Sulfate resistant cements

Sulfate-resisting cement, 5 498 Sulfate surfactants, 24 145 Sulfate titanium dioxide production process, 29 388-391 Sulfathiazole, 28 684 Sulfation, 23 513, 514, 536-538 higher aliphatic alcohols, 2 4 in higher olefins, 27 713 Sulfation operations, industrial changes affecting, 23 515-516 Sulfation processes, general overviews of, 23 555... 

It was shown earlier that aggregate types do not materially affect the performance of water-reducing admixtures. This is not true for cement and mixes containing special cements require particular care. Examples here are increased retardation with low C3A cement (for example, sulfate-resistant cement) and... 

Other types of cement than those of Table 1.3 are available for special uses. These are for instance low heat cements to be used when low heat of hydration is desired such as in massive structures, sulfate-resisting cements to be used to increase the resistance of concrete to sulfate attack, expansive cements, quick setting cements, white or coloured cements, etc. [2]. 

When S04 " leads to exposure class XA2 and XA3 it is essential to use sulfate-resisting cement. Where cement is classified with respect to sulfate resistance, moderate or high sulfate-resisting cement should be used for exposure class XA2 (and in exposure class XAl when applicable) and high sulfate-resisting cement should be used in exposure class XA3. 

With regard to protection against sulfate attack, the quality of the concrete is a crucial factor a low permeability is the best defence against this type of attack, since it reduces sulfate penetration. This can be obtained by decreasing the w/c ratio and using blended cement (i. e. pozzolanic or blast furnace slag cement that reduce the calcium hydroxide content and refine the pore stracture of the matrix). Finally, the severity of the attack depends on the content of CjA and, to a lesser extent, of C4AF in the cement. Standards in different countries provide for sulfate resistant cements with a C3A content below 3-5 %. 

For sulfate-resisting cements with low C3A content, the critical level of chlorides to initiate corrosion can be found among the lower values mentioned above, or at values even below those (e. g. 0.2 % by mass of cement). 

Photograph 7-12 Streak of belite crystals in sulfate-resisting cement clinker, suggesting nonuniformity in feed. Gas-fired, dry-process kiln, 770 tons/day. (S A6632)... 

Photograph 9-2 Angular alite and round belite crystals. Boxlike pattern of ferrite crystals in center. Sulfate-resistant cement clinker. (S A6729)... 

Photograph 9-17 Polished section of clinker, showing effects of 10-sec etch from water applied to Microcloth , reveals aluminate (highly irregular forms) and ferrite (smooth surface) in sulfate-resistant cement clinker. 

Sulfate-resistant cements used in mortar will inhibit this disintegration. 

Low heat Portland cement Modified low-heat Portland cement Sulfate resisting cement... 

Type V (High Sulfate Resistance). Type V Pordand cement is used in concrete exposed to severe sulfate attack of 1,500 to 10,000 ppm. Low concentrations of tricalcium aluminate [12042-78-3] give Type V its sulfate resistance. The sulfate resistance is improved with air entrainment and low water to cement ratios in the wet concrete. U.S. production of Type V Pordand cement in 1989 was 0.9% of the total Pordand cement production. 

Other countries have similar types, some classifications, as in Germany, are based on age-strength levels by standard tests (70). A product made in Italy and Prance known as Perrari cement is similar to Type V and is sulfate-resistant. Such cements have high iron oxide and low alumina contents, and harden more slowly. 

Tetracalcium aluminoferrite (4CaO Al O, FeOj) has little effect on the physical properties of the cement. For high-sulfate-resistant (HSR) cements, API specifications require that the sum of the tetracalcium aluminoferrite content plus twice the tricalcium aluminate may not exceed a maximum of 24%. 

Class H Intended for use as a basic well cement from surface to 8,000 ft (2,440 m) depth as manufactured, and can be used with accelerators and retarders to cover a wide range of well depths and temperatures. No additions other than calcium sulfate or water, or both, shall be interground or blended with the clinker during manufacture of Class H well cement. Available in moderate and high- (tentative) sulfate-resistant types. 

Select the most appropriate API class of cement that meets the depth, temperature, sulfate resistance and other well limitations. Select the cement class that has a natural thickening time that most nearly meets the cementing operation time requirement, or that will require only small amounts of retarding additives. 

Table 1.22 Sulfate resistance of reduced water-cement ratio and corresponding mix... 

Fig. 5.26 CaCl2 is least detrimental to sulfate resistance with Type V cement (low C3A (Shideler). 

Dunstan, E. R. 1980. A possible method for identifying fly ashes that will improve the sulfate resistance of concrete. Cement, Concrete, Aggregates, 2, 22-30. 

Another example of an important construction material in the Middle East is portland cement. For example, all-purpose Type I and sulfate-resisting Type V portland cements are manufactured in Saudi Arabia in three plants at Hofuf, Jeddah, and Riyadh. The cement production from the three plants totaled 1,790,000 tons in 1978 which is about a 38.5 percent rise over 1977. Portland cement is a basic construction material, and is primarily consumed by the construction industry. In Saudi Arabia cement does not seem to be encountering competition from any other building materials which are capable of endangering its present level of demand. 

Type II. Moderate-heat-of-hardening and sulfate-resisting portland cements are for use where moderate heat of hydration is required or for general concrete construction exposed to moderate sulfate action. 

Type IV. Low-heat portland cements contain a lower percentage of calcium silicate and calcium aluminate, thus lowering the heat evolution. Type V. Sulfate-resisting portland cements are those that, by their composition or processing, resist sulfates better than the other four types. Type V is used when high sulfate resistance is required. 

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