Civil Engineering Reference
In-Depth Information
Figure 16 represents the differential scanning calorimeter output of
hydrated CA at different scanning rates (at 28 days hydration). The
dehydration peaks of AH
3
and the C
3
AH
6
phases are well separated, the heat
energy being much higher for AH
3
.
Satava and Veprek (using DSC methods) studied the CA + C
-
H
2
and the C
12
A
7
+ C
-
H
2
systems.
[12]
In both systems (the former containing
up to 30% C
-
H
2
and the latter 3%), ettringite is primarily formed at
temperatures below 110°C as a result of the reaction with the saturated C
-
H
2
solution. Monosulfate is formed only above 110°C. The formation of a
film which retards the hydration of C
12
A
7
and CA is less pronounced than
that with C
3
A + C
-
H
2
.
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
2
O
3
•CaX
2
in which X is a halogen. The system's most studied
compound appears to be 11CaO•7Al
2
O
3
•CaF
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
2
O
3
•CaF
2
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
3
AH
6
at 320°C, and a decrease in height of the broad peak at 120°C
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.
