Page 289 - Handbook of Thermal Analysis of Construction Materials

Section 4.0 - Tricalcium Silicate 269

4.0 TRICALCIUM SILICATE

Superplasticizers affect the hydration of tricalcium silicate.
It is generally known that superplasticizers retard the hydration of
C S. [4][12]–[15] The effect of different amounts of SMF on the hydration of
3
C S can be illustrated by conduction calorimetric curves (Fig. 6). [4][5] By the
3
addition of 1% SMF, the induction period and the exothermic peak are
shifted to higher times suggesting that substantial retardation has taken
place. At 2 and 4% SMF, further retardation of hydration occurs with a very
low rate of heat development. There is evidence that the CaO/SiO ratio of
2
the C-S-H product is changed by SMF.
The effect of superplasticizers on the hydration of C S has also
3
been studied by estimating calcium hydroxide formed at different times by
applying DTA and TG. [16] Contrary to many other investigations, it is
reported in this work that superplasticizer does not affect the hydration of
C S. It is not easy to compare the results obtained by different investigators
3
as the rate of hydration depends on the type of superplasticizer, the cation
associated with it, the molecular weight, the amount and hydration condi-
tions, and the time at which the hydration degree is compared.
The TG technique has been used to follow the hydration of alite in
the presence of 2–4% SMF. [16] Calcium hydroxide and the non-evaporable
water contents were determined and not much difference in the hydration
rates was observed between the reference alite sample and that containing
the superplasticizer.
The effect of 0, 0.3, 1.0, and 3% SMF on the hydration of C S has
3
been investigated using the XRD and Franke methods of determining
lime. [15] At 12 hours, the degree of hydration, in terms of C S reacted, was
3
only 8% in the presence of the superplasticizer whereas for the reference
material the value was 34%. Thus, a significant amount of retardation
seems to have taken place. Thermal methods have also been applied to
determine the amount of lime formed at different times in the presence of
0, 0.32, and 1.0% SMF. The results are summarized in Table 2. At 1 day,
there is retardation in the formation of lime, and a severe retardation is
evident with 1% SMF. At 3 days and beyond, a slight acceleration seems
to occur with SMF.