Tricalcium aluminate, 1.25

Isometric, orthorhombic, tetragonal, and monoclinic forms of tricalcium aluminate (CajAl O ) with a melting point of approximately 1542°C are termed CjA in the cement industry. Tricalcium aluminate normally consists of uniform, small, xenomorphous to rectangular crystals (1 to 60 pm) in low-alkali or alkali-free clinker. CjA may comprise as much as 18 percent in ordinary clinker. Crystals show poor cleavage parallel to (001), conchoidal fracture, and a hardness of 6. Tricalcium aluminate is normally isotropic in cross-polarized light, colorless (in white cement) to tan and brown in transmitted light in ordinary portland cement, with an index of refraction of 1.710. It reflects gray on unetched polished surfaces and etches blue to 

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Portland Cement Manufacture. The second greatest use of limestone is as raw material in the manufacture of Pordand cement (10). The average limestone factor per ton of Pordand cement is 1.0—1.1 t of pulverized limestone. The limestone, calcined to lime in the cement rotary kiln, combines with siUca and alumina to form tricalcium siUcate and tricalcium aluminate and other lesser cementing compounds (see Cement). Most cement companies operate captive limestone quarries. 

Type V (High Sulfate Resistance). Type V Pordand cement is used in concrete exposed to severe sulfate attack of 1,500 to 10,000 ppm. Low concentrations of tricalcium aluminate [12042-78-3] give Type V its sulfate resistance. The sulfate resistance is improved with air entrainment and low water to cement ratios in the wet concrete. U.S. production of Type V Pordand cement in 1989 was 0.9% of the total Pordand cement production. 

Fig. 5. The early hydration reactions of tricalcium aluminate in the presence of gypsum and calcium hydroxide. Initial molar proportions l-C A ...

This section considers a number of extremely important structure types in which A1 combines with one or more other metals to form a mixed oxide phase. The most significant of these from both a theoretical and an industrial viewpoint are spinel (MgAl204) and related compounds, Na- -alumina (NaAlnOi ) and related phases, and tricalcium aluminate (Ca3Al20g) which is a major constituent of Portland cement. Each of these compounds raises points of fundamental importance in solid-state chemistry and each possesses properties of crucial significance to... 

The important compounds in Portland cement are dicalcium silicate (CazSi04) 26%, tricalcium silicate (CasSiOj) 51%. tricalcium aluminate (Ca3Al206) 11% and the tetracalcium species Ca4Al2Fe2 Oio (1%). The principal constituent of moistened cement paste is a tobermorite gel which can be represented schematically by the following idealized equations ... 

Tetracalcium aluminoferrite (4CaO Al O, FeOj) has little effect on the physical properties of the cement. For high-sulfate-resistant (HSR) cements, API specifications require that the sum of the tetracalcium aluminoferrite content plus twice the tricalcium aluminate may not exceed a maximum of 24%. 

Portland cement refers to a class of hydraulic cements in which the two essential constituents are tricalcium silicate (3Ca0-Si02) and dicalcium silicate (2Ca0-Si02) with varying amounts of alumina, tricalcium aluminate, and... 

The percentage of dicalcium silicate, sometimes abbreviated as C2S in the industry, determines the final strength of the cement. The amount of tricalcium silicate, C3S, is related to the early strength (7-8 days) required of the cement. Tricalcium aluminate, C3A, relates to the set in the cement. 

In this final peak, the remaining tricalcium aluminate reacts with both gypsum and water to form ettringite and subsequently the tricalcium aluminate monosulfate. C3A hydrates formed are of varying composition but... 

The principal cement and admixture factors that influence the rheological behavior in HPC, particularly at very low water-cement ratios, are the following (1) the quantity of tricalcium aluminate (C3A) and to a lesser degree... 

Although fly ash is largely non-crystalline glass, the major and minor elements in fly ash (O, Si, Al, Fe, Ca, Mg, and S) foim several different phases that have been characterized by XRD in many research projects (Diamond 1984 McCarthy 1988 Bergeson etal. 1988 Thedchanamoorthy McCarthy 1989 Ainsworth et al. 1993). The phases of major elemental constituents that have been commonly identified in fly ash include quartz mullite, Al6Si20 3 tricalcium aluminate, Ca3Al206... 

The soluble sulfate versus time curve for the cement containing the natural anhydrite is radically changed when CLS is present [130, 131]. The rate of solution of natural anhydrite, which is much slower than that of gypsum or calcium sulfate hemihydrate, is further retarded in the presence of chemical admixtures, which leads to a sulfate-starved system in the concrete, often producing rapid set and an increase in rate of concrete slump loss (Fig. 7.42). Apparently the adsorption of the lignosulfonate by the natural anhydride plus the rapid reaction between the soluble SO and the tricalcium aluminate keeps the SO level near zero concentration for the first 10-20 min causing rapid stiffening and quick set (approximately 15 min). It is also reported that chemical... 

The aluminate phase constitutes 5-10% of most normal Portland cement clinkers. It is tricalcium aluminate (Ca3Al206), substantially modified in... 

Sugama and Allan [5] used calcium aluminates (tricalcium aluminate, C -A, monocalcium aluminate, C A, or calcium dialuminate, C A2) as the cation donors and reacted them with an ammonium polyphosphate fertilizer solution and formed quicksetting cements. The purpose of this study was to develop cements that are not affected by the CO2 environment and are useful as downhole cements in geothermal wells (see Chapter 15). The composition of the fertilizer was 11.1 wt% N as ammonia, 37.0 wt% P2O3, 50.79 wt% water, and the rest trace elements. Differential scanning calorimetry (DSC) showed that the reaction rates of the three minerals are in the decreasing order ... 

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