ABSTRACT
From the performance of concrete in the marine environment (Chapter 4) and a review of the principal causes of concrete deterioration (Chapter 5), it is clear that the permeability of concrete is the most important factor determining the long-time durability. Therefore, with any new construction not only is it important to select materials and proportions for the concrete mixture that are most likely to produce a low-permeability product on curing but also necessary to maintain the watertightness of the structure as long as possible through the intended service life. In short, careful attention should be paid to all three of the following aspects of concrete construction:
• selection of concrete-making materials and mix proportions • good concreting practice • measures to prevent the widening of pre-existing microcracks
in concrete during service. It should be noted that many of the recent concrete sea structures, built during the last 15-20 years, are required to withstand unprecedented stress conditions. For example, coastal and offshore structures in the North Sea and the Arctic are exposed to enormous hydrostatic pressures, impact loading,
frost action, and abrasion/erosion loss from floating ice. Coastal structures in the Middle East are exposed to numerous cycles of temperature extremes (i.e. hot days and cold nights). Consequently, these structures made with high-strength concrete are very heavily reinforced as well as prestressed. The protection of the embedded steel with a low permeability concrete is of paramount importance from the standpoint of durability. To meet this challenge, i.e. to produce high-strength and low-permeability concrete, many new materials have been developed for use during the last two decades.
