Aluminate hydrates, 1.26

The reactions in the regulated-set cements containing Cjj A3CF2 (note mixed notation) as a principal phase resemble those in ordinary Portiand cements. Initial reaction rates are controlled by ettringite formation. Setting occurs with formation of the monosulfate, along with some transitory lower-limed calcium aluminate hydrates that convert to the monosulfate within a few hours. 

Chemical Name Tetrakis(hydroxymagnesium)decahydroxydialuminate dihydrate Common Name Magnesium aluminate hydrate monalium hydrate Structural Formula [Mg(DH)]4 [(HD)4AI(DH)(HO)AI(OH)4]-2H2D Chemical Abstracts Registry No. 1317-26-6... 

Tetracalcium aluminate hydrate, 5 477t Tetracalcium aluminate monosulfate, 10,8,x-hydrate, 5 479t 12-hydrate, 5 479t... 

The formation of the hexagonal aluminate hydrate and conversion to the cubic form is accelerated by TEA. 

One such Ca-aluminate hydrate mineral was observed in fly ash-water pastes (Tishmack 1999). The fly ash analysed in the study was washed with deionized water and Na-EDTA to selectively remove the soluble S-bearing minerals prior to being blended with additional CaO and water. The XRD analysis of the hydrated pastes showed peaks that closely matched the pattern of hydrogamet with one notable exception, a strong peak at 32.1° 2-theta. The phase may be a tetracalcium aluminate hydrate prototype AFm mineral noted to form in systems that have a low S C3A composition (Highway Research Board 1972). It may also be possible that the phase had a composition close to that of hydrogamet with some substitution of Si for Al. 

Turriziani, R. 1964. The calcium aluminate hydrates and related compounds. In Taylor, H. F. W. (ed) The Chemistry of Cements. Academic Press, London, Vol. 1, 233-286. 

An alternative to silicate-based Portland cement is the calcium aluminate cement, ciment fondu, which originated with the Lafarge company in France in 1908. Ciment fondu is typically made by heating limestone with bauxite, which is mainly AIO(OH) but contains much iron oxide (see Section 17.2). As noted above, calcium aluminate hydrates and hardens much more rapidly than alite, and so ciment fondu, either as such or mixed with Portland cement, can be used whenever a rapidly setting cement is required, for example, for construction at low temperatures. Concretes made from aluminate cements remain serviceable at higher temperatures than Portland cements and so are used to make cast refractories for pyrometal-lurgical applications. 

VELDE (B.) and KORNPROBST (J.), 1969. Stabilite des silicates d alumine hydrates. Contr. Min. Petr. 21, 63-74. 

The relative reactivity of the different mineral phases of cement with water is usually given as C A>C S>C S>C AF. Aluminate phases and their hydration products therefore play an important role in the early hydration process. Because of the high reactivity of calcium aluminate, the aluminate hydration reaction is carried out in the presence of sulfate ions. The latter provide control of the reaction rate through the formation of mixed aluminum sulfate products (ettringite and monosulfoaluminate) Calcium sulfate which is added to the cement clinker hence controls the properties of the aluminate hydration products. Sulfates thus play a crucial role in cement hydration and the influence of chemical admixtures on any process where sulfates are involved may be expected to be significant [127],... 

Common Name Magnesium aluminate hydrate Monalium hydrate... 

Mylius (M60) described the preparation of many calcium aluminate hydrates and related compounds. As with C-S-H, it is normally essential to exclude atmospheric CO2 and to avoid prolonged contact with glass apparatus. Dosch and Keller (D20) described methods for obtaining many AFm phases by anion exchange or other special procedures. 

The ettringite crystals on the surface of the cement particles are so fine that they cannot bridge the gap between the cement particles and therefore do not form a solid structure. This is the basis of the delay in solidification upon adding gypsum to cement. Without gypsum the tricalcium aluminate immediately reacts with water to calcium aluminate hydrate, which fills the space between the cement particles with its large crystals and leads to very rapid solidification of the cement slurry. 

The calcium aluminate still present reacts with the calcium hydroxide formed to tetracalcium aluminate hydrate. Calcium aluminum ferrite forms the analogous hydration product, which reacts more slowly. Part of the aluminum is replaced by iron ... 

Alcan Alumina Hydirate. [Alcan] Alumina hydrate intermediate for mfg. of low-iron aluminum sulfate, sodium aluminate, hydrated aluminum chloride, other aluminum chemicals. 

Stabilisation is a much slower process, which occurs progressively over several months, and involves the reaction of lime with the siliceous and aluminous components of the soil. The lime raises the pH to above 12, which results in the formation of calcium silicates and aluminates. These are believed to form initially as a gel, which coats the soil particles, and which subsequently crystallises as calcium silicate/aluminate hydrates. Those hydrates are cementitious products, similar in composition to those found in cement paste. The rate of crystallisation is temperature dependant and may take many months to reach completion. The resulting gain in strength (measured by the California Bearing Ratio Test [26.11]) is progressive, as illustrated in Fig. 26.2. 

The properties of cement mortar and concrete are closely related to the cement hydration. Polymers have good effect on the mechanical properties and durability of cement mortar and concrete. This improvement is probably come from the effect of polymer on the microstructures and the cement hydration. In this case, some reports about the effect of polymer on cement hydration are found in the references [1-3]. The authors have carried out some research on the influence of polymer dispersion and powder on cement hydration [4-7]. This paper will show some of the results focusing on the effect of SBR dispersion and powder on cement hydration, including the heat evolution, the calcium aluminate hydrates and the calcium silicate hydrates. 

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