International Concrete Abstracts Portal

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.

Deterioration of navigation lock wall concrete due to freeze/thaw cycles is a serious problem usually attributed to ineffective or a lack of air entrainment in the concrete. Most affected structures were made many years ago before air-entrained concrete was widely used. But, one of the largest locks in the world, Lower Monumental in Washington State, has been in service for only 10 years and also has serious surface deterioration. Conventional repair techniques of deteriorated surfaces call for removal of about 1 ft of face concrete, placing anchors and a reinforcing steel mat, and replacing the excavated concrete with new high-qualfty air-entrained concrete. However, at Lower Monumental, costs and repair time had to be taken into consideration. A coating which could be applied in a short period of time, could prevent continued freeze/thaw damage,.and be permanent under the adverse service conditions was needed. Six coatings of various portland cement and fine aggregate mixes were pneumatically applied to a section of the lock wall for evaluation. An accurate account of construction equipment, procedures, and production time was kept and "constructability" by these methods was evaluated. Total coating of the interior lock wall with a suitable latex-modified fiber-reinforced material was to be done in March 1980. This repair technique may be applicable to other structures, saving millions of dollars in construction costs and lost shipping time.

Concrete structures are being increasingly utilized for a wide variety of applications in the marine environment. As the structures become more sophisticated (e.g., prestressed); and as they are located in areas of more severe exposure (e.g., ice, open sea, etc.), subjected to dynamic cyclic and impact loads, their performance requirements have become increasingly severe and critical. A great deal of relevant research has been carried on in recent years as an outgrowth of the extensive use of concrete platforms in the North Sea and the Netherlands Delta Plan. A summary of these research programs furnishes a useful starting point. In addition, there are a number of proprietary programs from which the results are not yet publicly available. Important problems still remain. These can be divided into five categories: (a) relating to internal response of the structural ele-ments, (b) relating to the environmental conditions and forces under which the structure must serve, relating to new materials and configurations, (d) relating to construction practices, including repairs, and (e) relating to new uses in the ocean. Concrete is destined to play an increasingly important role in man's expansion into the oceans. A strong and viable research program is a necessary ingredient of this evolving technology, in order to ensure optimal performance.

The performance of structural lightweight concrete in a marine environment is reviewed beginning with the construction of concrete ships in World War I. Major laboratory programs, utilizing different methods of evaluating the durability characteristics of structural lightweight concretes are described. Physical properties that influence the weathering characteristics of structural lightweight concrete, that differ significantly from corresponding properties of normal weight concretes are reported. Long term field exposure of lightweight concrete structures, including a 60 year old ship and a 25 year old bridge deck are reported. Criteria for the construction of durable lightweight concrete structures exposed to marine conditions are recommended.

Cylindrical reinforced concrete specimens, 102 mm. in diameter by 457 mm. and containing 0-4% Ca(N02)2 by weight of cement were partially submerged in sea water. A single 356 mm. length of no. 4 reinforcing steel was symmetrically positioned along the central axis of each specimen with an electrical lead penetrating the top surface. The corrosion state of the embedded steel was characterized by periodic electrochemical potential measurements, and it was considered that the onset of significant corrosion corresponded to a noble-to-active potential shift. Corrosion exposure of some specimens was terminated subsequent to potential becoming active, and these specimens were cracked open and the reinforcing steel examined. It was determined that the time for potential of the reinforcing steel to become active lengthened with increasing Ca(N02)2. Possible reasons for the effectiveness of Ca(N02)2, in mitigating reinforcing steel corrosion are presented, and significance of the present results with regard to serviceability of reinforced concrete in corrosive applications is discussed.