Case histories of deteriorated Portland-cement concretes exposed to sea water, both in mild and cold climates, show that permeability is the most important characteristic determining the durability of concrete. Whether due to improper mix proportions, or poor concreting practice, or cracking of concrete, permeable concretes tend to deteriorate in marine environment. This is because the hydration products of portland cement are chemically unstable to certain aggressive components present in sea water. In this paper, the chemical reactions between the aggressive components of sea water and the constituents of hydrated portland cement are reviewed. The physical processes of deterioration associated with these chemical reactions are discussed. Also discussed are the fundamental anodic and cathodic reactions involving corrosion of reinforcing steel in concrete exposed to sea water. A summary of recent work on the effectiveness of various admixtures in reducing the permeability of hydrated portland cement is given.

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.

Although concrete in tropical marine environment is never exposed to freezing and thawing, high temperature and humidity accelerate corrosion of steel and deterioration of concrete. There are a number of other factors which make it difficult to obtain a durable concrete in tropical areas. These factors include quality of aggregates and workmanship, special design requirements for easy-to-build structures and problems related to the remoteness of many jobsites. Corrosion mechanisms are mentioned briefly, repair-methods are explained in detail, beginning with the removal of deteriorated concrete, the restoration of reinforcing steel, replacement of concrete with cement-bound mixtures or epoxide mortars to adequate surface protection. Epoxy mortar placemnt under water as a repair method for concrete piles is described in detail,using a fluid mix of a high-density epoxy compound, which is poured into suitable, recoverable metal forms and which has been in use for 5 years at the Maraven refinery in Punta Cardon,on the Paraguand peninsula, Venezuela.

Since March I976 the UK Government Department of Energy and twenty-four industrial firms through CIRIA have jointly funded a €400,000 programme of seven projects aimed at providing additional knowledge to improve the design construction and long-term performance of concrete oil production platforms. The programme is managed by a three-man committee which represents the sponsors. Each sponsoring organisation also has a representative on one of three technical steering groups which advise on the work on the various projects. The projects are undertaken by research design or construction organisations under contract to CIRIA and cover the following topics: the fundamental mechanisms of the corrosion of reinforcement in concrete in seawater, the relationship between crack width and corrosion, corrosion and fatigue of precracked reinforced concrete beams at 150-m depth in seawater and at the surface, surveys of the condition of reinforced concrete in existing maritime structures, the effect of temperature gradients on the walls of oil storage structures, the strength of large prestressed members in shear, and a study of the modes of failure of concrete platforms. Most of the work has been completed and more than twenty reports have been issued to the programme participants. A start has now been made on a further three-year programme estimated to cost €600,000.

SP65 The performance of concrete in a marine environment has assumed importance with the discovery of offshore gas and oil deposits. A collection of 33 papers from 12 countries, which opens with a review of durability of concrete in sea water. This is followed by a series of papers dealing with permeability and physio-chemical studies of cement pastes, mortars, and concretes exposed to sea water. Other papers describe the mechanisms of corrosion of reinforcing steel, case histories of performance of concrete in sea water, accelerated tests, and repair techniques. Research reports cover performance of lightweight concrete in sea water and use of corrosion inhibitors.