International Concrete Abstracts Portal

Paper deals with the evaluation in marine environment of normal and lightweight concretes incorporating supplementary cementing materials. A series of 175 concrete prisms, 305 x 305 x 915-mm in size, were cast over a nine-year period starting in 1978 for long-term exposure at Treat Island, Maine. The prisms were positioned at mid-tide level on a rack at the entrance to the Bay of Fundy, which is perhaps the most severe marine exposure condition for concrete. The test specimens are exposed to repeated cycles of wetting and drying, and to an average of about 100 cycles of freezing and thawing per year. The test specimens are monitored at yearly intervals: the specimens are photographed and rated on a visual basis. Ultrasonic pulse velocity is also determined. After up to nine years exposure, both normal-weight and lightweight air-entrained concretes show no degradation of the mass of the concrete; however, some of the specimens show significant surface deterioration. The amount of deterioration generally increases with an increasing water-to-cementitious materials ratio, and increasing replacement of cement with slag and fly ash. It appears that surface deterioration can be avoided if the cement content is kept to at least a certain minimum level. The tests confirm that over long exposure duration, non air-entrained concrete is not durable in this environment.

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.

Several projects in the "Concrete in the Oceans" program have measured electrical potentials and resistivities on reinforced concrete specimens exposed to a marine environment. A state of the art survey was also undertaken on corrosion monitoring techniques which led to experimental work to improve the use of these techniques, particularly on marine structures. The main conclusions from this test program are discussed. Two independent sets of electropotential and resistivity measurements taken on beam specimens exposed to a splash zone environment for periods up to five years have been compared with the actual corrosion found after the reinforcement was broken out of the specimens. The comparison of these two sets of data and the ability of these monitoring techniques to predict likely corrosion are discussed and related to the various parameters such as the disposition of the cracks, the depth of cover and the type of concrete. Based on the work described in this paper, the limitations of corrosion monitoring methods are also highlighted.

Presents comprehensive test data on the corrosion resistance of plain, galvanized, and epoxy-coated reinforcing bars exposed to marine environment. The bars were embedded in concrete prisms, precracked to a steel stress of 200 MPa, and then subjected to two exposure regimes in a loaded condition. A natural exposure in a corrosive tidal zone and an accelerated wetting and drying cyclic regime in sea water were chosen for the corrosion tests. In addition, tests were also conducted on bars provided with artificially damaged coatings; further marine exposure tests were also carried out on cracked prisms and damaged coatings in the cracked regions. The test results show that even a 70 mm cover is inadequate to protect uncoated bars from corrosion in marine environment. Galvanized bars exhibited improved performance but did not provide complete protection. Epoxy coated bars are shown to afford long term protection against corrosion even under severe exposure conditions and with damaged coatings.

A test building constructed in 1984 was exposed to marine environment under sub-tropical weather of Okinawa, Japan. Concentration of chloride ions in concrete, changes in the half cell potentials with time, and protective effects of surface coatings were investigated. Diffusion of chloride ions was monitored using Fick's law. The diffusion equation was converted to difference equation and solved under the initial condition in terms of time. These results were compared with those of the field, and the relationships were obtained.