Underwater concrete construction

This thesis addresses the evaluation of the durability of reinforced concrete marine structures subjected to fatigue loading. The laboratory investigation was carried out on full and half size reinforced concrete specimens with three different water cement ratios (0.3, 0.4, and 0.56), static and fatigue loading conditions, and epoxy-coated and regular black steel reinforcements; a mineral admixture (silica fume), and a corrosion inhibitor (calcium nitrite) were used for specimens made with water/cement ratio 0.4 concrete. The marine tidal zone was simulated by alternate filling and draining of the tank (wet and dry cycles), and a galvanostatic corrosion technique to accelerate corrosion of rebar was introduced. Half-cell potentials and changes of crack width were measured periodically during the exposure and followed by ultimate strength testing. The significant findings include adverse effect of fatigue loading, existence of an explicit size effect, poor performance of epoxy coated steel, and negative effect of the increasing water/cement ratio.

The objective of this investigati.on was to contribute to
the determination of a suitable metallic coating for steel
reinforcement in concrete exposed to a marine environment
and possibly to stray current. Concrete specimens embedded
with steel, aluminum, cadmium, copper, molybdenum, nickel,
and galvanized steel were exposed to sea water. Direct
current was impressed on these to accelerate corrosion of
the reinforcement so that cracking of the concrete could be
observed within the time limit of the investigation. Aluminum,
cadmium, copper, and nickel were found to have no beneficial
effect on concrete cracking as compared to steel. In
addition, no correlation between oxide-metal volume ratio
and concrete time-to-cracking could be observed. It was
found that corrosion of molybdenum has little or no tendency
to crack concrete and its corrosion potential and active
behavior approximates that of steel, indicating it may be
an excellent coating.