3D chemical segmentation of fly ash particles with X-ray computed tomography and electron probe microanalysis

Hu, Qinang; Ley, M. Tyler; Davis, Jeffrey M.; Hanan, Jay C.; Frazier, Robert

doi:10.1016/j.fuel.2013.07.037

Cited by 35 publications

(13 citation statements)

References 19 publications

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“…Figure 1B shows that the measured dissolution rate of all the fly ashes in this study decreases exponentially with the number of constraints, n c , for a given pH. 11,13,40 When the fly ash dissolution rates shown in Figure 1B are plotted along with additional dissolution rate data for glassy silica, quartz, and several aluminosilicate glasses including albite, jadeite, nepheline, and sodium silicate glass (denoted as "Natural" glass; see Figure 1C 18,35,36 )the exponential dependence of dissolution rate on n c is preserved § . It should be noted that decreases in dissolution rate generally correspond to lower concentrations of calcium in the fly ash, but this is not true in all cases.…”

Section: Methodsmentioning

confidence: 68%

“…1 To mitigate the impacts of such CO 2 emissions, it is common to replace OPC with supplementary cementitious materials (SCMs) such as fly ash in the binder fraction in concrete, a process commonly known as "dilution". [7][8][9][10][11][12] Establishing the origin of and controls on fly ash reactivity is prerequisite knowledge, needed to rank different fly ashes in terms of their suitability as an OPC replacement agent. [7][8][9][10][11][12] Establishing the origin of and controls on fly ash reactivity is prerequisite knowledge, needed to rank different fly ashes in terms of their suitability as an OPC replacement agent.…”

Section: Introductionmentioning

confidence: 99%

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Topological controls on the dissolution kinetics of glassy aluminosilicates

et al. 2017

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Fly ash which encompasses a mixture of glassy and crystalline aluminosilicates is an abundant supplementary cementitious material (SCM), valuable for replacing ordinary portland cement (OPC) in the binder fraction in concrete. Because higher OPC replacement levels are desired, it is critically important to better understand and quantify fly ash reactivity. By combining molecular dynamics (MD) simulations and vertical scanning interferometry (VSI), this study establishes that the reactivity of the glassy fractions in a fly ash with water (i.e., their aqueous dissolution rate) is controlled by the number of constraints placed on atoms within the disordered aluminosilicate network. More precisely, an Arrhenius‐like dependence of dissolution rates on the atomic network topology is observed. Such topological controls on fly ash reactivity are highlighted for a range of U.S. commercial fly ashes spanning CaO‐enriched and SiO2‐enriched compositions. The structure‐property relationships reported herein establish an improved framework to control and estimate fly ash‐cement interactions in concrete.

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Section: Methodsmentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Topological controls on the dissolution kinetics of glassy aluminosilicates

et al. 2017

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“…The X-ray absorption is a function of the density and mass attenuation coefficient. For a given X-ray energy level, the mass attenuation coefficient is a function of the average atomic number with some discontinuities caused by X-ray absorption edges [46–48]. No X-ray absorption edges were encountered for the instrument settings and materials investigated.…”

Section: Introductionmentioning

confidence: 99%

Direct three-dimensional observation of the microstructure and chemistry of C3S hydration

Aboustait

Kim

et al. 2016

Cement and Concrete Research

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Disagreements about the mechanisms of cement hydration remain despite the fact that portland cement has been studied extensively for over 100 years. One reason for this is that direct observation of the change in microstructure and chemistry are challenging for many experimental techniques. This paper presents results from synchrotron nano X-ray tomography and fluorescence imaging. The data show unprecedented direct observations of small collections of C3S particles before and after different periods of hydration in 15 mmol/L lime solution. X-ray absorption contrast is used to make three dimensional maps of the changes of these materials with time. The chemical compositions of hydration products are then identified with X-ray fluorescence mapping and scanning electron microscopy. These experiments are used to provide insight into the rate and morphology of the microstructure formation.

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“…This technique combines a series of X-ray radiographs at small angles of rotation to produce a 3D model or tomograph [38,39]. The X-ray absorption contrast of the materials as a function of density and chemistry permits extraction of 3D structural information [40-42]. New lab-scale nCT systems that can use X-ray imaging energies as low as 5.4 keV have been developed.…”

Section: Introductionmentioning

confidence: 99%

Direct measurements of 3d structure, chemistry and mass density during the induction period of C3s hydration

Aboustait

Kim

et al. 2016

Cement and Concrete Research

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The reasons for the start and end of the induction period of cement hydration remain topic of controversy. One long-standing hypothesis is that a thin metastable hydrate forming on the surface of cement grains significantly reduces the particle dissolution rate; the eventual disappearance of this layer re-establishes higher dissolution rates at the beginning of the acceleration period. However, the importance, or even the existence, of this metastable layer has been questioned because it cannot be directly detected in most experiments. In this work, a combined analysis using nano-tomography and nano-X-ray fluorescence makes the direct imaging of early hydration products possible. These novel X-ray imaging techniques provide quantitative measurements of 3D structure, chemical composition, and mass density of the hydration products during the induction period. This work does not observe a low density product on the surface of the particle, but does provide insights into the formation of etch pits and the subsequent hydration products that fill them.

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3D chemical segmentation of fly ash particles with X-ray computed tomography and electron probe microanalysis

Cited by 35 publications

References 19 publications

Topological controls on the dissolution kinetics of glassy aluminosilicates

Topological controls on the dissolution kinetics of glassy aluminosilicates

Direct three-dimensional observation of the microstructure and chemistry of C3S hydration

Direct measurements of 3d structure, chemistry and mass density during the induction period of C3s hydration

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