Publication

Quantification of amorphous siliceous fly ash in hydrated blended cement pastes by X-ray powder diffraction

Abstract

X-ray powder diffraction (XRPD)-based quantitative phase analysis is a common technique for studying the hydration of cementitious systems. Hydrated cements often comprise several amorphous or nanocrystalline phases. This paper presents a protocol for the quantification of amorphous siliceous fly ash in hydrated cement using XRPD based on the Rietveld PONKCS (partial or no known crystal structure) method. The protocol is validated by comparison against independent measurements, such as Ca(OH)(2) content by thermogravimetry and isothermal calorimetry to evaluate the fly ash degree of reaction. A sensitivity analysis of the protocol was carried out to test the robustness of the results with regard to sample preparation, data collection strategies and refinement model parameters. The key sensitive aspects of the protocol are (i) the preservation and preparation of the hydrated cement sample for XRPD measurement, (ii) the selection of a 2g theta angular range for the Rietveld analysis that avoids low-angle scattering interferences, and (iii) the use of the peak profile to account for the contribution of other amorphous phases such as the diffraction pattern of nanocrystalline calcium silicate hydrate (C-S-H). The results show good accuracy in terms of quantification if the initial fly ash content is more than 10 wt%. Example TOPAS fly ash and C-S-H codes, as well as the raw XRPD data set, are provided.

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Related concepts (34)
Cement
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Concrete is the most widely used material in existence and is behind only water as the planet's most-consumed resource.
Energetically modified cement
Energetically modified cements (EMCs) are a class of cements made from pozzolans (e.g. fly ash, volcanic ash, pozzolana), silica sand, blast furnace slag, or Portland cement (or blends of these ingredients). The term "energetically modified" arises by virtue of the mechanochemistry process applied to the raw material, more accurately classified as "high energy ball milling" (HEBM). This causes, amongst others, a thermodynamic transformation in the material to increase its chemical reactivity.
Powder diffraction
Powder diffraction is a scientific technique using X-ray, neutron, or electron diffraction on powder or microcrystalline samples for structural characterization of materials. An instrument dedicated to performing such powder measurements is called a powder diffractometer. Powder diffraction stands in contrast to single crystal diffraction techniques, which work best with a single, well-ordered crystal. Diffraction grating The most common type of powder diffraction is with x-rays, the focus of this article although some aspects of neutron powder diffraction are mentioned.
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