Abstract
In Sweden the problem of damage of large concrete structures, often originating from corrosion of the steel reinforcement and the freezing-thawing cycles, became a matter of real concern about 10 years ago. It was also obvious that the calculated lifetime for a number of structures had to be reconsidered if not repair and durability actions soon will be carried out. An essential cause of the problem was often defined to be the chloride and/or water content of the structure. The paper describes a number of case in Sweden, the different systems and methods used, experiences and conclusions and the aim is to give a view of the efforts made in this area mainly by The Swedish National Road Administration and The Stockholm City Street and Traffic Administration-Materials Testing Laboratory and the technical level today achieved. REF. 5,6,7, 8.
The 6,072 m long Öland Bridge is at present the longest bridge in Europe, close to the city of Kalmar in the south-east of Sweden. It was built during the years 1967-1972, extensive damage was found already 1980 in the form of cracks and delamination on several concrete piers. C.P. using sacrificial anodes was installed 1986 and followed up 1992, impressed current C.P. system was installed on four piers partly in water which were under trial repair 1988 and by means of continuous monitoring of the C.P. system during 1991-92 the design and system efficiency have been investigated and shall be continued for several years. Removing of salt from concrete by means of an electric force has been introduced as a way to reduce damage due to high chloride content. Investigations, laboratory as well as field tests show a certain reduction of chloride content but they show too the necessity of further research before the method is ready for use in practice. Several structures in Stockholm have in a test program been used in this project.
Moisture state has an important influence on the durability of most building materials including concrete. Investigations show that bydrophobation reduce the risk of damage. Further, tests show that impregnation in two steps can be expected to improve the durability of already partly damaged outdoor concrete structures. This have been carried out as a development and test project by The Stockholm City Street and Traffic Administration-Materials Testing Laboratory.
The future will bring new systems and products and maybe we shall be able to combine the new products with the experience. The hydrophilic polymer is a water-loving hydrogel material which can control and permit the passage of gases, especially when wet or in a very high humidity environment and control the passage of molecules at a controlled release rate, having good mechanical and chemical properties. The testing and research has just started and the target is corrosion and moisture.
