Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1998-07-29
2000-03-14
Green, Anthony
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106708, 106709, 106724, 106725, 106731, 106790, 106819, 106DIG1, C04B 713, C04B 2802
Patent
active
060367687
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a cement composition comprising partial reduction from combustion residues having an SiO.sub.2 /CaO ratio of >1, such as e.g. waste incineration slags, and containing alkali oxides (Na.sub.2 O and K.sub.2 O) in amounts exceeding 1.5% by weight, synthetic pozzolan, such as e.g. anionically active or anionic tensides, in particular, sulfonates.
2. Prior Art
Cement compositions containing cement and, in particular, portland cement and additionally more or less large portions of extenders or fillers are known. Also has already been proposed to employ cement along with natural pozzolans or synthetic pozzolans as well as carbonates as extenders, the majority of such extenders or fillers being limited merely in view of the desired strength values. With some such mixtures, demixing by sedimentation may occur, this applying, in particular, to fly ash, sand or blast furnace slag. The risk of demixing by sedimentation is faced, in particular, with low surface charges, wherein pozzolans, fly ash, microsilica and blast furnace slag, as a rule, have low to clearly negative surface charges. Pozzolans having clearly negative surface charges stand out for their good miscibility with cement, in particular, in the alkaline range. The same holds for micro-silica powders exhibiting extremely negative surface charges. Investigations have demonstrated that the respectively measured negative surface charge quite definitely is a function of the pH, wherein low surface charges remaining nearly constant over the total pH range were measured for fly ash and blast furnace slag.
Mixtures to be used for the production of coarse- and/or fine-grain-flux-containing concrete comprising 70 to 35% by weight of cement and 30 to 65% by weight of latent hydraulic substances as well as 0.05 to 1% by weight of a dispersant such as, for instance, lignin sulfonate have become known from DE-A1 31 05 054. In DE-A1 31 05 054, decreasing strength values were measured with increasing amounts of synthetic pozzolans.
Synthetic pozzolans and, in particular, those obtained by an at least partial reduction from combustion residues having an SiO.sub.2 /CaO ratio of >1, such as e.g. waste incineration slags, and containing alkali oxides in amounts exceeding 1.5% by weight are characterized by positive surface charges. Consequently, the admixture of such synthetic pozzolans usually has not resulted in enhanced strength properties, in particular, in terms of early strength. Due to the formation of agglomerates, mixed cement exhibits poor working properties. As expected, such cement mixtures have, therefore, strongly fallen short of the early strength values measured for portland cement or cement compositions containing other extenders or fillers.
SUMMARY OF THE INVENTION
Surprisingly, it has now been found that cement composition comprising partial reduction from combustion residues having an SiO.sub.2 /CaO ratio of >1, such as e.g. waste incineration slags, and containing alkali oxides (Na.sub.2 O and K.sub.2 O) in amounts exceeding 1.5% by weight, and
The strength values of the portland cement and pozzolan may be raised to values not only equal, but even superior to those of the best known standard cement if an activator is additionally added to reduce the positive surface potential of the synthetic pozzolan, such as e.g. anionically active or anionic tensides. The high alkali oxide content as observed, in particular, in acidic slags causes surface charging by sodium and potassium ions, pozzolanic hydration requiring from the material to have a relatively high density or small particle interspace. Without any activator, the positive surface charge causes the repulsion of the particles and hence a low particle density, thereby preventing or impeding hydration and, thus, any contribution to increasing strength. Such surface charges now may be compensated for by the activators mentioned, causing the pozzolanic particles to no longer repel mutually and rendering feasible a h
REFERENCES:
patent: 5453123 (1995-09-01), Burge et al.
Chemical Abstract No. 107:182259, abstract of European Patent Specification No. 220073, Apr. 1987.
Database WPI Week 9528 Derwent Publications Ltd., London, GB; AN 95-211839 abstract of Japanese Patent Specification No. 07-124535 (May 1995).
Chemical Abstract, vol. 90, No. 26, Jun. 25, 1979 columbus, Ohio, US; Abstract No. 209008m, abstract of USSR Patent No. 654567 (Mar. 1979).
Chemical Abstract, vol. 112, No. 16, Apr. 16, 1990, Columbus, Ohio,US; Abstract No. 144693g, abstract of Polish Patent Specification No. 143,446 (Dec. 1983).
Edlinger Alfred
Gebauer Juraj
Wolter Horst
"Holderbank" Financiere Glarus AG
Green Anthony
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