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cement, with high concentrations of tricalcium aluminate, is less resistant to sulfate attack. <br />Tetracalcium aluminoferrite also hydrates rapidly and develops only a low strength, but it does <br />not exhibit a flash set. <br />SULFATE RESISTANCE <br />The durability of concrete exposed to alkaline sulfate soils or water containing alkaline <br />sulfates has been a problem of long standing in many localities. The areas where alkaline sulfate <br />soils and ground waters occur are particularly prevalent in the western part of the United States. <br />Poor quality concrete made with cements of high tricalcium aluminate, C3A, content will <br />deteriorate rapidly when exposed to sulfate soils or sulfate waters. <br />Both laboratory tests and field experience have shown that good quality concrete made with <br />sulfate resistant cement, low C3A, has excellent resistance to sulfates. Such concrete will have <br />excellent durability when exposed to sulfate soils and sulfate waters. <br />It is both the quality of the concrete and composition of the cement that provides sulfate <br />resistance. A poor quality concrete with a high water/cement (W/C) ratio will not have good <br />sulfate resistance even when made with the best sulfate resistant cement. <br />Type II portland cement should be used in all concrete construction exposed to moderate <br />sulfate action. Type V cement should be used when high sulfate resistance is required. <br />A rich concrete mix with a maximum W/C of 5.0 gal]ons of water per sack of cement should be <br />used. With the lower W/C and lower porosity that accompany the use of richer mixes, high <br />resistance to sulfate attack has been attained with the use of sulfate resistant cements. <br />Table 1, taken from the Bureau of Reclamation Concrete Manual, provides a guide on the effect <br />of sulfate concentrations on concrete and the type of cement to be used. <br />Table I <br />Attack on Concrete by Soils and Waters Containing Various Sulfate Concentrations <br />Relative Degree of <br />Sulfate Attack Percent Water-Soluble Sulfate (as <br />SOq) in Soil Samples P.p.m. Sulfate (as SOa) in <br />Water Samples <br />egligible 00 to 0.10 __ O~to 150 <br />ositive' <br />- 10 to 0.20 I50 to 1000 <br />onsiderable ~ .20 to 0.50 1000 to 2000 <br />evere ver 0.50 ver 2000 <br />Use Type II cement `Use Type V cement <br />Extensive tests have shown that the use of pozzolans as admixtures will improve the sulfate <br />resistance of concretes made with Type I, high C3A, cements. Tests reported from the University <br />of California have shown that the best sulfate resistant concrete can be obtained by using Type <br />V, low C3A, portland cement. <br />Sea Water <br />Sea water contains a moderate quantity of sulfate and about 3.0 percent of sodium chloride. <br />The sulfate can attack poor quality concrete, while the chloride can cause rusting of the <br />reinforcement. Rusting of the reinforcement is accompanied by expansion which is likely to <br />cause spalling of concrete over reinforcing bars. <br />