Civil Engineering Reference
In-Depth Information
Isothermal conduction calorimetric curves of C
3
S hydrated with
different amounts of TEA are shown in Fig. 13.
[17]
In the C
3
S sample
hydrated without TEA, there is little heat development in the first few hours,
representing the dormant period. The curve starts to rise steeply at about 2.5
to 3 hours denoting the beginning of the acceleratory period. Maximum heat
develops between 7 and 8 hrs. By the addition of TEA, the induction period
is extended. The C
3
S hydration peak occurs later, but with a higher intensity
so that TEA acts like a delayed accelerator. The mono- and diethanolamines
also affect the hydration of C
3
S, similar to TEA.
Figure 13.
Conduction calorimetric curves of 3CaO•SiO
2
with different amounts of added
triethanolamine.
The hydration of C
2
S with 0.5% TEA has been followed by DTA
(Fig. 14).
[3][17]
Generally, endothermal peaks due to Ca(OH)
2
decomposi-
tion (450-480°C) are of lower intensity in
samples containing TEA. An
additional endotherm appears in these samples and has been attributed to
the presence of less crystalline Ca(OH)
2
.
In the DTA and TG studies of cement containing different amounts
of TEA, evidence was obtained for the formation of lower amounts of
Ca(OH)
2
in the presence of the admixture. In Fig. 15 the amount of lime
(DTA estimation) formed in the cement paste in the presence of TEA is
given.
[18]
Comparison of the results at the same degree of hydration has
revealed that TEA promoted the formation of C-S-H with a higher C/S ratio.
