Portland cement clinker manufacture

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. 

A knowledge of the relevant high-temperature phase equilibria is necessary for understanding the factors that govern acceptable bulk compositions for Portland cement clinker, the conditions under which the latter can be manufactured, and the phase composition and microstructure of the resulting material. This chapter deals with these equilibria and with the phases to which they relate, with the exception of the major clinker phases, which were described in Chapter I. Some anhydrous phases primarily of interest in relation to other types of cement are also considered here. Principles underlying the preparation of anhydrous silicate, aluminate and other high-temperature phases are outlined. 

In the manufacture of Portland cement clinker, the raw materials, typically a limestone and a clay or shale, are intimately mixed and heated, ultimately to a temperature of about 1450°C. The principal reactions taking place are conveniently divided into three groups, viz ... 

The cement type manufactured in the largest quantities and used most is Portland cement . It consists of so-called Portland cement clinkers admixed with gypsum or anhydrite. 

Lime- and clay-containing raw materials such as limestone, lime, clay, marl, lime marl, or clay marl (marls are naturally occurring mixtures of limestone and clay) are utilized as raw materials in the manufacture of Portland cement clinkers. 

Strength, it is important to ensure that as much tricalcium silicate as possible is obtained in the manufacture of Portland cement clinkers, by using appropriate mixing ratios of the raw materials and sintering in the existence range of tricalcium silicate (between 1250 and 2070"C). 

Gartner, E.M., "Physical and Chemical Aspects of Portland Cement Clinker Formation," Research on the Manufacture and Use of Cements, Proceedings of the Engineering Foundation Conference, Henniker, New Hampshire, 1985, pp. 1-20. 

The fundamental use of the microscope in portland cement clinker analysis is to bring to the observer a visual appreciation of phase identities, sizes, conditions, and mutual relationships. With only a basic assemblage of equipment, microscopical analysis can be easily performed, in many cases within a few minutes. The rapidity with which potentially energysaving information can be acquired clearly renders the analysis economicallyjustifiable, especially in routine quality-control and trouble-shooting situations. In addition, the microscope has obvious value in scientific research in the manufacturing process. 

Portland cement is manufactured by burning until partial melting of an intimate mixture of substances that mainly contain calcium Ca, silicon Si, aluminium A1 and iron Fe. During burning, so-called clinkers are formed. When ground, these clinkers are able to react with water - to hydrate - and to deposit hydrates with binder properties. A typical clinker mineral composition of Portland cement is ... 

In the manufacture of Portland cement, many otherwise-waste materials can be used either as a substitute for the traditional raw material, or as a secondary fuel (e.g., used tires) [334,1577]. In particular, drilling wastes can be introduced in the clinker burning process [878]. For both waste disposal and cement manufacturers, a mutual benefit will emerge. The cement manufacturing companies reduce their demand for traditional raw materials and save the limited capacity of landfills and other waste-treatment industries. 

There are three fundamental stages in the process of manufacture of Portland cement, namely. (I) preparation of the raw mixture. (2) production of the clinker. (3) preparation of Ihe cement. Whether the process used is wet or dry. the raw materials are selected, analyzed, and mixed so dial, alter ireatmeni, Ihe product, or clinker, has a desired, narrowly specified composition A factory analysis of slurry, where the wet process is in use. is as follows calcium oxide 44%. aluminum oxide 3.5%. silicon oxide... 

In the portland cement manufacturing process, three steps occur. First, raw materials are crushed and mixed. The raw materials are powdered limestone, alumina, iron, and silica. Second, the raw materials are fed to an inclined rotary kiln in which they are heated to at least 2700 F. A rock-like substance called clinker is formed, which exits the kiln and is cooled. Third, the cooled clinker is finely crushed, and about 5 percent gypsum is added to produce finished cement. Details of the process are explained below. 

Figure 4-4. Typical clinker production process during Portland Cement manufacture.3...

Various methods have been used to obtain cements that set and harden rapidly. They include the use of Portland cement with admixtures and of mixtures containing both Portland and calcium aluminate cements, described in Sections 11.5 and lO.I.IO, respectively. Another approach has been the manufacture of clinkers containing either CuAy CaF, or C 4A, S. both of which hydrate rapidly under appropriate conditions with the formation of ettringite. 

Portland cement is an aluminosilicate powder which sets to a solid mass on treatment with water. It is usually manufactured by grinding limestone and clay to a fine powder, mixing with water to form a slurry, and burning the mixture, with a flame of gas, oil, or coal dust, in a long rotary kiln. At the hot end of the kiln, where the temperature is about 1500 C, the aluminosilicate mixture is sintered together into small round marbles, called clinker. The clinker is ground to a fine powder in a ball mill (a rotating cylindrical mill filled with steel balls), to produce the final product. Over 100,000,000 barrels of cement per year is made in the United States. 

Portland cement was invented in 1824. The raw materials used in its manufacture are limestone, quartz sand, clay and iron ore. These supply the necessary ingredients lime, silica, alumina, and iron. Properly proportioned quantities of the raw materials are pulverized and fired to result in cement clinkers. These are finely ground and mixed with up to five percent gypsum to make the finished product. Thousands of tons are produced annually in the USA. A small percentage of this total is used for grouting. 

CAC require large industrial facilities, similar to those used to make ordinary Portland cement. The raw materials for CAC are typically bauxite and limestone, which are ball-milled and mixed together to form a feed of appropriate composition, which is fed into rotary kilns to form a calcium aluminate clinker. The clinker is ball-milled to produce the cement. Analysis for composition and mineralogy at various stages of manufacture are essential to ensure a consistent product, see for example Chakraborty and Chattopadhyay [32] for a discussion of the bulk processing of high alumina CAC. 

Zeolitic tuff is also utilised in the cement industry as pozzolanic addition (see Sub-sec. 5.2.2.) to portland cement. This application recalls the use of pozzolana, since the beginning of the 1900s, to obtain blended cements, able to fix the lime formed by the hydration of the calcium silicate components of the portland clinker. The utilisation of zeolitic tuff, as substitute of pozzolana, to obtain pozzolanic cements is based on both economic and technical considerations. On one hand, manufacturing blended cements allows a 40% fuel savings, without reducing the quality of the produced binder (it is to bear in mind that the mixture lime-pozzolana is itself a cement), on the other, it involves some advantages, e.g., the... 

In former USSR expansive cements were divided into 3 classes 20,40 and 60 their potential of self-prestressing was 2, 4 and 6 MPa respectively, Expansive clinker containing C A S, Portland cement phases, CaO, and anhydrite, The first producer nowadays this cement is manufactured in many countries among them in significant amount in Russia, AlEv—calcium aluminate expansive cements, PEv—Portland expansive cements, Very similar to that patented by Lafarge... 

Prout, J., "Trouble-Shooting Cement Manufacturing Problems," inMicroscopy of Clinker and Cement, Short Course, Portland Cement Association, Skokie, Illinois, 1979,7 pp., and Advanced Microscopy Seminar, Portland Cement Association, Skokie, Illinois, 1979. 

As the last step in Portland cement manufacture, Portland clinker, in combination with limited amounts of gypsum and/or anhydrite, has to be ground to a fine powder. A ball mill is the standard equipment used for this purpose. It was reported recently (Goldstein, 1997) that the power consumption in the grinding process may be reduced if—in place of a single clinker—a blend of two clinkers is used, of which one has a higher and the other a lower lime saturation factor. 

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