Civil Engineering Reference
In-Depth Information
methods are useful tools to compare the burnability of different raw mixes.
Burnability is influenced by the chemical, mineralogical, and granulometric
compositions of the raw materials. DSC has been utilized to evaluate the
burnability of raw meals. Figure 5 shows a good correlation between BI
(burnability index) and A
1
+A
2
(areas of peaks corresponding to the forma-
tion of belite).
[13]
Figure 5.
Correlation between burnability and DSC peak areas.
Although thermal curves for even the same raw materials vary,
individual cement clinker minerals always form in sequence and over a
certain narrow temperature range. Dilatometry is particularly useful in
conjunction with DTA to identify transitional phases. For example, cement
clinkers made by heating a mixture of class F fly ash, CaO, CaF
2
, and
gypsum have been analyzed by dilatometric and XRD techniques.
[21]
Pure
fly ash shows shrinkage from 700-1194°C. In fly ash mixtures no shrinkage
is observed between 950 and 1120°C that corresponds to the clinkering
reaction. Only above 1120°C is shrinkage registered.
Specific heat is an important thermodynamic parameter needed for
determining the heat balance of a reaction. The specific heat of crude
cement and clinker has been measured by DSC.
[18]
The results demon-
strate that the specific heat of crude powder is higher than that of the
clinker. In the temperature range 50-300°C the specific heat value is about
0.025 cal/g/°C.
