Adding Water On-Site to Concrete Mixtures
Concrete Technology
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> Adding water on-site  Adding
water on-site to concrete mixtures has been a controversial topic
for as long as concrete has been used as a construction material.
The addition of water is clearly covered in ASTM C94, Standard
Specification for Ready Mixed Concrete. The standard does allow
for on-site addition of water to adjust fresh concrete properties
so the material as delivered is suitable for the specific application.
Concrete that is delivered with a low slump may lack the workability
for proper concrete placement consolidation and finishing operations.
Additionally, low slump concrete mixtures in some cases may be deficient
in air content for durability in freezing and thawing environments
or where the material may be exposed to deicing chemicals. While
on-site additions of water may potentially reduce the final concrete
strength properties, in many cases the consequences of adding the
water may be less detrimental than attempting to place, consolidate,
and finish a concrete mixture that that lacks proper workability
and/or air content.
How Much Can I Add?
The general rule is that water may be added to adjust the slump
of the material to comply with specifications upon arrival as long
as the maximum specified water-cement ratio is not exceeded. Typical
additions of water on-site are in the order of 1 to 2 gallons per
cubic yard of concrete (this would amount to 10 to 20 gallons of
water in a ten cubic yard load). A general rule of thumb for the
effect of the addition of water to a concrete mixture is an increase
in slump of approximately 1 in. per gallon of water added to a cubic
yard of concrete.
In short, a small addition of water (1 to 2 gal per cubic yard of
concrete) can be beneficial to the quality of the hardened concrete
when appropriately added (not exceeding the maximum water-cement
ratio or maximum revolutions) on-site during the normal course of
concrete construction.
For more information see
Concrete Finisher’s Guide, (EB122).
Also register for the webinar Impact
of Water on Concrete Properties.
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