Sulfate-resisting Portland cement

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. 

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 %. 

Figure 6.4 Chloride threshold for corrosion initiation as a function of content of interfacial voids (concretes made with different types of cement OPC = ordinary Portland cement, SRPC = sulfate-resistant Portland cement) [14]...

Using ordinary and sulfate-resistant Portland cement to represent differing chloride environments, short-term electrochemical monitoring and SEM were used to characterize corrosion behavior [34]. Steel electrodes attained passivity in mortar with high levels of calcium aluminate, up to 1% wt. chloride. At 1.75% wt. chloride, steel electrodes corrode. All chloride levels resulted in steel corrosion for low levels of calcium aluminate. Pore solution was also impacted by mortar exposure conditions. Atmosphere exposure had a high influence on hydroxide concentration in pore solution but no impact on chloride concentration. Carbonation was also investigated samples in a sealed container had a chloride/hydroxide ratio half that of unsealed samples. 

A air curing W underwater curing HH hemihydrate gypsum OPC ordinary Portland cement SRPC sulfate-resistant Portland cement MS microsilica D disintegration of samples Source Odler and Balzer (1992)... 

Sulfate-resistant Portland cement is characterized by a reduced C,A content in clinker. 

OPC=ordinary Portland cement SRPC=sulfate-resisting Portland cement SSC=super-sulfated cement PFA=pulverized fiiel ash GGBFS=ground granulated blast-furnace slag... 

Sulfate-resistant Portland cement, unlike ordinary Portland cement, contains no or only reduced amoimts of C3A, and produces no or very little Friedel s salt, even in the presence of excessive amormts of CE. This cement is therefore particularly rrrtsrritable for applications in which protection of the steel reinforcement from chloride-induced corrosion is required. 

For adequate performance, concretes to be exposed to seawater must have a high cement content and a low water/cement ratio. In steel-reirrforced stmctures proper cover of the steel is essential. Portland cement may be rrsed in these applications, but the presence of pozzolanic constituents or blast furnace slag generally improves the corrosion resistance of the concrete (Eglinton, 1998). In a direct corrrparative study it was found that the penetration rate of chloride ions in concrete is smaller in mixes made with silica fume and blast furnace slag than in those made with ordinary or sulfate-resistant Portland cements (Sakoda ei a/., 1992). 

In terms of chemical composition. Class G and Class H oil well cements are low-CgA Portland cements, and the specifications of both are typically met by high-iron, sulfate-resistant Portland cements (see also section 2.8). The free lime content in these cements is not limited by the API specifications, but it should be below 0.5 wt% to avoid difficulties with cement slurty rheology and retarder response. In producing Class G and Class H oil well cements, iron oxide (in the form of hematite or pyrites residues) must usually be added to the raw mix to produce more ferrite phase at the expense of tricalcium aluminate. The required amount of Fe203 is greater when a cement of HSR rather than MSR grade is produced. 

The most commonly produced cement is Portland cement to British Standard BS 12, which represents 90% of the market, which includes products such as rapid hardening and coarse ground cements, and white Portland cement (WPC). Other cements covered by other British Standards include sulfate resisting Portland cement (SRPC), Portland blast furnace cement, high slag blast furnace cement, and Portland PFA cement. 

Type V Sulfate-resisting Portland cement (SRPC) 41 Has high sulfate resistance. It is a special cement used when severe attack is possible. 

Type V Sulfate-resisting Portland Cement (SRPC)... 

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