Degradation of Reinforced Concrete Structures of Aluminum Electrolysis Plants Subjected to Elevated Temperature and Cyclic Load

Abstract

Technical papers describing the temperature related degradation of concrete are abundant, and serious damages often occurred in concrete structures subjected to high temperature such as metallurgy factories, although such occurrences were seldom made public. Concrete structures in aluminum electrolysis plants are generally subjected to high temperature emitted from electrolysis cells and cyclic load of heavy vehicles. Besides, hydrogen fluoride emitted from cells and stray current through reinforcement may cause deteriorating effects. In the case of an electrolysis plant built in Niigata in late 1960's, a part of passageway slab collapsed within a year of operation. A few years later, mesh shaped cracks on operation floor and shear cracks on floor beams and columns were observed. And an overall investigation on floor beams of 4 smelter buildings was carried out to determine the extent of deterioration, in 1972. The residual strength decreased linearly with operation term. The extent of strength reduction in "t" years' operation that we named "Deterioration Factor" and limit of lifetime were estimated. Countermeasures to reduce cyclic load and to reinforce floor beams were then taken, as well as the application of the Deterioration Factor to the next electrolysis plant in Shikoku Island. Details of renewed design of S-Electrolysis Plant and degradation of concrete are discussed. These aluminum electrolysis plants in Niigata and Shikoku have stopped operation in 1985 due to the withdrawal of the refining company, and existing smelter buildings have been diverted to another use. Although this paper presents rather retrospective cases, the authors wish this would be still helpful as a case study on degradation in concrete structure due to elevated temperature.