106 Section 2 Construction Materials
Concrete
Concrete is a building material used in almost every type and size of
structure, Figure 6-1. In buildings it is used for footings, foundations, and
walls. It is used for flat structures of all kinds, like roadways and floors.
Ingredients
Concrete is made of three ingredients: Portland cement, water, and
aggregate. Steel reinforcing bars and welded wire fabric are used to
strengthen concrete.
Portland cement is made by mixing limestone, clay, and shale. The
mixture is burned in a oven at approximately 2700°F (1482°C), resulting in
rocklike shapes called clinker. The clinker is pulverized and mixed with a
small amount of gypsum to produce Portland cement. There are five types of
Portland cement, each designed for specific applications.
•
Type I—General purpose. Used when special properties are not
required.
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Type II—Moderate sulfate resistance. Used when surrounding soil
contains elevated levels of sulfate.
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Type III—High, early strength. Used when it is necessary to speed the
curing process.
•
Type IV—Low heat. Used in massive concrete structures, such as dams.
Type IV cement reduces the internal cracking that might occur as a
result of the heat generated during the curing process. Strength develops
more slowly when this type of cement is used.
concrete:
Manufactured
stone composed of
Portland cement,
water, and aggregate.
Portland cement:
An adhesive that
holds the aggregate
together to make
concrete.
Concrete Finisher
Concrete finishers place and finish concrete. Much of the work involves finishing floors,
driveways, and other flat surfaces. In addition to typical finishing processes, concrete finishers
may color the surface or apply special aggregate to produce an exposed aggregate surface.
Concrete finishers may also fabricate concrete columns, beams, and panels. Finishers also
repair damaged areas after forms are removed.
The work can be fast-paced and strenuous. Bending and working in a kneeling position
are typical. Work areas are often muddy, dusty, or dirty. Kneepads and water repellent boots
are often worn.
Concrete finishers learn the trade through apprenticeship programs, technical schools, or
on-the-job training. A high school diploma is often required. High school courses in general
science, mathematics, blueprint reading, and mechanical drawing are helpful.
Most work is done outdoors, so weather delays are common. Overtime is often required
to make up for weather delays. Overtime is also required because once concrete is poured, it
must be finished regardless of the time on the clock.
Job opportunities for concrete finishers are expected to grow for at least the next several
years. Most concrete finishers work for specialty contractors. Wages range from approximately
$9.00 to $26.00 per hour. Poor weather and slowdowns in construction business can result in
lower income.