COMPOSITES - Materials for Civil and Construction Engineers - page 445

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COMPOSITES
The need for materials with properties not found in conventional materials,
combined with advances in technology, have resulted in combining two or
more materials to form what are called composite materials. These materials
usually combine the best properties of their constituents and frequently ex-
hibit qualities that do not even exist in their constituents. Strength, stiffness,
specific weight, fracture resistance, corrosion resistance, wear resistance,
attractiveness, fatigue life, temperature susceptibility, thermal insulation,
thermal conductivity, and acoustical insulation can all be improved by
composite materials. Of course, not all these properties are improved in the
same composite, but typically a few of these properties are improved. For
example, materials needed to build aircraft and space vehicles must be light,
strong, and stiff and must exhibit high resistance to abrasion, impact, and
corrosion. An example of a composite material that is very useful for civil
engineers is fiberglass, which is strong, stiff, and corrosion resistant and can
be used to make concrete reinforcing rebars to replace corrosive steel rebars.
These combinations of properties are formidable and typically cannot be
found in a conventional material.
Composite materials have been used throughout history, with differing
levels of sophistication. For example, straw was used to strengthen the mud
bricks in ancient civilizations. Swords and armor were constructed with lay-
ers of different materials to obtain unique properties. Portland cement con-
crete, which combines paste and aggregate with different properties to form
a strong and durable construction material, has been used for many years. In
recent years, fiber-reinforced concrete has been used as a building material
that is strong in both tension and compression. The automobile industry has
been using composite metals to build lightweight vehicles that are strong
and impact resistant. Recently, a new generation of composites has been de-
veloped, such as fiber-reinforced and particle-reinforced plastics, that has
revolutionized the material industry and opened new horizons for civil and
construction engineering applications.