Chapter 6 Concrete 107
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Type V—Sulfate resistant. Used when concrete will be exposed to severe
sulfate conditions, such as those found in some western states.
The aggregate consists of fine sand (1/4″ diameter and less) and stones
(larger than 1/4″ diameter). The cement paste binds the aggregate together,
filling the spaces between particles. A chemical reaction between the water
and the Portland cement, called hydration, cures (hardens) the concrete.
When mixed with the proper amount of water, Portland cement makes
a paste that cures to bond the aggregate together. Tap water is generally
acceptable for making concrete. Avoid water containing large amounts of
sulfates.
Admixtures
Admixtures are special chemicals added to concrete to change one or
more characteristics of the product. Some chemicals make concrete set faster.
Other chemicals lengthen the setting time.
Air-entrained concrete
contains an
admixture that causes small air bubbles to form in concrete. This concrete is
easier to work and resists cracking from freezing and thawing. The letter A
is added to the type designation (Type I-A) of Portland cement that contains
air-entraining chemicals.
aggregate: The
sand and gravel in
concrete.
hydration: A
chemical reaction
between water and
Portland cement that
cures concrete.
admixtures:
Chemicals added
to concrete to
change one or more
characteristics of the
product.
air-entrained
concrete: A type of
concrete produced by
adding an admixture
that causes the tiny
bubbles to form in
concrete.
Figure 6-1. Concrete is used in a variety of ways. (HNTB Engineers; The Manitowoc Co.; Raymond
International, Inc.)