C2S and C3S constitute about 75% of the cement by weight. The ratio of C2S and C2S
plays an important role on the properties of cement. It is known that this ratio controls
the quantum of Ca(OH)2 in hydrated paste, as well as the rate of early stage of hydration
and strength development. Stochiometric calculations showed that hydration of C3S
produces about 2.2 times the Ca(OH)2 than the same amount of C2S. Liberation of
higher amounts of Ca(OH)2 is likely to increase sulfate attack due to several reasons.
The influence of C2S/C3S ratio on the sulfate resistance of cement has been studied
during laboratory tests on 2 cements which had fairly close C3A contents, 9.3% and
11.9% but widely differing C3S/C2S ratios of 2.57 and 7.88, respectively
[Rasheeduzzfar et al., 1990]. It was found that after 150 days of immersion in a Na2SO4
solution the deterioration in 7.88 C3S/C2S cement was 1.8 times more than 2.57
C3S/C2S cement. This type of attack is highly prevalent in the Middle East where a
sizable proportion of cement produced is type V, but has high C3S and C2S ratio.