This report describes an experimental study on the behaviour of concrete structures in marine environment conducted by C.E.B.T.P. and C.N.E.X.O. Two concrete structures, each composed of two U' form elements, one reinforced, the other prestressed, had been tested under dynamic loadings in two different environments : on land and in natural sea-water (splash zone).
The aim of the study is to investigate the behaviour of offshore structures in its service conditions, so the six months loading program the same in the two cases has been chosen for the simulation of wave induced forces in sea. The dimensions have been also adjusted for a good representation of the phenomena involved.
These tests give an opportunity to develop new means of control which could be applied in such constructions.
In the test conditions, natural sea-water did not induce much unexpected mechanical behaviour compared with that on land. However in sea water, cracks were the site of alterations (destruction and deposit) causing a higher level of residual deformation. Within the test duration, the steel of the reinforced concrete structure showed a beginning of corrosion, which did not reduce over all strength.
The state of corrosion of the reinforcements is evaluated by the electric potential method associated with measurements of the water content inside the concrete using capacity-resistance gauges. Strains in concrete are determined by vibrating wire gauges, and crack widths by an optical micrometer.
For the extraction of marine resources, steel was at first mainly used, in relatively shallow waters. But for deeper sea-beds, concrete is now more employed and offers solutions which are attractive from the technical and economical point of view, especially for durability. Concrete protects embedded steel reinforcement from environmental attack. However this advantage is effective only if the concrete covering has a sufficient thickness and compacity and if cracking can be reasonably limited. But we need actually more tests in sea conditions to determine the limitations of these requirements.
Among the different problems concerning a concrete structure placed in the open sea (I), we, have chosen to study at first its behaviour in its service life, under dynamical loads and corrosive action at sea, and to compare it with its behaviour on land.
This first stage of experimental research on concrete at sea, concerns essentially the comparison of the behaviour of bent elements placed either on land or at sea. These first tests also allow us to control that certain measuring devices will behave well in the marine environment.
To facilite the application of loads, U shaped structures have been adopted (fig. I). Four test elements of identical dimensions have been fabricated in the C.E.B.T.P. Laboratories at Saint-Remyles-Chevreuse near Paris.
