Page 24 - Masonry and Concrete

Understanding Concrete
23
UNDERSTANDING CONCRETE

Concrete Color Pigment Used

Black, Gray Black iron oxide, mineral black, carbon black
Brown, Red Red iron oxide, brown iron oxide, raw umber, burnt
umber
Rose and Pink Red iron oxide (varying amounts)

Buff, Cream, Ivory Yellow ocher, yellow iron oxide
White White cement and white sand
Green Chromium oxide, phthalocyanine green

Blue Cobalt blue, ultramarine blue, phthalocyanine blue

FIGURE 2-10
Pigments for various concrete colors.

2.3 Concrete Mix Designs

For work requiring more than one cubic yard of material, concrete is
usually ordered from a ready-mix supplier for delivery to the job site.
The supplier will need to know the minimum compressive strength,
the maximum aggregate size, and any special requirements such as air
entrainment for added freeze-thaw durability. The supplier will then
select a mix design that is appropriate for your needs. If you are mix-
ing small batches of concrete on site, you will need to understand the
basic principles of concrete mix design yourself. The proportion of dry
ingredients and the ratio of water to cement are the two most impor-
tant factors.
Cement and aggregates provide strength, durability, and volume
stability in concrete, but too much or too little of one in relation to the
other reduces quality.

■ Lean or oversanded mixes with low cement content and high
aggregate proportions are harsh and have poor workability.
■ Fat or undersanded mixes with high cement content and low
aggregate proportions are sticky and expensive.

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