Sulphate resisting

SURYVANSHI, A. K., SCANTLEBURY, J. D. LYON, S. B. 1995. The binding of chloride ions by sulphate resistant portland cement. Cement and Concrete Research, 25, 581-592. 

Destructive expansion from reaction with sulphates can occur not only if the latter are present in excessive proportion in the cement, but also from attack on concrete by sulphate solutions. The reaction involves the Al,0,-containing phases in the hardened cement, and in sulphate-resisting Portland cements, its effects are reduced by decreasing the proportion of the aluminate phase, sometimes to zero. This is achieved by decreasing the ratio of AljOj to Fe203 in the raw materials. In the USA, sulphate-resisting Portland cements are called Type V cements. 

Tentative composition for ferrite phase in sulphate-resisting clinkers. 

Sulphate-resisting Portland cements have relatively high ratios of iron to aluminium, and the ferrite phase cannot have the composition given above if it contains most of the iron. Tables 1.2 and 1.3 include a tentative composition and atomic ratios corresponding to it, based on scanty data for the interstitial material as a whole (G3,G4) and the requirement of reasonable site occupancies. 

Any attempt to understand the expansive process must thus consider the manner in which the deposition of the products affects the microstructure. The production of ettringite can cause expansion, but does not necessarily do so in a supersulphated cement (Section 9.2.9), much ettringite is formed, but there is no marked expansion. Comparable amounts of ettringite are reported to be formed when ordinary or sulphate-resisting Portland cements... 

Dimmig, A., and Kampfer, W. 2001. Investigations of the sulphate resistance of polymer-modified mortar (PCC). The Tenth International Congress on Polymers in Concrete and ICPIC/ICRlInternational Concrete Repair Workshop( Q0 ). 

Following oxidation, scrubbing solutions from the SO2 process mainly contain sodium sulphate. Since high sulphate concentrations (>600 mg/1) can lead to damage to sewerage systems, a limit value is set by the respective competent authority according to local conditions (e g. the presence of sulphate-resistant piping and dilution with other waste water). 

For moderated sulphate resistance CjA<8%, for high sulphate resistance C A eontent<5%. Mineral composition calculated according to Bogue formulae ... 

Orthorhombic or pseudotiigonal phase in clinker rich in alkalis In white clinkers In sulphate resistance clinker... 

In the opinion of experts, expressed during the workshop on the sulphate corrosion resistance, a low permeability of concrete is more important than the use of high sulphate resistant cement, in the case of sulphate corrosion hazard [65]. Therefore the w/c ratio maintained on a low level, together with higher cement content and proper curing of concrete at the early age of hardening, are of basic significance. 

The question of permeabihty growing with the decrease of cement content in concrete (Fig. 6.65), as well as with increasing w/c ratio should not be neglected, when the sulphate resistance is assessed [264]. 

The autoclaved concrete elements have the best sulphate resistance (Fig. 6.66) [71]. 

Mehta, P.K. Sulphate Attack on Conrete A Critical Review. In Skalny, J. (ed.) Sulphate Resistance of Concrete III. The American Ceramic Society, Westerville (1992)... 

The requirements for low heat (heat of hydration details are given in EN-196-8 and 9) and sulphate resistant (SR) cements are given in the standard EN-197-1, introduced in 2011. 

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