Cementitious materials - Concrete Mix Design, Quality Control and Specification - page 9

c. Improve mix cohesion (or make “sticky”)
d. Reduce bleeding
e. Deteriorate more quickly
f. Be more susceptible to cracking
g. Generally require more water (note that this may be less due to
any direct effect of fineness than to the reduced range of particle
sizes normally resulting from finer grinding)
3. Soundness (Pat, Le Chatelier, and autoclave tests) is intended to detect
excessive free lime (perhaps due to incomplete blending rather than
wrong chemical proportions). Some experts disagree that the inten-
tion is achieved, but this is beyond the present scope. Magnesia can
also cause unsoundness (if as periclase) but perhaps too slowly for Pat
or Le Chatelier, needs autoclave or chemical limit (and see Section
13.2.6.5 for intentional use of a proportion of magnesia).
4. Normal consistency—Generally just a starting point for other tests
but can show up undesirable grinding characteristics. Where very high
strength concrete is involved, large amounts of cement will be required
and a very low w/c ratio will be required. A cement with a high water
demand is a disadvantage in such circumstances. Interesting uses for
this test are as a compatibility check between admixtures and cement
or to determine the effect on water requirement of a percentage of fly
ash or silica fume.
5. Loss on ignition—Mainly a check on deterioration during storage.
The test drives off any moisture or carbon dioxide that may have been
absorbed. A 3% loss on ignition could mean a 20% strength loss if
this was due to moisture. However, up to 5% of limestone (CaCO 3 )
is permitted to be added to cement and this test would drive off CO 2
from limestone.
6. Sulfur trioxide/sulfide (SO 3 ) check on proportion of gypsum has
considerable significance for setting time, strength development and
shrinkage. The test determines the content of SO 3 from all sources
(e.g., added gypsum, oxidised sulfur in fuels, etc.) and in all states.
It therefore may not be an accurate guide to the amount of active
(soluble) SO 3 present. It is the amount of active SO 3 , which affects, for
example, setting time, rate of strength development, and tendency for
shrinkage and cracking.
7. Insoluble residue—Check on impurities or nonreactive content only,
the effect is the same as reducing the cement content by the percent-
age of the insoluble material. However, this test may characterise fly
ash as insoluble residue and any limit should be based on the portland
cement component or fillers only.
8. Compressive strength—This should be directly related to concrete
performance but there can be differences due to admixture interac-
tions, different water cement ratio etc. In some countries cement is