of calcium hydroxide within inner product is confirmed, For image analysis, the number of frames required for a selected level of confidence decreases as the magnification decreases, while the total area required increases as the magnification decreases. To achieve a desired level of confidence in image analysis for the phases of hydrated cement paste, unhydrated cement particles require the greatest number of frames, while inner product and calcium silicate hydrate require the least number of frames.