SEM/X-ray imaging of cement-based materials
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3.1 Analysis of fly ashes
The above techniques have been applied to analyzing a variety of fly ashes
[9]. Figures 4 and
5 contrast the appearance of a class F fly ash with that
of one obtained from the incineration of a municipal waste. For the class F
fly ash, the majority of the particles are spherical and monophase. Some
hollow cenospheres can be observed
as two-dimensional "rings" in the final processed image. For the
municipal
waste fly ash image, by contrast, the particles are irregularly shaped and
tend to be multi-phase in nature. For this particular waste fly ash, a
high concentration of calcium chloride is observed in the SEM/X-ray images,
as indicated by strong signals for Ca and Cl in the corresponding X-ray
images. Images such as these allow for a quantitative characterization
of the fly ash with respect to phase volume fraction, phase surface area
fractions, and phase distributions within the larger multi-phase particles.
This quantitative analysis can then be used as input for cement hydration and
microstructural models which include the reactions between the fly ash and
the portland cement phases [9]. Thus, these
images are critically
needed for predicting the influence of a fly ash on the hydration chemistry,
microstructure development, and properties of a cementitious system.
Figure 4: Final processed 2-D SEM/X-ray images for a class F fly ash.
Image is 256 µm by 200 µm. Colors correspond to the following
phases: red- silica, blue- aluminosilicate, green- calcium alumino-disilicate,
orange- C3A, aqua- anhydrite, and white- inert.
Figure 5: Final processed 2-D SEM/X-ray images for a municipal waste fly ash.
Image is 512 µm by 400 µm. Colors correspond to the following
phases: red- silica, blue- aluminosilicate, green- calcium alumino-disilicate,
orange- calcium chloride, aqua- anhydrite, and white-inert.
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Results for Example Applications