Conventional portland cement

Most complete insulators comprise metal components cemented to the porcelain insulator to join it to the line structure, or to build up a string of insulators. Various cements are used depending on application, although conventional Portland cement is most common. Galvanized malleable cast iron is preferred for the metal since its thermal expansion is closer to that of porcelain than most metals and it is comparatively inexpensive. None the less, the cost of the metal components when used is often 40-80% of the cost of the insulator. The form of the widely used rod-insulator is shown in Fig. 5.17. 

Overall, these characteristics demonstrate that ammonium dihydrogen phosphate makes excellent rapid-setting grouts for outdoor applications such as road-repair materials in winter time in cold countries, because cold weather retards the initial setting, release of ammonia does not affect the workers and users in an open atmosphere, and the high strength makes these cements superior to conventional Portland cement. Products based on this material have been marketed commercially. 

As shown in Table 13.4, the loading of wollastonite may be very high. Typically, the compressive and flexural strengths of conventional portland cement are 27 and 5 MPa... 

Calcium oxide is the main ingredient in conventional portland cements. Since limestone is the most abundant mineral in nature, it has been easy to produce portland cement at a low cost. The high solubility of calcium oxide makes it difficult to produce phosphate-based cements. However, calcium oxide can be converted to compounds such as silicates, aluminates, or even hydrophosphates, which then can be used in an acid-base reaction with phosphate, forming CBPCs. The cost of phosphates and conversion to the correct mineral forms add to the manufacturing cost, and hence calcium phosphate cements are more expensive than conventional cements. For this reason, their use has been largely limited to dental and other biomedical applications. Calcium phosphate cements have found application as structural materials, but only when wollastonite is used as an admixture in magnesium phosphate cements. Because calcium phosphates are also bone minerals, they are indispensable in biomaterial applications and hence form a class of useful CBPCs that cannot be substituted by any other. 

Cementing operations in oil and gas wells place demanding requirements on cement properties. In spite of this challenge, the drilling and completion industry has relied exclusively on conventional portland cement with a few modifications for its cementing needs. The properties of portland cement and its modifications used in the oil industry are discussed in Chapter 3 of Ref. [1]. 

Comparison of Ceramicrete-based Permafrost and Conventional Portland Cement. 

Chemically, CKD has a composition similar to conventional Portland cement [88-98]. The principal constituents are compounds of hme, iron, sihca and alumina. The free Hme content of LKD can be significantly higher than that of CKD (up to about 40%), with calcium and magnesium carbonates as the principal mineral constituents. There is very little, if any, free lime or free magnesia content in stockpiled CKD and LKD that has been ejq)osed to the environment for long periods. 

PIC is a precast and cured portland cement concrete that has been impregnated with a monomer that is subsequently polymerized in situ. This type of cement composite is the most developed of polymer-concrete products. PCC, on the other hand, is a modified concrete in which a part (10%-15% by weight) of the cement binder is replaced by a synthetic organic polymer. It is produced by incorporating a monomer, prepolymer-monomer mixture, or a dispersed polymer (latex) into a cement-concrete mix. To effect the polymerization of the monomer or prepolymer-monomer, a catalyst (initiator) is added to the mixture. The process technology used is very similar to that of conventional concrete. So, unlike PIC which has to be used as a precast structure, PCC can be cast-in-place in field applications. PC can be described as a composite that contains polymer as a binder instead of the conventional portland cement. 

Gong, J. et al. (1997) Modification of mixed cementing material of gypsum with conventional Portland cement. Hunan DaxueXuebao, Ziran Kexheban 24, 78-83 [ref. CA 128/260823]. 

Polymer concrete can be placed by either premix, dry pack or prepack methods. The premix method is similar to the conventional Portland cement concrete mixing and placing. The binder, fine aggregate and coarse aggregate are added to the mixer in that order and mixing is continued until all aggregate particles are thoroughly wetted. Then the material is placed where it is required and consolidated. It is usually recommended that the surface to be treated is primed with the binder before placement. 

Latex-modified concrete is conventional Portland cement concrete with the addition of a polymeric latex emulsion. The water of suspension in the emulsion hydrates the cement and the polymer provides supplementary binding properties to produce a concrete with a low water-cement ratio, good durability, good bonding characteristics and a high degree of resistance to penetration by chloride ions, all of which are desirable properties in a concrete overlay. 

Artificial carbonation to reduce the alkalinity of the matrix and thus improve the durability of E glass composite was studied by Bentur [96], Although a marked improvement could be obtained, the performance achieved was still no better than that of AR-GRC composites with a conventional Portland cement matrix. Also, to achieve complete carbonation, an elaborate vacuum drying process was involved, which is difficult to apply in practice. An alternative method of supercritical carbonation of GRC was studied by Purnell eta/. [97,98], using AR fibres. This study evaluated only the properties of unaged composites. 

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