Optimization of SEM-EDS to determine the C–A–S–H composition in matured cement paste samples

Abstract

Microanalysis of characteristic X-rays in the SEM is a powerful method to assess the chemical composition of phases in cement pastes, in particular the calcium silicate hydrate containing aluminium (C–A–S–H). Nevertheless, many variables may influence the results obtained, due mainly to the intimate mixing of C–A–S–H with other hydrate phases and the susceptibility of this phase to damage by the electron beam. In this study the effect of various acquisition parameters was examined, along with methods to determine an “average” C–A–S–H composition. The results acquired in the SEM were compared with the analysis of the same samples in the TEM, where phases can be analyzed without intermixing. A simple method was used to obtain compositions from SEM based analysis that are very close to those which can be obtained in the TEM.