Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1990-07-18
1992-03-17
Dixon, Jr., William R.
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106695, C04B 722, C04B 732
Patent
active
050964976
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a cement composition and in particular to such a composition for use in the production of concrete like materials for filling cavities in underground mines and like purposes. Compositions of the invention comprise two slurries to be mixed together. The invention is based on the realisation that by selecting specific phases for the cement component of one slurry certain advantages result in terms of cost and efficiency.
According to one aspect of the invention there is provided a composition to form a hardened cement, the composition comprising two slurries to be mixed together, the first slurry comprising water and a cement component comprising ferrite and C.sub.12 A.sub.7 or C.sub.11 A.sub.7 CX.sub.2 (where X is a halogen atom) and a reactive source of silica, and the second slurry comprising water, beta anhydrite, calcium oxide and/or calcium hydroxide.
The cement phase of the first slurry comprises a mixture of ferrite, ("C.sub.4 AF") and C.sub.12 A.sub.7 (these formulae are in cement industry nomenclature). As will be well known to those skilled in the art, the term ferrite embraces other phases based on .sub.C2 (,A F), as well as C.sub.4 AF. The presence of ferrite is beneficial because it is less reactive than the C.sub.12 A.sub.7 phase which gives the advantage of requiring less of a retarding agent to inhibit fast setting of the admixed slurries. Other cement phases typical of high alumina cements can be present and examples include CA, C.sub.2 AS, C.sub.2 S, Klein's compound and phases containing Fe0 or Fe0 itself. The ferrite and C.sub.12 A.sub.7 preferably make up about 50%, most preferably 65% to 85% by weight of the cement component. The C.sub.12 A.sub.7 may be replaced by C.sub.11 A.sub.7 CX.sub.2 where X is a halogen atom. The cement component will be made from a mineral clinker in known manner.
The reactive source of silica is preferably a ground granulated blast furnace slag. The blast furnace slag may be of any known type and derived from any source. The particle size may vary widely but should be related to that of the particles of the cement component. Preferably the slag has a specific surface area of about 3000 to about 6000 cm.sup.2 /g. The reactive source of silica may be provided by other ingredients in whole or in part such as pozzolans, pulverised fly ash, silica fume or other glassy mixtures of lime and silica.
The reactive source of silica is preferably present in a weight ratio of 0.1 to 0.6 silica source per 1 part cement component. Sufficient should be present to ensure that strength regression does not occur after admixture of the two slurries. If more of the reactive source of silica is present, the strength of admixture will be too low to provide early pack support for an underground road.
It is preferred to add a retarding/suspending system to the first slurry. Suitable retarders include polysaccharides, glucose, fructose, lactose, sucrose and the like. Suitable suspending agents include cellulose ethers, polymers such as polyacrylamides and polyethylene oxides and polyacrylates; gums such as guar gum, xanthan gum or gum acacia; starch, hectorite, bentonite, attapulgite and the like. It is essential that the second slurry contains calcium sulphate in the form of beta anhydrite because other forms of calcium sulphate when used alone do not give satisfactory results. Hydrated forms such as Plaster of Paris or gypsum both give strengths which are too low during the initial stages of the setting process and gamma-anhydrite hydrates very rapidly in water and gives similar results to the hydrated forms.
The beta anhydrite is preferably present in the second slurry so that when the slurries are mixed it will be present relative to the cement component in a ratio of from 3:7 to 4:1 by weight.
It is essential to include calcium oxide and/or calcium hydroxide to ensure that the maximum quantity of ettringite possible is formed.
In order to obtain sufficiently rapid and sufficiently high early strength development (a minimum of the order of 0.35 MNm.sup.-2
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Beale James
Mills Peter S.
Dixon Jr. William R.
Fosroc International Limited
Wright Alan
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