Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1997-04-29
1999-10-19
Marcantoni, Paul
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106808, 106819, 106823, 524 2, 524 5, C04B 2412
Patent
active
059682566
DESCRIPTION:
BRIEF SUMMARY
This invention relates to cementitious spraying compositions and to admixtures for use therein.
Cementitious compositions for application to a substrate by spraying, for example, "shotcrete", must be capable of being sprayed in the first place (that is, they must retain sufficient fluidity), and on contacting the surface, they must set quickly (generally within a few minutes) to give a stiff layer to which further layers may quickly be applied. The art-recognised way of achieving this has been the addition at the point of spraying (for example, by injecting into a spray nozzle) of an accelerator in the form of an aqueous solution. The accelerators used are generally strong alkalis such as sodium aluminate, sodium or potassium hydroxide or carbonate and triethanolamine (see, for example, "Concrete Admixtures Handbook", ed. Ramachandran (Noyes, 1984)).
The nature of such substances makes for unpleasant working conditions on spraying sites, and there has long been a need for an effective spraying accelerator which has less of the caustic character of the known accelerators. In a recent development, accelerators comprising amorphous aluminium hydroxide have been proposed. These have the advantage of low alkalinity and high performance. Typical examples of accelerators have been blends of amorphous aluminium hydroxide with gypsum or various water-soluble salts.
Accelerators applied at the nozzle are in liquid form. This means that, in the case of aluminium hydroxide, the solid accelerator must be dispersed in water. This can be done on site, but it is much more convenient if such an accelerator can be supplied in liquid form. This has hitherto not been possible with aluminium hydroxide, dispersions of which are not storage-stable for more than a few days.
It has now been found that a particular combination of aluminium hydroxide with another material not only has excellent storage stability but also is particularly effective as an accelerator for spraying cementitious compositions. There is therefore provided, according to the present invention, an accelerating admixture for use in the spraying of cementitious compositions, comprising (a) amorphous aluminium hydroxide and/or aluminium hydroxysulphate, and (b) at least one amine.
There is additionally provided a method of preparing a storage-stable, amorphous aluminium hydroxide and/or aluminium hydroxysulphate-based accelerating admixture by the dispersion of amorphous aluminium hydroxide and/or aluminium hydroxysulphate in water, there being additionally added at least one amine.
In the particular circumstances of this invention, aluminium hydroxysulphate is often a better accelerator than aluminium hydroxide and is therefore preferred. It is possible to use a mixture of aluminium hydroxysulphate with aluminium hydroxide and/or aluminium sulphate, but it is preferable to use the hydroxysulphate alone. A typical commercially-available aluminium hydroxysulphate is "Gecedral" (trade mark) L (ex Guilini Chemie GmbH, Ludwigshafen/Rhein, Germany).
The amines for use in this invention should be liquid or soluble in water. A highly preferred class of amines is that of the alkanolamines. The preferred alkanolamines are dialkanolamines and trialkanolamines, more preferably diethanolamine and triethanolamine. Most preferred is a mixture of diethanolamine and triethanolamine.
In an admixture according to the invention, the aluminium hydroxide and/or hydroxysulphate is combined with the alkanolamine in the weight ratio of from 1:10-1000:1, preferably from 1:0-100:1, more preferably from 1:1-0:1. When the preferred mixture of diethanolamine and triethanolamine is used, the ratio of diethanolamine to triethanolamine is from 1:1 to 0:1.
The constituents of the admixture may be added to a spray nozzle separately or preferably as a pre-mixed blend. The invention therefore also provides an accelerating admixture which is a mixture of the aforementioned constituents. In either case the weight ratio of the constituent on cement is from 0.5-10% for the aluminium hydroxide/hydroxysu
REFERENCES:
patent: 5560774 (1996-10-01), Burge et al.
Marcantoni Paul
MBT Holding AG
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