Civil Engineering Reference
In-Depth Information
Figure 23.
Rate of heat development of C
3
S hydrated in the presence of NaOH.
There has been continued interest in developing an organic-based
accelerator. Ramachandran and coworkers studied the effect of
o, m,
and
p
-
nitrobenzoic acids on the hydration of tricalcium silicate.
[27]
The
m
and
p
nitrobenzoic acids acted as accelerators (Fig. 24). Paranitrobenzoic acid
appears to be the best accelerator. The acceleratory effect was attributed to
the complex formation between the organic compound and the C-S-H phase
on the surface of the tricalcium silicate phase.
In addition to studies on C
3
S,
[25]
Ramachandran and Zhang-Chun-
mei
[28]-[31]
have also carried out extensive investigations of the effect of
calcium carbonate on the hydration of C
3
A, C
3
A + gypsum and cement
utilizing DSC and TG techniques. Calcium carbonate was found to suppress
the formation of calcium aluminate hydrate in the hydration of C
3
A. It
accelerates the formation of ettringite and the conversion of ettringite to
monosulfoaluminate in the hydration of C
3
A + gypsum. In Fig. 25, DSC
curves for C
3
A containing 12.5% gypsum and 12.5% calcium carbonate
hydrated for 5 minutes to 3 days are given. In the C
3
A-gypsum mixture,
