Title: Performance of Portland and Blastfurnace Slag Cement Concrete in Marine Environments
Author(s): G. J. Osborne
Publication: Symposium Paper
Appears on pages(s): 1303-1324
Keywords: blast furnace slag; chemical attack; chlorides; C 3A; concretes; durability; freeze-thaw durability; marine atmospheres; mix proportioning; performance; permeability; portland cements; Materials Research
A series of portland and blast furnace slag cement concretes were placed as 100-mm cubes in tidal and full-immersion environments at the Building Research Establishment's marine exposure site near Southend in the UK. The concrete cubes were photographed and their performance assessed in terms of their attack ratings and compressive strength retained after 1, 2, and 5 years of exposure to these aggressive conditions. The results showed that most concretes made with blends of ground granulated or pelletized blast furnace slag and portland cements had good resistance to attack by seawater, and compared favorably with the performances of concretes made with plain ordinary portland cement (OPC) or sulfate-resisting portland cement (SRPC) of similar mix proportions. The effects of the tricalcium aluminate (C 3A) content of the portland cement, alumina level of the slag, and the proportions of slag to portland cement on the durability of these concretes are discussed. The extent of chemical attack, degree of frost resistance, and ingress of chloride ions were shown to be affected by both the type of cement in the concrete and the storage environment. The most durable concrete in both tidal and full-immersion zones was the one containing the OPC of medium C 3A content. The blast furnace slag cement concretes had good chemical resistance, especially at 60 and 70 percent replacement levels, but showed signs of surface frost damage in the tidal zone. For these concretes, the need for air entrainment is recommended where severe conditions of freezing and thawing are likely to occur. The low-C 3A SRPC and high-C 3A OPC concretes were more prone to chemical attack when fully immersed than in the tidal environment, but were not affected by frost attack. The implications of these findings are considered in relation to concrete practice for maritime structures.