Page 44 - Handbook of Thermal Analysis of Construction Materials

28 Chapter 1 - Thermoanalytical Techniques

Chemical admixtures in small amounts are added to concrete to
enhance the physical, mechanical, chemical, and durability characteristics
of concrete. Superplasticizers are admixtures that have the ability to
increase the workability of concrete (for easy placement), but also produce
high strength concretes. The relative rates of hydration of cement contain-
ing superplasticizers at different temperatures are conveniently followed
by conduction calorimetry. In Fig. 11 both the rates of hydration and the
cumulative amounts of heat developed in cement pastes hydrated at
temperatures of 20, 40, and 55°C are plotted as a function of time. [75] In the
figure, SMF refers to the superplasticizer based on sulfonated melamine
formaldehyde. The addition of the superplasticizer retards the hydration of
cement. The retardation increases with the dosage of the superplasticizer.
Also, the retardation effect becomes less significant as the temperature of
hydration is increased.

Figure 11. Conduction calorimetric curves of superplasticized cement at different
temperatures.