Page 161 - Handbook of Thermal Analysis of Construction Materials

144 Chapter 4 - Introduction to Concrete Admixtures

1. Chemical admixtures: They are generally water-soluble,
added mainly to control setting and early hardening of
fresh concrete, and to reduce water requirements. Chemi-
cal admixtures include accelerators, normal water reduc-
ers, superplasticizers, and retarders. The accelerators
may contain calcium chloride, alkali hydroxide, calcium
formate, calcium nitrate, etc. Examples of retarders are
Na, Ca, or NH salts of lignosulfonic acids, hydroxy
4
carboxylic acids, or derivatives of carbohydrates. Normal
water reducers may contain salts of refined lignosulfonic
acids, hydroxycarboxylic acids, hydroxylated polymers,
etc. Superplasticizers may contain sulfonated melamine
formaldehyde, sulfonated naphthalene formaldehyde, car-
boxylated synthetic polymers, etc.

2. Air-entraining agents: These are used to improve the
durability of concrete. They comprise resins such as
neutralized vinsol resin, synthetic detergents, salts of
petroleum acids, etc.
3. Mineral admixtures: These finely divided materials im-
prove workability, durability and other properties of
concrete; examples are fly ash, slag, silica fume, rice husk
ash, etc.

4. Miscellaneous admixtures: Those other than what have
already been described and are known to impart many
benefits to concrete. Examples are: latexes, corrosion
inhibiting admixtures, alkali-aggregate expansion reduc-
ing admixtures, pigments, pumping aids, shotcreting ad-
mixtures, etc.

Thermal analysis techniques have been applied to investigate many
aspects of concrete science and technology. They include hydration kinet-
ics, mechanism of hydration, deterioration of concrete, examination of the
role of newly developed admixtures, admixture detection and estimation,
composition of the products, identification of new compounds, etc.
In this chapter an introduction to the role of different types of
admixtures on cement and concrete properties is given. This should serve
as a useful guide for following the application of thermal techniques to the
evaluation of the effect of admixtures on cement and concrete.