The excellent performance of aluminous cement concrete in sea-water is illustrated by a summary of long term exposure tests. Visual examination of laboratory semi-immersed 50 x 100 x 100 mm mortar prisms over 20 years confirms this result. Only rapidly converted (hot cured) specimens at total water/cement ratios >_0.6 show signs of attack after several years. To obtain more up to date information at low water/cement ratios, small (20 x 20 x 100 mm) mortar prisms have been tested for 5 years by semi-immersion in reconstituted sea-water and in tap water. Visual examination at chosen ages is followed by crushing tests on the submerged and exposed halves of each specimen. 16 low ( < 5 % ) C3A portland cements and 7 different aluminous cements have been studied, at constant mortar consistency. Visual examination of small prisms does not provide conclusive comparisons. The crushing strength tests show that the aluminous cements outperform the portland cements, and also enable the relative performance of individual aluminous cements to be established. Complementary data shows that the porosity of converted aluninous cement is similar to and not greater than that of portland cement at the same water/cement ratio. Further work is in progress to distinguish between the role of intrinsic factors (chemical) and physical factors (porosity/permeability) in the relative resistance of portland cements and aluminous cements to sea-water and other corrosive agents.

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.

The paper discusses the results obtained by testing concrete quality and the degree of reinforcement protection in the piles of the submarine tunnel for the Coke Plant at Bakar, and in the walls of the water intake for the Rijeka Thermo-Power Plant, both placed by the tremie method. The shafts of the high chimney stacks of the Rijeka Thermo-Power Plant and the Bakar Coke Plant, erected by slip forms, were similarly investigated. The results obtained by tests and observations show that concrete for thin and highly-reinforced elements, to be placed by tremie, must be made with pure portland cement, or portland cement incorporating slag, having a low need of water for standard consistency, (measured according to Vicat), and with clean well-graded sand and coarse aggregate. Otherwise, mass concrete structures are preferred. Slipform erection of structures by the sea should be avoided, or, if used, the surface of the concrete should be protected additionally and completely (while slipform advancement is still under way) with cement mortar reinforced by the addition of polymer binders . This operation must be planned at the design stage and clearly specified.

This paper presents data, based on extensive rehabilitation of the underside of concrete pier in the harbor of Portland, Maine, of the compressive strengths of shotcrete used as the sole repair material. This paper reviews the principal causes of damage to concrete in a marine environment, including erosion by "scour action," alternate wetting and drying in the "splash zone" and the problems resulting from intrusion of the salts contained in sea water into the concrete. Recommendations as to proper proportioning and mix designs for shotcrete to be used as the repair material for such structures is presented as well as criteria for the use of accelerating admixtures in the shotcrete material. A discussion of the use of both latex modified and calcium aluminate cement shotcrete for rehabilitating deteriorated concrete in an aquatic environment is offered. This paper also considers the proper preparation of the surfaces to be repaired as well as the special problems associated with the placement of shotcrete while working in areas subjected to tidal and wave action.

Concrete structures are being increasingly utilized for a wide variety of applications in the marine environment. As the structures become more sophisticated (e.g., prestressed); and as they are located in areas of more severe exposure (e.g., ice, open sea, etc.), subjected to dynamic cyclic and impact loads, their performance requirements have become increasingly severe and critical. A great deal of relevant research has been carried on in recent years as an outgrowth of the extensive use of concrete platforms in the North Sea and the Netherlands Delta Plan. A summary of these research programs furnishes a useful starting point. In addition, there are a number of proprietary programs from which the results are not yet publicly available. Important problems still remain. These can be divided into five categories: (a) relating to internal response of the structural ele-ments, (b) relating to the environmental conditions and forces under which the structure must serve, relating to new materials and configurations, (d) relating to construction practices, including repairs, and (e) relating to new uses in the ocean. Concrete is destined to play an increasingly important role in man's expansion into the oceans. A strong and viable research program is a necessary ingredient of this evolving technology, in order to ensure optimal performance.