Page 337 - Handbook of Thermal Analysis of Construction Materials

314 Chapter 8 - Supplementary Cementing Materials

Thermogravimetric Analysis has also been carried out to estimate
Ca(OH) in slag cements. TG yields similar results to those obtained by
2
DTA.
The hydration behavior of slag cement also depends on its surface
area. Addition of finer slag promotes acceleration of hydration of the alite
phase. For example, a slag cement (40% slag), containing slag having a
2
specific surface area of 4000 cm /g, exhibits an exothermic peak at about
11–12 hours in conduction calorimetry. However, in the presence of slag
2
with a specific surface area of 5920 cm /g, a more intense peak appears
1–2 hours earlier. [4]
Superplasticizing admixtures are used widely in high performance
concrete production. Not only do they influence the rheological parameters,
but also the setting characteristics. These effects depend on the type and
dosage of the admixture. In Fig. 17, the role of three types of superplasticizers,
viz., 0.5% Ca-SNF, commercial SMF, or Na-SNF on the hydration of slag
cements is examined. [43] Addition of the superplasticizer results in the
retardation in terms of the time of appearance of the exothermal peak and
also a decrease of the peak intensity. Na-SNF retards most of the
superplasticizers studied.
Steel slag, a by-product obtained in the manufacture of steel, has
been used as an aggregate. Conduction calorimetric investigations have
shown that steel slag hydrates slowly compared to iron slag, as evidenced
by a decrease in the intensity of the exothermic peak. [44]

Figure 17. The influence of superplasticizers on the rate of heat development in slag
cements.