Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1988-03-10
1991-03-12
Dixon, Jr., William R.
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106724, 106725, 106726, C04B 702, C04B 1404
Patent
active
049990560
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and a composite material mix for preparing a shaped article with a binder matrix based on cement a concrete superplasticizer, and water, in particular based on cement, a silica-rich powder, a concrete superplasticizer, and water.
In the present context, the term "shaped article" designates any kind of structure formed by solidification of such a cement-containing mix.
When preparing shaped articles comprising binder matrices based on cement and water, it is of great importance for the quality of the final shaped article that the mix has suitable flow properties so that it will fill the cavity in which it is to be cast. It is also important that the mix has a high degree of homogeneity, so that, for example, there are no large agglomerates of, e.g., silica particles which would affect the quality, e.g., the durability of the final cast article. Thus, the ideal is to obtain a good flow and a high degree of homogeneity, as low content of water as possible, as it is known that the quality of the final shaped article such as the compressive strength, the durability, etc. is the higher, the lower the water content is. With badly dispersed systems, a higher water content in the mix is necessary in order to obtain the required fluidity. By adding more water, the necessary fluidity may be obtained, but in a system which is not well dispersed, this does not ensure the desired homogeneity of the fine powders. The problems in connection with the achievement of homogeneity are greater when dealing with a binder matrix system comprising two fine powder components such as cement and a fine silica-rich powder, the reason for this being that an intermixing of the two different powders is required as a basic necessity for obtaining homogeneity.
The smaller the fine silica-rich particles are, the more difficult is it to obtain the desired homogeneity, because locking surface forces will tend to counteract the homogeneous distribution and locking surface forces increase with decreasing size of the particles. Thus, when going from medium fine particles such as cement (typical specific surface 400 m.sup.2 /kg) to ultra-fine silica fume with a surface of typically 25,000 m.sup.2 /kg, there is a dramatic increase in the surface forces to be overcome. These problems are especially pronounced in systems with a low water content and are also very pronounced in systems with a high content of ultra-fine silica.
It is known in the art to reduce the water content or improve the fluidity of cement mixes by adding a surface-active dispersing agent, such as a concrete superplasticizer. However, even the use of concrete superplasticizers will not always eliminate the problems associated with obtaining a good flow and homogeneity at a low water content.
According to the present invention, it has been found that the fluidity and homogeneity of mixes based on cement, a concrete superplasticizer, and water, in particular based on cement, a fine silica-rich powder, a concrete superplasticizer, and water, are strongly improved by reducing the water-soluble alkali content of the cement (and of the fine silica when present).
Thus, in one aspect, the invention relates to a method for preparing a shaped article with a binder matrix based on cement by preparing a mix comprising the cement, water, and a concrete superplasticizer, the weight ratio between the water and the cement being at the most 0.30. preferably at the most 0.25, arranging the mix in the desired configuration and allowing the mix to solidify, characterized in that the weight amount of water-soluble alkali in the mix originating from the mineral solids in the mix is reduced to at the most 0.30%, preferably at the most 0.25%, more preferably at the most 0.20%, calculated as Na.sub.2 O equivalents, relative to the weight of the cement in the mix.
In the very important aspect where a fine silica-rich powder is incorporated, the invention relates to a method for preparing a shaped article with a binder matrix based on cement and fine silica-rich po
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Densit A/S Rordalsuej
Dixon Jr. William R.
Green Anthony J.
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