Sulfoaluminate

ASTM C845 Type E-I (K) expansive cement manufactured ia the United States usually depends on aluminate and sulfate phases that result ia more ettriagite formation duriag hydration than ia normal Portland cements. Type K contains an anhydrous calcium sulfoaluminate, C A SI. This cement can be made either by iategraHy burning to produce the desired phase composition, or by intergrinding a special component with ordinary Portland cement clinkers and calcium sulfate. 

The most widely used single component, calcium sulfoaluminate admixture, is composed of 30% C4A3S, 50%... 

Anhydrous calcium sulfoaluminate is formed by calcination of lime, gypsum and bauxite. The active expansive ingredient, C4A3S is formed by solid-state reaction from mixtures of compounds composed of calcium oxide,... 

The most widely used single component, calcium sulfoaluminate admixture, is composed of 30% CAS, 50% CaSO and 20% CaO with small amounts of glassy phase. Particle s3ize is coarser than that of Portland cement. Larger particle size ensures that the potential expansion due to hydration is extended over a period of time. Chemical and physical properties of the most widely used proprietary product, Denka CSA, are given in Table 6.10 [74], Other CSAs include mixtures of C ASH and 2 CS (monosulfate and gypsum) and mixtures of Type I cement, liigh-aiumina cement, CaSO, 2H O, Ca(OH) and CaO [75], 4 2... 

Anhy2drous calcium sulfoaluminate is formed by calcination of lime, gypsum and bauxite. The active expansive ingredient, C A S is formed by solid-state reaction from mixtures of compounds composed of calcium oxide, aluminum oxide, sulfur trioxide gas formed during the calcination of gypsum, and bauxite. Crystal growth of CSAs is encouraged to proceed at a slow rate to preserve the potential force of expansion for extended periods [76],... 

The hydrated components (C-S-H, portlandite, sulfoaluminates) in the cement matrix of concrete are in equilibrium with the pore liquid that is characterized by a high pH, due to the presence of OH (balanced by Na and K ). When concrete comes into contact with acid solutions, these compounds may dissolve at a rate that depends on the permeability of the concrete, the concentration and the type of acid. In soil with acidic ground water, the rate of refreshing is important Acids that can attack concrete are sulfuric acid, hydrochloric acid, nitric acid, organic acids such as acetic acid and humic adds and solutions of CO2. The rate of attack on the cement matrix depends on the solubility of the salts that are formed... 

Mehta, P.K. Effect of Lime on Hydration of Pastes Containing Gypsum and Calcium Alu-minates or Calcium Sulfoaluminate. J. Am. Ceram. Soc. 56, 315 (1973). (published by John Wiley Sons Ltd, reproduced with the permission of Wiley Sons)... 

Two temaiy compounds exist in the system C-S-A-S calcium sulfoaluminate and calcium sulfosilicate. 

Sulfoaluminate-belite cement (SAB) cement in which belite is the main constituent ... 

Belite-sulfoaluminate cement (BSA) or just Belite-suUbaluminate cement cement in... 

Belite-sulfoaluminate-ferrite cement (BSAF) suhbbehte cement with a particulariy... 

Tetracaldum trialuminate sulfate (calcium sulfoaluminate, C4A3S) is the phase that is mainly responsible for the early strength development of the cement. For best performance the C4A3S content in non-expansive suhbbehte cements should he between 30% and 40% (Beietka et al, 1996). In the presence of iron oxide in the raw meal, a small amount of this oxide may enter into solid soluhon with the sulfoaluminate phase,... 

The ferrite phase (calcium aluminate ferrite C2(A,F)) is formed in the presence of Fc203 in the raw meal. The ferrite phase present in sulfoaluminate cements possesses a higher reactivity than in ordinary Portland cement, presumably because of its formation at a lower temperature (Sharp et al., 1999). It contributes to both the short-term strength and the ultimate strength of the cement. 

The development of strength and the extent of expansion will depend on the composition of the cement and the proportions of the phases involved. Within reasonable limits and at appropriate calcium sulfate contents the early strength will increase with increasing amounts of the sulfoaluminate phase in the cement and— to a lesser extent— with increasing content of the ferrite phase. However, the belite phase will affect maiidy the final strength of the cement. Table 4.2 shows the effect of cement composition on the compressive strength development of a series of sulfobelite cements. 

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