Page 447 - Handbook of Thermal Analysis of Construction Materials

422 Chapter 10 - Non-Portland Rapid Setting Cements

Figure 16 represents the differential scanning calorimeter output of
hydrated CA at different scanning rates (at 28 days hydration). The
dehydration peaks of AH and the C AH phases are well separated, the heat
3
3
6
energy being much higher for AH .
3 –
Satava and Veprek (using DSC methods) studied the CA + CSH
– 2
and the C A + CSH systems. [12] In both systems (the former containing
12 7 – 2
up to 30% CSH and the latter 3%), ettringite is primarily formed at
2
–
temperatures below 110°C as a result of the reaction with the saturated CS
H solution. Monosulfate is formed only above 110°C. The formation of a
2
film which retards the hydration of C A and CA is less pronounced than
12
7
–
that with C A + CSH .
2
3
3.0 JET SET (REGULATED-SET) CEMENT
Jet Set or regulated-set cement is a modified portland cement
composition capable of developing a high early set strength upon hydra-
tion. [13] The cement consists essentially of portland cement and from about
1 to 30% by mass of a calcium halo-aluminate having the formula
11CaO•7Al O •CaX in which X is a halogen. The system’s most studied
2 3 2
compound appears to be 11CaO•7Al O •CaF .
3
2
2
Uchikawa and co-workers [14]–[16] have reported extensively on the
use of thermal analysis to monitor the hydration process of Jet Set cement
and combinations of its mineral constituents.

3.1 Hydration of 11CaO•7Al O •CaF 2
2
3
DTA and conduction calorimetry were used to follow the hydration
of pastes (water/solid ratio = 0.60). [14] In Fig. 17, DTA thermograms of the
reference calcium fluoroaluminate (top left) with calcium sulfate (top
right), gypsum (bottom left), and hemihydrate (bottom right) are shown.
The curves indicate a gradual increase in height of the endothermal peak of
C AH at 320°C, and a decrease in height of the broad peak at 120°C
3
6
indicative of the hexagonal calcium aluminate hydrate. In the presence of
anhydrite after 10 hours, the endothermal peak of the monosulfate hydrate
appeared at 200°C. The peaks of ettringite at 140°C and 270°C also
appeared after 1 day.