Page 385 - Handbook of Thermal Analysis of Construction Materials

Section 4.0 - Calcium Aluminate Cements 363

important characteristics including early strength gain, chemical resistance,
and excellent refractory properties. [20]–[23]
The principal cementing compound in CAC is calcium
monoaluminate (CA) present in amounts up to 60%. C A and CA are
12 7 2
present; β-C S and C AS may also exist. Minor compounds include FeO,
2
2
aluminoferrites, pleochroite and pervoskite. Glass content varies between
5 and 25% depending on the cooling conditions.

4.2 Hydration

Calcium monoaluminate reacts rapidly with water as follows:

Eq. (1) CA + H → CAH + C AH + AH x
8
2
10
The relative amounts of reaction products are dependent on external
factors. The reaction products are metastable and can enter into the
following reactions:

Eq. (2) AH (alumina gel) → γ-AH (gibbsite) + (x-3)H
x
3
Eq. (3) 3CAH → C AH + 2AH + 18H
3
3
6
10
Eq. (4) 3C AH → 2C AH + AH + 9H
8
3
3
6
2
The last two reactions showing the formation of hydrogarnet
(C AH ) are known as conversion reactions. Direct formation of hydrogarnet
3 6
from CA can occur in the presence of water at elevated temperatures:
Eq. (5) 3CA + 12H → C AH + 2AH 3
6
3
The iron analogue of the hydrogarnet phase can also form:
Eq. (6) 3C F + xH → 2C FH + F + (x-12)H
6
2
3
Strätlingite formation results from the interaction of β-C S, alumina and
2
water:

Eq. (7) β-C S + A + 8H → C ASH
2 2 8