Civil Engineering Reference
In-Depth Information
without the chloride.
[10]
This would imply that a higher C/S ratio C-S-H
product results in the presence of calcium chloride. There is also evidence
that in the hydration of C
2
S some chloride is bound rigidly.
The reaction of C
3
A with calcium chloride results in the formation
of high and low forms of tricalcium chloroaluminates. Under normal
conditions of hydration, the low form, viz., C
3
A•CaCl
2
•XH
2
O is obtained.
The DTA technique may be used to differentiate between the two forms.
Endothermal effects at about 190 and 350°C are caused by the low form and
the endotherm at about 160°C is exhibited by the high form. In the system
C
3
A-CaO-CaCl
2
-H
2
O, at higher concentrations of calcium chloride, cal-
cium hydroxychloride is formed that is identified by peaks at 130, 145, and
485°C.
[11]
Calcium chloride influences the rate of hydration of C
3
A + gypsum
mixtures. In Fig. 6, the conduction calorimetric curves of the mixtures C
3
A
+ 20% gypsum + 12.5% CaCl
2
are given along with the identified com-
pounds at different times.
[3][7]
A comparison of this curve with that obtained
with C
3
A + gypsum (G) or C
3
A + CaCl
2
would lead to the following
conclusions. The reaction between C
3
A and gypsum is accelerated by
calcium chloride. Monochloroaluminate (MCA) is formed after gypsum is
consumed in the reaction with C
3
A. Conversion of ettringite (TSA) to
monosulfoaluminate occurs only after all CaCl
2
has reacted.
[12]
Figure 6
. The rate of consumption of various components in the C
3
A-gypsum-CaCl
2
-H
2
O
system.
