Cement compostion

Details Cement compostion Cement compostion

1995-01-04

1996-12-17

Bell, Mark L.

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

106714, 106715, 106716, 106738, 106724, 106734, 106735, 106736, 106778, 106787, 106799, 106800, 106815, 106816, 106817, 106819, 106823, C04B 702, C04B 706

Patent

active

055849261

DESCRIPTION:

BRIEF SUMMARY
This application is the National Phase of International Application No. PCT/DK93/00132, filed Apr. 13, 1993.


FIELD OF THE INVENTION

The present invention relates to compositions of extended hydraulic cements, that is cements which, upon mixing with water set and harden to give substantial strength, and more particularly to extended cement compositions exhibiting high strength.


BACKGROUND OF THE INVENTION The chemical parameters LSF, S/R and A/F
referred to in this specification are: ##EQU1## In the foregoing ratios, the chemical symbols represent percentage by weight of the identified substance present in the composition. In the following description and claims the percentages referred to are by weight.
Four cement minerals are usually regarded as the major constituents of Portland cement clinker: Alite which mainly consists of tricalcium silicate (3CaO.SiO.sub.2) designated C.sub.3 S, belite which mainly consists of dicalcium silicate (2CaO.SiO.sub.2) designated C.sub.2 S, tricalcium aluminate (3CaO.Al.sub.2 O.sub.3) designated C.sub.3 A, and tetracalcium aluminate ferrite (4CaO.Al.sub.2 O.sub.3.Fe.sub.2 O.sub.3) designated C.sub.4 AF.
Throughout this specification, the quantity of the main clinker compounds have been calculated according to the Bogue formulas, corrected for the presence of SO.sub.3 in the clinker (F. M. Lea: "The Chemistry of Cement and Concrete." Edward Arnold (Publishers) Ltd., third edition London, p. 115-116). It is also possible to determine the content of C.sub.3 S directly by quantitative X-ray diffraction, although it is necessary to apply a correction allowing for the increased C.sub.3 S content due to the solid solution of Al, Fe, F, Mg, and other elements into the C.sub.3 S in order to obtain results that can be compared with the C.sub.3 S content calculated according to Bogue.
A number of minor components such as MgO, TiO.sub.2, Mn.sub.2 O.sub.3, K.sub.2 O and Na.sub.2 O are present in the clinker although they usually do not amount to more than a few percent of the cement. Two of the minor components are of particular interest: sodium oxide (Na.sub.2 O) and potassium oxide (K.sub.2 O) also known as the alkalies (although other alkali metals also exist in cement). They have been found to react with some aggregates by an expansive reaction, the so-called alkali-aggregate reaction. The products of this reaction may cause disintegration of the concrete, and necessitate costly repair or even demolition of structures.
It has been found that expansion due to alkali-aggregate reaction can be reduced or eliminated by the use of cement with low alkali content. In several countries the use of cement with high alkali content is therefore restricted by standards, recommendations and other regulations. For example, in Denmark the alkali content of cement should preferably be less than 0.8% sodium oxide equivalent to be used for ready mixed concrete and for concrete element production. For other applications, even lower alkali contents are preferred. Generally, it is desirable that the alkali content should be as low as possible.
Portland cement is typically manufactured by a process, according to which clinker is obtained by heating to partial fusion a mixture comprising limestone and a combination of various materials containing the necessary quantities of silica, alumina and iron oxide, such as sand, shale, clay or fly ash. The burning process is typically performed in a rotary kiln. The clinker is finely ground in a mill to obtain the finished Portland cement. Minor amounts of gypsum or other retarders are typically added to the mill in order to control the setting behaviour of the cement.
Cement production is a very energy-intensive process. Considerable energy is required to decompose CaCO.sub.3 to CaO and CO.sub.2, to heat the clinker to the required sintering temperature of typically 1450.degree.-1550.degree.C., and to grind the clinker to the required cement fineness. Furthermore, if wet raw materials are used, significant amounts of energy are spent evaporating the water.
V

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Barnes, "Structure & Performance of Cements", 1983 (no month) applied science publishers, England pp. 127-128, 145, 212.
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Zement, Kalk, Gips., vol. 43, No. 4, 1990, Wiesbaden De, pp. 199-208, XP115224, J. Strunge et al. (no month).
Chemical Abstracts, vol. 113, No. 24, Dec. 10, 1990, Abstract No. 217024x & CN, 1,042,530, May 30, 1990.
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