WO1997036839A1 - Addition of accelerators in gunite - Google Patents

Abstract

Accelerator or accelerator-component for sprayed concrete consisting of lithium silicate and/or lithium aluminate and/or aluminium in an acid or basic solution, with anions or cations which are not aggressive to the concrete, and/or aluminium oxalate. A method according to which at least two accelerators, optionally also a consistency regulator and a setting regulator are added selectively in separate lines to a spray nozzle for concrete and regulated during the spraying. An apparatus for adding an accelerator, eventually also a consistency regulator or a setting regulator, to sprayed concrete during spraying, comprising a spray nozzle for concrete with two or more lines for said additives and means for selective regulation of the flow in each line, e.g. valves.

Description

Addition of accelerators in gunite.

The present invention relates to an accelerator or an accelerator constituent for addition to gunite. Moreover, the invention relates to a method of adding an accelerator and/or consistency adjusting or solidification adjusting means to gunite, and equipment for adding an accelerator and/or consistency adjusting or solidification adjusting means to gunite during spraying, comprising a spray- mouthpiece and a conduit coupled to the mouthpiece for admission of gunite.

An accelerator is an additive which promotes curing of the concrete after spraying on a substrate. Liquid accelerator is added to the gunite immediately prior to spraying, by being admitted to a spray-mouthpiece for the gunite. Due to the use of an accelerator relatively thick layers can be sprayed, and the progress of the spraying may be faster than by spraying without any accelerator.

Prior art.

Sodium silicate and -aluminate, potassium silicate and -aluminate have been used as an accelerator. Such substances lead to alkalic reactions in the concrete, and there is a danger of alkaline-siiicium reaction on the aggregates in the concrete, which may have a detrimental effect with respect to the durability of the concrete. The reaction takes place when Na ⁺ and K⁺ are present in excessive amounts, and when the aggregates are reactive. The reaction usually appears after a long time, for instance 10 to 1 5 years, and may then have caused considerable damage in the concrete.

Also non-alkalic accelerators are used, for instance on basis of aluminium hydroxide, but these accelerators are not liquid. Although such powder accelerators can be used to prepare a liquid slurry and dosed i a liquid state, - there are large problems related to durability during storage and the application.

Summary of the invention. In accordance with the present invention it has been realized that as an accelerator or constituents in an accelerator can be used litium silicate and/or litium aluminate, and /or aluminium in acid or basic solution, with anions or cations which are not aggressive to concrete, and/or aluminium oxalate. The accelerator may comprise aluminium formiate and aluminium nitrate, in the form of pure salts or mixtures.

By use of such accelerators alone, or mixed with sodium- or potassium silicate/sodium- or potassium aluminate, no or only a limited alkalic reaction in the concrete takes place. These accelerators may, thus, be used alone or together with sodium silicate and/or sodium aluminate and/ or potassium silicate and/or potassium aluminate, whereby the addition of silicates or aluminates which cause alkalic reactions is eliminated or reduced.

In view of the high cost of litium the litium silicate or-aluminate alone should only be used in particular cases.

When the accelerator consists of or comprises oxalic acid or oxalate there will, when the accelerator is added to gunite, be formed potassium oxalate due to the potassium contents in the concrete. The potassium oxalate constitutes a nearly inert filler substituent, which is heavily soluble. When the accelerator contains or consists of aluminium oxalate, aluminium iones are brought into the concrete. The aluminium oxalate may form a part of an aqueous solution, which may also contain other aluminium salts which in small amounts do not have any detrimental effect, for instance sulfate or nitrate.

In the method according to the invention two or more accelerators are added selectively by being admitted to a spray mouthpiece for gunite in separate conduits, for adjusting of the rate of mixture between two or more -accelerators. Alternatively, or in addition, substituents may be added to the gunite prior to the reaching of the spray mouthpiece, in order that the constituents have more time to react prior to the spraying of the gunite. Moreover, for instance viscosity- or consistency adjusters, or solidification adjusters, may be added, such as polyethylene oxides and small amounts of naphtalene sulphanates, for instance thixotropying means which by being added immediately prior to the spraying alter the consistency of the gunite from liquid and well pumpable and sprayable to viscous and thixotropic.

The equipment according to the invention is adapted for addition of selective amounts of two or more accelerators, consistency adjusters or solidification adjusters during spraying of gunite. The equipment can permit addition to a spray mouthpiece and/or addition to the gunite prior to its arrival at the mouthpiece. Thereby for instance litium silicate or- aluminate, aluminium in solution or aluminium oxalate, respectively, can be added alone when it is desired to avoid any alcaline silicium reaction on the aggegates. In cases, or on places where a certain reaction is accepted, litium silicate or- aluminate, or aluminium in solution, or aluminium oxalate may be added together with accelerators based on sodium or potassium, and the mixture rate can be determined automatically or by the spray operator.

Thus, the equipment according to the invention comprises a gunite spray mouthpiece, to which is coupled a conduit for admission of gunite, and to which are coupled two or more conduits for accelerator, possibly consistency adjusters or solidification adjusters, with means for selective adjustment of the flow in each conduit, for instance valves which can be controlled automatically or operated manually by an operator. The spray mouthpiece may be extended rearwardly and be provided with one or more couplings spaced from the mouth of the mouthpiece, or one or more conduits may be provided with a coupling, which also is situated spaced from the mouth of the mouthpiece.

-Brief disclosure of the drawing.

Two examples of spray mouthpieces according to the invention are shown diagrammatically on the accompanying drawing. Fig. 1 shows spray equipment for selective addition of two accelerators. Fig. 2 shows spray equipment for selective addition of three accelerators.

Description of examples of embodiments. Each of the three examples of spray equipment according to the invention comprises a spray mouthpiece 1 , a mixing chamber 2, a supply conduit 3 for liquid concrete and a pressurized air conduit 4.

Fig. 1 shows two supply conduits 5, 7 for accelerator, with a control valve 6, 8 for each of the conduits 5, 7. Thus, accelerators can be added selectively through the conduits 5 and 7. One of the conduits 5, 7 can be shut off, for addition of only one accelerator, through the other conduit.

Fig. 2 also shows a supply conduit 9 coupled to the conduit 7, and the conduit 9 also has a control valve 10. This gives increased possibilities for selective addition. One of the conduits 5, 7, 9 can be used for addition of a consistency adjusting means or a thixotropying means.

Under all circumstances the mixture of gunite, accelerator/accelerators and possible solidification adjusting means or consistency adjusting means (flow- or thixotropying means) is driven out through the mouthpiece 1 . The operator can choose the additives and the rate of mixture therebetween by means of the valves 6, 8, 10, or the valves may be controlled automatically.

Claims

Claims.

1. Accelerator or an accelerator constituent for addition to gunite, c h a racte rized i n that it consists of litium silicates and/or litium aluminates, and /or aluminium in acid or basic solution, with anions or cations which are not aggressive to concrete, and/or aluminium oxalate.

2. Accelerator or constituent according to claim 1, c h a ra ct e rized i n comprising aluminium formiate and aluminium nitrate, in the form of pure salts or mixtures.

3. A method of adding an accelerator and/or consistency adjusting or solidification adjusting means to gunite, cha racterized in adding at least two of said constituents are added selectively by being admitted to a spray mouthpiece for gunite in separate conduits, for adjusting of the rate of mixture between two or more constituents during the spraying.

4. A method according to claim 3, c h a ra cte ri zed i n adding at least two of said constituents at a location rearwardly spaced from the mouthpiece.

5. Equipment for adding an accelerator and/or consistency adjusting or solidification adjusting means to gunite during spraying, comprising a spray- mouthpiece and a conduit coupled to the mouthpiece for admission of gunite, c h a ra cte rized i n that two or more conduits (5, 7, 9) are coupled to the mouthpiece (1) for said constituents, with means for selective adjustment of the flow in each conduit, for instance valves (6, 8, 10) which can be controlled automatically or operated manually by an operator. -

6. Equipment according to claim 5, c h a ra cte ri z ed i n comprising means for addition of at least one of said constituents in a distance from the spray mouthpiece.

7. Equipment according to claim 6, c ha ra cte ri zed i n that the spray mouthpiece has an extension rearwardly from the mouth and that at least one conduit for addition to the gunite is coupled to the extension.

8. Equipment according to claim 6 eller 7, c h a ra cte r ized i n that at least one of said conduits for said constituents is coupled to the conduit for addition of gunite in a distance rearwardly from the mouthpiece.