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Concrete, or portland cement concrete, as it
is technically called is a simple material in appearance with a COMPLEX
internal nature. In contrast to its internal complexity, concrete's
VERSATILITY, DURABILITY and ECONOMY have made it the world's most used
construction material. This can be seen in the variety of structures it is used
in, from highways, bridges, and dams to floors, sidewalks and even works of
art.
Concrete is basically a mixture of two
components: aggregates and paste. The paste, comprised of portland cement and
water, binds the aggregates ( sand and gravel or crushed stone ) into a
rocklike mass as the paste hardens because of the chemical reaction of the
cement and water.
Aggregates are generally divided into fine
aggregates or sand and course aggregates or gravel. The paste is composed of
cement, water and entrained air. The quality of the concrete depends to a great
extent upon the quality of the paste. In properly made concrete, each particle
of aggregate is completely coated with paste and all of the spaces between
aggregate particles are completely filled with paste.
The quality of concrete is
generally determined by the amount of water used in relation to the amount of
cement. The less water used, the better the quality of the concrete - provided
it can be mixed properly. This mixing is completed in a specially designed drum
which can turn on the trip to the site where the concrete is to be placed.
After completion of proper
proportioning, batching, mixing, placing, consolidating, placing and curing,
hardened concrete becomes a strong, noncombustible, durable,
abrasion-resistant, and practically impermeable building material that requires
little or no maintenance.
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