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This paper deals with corrosion of reinforcing steel, the critical problem for the durability of reinforced concrete structures in marine environment. The results of tests using various electrochemical methods are summarized as follows; (1) As the water cement ratio of concrete increases, the natural potential of reinforcing steel becomes less noble and the electric resistance of wet concrete becomes lower due to low permeability which accelerates the corrosion of reinforcing steel. (2) Cracks in reinforced concrete structures make reinforced concrete so heterogeneous as to cause macrocell corrosion of reinforcing steel. (3) According to the experimental method used here, it may be considered that critical crack width is between 0.1 and 0.2 mm. (4) Water cement ratio influences both the macrocell corrosion rate at cracks, and the mechanism of corrosion. (5) It is concluded that the potential difference between macro anode (vicinity of cracks) and cathode (in concrete) is the electromotive force giving rise to the macrocell corrosion. (6) As the ratio of cathodic area to anodic area increases, the macrocell current density and the corrosion rate at cracks becomes larger.

Electrolysis has been used to investigate the deterioration of flexural bond in reinforced concrete structures under combined effects of exposure to marine environment and heavy sustained loads. Beams were loaded to develop specific crack widths, and loadings were then maintained to simulate the service condition. Direct current was impressed on the beams to accelerate corrosion of reinforcement so that the crack of concrete could be observed within the time limit of this investigation. The effects of impressed current on the reinforced concrete in relation to the crack width, sustained load and overload are described. Beams designed with tension reinforcement overlapped at midspan were subjected to impressed current until the concrete cracked. The average ultimate bond stress of the cracked beams was calculated based on the tension force developed in the reinforcement. A reduction in average ultimate bond stress due to corrosion of reinforcement is reported.

Reinforced concrete test specimens of 23 kinds were exposed on the sea in Tokyo Bay for about 1000 days, and corrosion of the reinforcement in the concrete was measured. As the result, the following were disclosed: 1) Corrosion of the reinforcement in concrete is affected greatly by both the cover thickness and water- cement ratio; 2) Test specimens exposed from seawater into air had no corrosion produced in the submerged portion but had corrosion produced at a particular height above the sea surface; 3) Test specimens exposed in air above the sea surface had irregular partial corrosion produced; 4) Electric resistance of theconcrete where corrosion occurred was low, and so was the natural potential of the reinforcing steel, and the corrosion occurred at valleys of the distributions of electric resistance and natural potential; and 5) From the foregoing, partial corrosion of the reinforcing steel in concrete is due to macro-corrosive current flow as the potential distribution in the reinforcing steel had peaks and valleys produced.

This paper describes an experimental investigation into the behavior of sulphur-infiltrated concrete in a sodium chloride solution with respect to corrosion of the reinforcing steel. The plasticized sulphur-infiltrated concrete as well as the elemental sulphur-infiltrated concrete were used in the investigation. The electrical measurement, both for natural process and accelerated process, has been used in this study as the criterion for the determination of the time to corrosion. The minimum sulphur loading is determined for concrete with different water-cement ratios, above which, the corrosion of reinforcement in concrete will notoccur.

From the historical records of the operations of the Canada Cement Company, now known as Canada Cement Lafarge Limited, changes in Normal Portland cement composition over the past 75 years are reviewed. Reference is made to the effect on cement composition of improved production technology, and establishment of definite limits i n chemical composition from the standpoint of quality and economy of production. The development of special cements to deal with specific field problems is discussed and essential differences in chemical composition are illustrated. Early attempts to solve the problems of concrete failure in a marine environment by altering the composition of related cements leads to a brief description of a test project conducted in the port of Saint John, New Brunswick, in which several types of cement were used in a pier installation and examined after a ten year period for comparison performance. Major harbour installations, located at Halifax, Nova Scotia, are identified, to illustrate the importance of good concreting techniques in minimizing the effect, of high C3A Normal Portland cement. The effect on cement composition of conformity to environmental requirements is mentioned and the author concludes with a comment on future developments in cement composition arising from the activities of the Canadian Standards Association.