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Experience has shown that good quality concrete made with either Type II or Type V portland cement will resist the sulfate attack by sea water. It will also prevent the rusting of the reinforcement when adequate coverage is provided. A rich concrete mix with a maximum W/C of 5.0 gallons of water per sack of cement should be used for all concrete construction exposed to sea water. The reinforcing steel should have a minimum cover of three inches of concrete. The low permeability attained with the low W/C will prevent rusting of the steel with such coverage; and the low W/C together with the use of sulfate resistant cement will prevent sulfate attack of the concrete. The use of pozzolan can help reduce the W/C ratio and develop a less porous surface. TYPES OF CEMENT Blended cements may be used in concrete construction when specific properties or costs are required. Recent concern with energy conservation has prompted the use of by-product materials in portland cement concrete. Blended hydraulic cements are produced by intimately and uniformly blending two or more types of fine materials. Type I portland cement is ageneral-purpose cement suitable for all uses where the special properties of other types are not required. It is used in concrete that is not subject to aggressive exposures, such as sulfate attack from soil or water, or to an objectionable temperature rise due to heat generated by hydration. Its uses in concrete include pavements, floors, reinforced concrete buildings, bridges, railway structures, tanks and reservoirs, pipes, masonry units, and other pre-cast concrete products. Type II portland cement is used where precaution against moderate sulfate attack is important, as in drainage structures where sulfate concentrations in ground waters are higher than normal but not unusually severe. Type II cement will usually generate less heat at a slower rate than Type I. This cement can be used in structures of considerable mass, such as large piers, and heavy abutments and retaining walls. Its use will reduce temperature rise, which is especially important when concrete is placed in warm weather. Type III portland cement provides high strengths at an early period, usually a week or less. It is chemically and physically similar to Type I cement, except that its particles have been ground finer. It is used when forms need to be removed as soon as possible or when the structure must be put into service quickly. In cold weather its use permits a reduction in the controlled curing period. Although richer mixes of Type I cement can be used to gain high early strength, Type III may provide it more satisfactorily and more economically. Type IV portland cement is used where the rate and amount of heat generated from hydration must be minimized. It develops strength at a slower rate than other cement types. Type IV cement is intended for use in massive concrete structures, such as large gravity dams, where the temperature rise resulting from heat generated during hardening must be minimized. Type V portland cement is used only in concrete exposed to severe sulfate action -principally where soils or ground waters have a high sulfate content. It gains strength more slowly than Type I cement. The high sulfate resistance of Type V cement is attributed to a low tricalcium aluminate content. Sulfate resistance also increases with air entrainment and increasing cement contents (low water-cement ratios). Type V cement, like other portland cements, is not resistant to acids and other highly corrosive substances. 3