International Concrete Abstracts Portal

Twenty post-tensioned I beams, eight feet long, were placed in the tidal zone at Treat Island, Maine in 1961 to determine the behavior of various types of end anchorage protection. In 1973 and 1974, eight beams were removed to the Vicksburg Waterways Experiment Station for testing and detailed examination. The behavior of all components of the eight beams are reported on, as well as the behavior of the twelve remaining beams still in the tidal zone. The continuing study has revealed some unexpected behavior of concrete and epoxy. It has shown that in eleven years, the prestressing steel was not structurally damaged by exposure to severe freezing and thawing sea-water environment and that the same seems to be indicated for the beams exposed seventeen years. The best type of end anchor protection appears to be a flush or pocket type.

This progress report describes the CANMET research project for the determination of durability of portland cement/ granulated blast-furnace slag/fly ash concretes in marine environment. The research project has been divided into three phases. Experimental work associated with Phases I and II is :partly complete and the experimental work for Phase III will commence in May-June, 1980. The work entails making mixtures of 0.1 m3 size with water to cementitious materials ratios ranging from 0.40 to 0.60. The cementitious materials used employed various replacements of portland cement with fly ash and granulated blast-furnace slag. The prisms and cylinders have been installed at a natural weathering station at Treat Island, Maine, where they are exposed to the effects of the alternating conditions of immersion of the specimens in sea water, then exposure to cold air and the effects of more than 100 cycles of freezing andthawing per winter. The test specimens at Treat Island are being monitored at yearly intervals for visual deterioration, and measurements are being taken to determine changes in pulse velocity and fundamental resonant frequency. The specimens from Phase I have nou been exposed for one year and the results of first yearly inspection indicate no significant deterioration of any specimens except for some surface scaling on those made with high water-cement ratios and incorporating high percentages of slag.

The corrosion of steel in concrete exposed to maritime conditions is dependent on the rate of chloride penetration to activate the steel, the resistivity of the concrete and the oxygen diffusion through the cover regions. Reinforcement corrosion may result in spalling of the concrete depending on the depth of cover, the physical shape of the member and the strength of the concrete. The paper considers the mechanisms involved and relevant measurements made by the author's laboratory and others particularly in relation to offshore, coastal and land based concrete structures in the North Sea, UK and overseas. This work has implications both to the specification of concrete design details, inspection techniques and remedial measures where corrosion or damage has, or might occur.

The use of large offshore concrete structures for oil and gas production created several questions regarding the behaviour of reinforced concrete in a marine environment. Some of these questions concerned corrosion of exposed and embedded steel. This study reports the up-to-date results and conclusions from a test program which has been running since December 1976. A total of 70 reinforced concrete beams, some of them cracked, are submerged in the sea on the West Coast of Norway. All specimens have been monitored intermittently by electrochemical methods, and some specimens were removed and broken open after 18 months of exposure. From the analysis of the current test results it is concluded that many of the questions posed regarding reinforcement corrosion in marine concrete may be laid to rest. There are clear indications that corrosion in cracks in the cover, galvanic corrosion of exposed steel coupled to embedded steel, excessive consumption of current in cathodic protection systems and pitting due to penetrating chlorides are problems which in the long run will cease to have any significance. This encouraging result is due to inhibition of oxygen flux to the reinforcement, and this has as a direct consequence that the free corrosion potential of the embedded steel after 6-18 months stabilize at a very low value, (typically -900 mV Vs. Ag/AGC1). Then the steel is in an active state of corrosion at an extremely low rate (< 10 um/year). It seems that the crack-width criteria which are currently enforced are overly conservative, and future efforts should include re-evaluation of current codes.

This report deals with a calculation model for the corrosion of steel in concrete. The aim has been to make a highly complicated durability problem sufficiently simple to obtain a survey of the importance of various factors for the service life of the concrete structure. Some researchers will doublessly regard the model as an excessively rough simplification of the actual process but 90 to 95% of all corrosion problems which occur in practice agree well with this theory. The service life for concrete structures with regard to reinforement corrosion is broken down into a initial stage and a propagation stage. This breakdown is suitable since the primary parameters are different in the two sub-processes. The penetration of various passivation-breaking and activation substances to the steel is studied in the initiation stage, as well as the concentrations which give rise to corrosion or a marked increase in corrosion. The corrosion rate has increased considerably in the propagation stage and the factors which determine the rate of corrosion thus become interesting. In addition, the degree of corrosion which can be permitted with regard to load bearing capacity, esthetic aspects etc, must be determined. The report also presents examples of a number of material coefficients which are necessary for the model.