Cement sulfate resistance

Portland cement clinker potential phase composition is presented in Table 4. It could be seen that the C3A content in the clinker was 9.46% which is important for the cement hydration rate and cement sulfate resistance. Common Portland cement is not resistant to the sulfate influence because of the significant C3A content, whose hydrates react with sulfate ions resulting in expansive compounds. Portland cement with the higher resistance to sulfates must have low C3A content. Moderate to high content of mineral alite - C3S (54.72%) is usual for the Serbian cement plants and enables the addition of higher quantities of mineral admixtures without influencing the quality of final cement. 

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. 

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... 

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. 

Another version of Portland cement mortar or concrete is the replacement of some of the Portland cement with rice hull ash. This ash additive markedly improves the resistance of the mortar or concrete to food acids and similar chemicals. Flyash (pozzolanic admixture) meeting ASTM C618 has also been widely used to improve the properties and sulfate resistance of Portland cement... 

Portland cements are available commercially in many different forms, including varieties for high early strength and for sulfate resistance and very finely ground materials called microfines. 

CACs were developed in response to the need for cements resistant to groundwater and seawater attack and are the only cements, other than Portland cement, that are in continuous long-term production [2], The property of CAC that was most important in their commercial development is the resistance to sulfate attack, which contrasted with the poor-sulfate resistance of contemporary Portland cements [2], and CAC was first patented in 1908 [2], Most early applications, in construction projects following the First World War, were in structures exposed to seawater, such as harbor pilings. Because CAC hardens rapidly, it was adopted for prestressed concrete beams in the post World War II construction boom, with some unfortunate results. Poor understanding of the material properties of CAC and incorrect water to cement ratios led to the collapse of several buildings, and the use of Portland cements, which are cheaper, has replaced CAC in prestressed concrete beams[2]. 

There are, however, several important niche applications for CAC. Most notably, CACs are used as linings to sewers and mine tunnels. Calcium aluminate cements are resistant to chemical attack from sulfate-producing bacteria that thrive in sewer systems (especially in warmer climates), and sprayed concrete linings to sewers have been shown to resist degradation for periods up to 30 years. The high impact and abrasion resistance of CAC also makes it suitable as a lining material for ore tunnels in mines and because CAC sets rapidly, it can be sprayed onto tunnel walls (as shotcrete ) and even used as a tunnel lining. 

Chlorides, generally in the form of the sodium salt are found in sedimentary deposits, particularly in marine and coastal areas. In reinforced concrete, they can increase the corrosion rate of the steel. Chlorides can also adversely affect the performance of sulfate-resisting Portland cements. BS 5328 [8.9] specifies chloride contents in concrete for various types and uses. BS 882 (Appendix C) [8.2] provides guidance on limits for chloride in aggregates when it is required to limit the chloride ion content , ranging from 0.01 to 0.05 %. 

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. 

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