Experience and research have shown that reinforcement in submerged concrete appears to be well protected against corrosion. Questions have been raised as to whether this durability will be present in structures subject to dynamic loads and in structures spanning through several environment zones. To clarify the effect of loading, eight concrete beams were exposed dynamically loaded at a seawater laboratory. Four of the specimens were allowed to corrode freely, while the rest were cathodically protected. To study the corrosion behavior of multizone exposed concrete structures, eight concrete columns with a diameter of 0.6 m and a height of 5 m were installed in the sea. One of the main objectives was to study the cathodic current density demands of embedded steel exposed to different environmental zones and of multizone exposed embedded steel. This paper presents the results from the laboratory and field tests, and the main conclusion is that the corrosion conditions found on a multizone exposed concrete structure differ from those found on a completely submerged structure.

Load-carrying capacity and fatigue strength before and after repairing were investigated for a coastal structure in Tokyo Bay, which was subjected to serious damage by chloride for 15 years. Static and cyclic load tests together with investigation on effectiveness of repair were carried out on specimens taken from the site. It was found that the bearing and yielding capacities of deteriorated slab are 90 and 80 percent, respectively, of those of sound structure. These losses were mainly caused by 10 percent loss of reinforcement corrosion. The specimens repaired by material with high tensile strength suggested brittle failure in static load tests. It was also found that fatigue failure of deteriorated reinforcements was accelerated by pitting corrosion.

For selecting concrete cover for reinforcement in marine structures, consideration of the corrosion protection of steel bars is indispensable. Therefore, requirements for quality and thickness of concrete cover must be established so the concrete cover prevents chlorides, oxygen, water, etc., from reaching reinforcement through the life of the structure. To insure good performance of concrete cover, the chloride penetration process should be understood. A dualistic diffusion equation was adopted to explain this. In solving equations, the following were clarified through referral to data of experiments: 1) The relationship between the quality of concrete and chloride diffusion coefficients; 2) the effect of the chemical or physical adsorption of chloride in concrete on the diffusion process; and 3) boundary condition to concrete surface for chloride concentration in various marine environments. On the basis of these studies, a close agreement between observed and calculated values was obtained. Through the calculations of chloride penetration, the rational design for quality and thickness of concrete in various marine environments has been suggested.

Ferrocement has attracted world-wide interest because of its proven suitability for marine structures as well as its potential as a repair material. The first part of the paper describes methodology for accelerated exposure of specimens to the marine environment simulated in the laboratory. The main features of this methodology were: the cyclic temperature and moisture environment, and the preloading of specimens up to the state of cracking before placing them in this environment. The second part reports and discussed the influence of the duration of load and the cyclic environment on the fatigue properties measured from tests performed under cyclic loading. These properties are compared with those of the specimens stored in a normal curing room. Fatigue results obtained from the ferrocement specimens are compared with those from the reinforcing wires tested in the air. The fatigue performance of reinforcement in the air was found to be considerably lower than that in the composite.

Focus is the study of basic properties of the low water-absorption lightweight aggregate and the water-absorption reducing agent that were developed to make the pumping of lightweight concrete using non-presoaked lightweight aggregate possible. The water absorption of the low water-absorption aggregate was extremely small. The compressive strength and modulus of elasticity of the concrete were found to be considerably higher than those of the concrete using ordinary calcined expanded shale aggregate. The water-absorption reducing agent reduced water absorption under pressure considerably. The compressive strength and modulus of elasticity of the concrete using the aggregate that was treated with the agent were not significantly influenced by the agent. The concrete using the dry low water-absorption aggregate without presoaking that was treated with the agent was pumped through a pipeline with an equivalent horizontal length of 160 m. However, as the aggregate absorbed water, it showed a drop in slump, an increase in compressive strength, and a particular internal pressure distribution along the pipeline.