On-site slurry anddry-wet systemsTh

On-site slurry and
dry-wet systems
There are two methods for manufacturing
liquid colors on-site at a concrete
producer's facility. In the on-site slurry
system, a concrete producer manufactures
liquid colors in bulk In the "drywet"
system, dry-pigments are blendedin water on a batch-by-batch basis. Both
of these methods combine some of the
features typically associated with both
dry powder and liquid coloring systems.
On the plus side, they both allow the use
of low-cost powder pigments plus the
flexibility of being able to locate coloring
operations away from the concrete
mixer. On the minus side, they still have
most of the dusting concerns that come
from handling dry pigments.
In the on-site slurry process, a concrete
producer formulates liquid colors
in the same way a pigment manufacturer
would. Large mixing and storage
tanks and a scale are required, plus all
the equipment required to dispense liquid
colors. The concrete producer takes
full responsibility for quality control of
the liquid color and requires properly
trained personnel to blend colors and
assure consistency from batch to batch.
Despite these limitations, on-site slurry
can be a viable system for concrete producers
who use a large volume of color
and prefer a liquid coloring system.
In the dry-wet system, powdered
pigments are fed as required into a small
mixing tank. The mixer is covered to
limit dust problems and is equipped
with a load cell to weigh the pigments as
they are added. Computer controlled
meters dispense the required amounts
of the primary colors and water. The
ingredients are then mixed, and upon a
signal from the system, transported
with compressed air or pumped into the
concrete mixer. A water spray washes
out the mixer bowl and is then forced
into the concrete batch to clean the
hose. Due to the time required for these
operations, some dry-wet systems may
not be able to cycle quickly enough to
use in plants with multiple concrete
mixers.
Granular colors
Granular pigments are the fastest growing
type of concrete coloring. The first
successful granular system was introduced
in 1989 by Brockhues Corp. and
is now marketed by Davis Colors. The
patented method uses an automated
metering system and color granules
made with an organic binding ingredient
which holds the pigment together
during transport and then dissolves to
enhance color development when
mixed into concrete The small,
microbeads of pigment are free-flowing, very low in dust, and disperse readily
upon being added to a concrete mix
to develop full tint strength. These pigments
have been successfully used in
over 300 concrete plants, including
block, paver and retaining wall production
facilities around the world.
The organic binder used in
Brockhues-type granules dissolves in
water and disperses readily in any type
of concrete mixer. A newer type of
granular pigment uses an inorganic
binder that does not dissolve in water. It
depends instead upon the shearing
action of the aggregate to break down
the granules and may not achieve full
color development with certain concrete
mixes, types of mixers and batching
sequences. Under optimum conditions,
inorganically bound granules will
develop only 80 to 90 percent of the
tinting strength of an organically bound
granule or good powdered pigment.
Granular pigments offer all the benefits
of automation without many of the
limitations of other forms of automation.
The pneumatic dispensing systems
offer very accurate metering and
fast production cycles, can serve multiple
concrete mixers, and can be located
up to 180 feet from the concrete mixers.
They are the most compact form of pigments
available, saving about half the
volume of powders. Similarly, they cannot
freeze, are not limited by shelf life or
settlement problems, will not dry out in
hoses, and can be used in mixes which
can not accept additional water.
In a typical installation, supersacks
of granules are hung in a rack above a
color metering system. The computercontrolled
metering system weighs out
the required amount of each of the primary
colors and drops the blended colors
into a pressure vessel. From there
they are pneumatically transported to a
hopper above the concrete mixer. Upon
a signal from the concrete mixer, the
pigments cascade into the mix and disperse
throughout the concrete.
Granules offer savings when compared
to liquid colors; since they contain
no water, they cost less to ship and
have greater tint-strength on a poundfor-pound
basis. Granules are also used
in manual coloring operations where
they are selected over powders for their
ease of use and cleanliness. They are
packaged in supersacks and 50 pound
bags.