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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.

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.

Concrete roads have been in use in Denmark since 1923. Many of the old roads are still in use today and exhibit excellent durability. The Danish Technological Institute has investigated some of the old roads from the 1930s. The investigations include thin-section analysis of cores from the roads. This technique was used extensively by G. M. Idorn during the 1950s and 1960s, and in the late 1970s, the technique was further developed by the Danish Technological Institute. The results of the investigation show that the old durable concrete is a dense, strong concrete without signs of internal deterioration.

Five dormitory buildings on the Amherst College campus in Amherst, Massachusetts have essentially identical exposed aggregate precast concrete curtainwall panels. The panels on the three buildings that were constructed in 1963 are severely cracked and spalled; the buildings constructed in 1964 are relatively free of deterioration. The concrete used in the panels of all the buildings is composed of crushed quartz coarse and fine aggregate with strong and hard portland cement paste with low water-cement ratio and low void content. The significant difference between the materials used in the buildings is the amount of alkalies: the alkali content of the portland cement in the 1963 buildings is almost twice as high as in the 1964 buildings. A network of fine cracks developed in the panels due to alkali-silica reaction. These cracks allowed water to enter the panels and freeze during cold weather. The resulting progressive damage has led to disintegration of the cement paste, severe spalling, and corrosion of the reinforcing steel. The phased repair program, which began in the summer of 1989 and is expected to require several years to complete, involves removal and/or replacement of severely damaged panels, repair of damaged panels in place, modification of structural and waterproofing details to reduce exposure, and treating of undamaged panels to prolong their life.

Assessment of durability of concrete motorway bridges in Northern Ireland is part of a program of collaborative research of the Civil Engineering Department with the Roads Services of the Department of Environment (Northern Ireland). This involves testing bridges on site to develop methods that can be used to investigate the condition of approximately 1300 reinforced concrete bridges in the province so that a planned maintenance scheme can be proposed. Describes results of comprehensive tests that were carried out on a severely delaminated motorway bridge both prior to and after repair. Five other motorway bridges that represent the general population in terms of age, construction form, and past maintenance were also tested and the results compared. It has been observed that concrete strength is not a reliable index of proneness to deterioration, but permeability results allied to the knowledge of exposure to salt are more likely to provide a useful guide to durability. The in situ tests for sorptivity indicated that, with the two silane-treated bridges, one keeps the moisture out, whereas the other fails to do so. High-permeability concrete combined with leaking expansion joints have been found to be the main cause of absorption of chloride and the corrosion of steel.