A new model of ordinary portland cement hydration derived by means of ESEM-FEG

Abstract

The visualization of structures resulting from processes taking place within a few nanometers is immensely important when studying the properties of concrete and mortar. Electron microscopy is in principle capable of obtaining images of structural constituents in this size range. Unfortunately, studies with conventional electron microscopes are subject to serious limitations: the specimens must be high-vacuum-stable or correspondingly prepd. and the specimen must generally be elec. conductive or be made conductive by a coating of the surface. For these reasons, an Environmental Scanning Electron Microscope with Field Emission Gun (ESEM-FEG) in different operating modes has been used to investigate wet materials in their native state. These methods provide deep insights into the moist micro and nano world. It even makes it possible to carry out sophisticated observations of hydration processes in complicated mufti-phase systems, such as Portland cement. The article describes the investigations of the phase development during the hydration of OPC from the induction to the final period. The results are summarized in a scheme for a new model of ordinary Portland cement hydration.