Building Materials, Third Edition

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The purpose of using water with cement is to cause hydration of the cement. Water in excess
of that required for hydration acts as a lubricant between coarse and fine aggregates and
produces a workable and economical concrete. As discussed later in Chapters 10, 11 and 12,
there is a definite optimum water requirement for a particular concrete and mortar. In case of
excess water, the cement along with water comes to the surface by capillary action and forms
a thin layer over surface known as laitance. This weakens bond between the successive lifts of
concrete. The excess water may leak through the form work, resulting in honeycombed concrete
and on evaporation makes the concrete porous. On the other hand lesser water makes it
difficult to work with concrete and because of nonuniform mixing the resultant concrete is
weaker in strength. The amount of water must therefore be limited to produce concrete of the
quality required for a job. Water is also used for washing aggregates and curing.

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Almost any natural potable water that has no pronounced taste or odour is acceptable for the
concrete mix. Many sources of water unsuitable for drinking may also be used. In case of a
doubt, water samples should be tested for suitability. Excessive impurities may affect setting
time, strength, durability and may cause efflorescence, surface discolouration, and corrosion of
steel.
The effects of impurities in water are mainly expressed in terms of setting time of Portland
cement. The initial setting time of the mixes with impure water and that with the pure water
are obtained. Their difference in the initial setting time of ± 30 minutes with initial setting time

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