Civil Engineering Reference
In-Depth Information
Figure 1.
Amount of lime formed in the fly ash mortar containing different percentages of
fly ash.
Studies involving DTG, TG, and DTA show that the composition
and character of hydration products formed in the portland cement and
portland cement-fly ash pastes are not very different while the relative
proportions of the products vary.
[6]
Conduction calorimetric curves for cement with 40% ordinary fly
ash are different from that containing 40% high calcium fly ash (Fig. 2).
[4]
Both ordinary and high calcium fly ashes delay the appearance of the peak
effect due to alite hydration. The appearance of the peak, however, is
delayed to a greater extent by high calcium fly ash. Fly ash with a low
calcium adsorption capacity, higher contents of Ca
2+
, dissolved alkalis, and
unburned carbon retards the hydration of alite, by hindering the saturation
rate of Ca(OH)
2
in the liquid phase.
It has been shown by conduction calorimetry that Type 10 (Type I
ASTM) cement containing 25% fly ash exhibits similar behavior to Type
40 (Type IV ASTM) low heat cement containing no fly ash.
[7]
Both these
cements have lower heats of hydration compared to pure Type 10, normal
portland cement (Fig. 3).
