Cement oxide components

Table 15.2. Common letter designation of cement oxide components ...

As with LSF, the approach is applicable to cements if CaO is further corrected by deducting O.7SO3. Because minor oxide components are ignored, the total for the four main phases plus free lime will not add up to 100%. It is implicit in the approach that all the MgO is assumed to occur as periclase. The phase composition calculated by Bogue s method is related to the LSF in that a ratio of 38 to CjA 0.546, calculated without correcting the CaO content for free lime, corresponds to an LSF > 1.0 (D2). 

Ground clinker or cement may be analysed by standard methods, such as X-ray fluorescence (XRF). Determination of free lime is discussed in Section 4.3.3. With XRF or other methods in which no fraction of the material is excluded from the analysis, insoluble residue (determined separately) is included in the oxide components and therefore should be omitted from the total. It can often be assumed that two-thirds of it is SiOj and the rest... 

Any standard method of matrix inversion, such as the Gauss-Jordan method (N13), may be used to solve the equations. The coefficients in equations 4.11-4.14 may be used without serious error for most ordinary Portland cement clinkers in which the alite composition is not too different from that assumed here. As a byproduct of the calculation described in this section, and using the full compositions of the phases given in Table 1.2, one may calculate a mass balance table (Table 4.3) showing the distributions of all the oxide components among the phases. 

Table 4.3 Distribution of oxide components among phases in a typical Portland cement clinker, calculated from the bulk chemical analysis... 

In the first effective studies of hydrated cements by DTA, Kalousek and co-workers (K27,K32,K33) observed the early formation of ettringite and its subsequent replacement by what was termed a solid solution, but which was probably a mixture of AFm phases. They found no CjAHg or other hydrogarnet phases. Quantitative or semiquantitative determinations of gypsum and ettringite indicated that less than half the total SO3 present could be accounted for by these phases. The authors concluded that the solid solution was eventually replaced by a product which they termed Phase X , and which was possibly a gel containing all the oxide components of the original cement. 

For any selected drying condition, a table is now completed, similar to the previous one, but with the HjO and CO2 content of each phase included and the quantities of elements expressed as weight percentages of oxide components. Table 7.3 shows results for a typical, mature cement paste thus calculated. It was assumed that the C-S-H had Ca/Si = 1.7 and Al/Ca = 0.02, that the AFm and AFt phases each had Si/Ca = 0.05 and that the hydrogarnet-type phase had the composition Ca2.95Alo.1Fe1 7sTio jMn 05-... 

DTA (K32,025) and XRD (A29) studies indicate that cement pastes cured at temperatures of or approaching lOO C contain little or no detectable hydrated aluminate phases, the observation of hydrogarnet noted above thus being unusual. Kalousek and Adams (K32) considered that the Al , 864 and other ions were incorporated into a Phase X , which possibly included all the oxide components of the cement. In pastes cured normally, much of the AFm phase is probably poorly crystalline and intimately mixed with the C-S-H (Seetion 7.3.1). This tendency may be increased if hydration takes place more rapidly. 

Next to Cr C2, TiC is the principal component for heat and oxidation-resistant cemented carbides. TiC-based boats, containing aluminum nitride, AIN, boron nitride, BN, and titanium boride, TiB2, have been found satisfactory for the evaporation of metals (see Boron compounds, refractory boron compounds Nitrides). 

Pordand cement clinker is formed by the reactions of calcium oxide and acidic components to give C S, C2S, C A, and a ferrite phase approximating... 

Phases Formed in Pordand Cements. Most clinker compounds take up small amounts of other components to form soHd solutions (11). Best known of these phases is the C S soHd solution called aHte. Phases that may occur Hi Portiand cement clinker are given Hi Table 1. In addition, a variety of minor phases may occur Hi Portiand cement clinker when certain minor elements are present Hi quantities above that which can be dissolved Hi other phases. Under reducHig conditions Hi the kiln, reduced phases, such as ferrous oxide [1345-25-17, FeO, and calcium sulfide [20548-54-3] CaS, maybe formed. 

The powder contains 2inc oxide and magnesium oxide (36), and the Hquid contains an aqueous solution of an acryHc polycarboxyHc acid. Water settable cements have been formulated by inclusion of the soHd polyacid in the powdered base component. The set cement mainly consists of partially reacted and unreacted 2inc oxides in an amorphous polycarboxylate matrix (27,28). 

The ionic bond is the most obvious sort of electrostatic attraction between positive and negative charges. It is typified by cohesion in sodium chloride. Other alkali halides (such as lithium fluoride), oxides (magnesia, alumina) and components of cement (hydrated carbonates and oxides) are wholly or partly held together by ionic bonds. 

The Arrhenius definition is not suitable for AB cements for several reasons. It cannot be applied to zinc oxide eugenol cements, for these are non-aqueous, nor to the metal oxychloride and oxysulphate cements, where the acid component is not a protonic acid. Indeed, the theory is, strictly speaking, not applicable at all to AB cements where the base is not a water-soluble hydroxide but either an insoluble oxide or a silicate. 

Crisp and coworkers found that the development of surface crystallinity was related to the speed of set. The faster the reaction, the shorter was the inhibition period before surface crystallization took place. When the setting time of a cement was between two and three minutes, surface crystallinity developed in a few minutes. When it was seven minutes, surface crystallinity was delayed by three hours. The reaction rate was affected by the chemical composition and physical state of the cement components. Well-ignited zinc oxide, the presence of magnesium in the... 

Oxysalt bonded cements are formed by acid-base reactions between a metal oxide in powdered solid form and aqueous solutions of metal chloride or sulphate. These reactions typically give rise to non-homo-geneous materials containing a number of phases, some of which are crystalline and have been well-characterized by the technique of X-ray diffraction. The structures of the components of these cements and the phase relationships which exist between them are complex. However, as will be described in the succeeding parts of this chapter, in many cases there is enough knowledge about these cements to enable their properties and limitations to be generally understood. 

Silver white, relatively soft metal that is only applied in alloys. Oxygen and water attack pure Ca. The most prominent compound is the oxide (CaO) = burnt calcium, which hardens to calcium carbonate in mortar. Annual production of about 120 million tons. Burnt gypsum (CaS04 0.5 H20) hardens with water. A great step in evolution was the replacement of hard shells of brittle calcium carbonate by an internal skeleton of tough calcium phosphate (hydroxylapatite)-protein composite. Calcium is essential for all life forms. The daily requirement is 0.7-1.0 g. Humans (70 kg) contain 1 kg of calcium. Calcium silicate is the main component of cement. Marble is calcium carbonate in polycrystalline form and the favorite material of sculptors. 

Calcinating a mineral removes its volatile components, such as water or carbon dioxide and leaves an usually crumbly solid residue. Calcinated secondary minerals such as limestone are the basic components of building cements, and in extractive metallurgy operations they facilitate the smelting of metals. Calcinating limestone (composed of calcium carbonate), for example, drives away carbon dioxide, leaving a solid, friable residue of quicklime (composed of calcium oxide) ... 

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