Page 90 - Handbook of Thermal Analysis of Construction Materials

Section 2.0 - Raw Materials 73

DSC (Differential Scanning Calorimetry) has also been used in
cement science investigations to some extent. It is based on a power
compensated system. In this technique the reference and the sample under
investigation are maintained at a constant temperature throughout the
heating schedule. The heat energy required to maintain the isothermal
condition is recorded as a function of time or temperature. There are some
similarities between DTA and DSC including the appearance of thermal
curves. DSC can be used to measure the heat capacities of materials. DSC
measures directly the heat effects involved in a reaction.
In thermogravimetric analysis (TG), the weight changes are deter-
mined as the sample is heated at a uniform rate. It differs from the semi-
static or static method in which the sample is held at a constant temperature
for a required period of time. In concrete investigations, TG is commonly
used with DTA to follow the hydration reactions. The first derivative of
change of mass (DTG) can also be used for identification purposes as it
yields sharper peaks. TG cannot detect crystalline transitions as they do not
involve weight losses.
Conduction calorimetry is another technique that is extensively
used for following the hydration reactions of cement and cement com-
pounds. In this method, heat evolved during the hydration reactions is
followed as a function of time from the moment water comes into contact
with the cement. The curves are obtained under isothermal conditions. This
technique can also be used to study the rate of hydration at different
temperatures. Conduction calorimetry has been used to determine kinetics
of hydration and for studying the role of admixtures, relative setting times
of cement, and for identification purposes.
A few other thermal techniques such as thermomechanical analy-
sis, dilatometry, emanation analysis, etc., are only used to a limited extent
in concrete investigations. Several publications have appeared which
exclusively deal with the application of thermal analysis to the investiga-
tion of cementitious systems. [1]–[9]

2.0 RAW MATERIALS

The raw mix for the production of cement clinker comprises
calcareous and siliceous materials. They are characterized by techniques
such as DTA, XRD, chemical analysis, volatility test, burnability test,
TG, etc.