In the construction world the 21st century will be known as the
century of concrete in the oceans. There are a number of reasons
for this prediction. Human population is expected to grow to more
than six billion by the end of the 20th century. Improvement in
living conditions around the world has not kept pace with this
increase in the population. To improve the standard of living, the
search for solutions has already provided a major impetus for the
exploitation of coastal and undersea energy and mineral resources.

Many industrial materials, commonly used for structural
purposes, do not show long-term durability in the marine
environment. Portland cement concrete has proved to be an exception
and is, therefore, increasingly used for the construction of concrete
structures. During the fourth quarter of this century, already twenty
oil and gas production platforms consisting of heavily reinforced
and prestressed concrete elements have been built in the North
Sea. Many sophisticated structures, such as superspan cantilever
concrete bridges, undersea concrete tunnels, storm barriers, and
man-made concrete islands are either under construction or under
planning and design. Compared to structural steel elements, cost
and durability considerations are tipping the scale in favor of
reinforced and prestressed concrete elements because it is well
accepted now that, from the standpoint of engineering behavior,
both materials can be used to give satisfactory performance under
loading conditions normally encountered in service.

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