Page 303 - Handbook of Thermal Analysis of Construction Materials

280 Chapter 7 - Superplasticizing Admixtures

In gypsum-less cement, a conduction calorimetric study showed
that a strong retardation of hydration occurred in the presence of a
lignosulfonate-based superplasticizer containing sodium carbonate. [29]
The rate of hydration of cement is influenced by the temperature to
which it is exposed. In the presence of superplasticizers, the hydration rate
is modified depending on the temperature. The rate of heat development as
well as the cumulative heat effect in cement containing SMF and hydrated
at 20, 40, and 55°C are compared in Fig. 13. [6][14][19] At all temperatures, the
peaks are shifted to higher times, showing that the hydration is retarded by
SMF. This effect seems to increase at 40°C and decreases at a higher
temperature. In TG/DTG and DTA, the decomposition of the AFm phase
and calcium hydroxide, migration of calcium hydroxide to the C-S-H phase,
and the interaction of Ca(OH) with the superplasticizer have to be taken
2
into account for the interpretation of the curve. [30]

Figure 13. Conduction calorimetric curves of portland cement hydrated at different
temperatures in the presence of SMF superplasticizer.