Incorporation of Aluminum into C–S–H Structures: From Synthesis to Nanostructural Characterization
Abstract:C–A–S–H (C=CaO, A=Al2O3, S=SiO2, H=H2O in cement nomenclature) phases have been synthesized from CaO, SiO2, and AlNaO2. The initial CaO/SiO2 (C/Sinitial) ratios varied from 0.8 to 1.5 and the initial Al2O3/SiO2 (A/Sinitial) ratio was set to 0.1. Samples were characterized by X-ray diffraction and chemical analyses of their equilibrium solutions. This paper describes experiments using a low-voltage scanning transmission electron microscopy (STEM-in-SEM) imaging system that allows transmission observations in an environmental scanning electron microscope. Observations of the nanostructure were also performed by transmission electron microscopy (TEM). Two types of morphologies were clearly observed: fine fibrillar aggregates and small plates, the latter being particularly sensitive to beam damage. Despite their different appearance, both of these phases were amorphous, and the small plates were richer in aluminum. The fraction of the small plate phase increased with the C/Sinitial ratio. TEM interpretations showed that C–A–S–H phases were not stable under the electron beam and high-magnification observations could significantly modify their structure. Images and chemical analyses acquired with STEM-in-SEM appeared as valuable sources of information because they offered a large observation field comparable to a transmission electron microscope and better magnification resolution than a classical scanning electron microscope.
Document Type: Research Article
Publication date: 2008-07-01