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.

Subsequent to the investigation of the correlation between laboratory accelerated freezing and thawing and weathering at Treat Island, Maine, reported in 1953 (1) there have been some developments especially in the field of sulfate resistance of concrete that serve to further elucidate the findings then reported. There have also been many contributions to improve understanding of the causes and nature of the many different kinds of chemical reactions that can and do occur between aggregates of all kinds and the surrounding cement paste, so long as the exposure of the concrete is such as to keep it moist--as is the case at Treat Island, Maine. This paper suggests that there is a complex series of interactions among the constituents of cements, aggregates, and seawater not previously appreciated. Sulfate susceptibility of blended cements is becoming better understood and the use of certain blended cements promises to provide a useful alternative to moderately or highly sulfate-resisting portland cements. It also now is clear that no aggregate particle in portland-cement concrete long stored in an environment of moistness and moisture movement can be regarded as completely inert. What is becoming clear is that aggregates differ greatly in the nature, degree, and consequences of their chemical activity.

This paper presents data, based on extensive rehabilitation of the underside of concrete pier in the harbor of Portland, Maine, of the compressive strengths of shotcrete used as the sole repair material. This paper reviews the principal causes of damage to concrete in a marine environment, including erosion by "scour action," alternate wetting and drying in the "splash zone" and the problems resulting from intrusion of the salts contained in sea water into the concrete. Recommendations as to proper proportioning and mix designs for shotcrete to be used as the repair material for such structures is presented as well as criteria for the use of accelerating admixtures in the shotcrete material. A discussion of the use of both latex modified and calcium aluminate cement shotcrete for rehabilitating deteriorated concrete in an aquatic environment is offered. This paper also considers the proper preparation of the surfaces to be repaired as well as the special problems associated with the placement of shotcrete while working in areas subjected to tidal and wave action.

This paper explains some of the current programs and future plans for the Treat Island Exposure Station. During the past few years, the U. S. Army Corps of Engineers has been very interested in research and technology transfer, and as such determined to do everything possible to avoid duplication of other research programs. To coordinate all of this research requires knowledge of work being performed by government agencies and private qrganizations around the world. Because the Corps already has the Treat Island facilities, many specimens from other research organizations have been incorporated into the programs, consequently reducing the cost for these other organizations in maintaining a facility of their own. Future plans are to include more specimens. Another area requiring much work is to correlate the Treat Island results with in situ concrete structures. In the past, many of the results reported could be visually determined by inspection; in the future, a greater in-depth analysis will need to be developed so that the contribution of all of the parameters including concrete constituent properties to deterioration may be analyzed.