Civil Engineering Reference
In-Depth Information
WHITE AND
COLORED
CONCRETE
White
Concrete
White portland ce-
ment is used to pro-
duce white concrete,
a widely used ar-
chitectural material
(Fig. 18-14). It is also
used in mortar,
plaster, stucco, ter-
razzo, and portland
cement paint. White
portland cement is
manufactured from
raw materials of low
iron content; it con-
forms to ASTM C
150 (AASHTO M 85) even though these specifications do
not specifically mention white portland cement.
White concrete is made with aggregates and water that
contain no materials that will discolor the concrete. White
or light-colored aggregates can be used. Oil that could stain
concrete should not be used on the forms. Care must be
taken to avoid rust stains from tools and equipment. Curing
materials that could cause stains must be avoided. Refer to
Farny (2001)
and
http://www.portcement.org/white
for
more information.
Fig. 18-14. Office building con-
structed with white cement con-
crete. (55828)
Fig. 18-15. Colored concrete, used for a rapid transit plat-
form. (67328)
The amount of color pigments added to a concrete
mixture should not be more than 10% of the mass of the
cement. The amount required depends on the type of pig-
ment and the color desired. For example, a dose of pig-
ment equal to 1.5% by mass of cement may produce a
pleasing pastel color, but 7% may be needed to produce a
deep color. Use of white portland cement with a pigment
will produce cleaner, brighter colors and is recommended
in preference to gray cement, except for black or dark gray
colors (Fig. 18-15).
To maintain uniform color, do not use calcium chloride,
and batch all materials carefully by mass. To prevent
streaking, the dry cement and color pigment must be thor-
oughly blended before they are added to the mixer. Mixing
time should be longer than normal to ensure uniformity.
In air-entrained concrete, the addition of pigment
may require an adjustment in the amount of air-entraining
admixture to maintain the desired air content.
Dry-Shake Method.
Slabs or precast panels that are cast
horizontally can be colored by the dry-shake method.
Prepackaged, dry coloring materials consisting of mineral
oxide pigment, white portland cement, and specially
graded silica sand or other fine aggregate are marketed
ready for use by various manufacturers.
After the slab has been bullfloated once, two-thirds of
the dry coloring material should be broadcast evenly by
Colored Concrete
Colored concrete can be produced by using colored aggre-
gates or by adding color pigments (ASTM C 979) or both.
When colored aggregates are used, they should be
exposed at the surface of the concrete. This can be done
several ways; for example, casting against a form that has
been treated with a retarder. Unhydrated paste at the sur-
face is later brushed or washed away. Other methods
involve removing the surface mortar by sandblasting,
waterblasting, bushhammering, grinding, or acid
washing. If surfaces are to be washed with acid, a delay of
approximately two weeks after casting is necessary.
Colored aggregates may be natural rock such as quartz,
marble, and granite, or they may be ceramic materials.
Pigments for coloring concrete should be pure min-
eral oxides ground finer than cement; they should be in-
soluble in water, free of soluble salts and acids, colorfast in
sunlight, resistant to alkalies and weak acids, and virtu-
ally free of calcium sulfate. Mineral oxides occur in nature
and are also produced synthetically; synthetic pigments
generally give more uniform results.
