EP2121541A1

EP2121541A1 - A solidification and hardening accelerator for hydraulic binders and process for its preparation

Info

Publication number: EP2121541A1
Application number: EP08716832A
Authority: EP
Inventors: Heinz Schürch; Franz Wombacher; Benedikt Lindlar; Didier Lootens; Robert Flatt
Original assignee: Sika Technology AG
Current assignee: Sika Technology AG
Priority date: 2007-02-13
Filing date: 2008-02-13
Publication date: 2009-11-25
Also published as: CA2677778A1; EP1964824A1; CA2677778C; BRPI0807674A2; MX2009008651A; US8221543B2; CN101605737A; CN101605737B; AU2008214598A1; US20100018440A1; JP2010517923A; CL2008000453A1; WO2008098961A1

Abstract

The present invention relates to a fluoride-free solidification and hardening accelerator for hydraulic binders, comprising sulphate, aluminium and organic acid, the molar ratio of aluminium to sulphate being less than 0.83.

Description

RENOVATION AND CURING ACCUMULATOR FOR HYDRAULIC BINDER AND METHOD FOR THE PRODUCTION THEREOF

Technical area

The invention relates to a solidification and hardening accelerator for hydraulic binders, to a process for preparing a solidification and hardening accelerator for hydraulic binders, and to the use of the setting and hardening accelerator in a shotcrete or sprayed mortar.

State of the art

Many substances are known which accelerate the solidification and hardening of concrete. For example, strongly alkaline substances such as alkali metal hydroxides, alkali metal carbonates, alkali silicates, alkali aluminates and alkaline earth chlorides are commonly used. However, with the strongly alkaline reactants, unwanted nuisance of the processor, such as chemical burns, may occur and reduce the final strength and durability of the concrete.

EP 0 076 927 B1 discloses alkali-free solidification accelerators for hydraulic binders which are intended to avoid these disadvantages. To accelerate solidification and hardening of a hydraulic binder such as cement, lime, hydraulic lime and gypsum and mortar and concrete made therefrom, the mixture containing said binder is from 0.5 to 10% by weight based on the weight of this binder , an alkali-free solidification and hardening accelerator, this accelerator containing aluminum hydroxide. Such mortars and concretes are due to the accelerated solidification and hardening particularly well suited as sprayed mortar and concrete.

EP 0 946 451 B1 discloses solidification and hardening accelerators in dissolved form for hydraulic binders, which can be mixed more easily with the concrete when spraying the concrete. Such a solidification and hardening accelerator consists, inter alia, of aluminum hydroxide, aluminum salts and organic carboxylic acids. From WO 03/106375 A1, solidification and hardening accelerators are known which contain at least aluminum sulfate, alkanolamine and hydrofluoric acid.

WO 2005/075381 A1 describes a solidification and

A hardening accelerator comprising aluminum hydroxide, aluminum sulfate and organic acid, wherein the accelerator has a molar ratio of aluminum to organic acid of less than 0.65 and a molar ratio of

Aluminum to sulfate of greater than 0.83 has.

From WO 00 / 78688A is an additive for accelerating

Shotcrete known, wherein the additive comprises the reaction product of aluminum hydroxide and an organic acid, and aluminum sulfate and at least one alkanolamine. The additive preferably contains 16-18

Wt .-% aluminum hydroxide and contains no magnesium salt.

Such known accelerators require relatively much amorphous aluminum hydroxide for production, which is very expensive. In addition, in such

Accelerators a relatively high amount of organic carboxylic acids needed to stabilize the accelerator enough. In addition, the use of fluoride-containing compounds, such as

Hydrofluoric acid, harmful to health and the environment and is therefore undesirable. Other disadvantages of such solidification and

Hardening accelerators are also a relatively low early strength in the first few hours and days and the insufficient stability of the solution. Presentation of the invention

The invention has for its object to achieve the best possible accelerator with the highest possible stability with the longest possible stability of the accelerator at a solidification and hardening accelerator for hydraulic binders of the type mentioned.

According to the invention this is achieved by the features of the first claim.

The advantages of the invention can be seen, inter alia, in the fact that the accelerators according to the invention have high stability, i.

Stabilization of the accelerator solution is achieved and that high

Strengths can be achieved in the first few hours and days. In addition, the inventive accelerator is cheaper than conventional accelerators.

Further advantageous embodiments of the invention will become apparent from the description and the dependent claims.

Way to carry out the invention

Inventive solidification and hardening accelerators for hydraulic binders are fluoride-free and include sulfate, aluminum and and 1 to 16% by weight of organic acid, based on the total weight of the accelerator, with the molar ratio of aluminum to sulfate being less than 0.83. Such accelerators can be produced in various ways. The accelerator is preferably a water-based accelerator which may occur as a solution, with partially finely dispersed particles or as a dispersion.

The accelerator according to the invention is alkali and chloride-free. Under an alkali and chloride-free accelerator is used in construction chemistry Usually understood as an accelerator which has less than 1 wt .-% alkali, or alkali metal or chloride ions, based on the weight of the accelerator. In addition, a preferred accelerator according to the invention preferably contains no mineral acid.

Such a fluoride-free solidification and hardening accelerator according to the invention advantageously comprises:

From 17 to 35% by weight of sulphate,

From 3.2% to 9.5% by weight aluminum (or 6% to 18% Al ₂ O ₃ ), from 1% to 16% by weight organic acid,

0 to 6% by weight of magnesium,

0 to 10% by weight of alkanolamine,

0 to 5% by weight of a further divalent or higher metal sulphate, 0 to 5% by weight of flow agent,

0 to 35% by weight of silica,

0 to 8% by weight of glycehn,

- And water, wherein the molar ratio of aluminum to sulfate is less than 0.83.

The abovementioned substances are advantageously to be found as ions in solution, but may also occur in complexed form or undissolved in the accelerator. This is particularly the case when the accelerator occurs as a solution with partially finely dispersed particles or as a dispersion.

In a preferred embodiment, the accelerator according to the invention comprises from 17 to 35% by weight of sulphate, from 3.2 to 9.5% by weight of aluminum and from 1 to 10% by weight of organic acid. Even more preferred is an accelerator comprising 24 to 29% by weight, preferably 24.5 to 27% by weight, more preferably 24.95 to 27% by weight of sulfate, 4 to 6.5% by weight of aluminum and 2 to 8% by weight. % organic acid, based on the total weight of the accelerator. A particularly suitable accelerator comprises magnesium, preferably in an amount of 0.01 to 6 wt .-%, in particular 0.4 to 3.1 wt .-%, based on the total weight of the accelerator.

Furthermore, the accelerator according to the invention may additionally comprise glycehn, preferably in an amount of from 0.1 to 8% by weight, in particular from 2 to 4% by weight, based on the total weight of the accelerator.

An inventive fluoride-free solidification and hardening accelerator for hydraulic binders can be prepared, for example, from at least 40 to 60 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) ₃ ^* 14H ₂ O) and 1 to 16 wt .-% of organic acid, based on the total weight of the accelerator, wherein the molar ratio of aluminum to sulfate is less than 0.83.

The aluminum sulfate used for the preparation may contain a different amount of water of crystallization. The aluminum sulfate is typically used is aluminum sulfate tetradecahydrate (AI ₂ (SO ₄₎ 3 ^* 14H ₂ O). It is also commonly referred to as 17% aluminum sulfate because it contains 17% Al ₂ O ₃ . The amounts of aluminum sulphate mentioned in this document refer to Al ₂ (SO ₄ ) ₃ .14H ₂ O. If the aluminum sulphate contains other amounts of water of crystallization, the amounts of aluminum sulphate required for the present invention are easily calculated. Thus, 40 to 60% by weight of Al ₂ (SO ₄ ) ₃ * 14H ₂ O would correspond to an amount of a water-free Al ₂ (SO ₄ ) _{3 of} from 23 to 35% by weight.

The aluminum sulfate can also be produced by a reaction of aluminum hydroxide with sulfuric acid in the preparation of the accelerator, forming corresponding sulfate ions in the aqueous solution. Generally, aluminum sulfate can be produced by a reaction of a basic aluminum compound with sulfuric acid. In a preferred embodiment, at least 45 to 55 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) ₃ * 14H ₂ O) is used in the preparation of the inventive accelerator. Even more preferred is an amount of over 50% by weight. Particularly good results are achieved with 51 to 55 wt .-%, in particular with 51 to 53 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) 3 ^* 14H ₂ O), each based on the total weight of the accelerator achieved.

The molar ratio of aluminum to sulphate must always be less than 0.83. Preferably, the molar ratio of aluminum to sulfate is less than 0.80, more preferably less than 0.7.

The molar ratio of aluminum to the organic acid is preferably greater than 0.67. Particularly preferred is a molar ratio of aluminum to organic acid of more than 1.

As the organic acid, it is preferable to use a carboxylic acid, more preferably a monocarboxylic acid. Particularly preferred is the formic acid, but other equivalent organic acids such as e.g. Acetic acid can be used. Preferably, the acid is used in an amount of from 1 to 16% by weight, preferably from 1 to 10% by weight, more preferably from 2 to 7% by weight, based on the total weight of the accelerator.

The accelerator according to the invention can be produced particularly favorably, since in a particularly preferred embodiment it can be produced without the expensive aluminum hydroxide Al (OH) ₃ and is thus free of aluminum hydroxide. Preferably, in the production of aluminum hydroxide in one

Amount of less than 5 wt .-%, in particular 0 to 3 wt.%, Even more preferably less than 1 wt .-%, based on the total weight of the accelerator used. The aluminum hydroxide can be in amorphous or crystalline form can be used. Advantageously, amorphous aluminum hydroxide is used. The aluminum hydroxide may also be used in the form of aluminum hydroxide carbonate, aluminum hydroxysulfate or the like. Advantageously, for the production of the inventive

Accelerator no aluminum hydroxide used.

In order to obtain accelerators having an increased storage stability, magnesium hydroxide Mg (OH) ₂ , preferably in an amount of from 0.1 to 10% by weight, in particular from 1 to 5% by weight, based on the total weight of the accelerator, is additionally used for the preparation , Instead of the magnesium hydroxide, it is also possible to use the corresponding amount of another magnesium compound, in particular a magnesium salt or oxide, for example magnesium oxide MgO, magnesium oxyhydroxide or magnesium carbonate.

The accelerator according to the invention may additionally contain alkanolamine during the preparation, preferably in an amount of 0.1-10% by weight, based on the total weight of the accelerator. As the alkanolamine, diethanolamine DEA is advantageously used.

In addition, for the preparation of the accelerator according to the invention, at least one further divalent or higher metal sulfate may be used, preferably in an amount of 0.1-5% by weight, based on the total weight of the accelerator. Particularly preferred as another metal sulfate is the manganese (II) sulfate. Also suitable is iron sulfate.

Stable accelerators and good results are also obtained with an accelerator according to the invention which additionally comprises silicic acid.

The term "silicic acid" throughout the present specification is understood to mean a silica, in addition to the ortho-silicic acid all Forms of silica, so the anhydride of ortho-silica, the actual silicon dioxide, as well as colloidal, precipitated or fumed silica or silica, counted. The silica used in the accelerator according to the invention is or preferably therefore contains colloidal, precipitated, fumed silica or microsilicic acid (silica fume) or a mixture thereof. Examples of particularly suitable silicas are colloidal silica, silica, Aerosil® or Sipernat®. The silica particularly suitable for the present invention has compact or porous particles, typically with a specific surface area of 50-1000 m ² / g, in particular from 80 to 500 m ² / g and a particle size in the range of 4 to 1000 nm, in particular from 7 to 500 nm. Particular preference is given to colloidal silica particles, so-called nanoparticles. The silica particles used in the accelerator according to the invention may have a different size distribution. Thus, for example, small and large silica particles can be present together in the accelerator. The silica particles suitable for the present invention may also be waste products obtained, for example, by chemical mechanical polishing (CMP) of silica products. The surface of the silica particles can also be chemically modified.

The content of silicon dioxide, or the solids content of the silica, based on the total weight of the accelerator, is preferably 0.1 to 40% by weight, preferably 1 to 30% by weight, more preferably 3 to 20% by weight, in particular 6 to 15% by weight. Preferably, the silica is present as a silica dispersion and contains silica particles. In particular, water is used as the liquid medium. Silica sol is particularly preferred as the silica dispersion. The silica sol preferably contains colloidal silica, in particular amorphous colloidal silica, having a particle size in the range from 4 to 1000 nm, in particular from 7 to 500 nm. Typically, the silica sol has a specific surface area of 50-700 m ² / g, in particular from 80 to 500 m ² / g. Also particularly suitable as a silica dispersion is a dispersion with silica. The accelerator of the invention preferably comprises a silica sol having a silica content, based on the total weight of the silica sol, of from 1 to 60% by weight, in particular from 5 to 50% by weight, more preferably from 10 to 40% by weight. The proportion of the silica dispersion, in particular of silica sol, in the accelerator is preferably from 0.1 to 60% by weight, in particular from 5 to 55% by weight, based on the total weight of the accelerator. Particular preference is given to accelerators which have a proportion of silica sol or of a silica foam dispersion of more than 20% by weight, in particular in a proportion of from 23 to 55% by weight, more preferably in a proportion of from 25 to 40 wt .-%.

The accelerator according to the invention may additionally comprise flow agents, in particular polycarboxylates, or stabilizers.

Of course, the accelerator according to the invention may comprise further suitable additives known to the person skilled in the art. Preferably, however, it contains no further thickening agents or thixotropic agents.

A preferred according to the invention fluoride-free solidification and

Hardening accelerator can be prepared from (in% by weight, in each case based on the total weight of the accelerator):

- 40 - 60 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) 3 ^* 14H ₂ O), - 1 - 16 wt .-% organic acid, - 0 to less than 5 wt .-% aluminum hydroxide (Al (OH) ₃ ),

0.1 to 10% by weight of magnesium hydroxide,

0-10% by weight of alkanolamine,

0 to 5% by weight of a further divalent or higher metal sulphate,

- 0 - 35 wt .-% silica, - 0 - 8 wt .-% glycerol,

- 0 - 5 wt .-% of flow agent,

- remaining amount of water, wherein a molar ratio of aluminum to sulfate is less than 0.83. To produce particularly advantageous solidification and hardening accelerators are used essentially (in wt .-%):

- 45 - 55 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) 3 ^* 14H ₂ O), preferably 51 - 55 wt .-%,

From 1 to 10% by weight of organic acid, in particular from 2 to 7% by weight,

- 0 - 3 wt .-% aluminum hydroxide (Al (OH) ₃ ), in particular 0 - 2 wt .-%,

1 to 5% by weight of magnesium hydroxide, 1 to 3% by weight of alkanolamine,

1 to 3% by weight of a further divalent or higher metal sulphate, in particular manganese sulphate,

0 to 20% by weight of silica, 2 to 4% by weight of glycerol, 0 to 3% by weight of liquid medium,

- remaining amount of water, wherein a molar ratio of aluminum to sulfate less than 0.8, preferably less than 0.7.

If the silica is present, for example, as a silica dispersion, in particular as silica sol, the water can be completely introduced into the silica dispersion and no additional water must be used in the preparation of the accelerator.

Compared to conventional solidification accelerators, the amount of aluminum sulfate used in the production is increased and the

Reduced amount of acid used and in particular the aluminum hydroxide. It is even possible to get an accelerator free of

To produce aluminum hydroxide, resulting in a particularly favorable

Accelerator leads. Particularly good results are also obtained with an accelerator which contains a small amount of aluminum hydroxide, in particular less than 1% by weight. Preferably, up to 10% of magnesium hydroxide and / or a corresponding amount of magnesium oxide are used in the preparation of the accelerator. The pure Mg Amount based on the total amount of accelerator is 0 to 6 wt .-%, preferably 0.4 to 4.2 wt .-%, more preferably 0.8 to 2.9 wt .-%, in particular 1, 3 to 2 , 1% by weight.

The ratio of aluminum to sulfate is increased by the

Sulfate content and lower aluminum content to a value less than 0.83, preferably less than 0.8, in particular set less than 0.7.

The reduced by up to 25% of the amount of aluminum used in the production, the sulfate resistance is promoted. This is a

Advantage over conventional accelerators, where the

Sulfate resistance is drastically worsened by the accelerator. The

Reduction of sulfate resistance by aluminum entry is particularly caused by the fact that the aluminate phases have a particular affinity for sulfate. The extra aluminum increases the

Proportion of aluminate phases in the concrete, which then at external

Sulfateinwirkung on the cured concrete a not insignificant

Cause crystallization pressure by Ettringitbildung and thus cause damage. The aluminum content given as Al ₂ O ₃ is therefore preferably chosen to be less than 14%, more preferably less than 13% and in particular less than 12% Al ₂ O ₃ .

If magnesium hydroxide and / or oxide is used in the preparation of the accelerator, the temperature of the mixture increases so much due to the strong reaction of the magnesium hydroxide and / or oxide with the organic acid that the water does not have to be heated for these mixtures. The other components are then added to this heated mixture. The components can also be added in any other order. This simplifies the process and requires less energy. An additional advantage of the use of magnesium is the significantly higher storage stability of the accelerators caused by the magnesium ions. Even at a content of 1 wt .-% of magnesium hydroxide in the production is a good Shelf life achieved. At higher levels, storage stability is at least three months. In addition, the stability of the accelerators is positively influenced by the reduced amount of aluminum. Due to the reduced amount of aluminum or the reduced ratio of aluminum to sulfate and the sulfate resistance is increased.

The development of the pressure resistance of the sprayed concrete in the first few hours and days is also influenced very positively and is better than with conventionally used accelerators.

The accelerators according to the invention can be present, for example, as a solution, dispersion or in powder form, it being preferred that an accelerator present as a powder is dissolved or dispersed in water before use.

Furthermore, the present invention relates to a method for accelerating the solidification and hardening of hydraulic binders and mortar or concrete produced therefrom, characterized in that the mixture containing hydraulic binder, a fluoride-free solidification and hardening accelerator according to the invention in an amount of 0.1 to 15 wt .-%, in particular from 1 to 10 wt .-%, based on the weight of the hydraulic binder, is added.

The inventive accelerator can accelerate the setting and hardening of hydraulic binders, hydraulic

Binders in admixture with latent hydraulic binders or inert

Fillers, mortar or concrete can be used. A preferred

Use in the sprayed mortar or shotcrete after the dry or

Wet spraying method, wherein the accelerator to the dry or water-applied binder, mortar or concrete in the delivery line, the

Pre-wetting nozzle or spray nozzle, directly into the mixture or ins

Mixing water added resp. is added. Preferably, a

Accelerator in the form of a solution or dispersion with a Metered liquid metering device, a powdered accelerator with a powder metering device.

Examples of binders, their hardening and setting by the accelerator according to the invention, respectively. the process can be accelerated are cement such as blended cements, lime, hydraulic lime and gypsum, each alone or in admixture with latent hydraulic binders or inert fillers, and examples of blends containing these binders are mortar and concrete, especially sprayed mortar and shotcrete ,

Another object of the present invention is also a curable resp. hardened binder-containing mixture containing the accelerator according to the invention, in particular sprayed mortar and shotcrete containing the inventive accelerator.

By using the solidification and hardening accelerators according to the invention, an extremely rapid setting of the corresponding binders or of the mixtures containing such binders is effected, and high initial and final strengths are achieved. The setting and hardening accelerators are not corrosive or toxic to the processor or the environment.

embodiments

Several samples of accelerators according to the invention were prepared according to the values given in Table 1 using aluminum sulphate with 17% Al 2 O 3, 85% formic acid, silica sol with 30% by weight silica particles based on the weight of the silica sol and aluminum hydroxide amorphous aluminum hydroxide, and with a comparative example without acid (B1), a comparative example with more than 16% by weight of acid (B3) and a conventional accelerator (B2). As a conventional accelerator (B2), Gecedral® F2000W (available from BK Giulini GmbH) was used.

Table 1: Sample composition in% by weight

To prepare the accelerators with magnesium hydroxide, water was placed unheated. The magnesium hydroxide was slurried therein and formic acid was added, whereby the temperature increased. Thereafter, the aluminum sulfate, if present, the aluminum hydroxide, and the manganese sulfate or iron sulfate, was added and dissolved at elevated temperature. Finally, if present, glycehn and diethanolamine DEA were added. The whole was then stirred until the reaction had subsided and the temperature had dropped to about 40 ⁰ C after about one hour. The result is a solution which may also have finely dispersed particles depending on the composition.

For the preparation of the accelerator without magnesium hydroxide was

Water preheated presented. The formic acid was added to the water and then optionally the aluminum hydroxide added. Thereafter, the aluminum sulfate, the manganese sulfate or the iron sulfate, the glycerol and the diethanolamine were added. The whole was then stirred until the reaction subsided.

Table 2 shows the molar ratios of aluminum to sulfate and of aluminum to the organic acid, here formic acid, of the samples measured. The values of the molar ratios of aluminum to organic acid are above 0.67, the values of the molar ratios of aluminum to sulfate below 0.83. Further, the aluminum content of the various examples is given.

Table 2: Molar ratios

From 0.1 to 15% by weight, in particular from 1 to 10% by weight, of the accelerator according to the invention can be added to hydraulic binders.

To determine the effectiveness of the inventive accelerator according to Examples A1 to A30 and Comparative Examples B1, B2 and B3 of a mortar mixture (particle size 0-2.2 mm, w / z = 0.48 and 1, 0% Sika® ViscoCrete® SC305 (available at Sika Schweiz AG)) in each case 6% of the accelerator based on the content of the hydraulic binder mixed. Portland cement was used as the hydraulic binder. The test was performed using a needle penetrometer (Mecmesin BFG500) and prisms (40 x 40 x 160 mm). The compressive strength of the prisms was determined by means of a hydraulic press (Table 3).

Table 3: Strengths in MPa and storage stability in days; in Examples A1 to A8 and B1 and B2, the storage stability was not measured. In Comparative Example B3, the strength could not be measured because the accelerator precipitated in the production.

Surprisingly, it has been found that due to the high proportions of aluminum sulfate and magnesium, despite the reduced or absent aluminum hydroxide content and the reduced acid content, the strengths after a few hours to several days are better than conventionally known accelerators, see Table 3. Particularly good Results were obtained with accelerators that are free of aluminum hydroxide. The more aluminum hydroxide contained in the accelerator, the more the strengths decrease after 1 or 7 days. moreover also decreases storage stability (see examples A24 and A25 as well as A29 and A30).

Especially suitable are accelerators with magnesium hydroxide.

This accelerator could be obtained with a particularly good storage stability, while accelerators without magnesium hydroxide, although good

Strength values have but already failed after a few days (see

Example A19).

It has also been found that a suitable accelerator contains less than 16% by weight, in particular less than 10% by weight, of formic acid, based on the total weight of the accelerator. Comparative Example B3, which contains 17 wt .-% of formic acid (or 20 wt .-% of an 85% formic acid) more than 16 wt .-% formic acid, precipitated in the preparation and could not be used as an accelerator. Comparative Example B1 without acid shows in particular less good early strength after 6 hours or 1 day compared with the accelerators according to the invention. Although Example A18 with 11.9 wt .-% formic acid (or 14 wt .-% of an 85% formic acid) shows good strength values, but was stable only about 1 week. Particularly good results were achieved with an accelerator which contained between 1 and 7% by weight of formic acid, more preferably from 2 to 6% by weight of formic acid. Thus, examples A16 and A17 with 1.7% by weight (or 2% by weight of an 85% formic acid) or 6.8% by weight of formic acid (or 8% by weight of an 85% formic acid) show good strength values , Particularly suitable is an accelerator which contains 4.25% by weight of formic acid (or 5% by weight of an 85% formic acid) (see Example A9). In addition to good strength values, it also shows excellent storage stability of over 3 months.

The additional use of silica sol in the accelerator causes the accelerator to have both good strength values (Example A27) and, in addition, a better storage stability (see in particular Example A28 compared to A17)

Of course, the invention is not limited to the embodiments shown and described.

Claims

claims

A fluoride-free solidification and hardening accelerator for hydraulic binders comprising sulfate, aluminum and 1 to 16% by weight of organic acid, based on the total weight of the accelerator, wherein the molar ratio of aluminum to sulfate is less than 0.83.

2. Accelerator according to claim 1, characterized in that it contains 17 to 35 wt .-% sulfate, 3.2 to 9.5 wt .-% aluminum and 1 to 10 wt.

% organic acid based on the total weight of the accelerator.

3. Accelerator according to one of the preceding claims, characterized in that the molar ratio of aluminum to the organic

Acid is greater than 0.67.

4. Accelerator according to one of the preceding claims, characterized in that the accelerator is free of aluminum hydroxide.

5. Fluoride-free solidification and hardening accelerator for hydraulic binders according to one of the preceding claims, preparable from at least 40 to 60 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) ₃ ^* 14H ₂ O) and 1 to 16 wt .-% of organic acid , based on the total weight of the accelerator, wherein the molar ratio of aluminum to sulfate is less than 0.83.

6. Accelerator according to claim 5, characterized in that in the preparation at least 45 to 55 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) ₃ ^* 14H ₂ O) and 1 to 10 wt .-% organic acid is used, respectively based on the total weight of the accelerator.

7. Accelerator according to one of claims 5 or 6, characterized in that in the preparation at least 51 to 55 wt .-% aluminum sulfate (Al ₂ (SO ₄ ) ₃ * 14H ₂ O) are present, based on the total weight of the accelerator.

8. Accelerator according to one of the preceding claims, characterized in that in the preparation additionally 0.1 to 10 wt .-%, in particular 1 to 5 wt .-%, magnesium hydroxide or the corresponding amount of another magnesium salt, based on the total weight of the accelerator is present ,

9. Accelerator according to one of the preceding claims, characterized in that the molar ratio of aluminum to sulfate is less than 0.80, in particular less than 0.7.

10. Accelerator according to one of the preceding claims, characterized in that in the preparation of 0.1 - 5 wt .-% of at least one further divalent or higher metal sulfate, in particular a manganese (II) sulfate and / or iron sulfate, is present.

11. Accelerator according to one of the preceding claims, characterized in that the organic acid is formic acid.

12. Accelerator according to one of the preceding claims, characterized in that the accelerator comprises silica, in particular colloidal, precipitated or fumed silica or silica or a mixture thereof.

13. A method for accelerating the solidification and hardening of hydraulic binders and mortar made therefrom or

Concrete, characterized in that a mixture containing hydraulic binder, a fluoride-free solidification and hardening accelerator according to Claims 1 to 12 in an amount of 0.1 to 15 wt .-% based on the weight of the hydraulic binder is added.

14. Use of the fluoride-free solidification and hardening accelerator according to claim 1 to 12 as an accelerator in a shotcrete or sprayed mortar.

15. Binder-containing mixture, characterized in that it contains the accelerator according to one of claims 1 to 12.