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Corrosion of reinforcing steel is now recognized as the most critical limit state affecting the durability and long-term stability of concrete structures. Although concrete is inherently alkaline and provides a natural protection to any embedded steel in it, thereby insuring its chemical passivity, concrete structures deteriorate for a variety of reasons. Steel corrosion is the most insidious and destructive form of damage, and once it starts, it is almost impossible to stop the process (unless such remedial measures as cathodic protection systems are applied), until eventually the safety, stability, and design life of the structure are all drastically reduced in time. The primary causes of steel corrosion are inadequate cover to steel, carbonation, neutralization due to atmospheric pollutants, and/or chloride penetration. The quality of concrete, its pore structure, and permeability characteristics are thus major factors controlling steel corrosion. However, it is inherent in the nature of concrete construction that there is no single method of corrosion protection that may be presumed to insure satisfactory serviceability throughout the life of a structure. This paper briefly reviews the factors that influence concrete deterioration and loss of alkalinity. It is shown that long-term durability of concrete structures can only be insured by a dual approach--developing a durable concrete, and providing a protective coating to the steel. Such methods of steel protection as cement-slurry coating, epoxy coating, and galvanizing are discussed. Extensive test results are presented on the corrosion resistance of plain, epoxy-coated, and galvanized bars when exposed to a marine environment, and chloride intrusion in cracked members. Cracking, cover, and concrete quality are identified as the major parameters influencing steel corrosion, but cover to steel is the most critical factor in preserving the electrochemical stability of steel. The paper shows that both epoxy-coated reinforcing bars and galvanized reinforcing bars can provide excellent resistance to chloride-induced corrosion.

Mechanisms of corrosion of concrete have been extensively studied and elucidated by various workers, but rate-determining factors have been neglected, as have the interactions between different corrodents. However, by considering all relevant influences as part of the total corrosive environment, it is possible to quantify aggressiveness as indexes and use them to select the appropriate technology for the circumstances under consideration.

SP131 The G. M. Idorn International Symposium on Durability of Concrete, sponsored by the ACI Committee 201 on Durability, was held at the 1990 annual ACI Convention in Toronto, Ontario, Canada. This symposium was dedicated to Dr. G. M. Idorn in view of his many decades of relentless dedication to the subject of improving concrete durability. A total of 32 paper are included in this publication. The volume has been divided into 4 parts, which all deal with the durability of cover. Part 1 covers durability aspects in relation to effects of environment on placement. Part 2 covers effects of composition. Part 3 deals with the assessment of durability, and in Part 4, various case histories are given.

The greatest threat to the durability of reinforced concrete structures is the reinforcement corrosion. The paper presents the importance of the concrete protective cover and the conditions causing the reinforcement corrosion under the action of chlorides and carbonic acid. Processes of absorption, diffusion and flow, i.e. of transport of media through concrete depend on the pore system and the amount of water in the pores.Physical laws describing the penetration of aggressive agents into concre-te can serve as a basis for engineering calculations of reinforcement durability in the concrete as well as for the designing of the concrete cover. Physical laws and corresponding material parametars are briefly reviewed in the paper. For engineering purposes, in calculating the durability, four typical tasks can be solved. The processes of degradation depend on the pore system in the concrete structure, and the paper indicates some possible technological measures of structure modifications.

As the sole domestic building material in Iceland, concrete is widely used for house construction as well as for other construction, such as dams, bridges, and harbors. In Iceland, conditions are in many ways extreme: the climatic conditions are harsh, the cement is high in alkalies, aggregates are of varying quality (some being reactive), and codes and standards have been sparse. Field surveys have shown that alkali-aggregate reaction (AAR) damage occurs where no preventive measures were taken and other conditions were unfavorable. Preventive measures taken in dam and bridge construction have proven to be effective. No AAR damage has been found in constructions erected after 1979, when several preventive measures were taken. The most important one is 5 to 7+ percent replacement of cement with silica fume Stricter criteria have been enforced to secure freeze-thaw durability, and durability design is improving. Research in repair and maintenance methods has had considerable influence on the construction industry.