Cementitious materials - Concrete Mix Design, Quality Control and Specification - page 11

2.1.3 Types of cement
Cement chemistry is extremely involved and not within the scope of this
topic, however limited comment on the different types of cement commonly
available may be useful. All Portland cement is conveniently regarded as
composed of four compounds:
C 2 S, dicalcium silicate—Slow reacting, low heat generation, best
long-term strength and durability
C 3 S, tricalcium silicate—Quicker reacting, more heat generated, still
good strength and durability but not as good as C 2 S
C 3 A, tricalcium aluminate—Very rapid reaction, high heat generation,
responsible for early (but not high) strength and setting, readily reacts
with chemicals
C 4 AF, tetracalcium aluminoferrite—Relatively little influence on prop-
erties of concrete (except colour), present because needed during
manufacture
The relative amounts of these compounds are varied to produce different
types of cement to suit different uses:
Type I—Also known as type A, OPC (ordinary Portland cement), GP
(general purpose), C
Type II—Modified low heat cement
Type III—High early strength or rapid hardening
Type IV—Low heat cement
Type V—Sulfate resisting cement
A fifth compound, CaSO 4 (gypsum) is interground with the cement
clinker to control setting. It is also thought to have a substantial beneficial
influence on shrinkage and to produce improved strength. However, an
excess can cause slow setting and also unsoundness (destructive expansion).
Gypsum can be rendered less effective by excessive heat during grinding.
The reader will be able to work out from the above or consult other
sources about which compounds will predominate in which cements.
However, there are a few matters that are often misunderstood and so
should be brought to the reader's attention:
1. Sulfate resisting cement is made by limiting the amount of C 3 A.
Unfortunately C 3 A, although responsible for expansive reactions with
sulfate, happens to be the compound that also reacts with chlorides
reducing their rate of penetration. In some parts of the world, this
cement is assumed to be a general high-durability cement and used