African Design Magazine ADM #40 May 2018 | Page 54

TECHNOLOGY
min and the maximum temperature was
900°C in TG tests. The TG-DTG results
of the three kinds of pastes at the age
of 3, 28, 90, and 360 days are presented
in Figure 5, and the corresponding
Ca(OH)2 contents are shown in Table
2. Δ1 and Δ2 in Table 2, respectively,
represented the difference values in
Ca(OH)2 contents of FA-25% and GFA-
25% compared to 75% Ca(OH)2 content
of Cement.
The continuous hydration of cement
leads to the constant increase of
Ca(OH)2 content, but the pozzolanic
reaction of fly ash will consume some
Ca(OH)2. A large
number of studies
Figure 5: TG-DTG curves of composite cementitious materials.
[29, 30] have
shown that the
reaction degree
of fly ash at the
age of 3 days is
generally less than
5% and at the
age of seven days
less than 10%. It
can be referred
from Table 2 that
Ca(OH)2 content of
FA-25% and GFA-
25% increased
first and then
decreased with
the increase of
ages, which was
due to the relative
values between
forming rate and
consuming rate of
Ca(OH)2. However,
Table 2: The content of Ca(OH)2 in the hardened cement paste at
Ca(OH)2 content
different ages (%).
of GFA-25% was
less than that of
FA-25% at all ages.
Furthermore,
Ca(OH)2 content of
GFA-25% reached
its maximum at
the age of 90 days
while Ca(OH)2
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AFRICAN DESIGN MAGAZINE © | MAY 2018