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Concrete structures in severe environments include a variety of different types of structure in various types of environment. In addition to all the important concrete infrastructures which are severely exposed to aggressive environments from deicing salts, most of the extensive experience on concrete structures in severe environments is related to the marine environment.
Of the total surface area of the globe, about 70 per cent is covered by ocean water, which means that the area of the oceans makes up about two and a half times the area of the land. When considering the even smaller part of the land area which is inhabitable and increasingly more populated, this indicates an increasing need in the years to come of moving even more activities into the ocean waters and marine environments.
This increasing need may be briefly characterized by a few keywords such as raw materials, energy, transportation and space. Already in the early 1970s, the American Concrete Institute (ACI) came up with a technological forecasting on the future use of concrete, where the rapid development on the continental shelves was pointed out.
In this report, not only activities and structures related to oil and gas explorations but also activities and structures that would relieve land congestion were discussed. At an international symposium on concrete sea structures organized by Fédération Internationale de la Précontrainte (FIP) in Tibilisi in 1972, a great variety of new technological solutions to meet this development were discussed.
Without going into details, it should be noted that a variety of concrete structures would play an increasing role as a basis for the further activities in ocean and marine environments. Such structures would be of widely differing types and categories, such as:
• non-anchored free-floating structures, e.g. ships, barges and containers;
• anchored structures floating at water surface level, e.g. bridges, operation platforms, moorings, energy plants, airports and cities;
• anchored structures (positive buoyancy) resting above seabed level, e.g. tunnels and storage units;
• bottom-supported structures (negative buoyancy) resting at or below seabed level, e.g. bridges, harbour structures, tunnels, buildings, storage units, caissons, operation platforms and energy plants.
To a great extent the above rapid development has taken place and still will for many years to come; concrete will be the cheap and easily available construction material which can be provided in large quantities. It is well known that the properties of this material can be varied within wide limits.
Thus, the density can be varied from 500 up to 4500kg/m3 if necessary, either from a buoyancy or structural point of view, while a compressive strength of up to more than 100MPa can be produced. Experience has also shown that concrete structures in severe environments can remain serviceable for a very long time provided that current knowledge and experience are properly utilized.
Upon completion of new concrete structures, however, experience has shown that the achieved construction quality always shows a high scatter and variability, and in severe environments any weakness in the concrete structure will soon be revealed whatever its constituent materials may be.
Hence a performance-based concrete quality control during concrete construction with proper documentation of achieved construction quality is also very important. For a very long time, huge amounts of money and natural resources have been spent on repairs and rehabilitation of concrete structures in severe environments, and this is primarily due to premature corrosion of embedded steel.
In recent years, therefore, a rapid development of more advanced procedures for durability design and concrete quality control during concrete construction has taken place, some current experience with which is outlined and discussed in this book.