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Concrete, the most
commonly used man-made building material, is composed of cement and
an aggregate of gravel or crushed rocks, sand and water. The
chemical reaction of the cement mixture and water is called
hydration, and results in a very hard and long-lasting, stone-like
material. Cement, by itself, can sustain high compressive force but
it is relatively weak in tension. Concrete is cement with the addition of aggregate,
which makes it
much more resistant to shear stress, and heavy,
concentrated loads which would fracture ordinary cement.
Concrete Cross-Section
Additives
Other
ingredients can be added to improve and enhance concrete, or to add a desired property such as
color, toughness, resistance to thermal expansion and contraction,
environmental exposure, insulation properties, or, to change it's weight and/or strength.
Concrete is often reinforced with steel to increase its tensile and
shear stress performance.
Curing
The first three days of hydration and hardening are critical. If
concrete is dried too fast, shrinkage and cracking can occur.
Concrete that is kept damp during curing promotes strength, and
because that keeps stress to a minimum, cracking is minimized.
Factors to be considered include the thickness of the concrete,
ambient temperature and humidity, and even wind which contributes to
drying. It's important that freezing and overheating be avoided
during curing, or the strength of the concrete will be compromised;
and other problems may develop such as scaling, cracking and lower
abrasion resistance. Proper curing will maximize
concrete's properties and performance.
Applications
Cement is used to bind
brick and stone components together, while concrete is used to make
a wide variety of components and structures, such as paving stones,
pipe, blocks, footings for fences, walls and foundations for
buildings. Because of its relatively inexpensive and easy application, concrete is a popular pavement material for roadways,
driveways, sidewalks. In fact, entire structures have been made of
the material.
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