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FIGURE 9.8 Differential thermogravimetric (DTG) analysis of a portland cement:Class F
fly ash (1:1) matrix (W/S = 0.5).
hydroxide is detected in the 3-year-old specimen. Class F fly ash hydration reactions
proceed much more slowly compared to other pozzolans such as Class C fly ash,
silica fume, and granulated blast furnace slag. This reaction thus would have been
much faster in the presence of the latter pozzolans. Figure 9.9 shows the effect of
a sodium arsenite waste on the portland cement:Class F fly ash binder. No calcium
hydroxide is detected in specimens containing sodium arsenite up to 1 year of age,
and it is detected only in specimens 3 years of age. Sodium arsenite is thus clearly
retarding the hydration process of the binder. The peaks corresponding to other
phases such as ettringite and gypsum are less pronounced in the binder in the
FIGURE 9.9 The effect of a sodium arsenite waste on a portland cement:Class F fly ash
(1:1) matrix (W/S = 0.5).
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