Accelerator for mineral binder compositions

Abstract

The invention relates to an accelerator for mineral binder compositions, comprising a) an aqueous suspension of calcium hydroxide, and b) at least one material I selected from the group consisting of alkanolamines, sodium thiocyanate, sodium nitrate, sodium nitrite, calcium nitrate, calcium silicate hydrate, sodium silicate, aluminum sulfate, sodium sulfate, sodium aluminate, alkali metal carbonates, in particular lithium carbonate, alkali metal bicarbonate, especially sodium bicarbonate, an organic acid or a mixture thereof. The invention also relates to a method for accelerating a mineral binder composition with such an accelerator.

Description

Technical Field

[0001] The present invention relates to an accelerator for a mineral binder composition. The present invention also relates to a method for accelerating a mineral binder composition. Background Art

[0002] Cement is a mineral binder and is mainly used in concrete and mortar. When cement is mixed with water, it solidifies and hardens in a chemical process known as cement hydration. The cement hydrate thus formed acts as a binder for aggregates (usually sand, gravel and stone) in concrete and mortar to form a solid material. Mortar or concrete has many applications, in which rapid solidification and hardening and therefore rapid development of strength are very important.

[0003] There are various methods for accelerating the setting and / or hardening of cement. A very common solution is to add accelerators, such as calcium chloride, calcium nitrite or sodium nitrite, and / or amines, such as alkanolamines. Some accelerators are known to affect the setting of mineral binders in particular, while others are known to affect the hardening and lead to an increase in the early strength and / or later strength of the mineral binder composition.

[0004] Many accelerators for mineral binder compositions are known in the prior art. For example, EP 3 536 677 (Yara International) discloses the use of nitrates as setting and hardening accelerators, while US 4 337 094 (Euclid Chem) discloses the use of nitrates and alkanolamines in combination. For example, DE 2 611 419 (Degussa) discloses the use of calcium formate and thiocyanate as accelerators for Portland cement. US 4 373 956 (Martin Marietta) discloses a combination of thiocyanate and alkanolamine. WO 2010 / 026155 (Construction Research & Technology) discloses hydrated calcium silicate as an accelerator for mineral binder compositions.

[0005] A particularly useful accelerator for mineral binder compositions is calcium hydroxide. Aqueous suspensions of calcium hydroxide and their use as accelerators for mineral binder compositions are known from WO 2019 / 180191 (Sika Technology).

[0006] Known accelerators for mineral binder compositions do not always improve both early and late strengths. Furthermore, it would be desirable to have accelerator compositions that improve both early and late strengths of mineral binders consisting essentially of Portland cement as well as mineral binders based on blended cements, such as limestone cement, slag cement, or mixtures of Portland cement with other supplementary cementitious materials.

[0007] Therefore, there is a continuing need for improved accelerator compositions and methods of accelerating mineral binder compositions, especially cement-based mineral binder compositions. Summary of the invention SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide an accelerator for a mineral binder composition. The accelerator of the present invention should in particular improve the early strength of the mineral binder composition when compared to the same mineral binder composition without the accelerator. Early strength refers to the strength, in particular the compressive strength, measured within 1 to 24 hours after water is added to the mineral binder composition. In particular, the accelerator of the present invention should improve the early strength of the blended cement.

[0010] The object of the present invention is also to provide a method for promoting a mineral binder composition, in particular a mineral binder composition based on admixture of cement.

[0011] Surprisingly, these objects are achieved by the accelerators and the method as claimed in the independent claims.

[0012] Preferred embodiments of the invention are subject matter of the dependent claims.

[0013] Embodiments of the present invention

[0014] In a first aspect, the present invention relates to an accelerator for a mineral binder composition, the accelerator comprising:

[0015] a) an aqueous suspension of calcium hydroxide, and

[0016] b) at least one material I selected from alkanolamines, sodium thiocyanate, sodium nitrate, sodium nitrite, calcium nitrate, calcium silicate hydrate, sodium silicate, aluminum sulfate, sodium sulfate, sodium aluminate, alkali metal carbonates, especially lithium carbonate, alkali metal bicarbonates, especially sodium bicarbonate, organic acids or mixtures thereof.

[0017] Acceleration of a mineral binder composition can be measured as an increase in the strength, in particular the compressive strength, of the mineral binder composition measured at a given point in time after the start of hardening and compared with an identical mineral binder composition but without the addition of the accelerator.

[0018] Promotion can also be measured as a reduction in clotting time.

[0019] The mineral binder composition may be a mineral binder, such as cement or a binder comprising cement. The mineral binder composition may also be a formulated product, such as dry mortar or wet mortar or concrete.

[0020] Therefore, the mineral binder composition is characterized in that it comprises at least one mineral binder. The mineral binder herein is especially cement. The mineral binder composition may contain other materials commonly used in the concrete or mortar industry. The mineral binder composition may especially contain fillers, aggregates and admixtures.

[0021] An "aqueous suspension" herein is a suspension of particles in a continuous liquid phase comprising water or consisting essentially of water. In particular, the continuous liquid phase does not contain other solvents, such as alcohols, glycols or ketones, besides water. The liquid phase may contain a surfactant.

[0022] Very preferably, the calcium hydroxide is present in the aqueous suspension in the form of suspended nanoparticles. "Nanoparticles" are particles with a particle size in the nanometer range. These ultrafine particles are known for a very high specific surface area and therefore specific properties. "Nanoparticles" herein refer to particles with a particle size below 1 μm. The particle size of the nanoparticles in the suspension can be measured by dynamic light scattering using photon cross-correlation spectroscopy according to standard ISO 22412:2017.

[0023] In this context, the average particle size corresponds in particular to the D50 value (50% of the particles are smaller than the specified value, and 50% are correspondingly larger). Thus, the value "D10" indicates the particle size at which 10% of the particles are smaller than this value. The value "D90" indicates the particle size at which 90% of the particles are smaller than this value.

[0024] According to an embodiment, the accelerator of the invention is characterized in that the aqueous suspension comprises calcium hydroxide in the form of nanoparticles, in particular calcium hydroxide having a particle size D90 measured by dynamic light scattering using photon cross-correlation spectroscopy according to standard ISO 22412:2017 lower than 800 nm, preferably lower than 600 nm, more preferably lower than 400 nm and in particular lower than 200 nm.

[0025] For the present invention, the particle size of the calcium hydroxide particles was determined using a Nanophox instrument from Sympatec, Germany. In this case, the particle size was determined by dynamic light scattering using photon cross-correlation spectroscopy.

[0026] The suspension comprising calcium hydroxide particles having a particle size as defined above is particularly storage-stable and very effective for promoting mineral binder compositions, especially cementitious compositions.

[0027] According to an embodiment, at least 50% by weight, preferably at least 66% by weight, more preferably at least 90% by weight, and in particular substantially all of the calcium hydroxide present in the aqueous suspension is in the form of suspended nanoparticles.

[0028] According to a preferred embodiment, the aqueous suspension further comprises at least one organic compound for stabilizing the suspension. The at least one organic polymer comprises carboxylate groups, sulfate groups, sulfonate groups, phosphate groups and / or phosphonate groups. The organic polymer preferably also serves as a plasticizer for a mineral binder composition, especially a cementitious composition. The example of a suitable organic polymer includes lignin sulfonate, sulfonated naphthalene-formaldehyde condensate, sulfonated melamine-formaldehyde condensate, sulfonated vinyl copolymer, poly(methyl)acrylic acid, (methyl)acrylic acid and (methyl)acrylate or (methyl) hydroxyalkyl acrylate copolymer, polyalkylene glycol with phosphonate groups, polyalkylene glycol with phosphate groups, comb polymers with anionic groups and polyether side chains, or its salt or a mixture of these polymers.

[0029] The organic polymer is more particularly a comb polymer comprising a polymer backbone with polyalkylene oxide side chains and anionic groups bonded to the backbone. The side chains here are bonded to the polycarboxylate backbone in particular via ester, ether, imide and / or amide groups. The comb polymer preferably comprises polyalkylene oxide units, more particularly polyethylene oxide units.

[0030] The aqueous suspension of calcium hydroxide is preferably obtained as described in WO 2019 / 180191 (Sika Technology).

[0031] The at least one material I is selected from alkanolamines, sodium thiocyanate, sodium nitrate, sodium nitrite, calcium nitrate, calcium silicate hydrate, sodium silicate, aluminum sulfate, sodium sulfate, sodium aluminate, alkali metal carbonates, especially lithium carbonate, alkali metal bicarbonates, especially sodium bicarbonate, organic acids or mixtures thereof.

[0032] Alkanolamines are amines having at least one hydroxyalkyl side group. Preferred alkanolamines are monoethanolamine, diethanolamine, diisopropanolamine, triethanolamine (TEA), isopropanolamine, triisopropanolamine (TIPA), N-methyldiethanolamine (MDEA), N-methyldiisopropanolamine (MDIPA), ethyldiisopropanolamine (EDIPA), diethanolisopropanolamine (DEIPA), tetrahydroxyethylethylenediamine (THEED) and tetrahydroxyisopropylethylenediamine (THIPD). Particularly preferred alkanolamines are triethanolamine (TEA), triisopropanolamine (TIPA) and N-methyldiethanolamine (MDEA).

[0033] Suitable organic acids are, in particular, formic acid, acetic acid, propionic acid, caprylic acid, lauric acid, linolic acid, linoleic acid, myristic acid, oleic acid, behenic acid, benzoic acid, oxalic acid and succinic acid.

[0034] Particularly suitable materials I are mixtures of sodium nitrate and alkanolamines, in particular mixtures of sodium nitrate and triethanolamine (TEA), triisopropanolamine (TIPA) or N-methyldiethanolamine (MDEA).

[0035] Another particularly suitable material I is a mixture of sodium nitrate and sodium thiocyanate.

[0036] Another particularly suitable material I is a mixture of sodium nitrate, calcium nitrate and sodium thiocyanate.

[0037] Another particularly suitable material I is a mixture of sodium nitrate, calcium nitrate, sodium thiocyanate and an alkanolamine, in particular triethanolamine (TEA), triisopropanolamine (TIPA) or N-methyldiethanolamine (MDEA).

[0038] Another particularly suitable material I is a mixture of sodium nitrate, calcium nitrate, sodium thiocyanate, formic acid and an alkanolamine, in particular triethanolamine (TEA), triisopropanolamine (TIPA) or N-methyldiethanolamine (MDEA).

[0039] According to an embodiment, the accelerator of the present invention is in the form of a single component as an aqueous suspension.

[0040] The term "single component" means that the aqueous suspension of calcium hydroxide also contains the at least one material I. Preferably, in the single-component accelerator, the at least one material I is dissolved in the aqueous suspension of calcium hydroxide. In other words, the accelerator of the present invention is in the form of a single component comprising an aqueous suspension of calcium hydroxide and the at least one material I in one container. Such a single-component accelerator is particularly easy to handle and meter.

[0041] According to an embodiment, the accelerator according to the invention is in a two-component form, wherein the aqueous suspension of calcium hydroxide and the at least one material I are stored in spatially separate containers and are combined only during or shortly before use.

[0042] The term "two-component" means that the aqueous suspension of calcium hydroxide and the at least one material I are stored in spatially separate containers and are combined only during or shortly before use. In such a case, the at least one material I may be in the form of a powder or an aqueous preparation, preferably in the form of an aqueous solution. Such a two-component accelerator has the advantage that the dosage ratio of the individual components can be easily adjusted.

[0043] According to an embodiment, the accelerator according to the invention is characterized in that calcium hydroxide is present in an amount of 5-65% by weight, preferably 8-15% by weight, and the at least one material I is present in an amount of 20-66% by weight, in each case relative to the total weight of the accelerator. It is clear to a person skilled in the art that water and further additives, in particular at least one organic polymer as described above, make up the accelerator to a total of 100% by weight.

[0044] In the case where the at least one material I comprises a mixture of two or more of alkanolamines, sodium thiocyanate, sodium nitrate, sodium nitrite, calcium nitrate, calcium silicate hydrate, sodium silicate, aluminum sulfate, sodium sulfate, sodium aluminate, alkali metal carbonates, especially lithium carbonate, alkali metal bicarbonates, especially sodium bicarbonate, and organic acids, this dosage range refers to the sum of all these chemicals in this mixture.

[0045] The accelerator of the invention may contain further additives. For example, the accelerator of the invention may contain a retarding additive, such as a sugar, a sugar acid or a hydroxycarboxylic acid, in particular citric acid, lactic acid or tartaric acid. For example, the accelerator of the invention may contain a thickener, such as a cellulose ether, a starch, a modified starch, a sheet silicate or an alkaline thickening polymer. For example, the accelerator of the invention may contain a defoamer, a biocide, a corrosion inhibitor or a pigment.

[0046] The accelerator of the present invention may contain other materials selected from glycols, surfactants, especially nonionic surfactants, such as alkyl polyglucosides, Gemini-surfactants, sodium lauryl ether sulfate, calcium stearate, silicones, alkoxylated phosphonates or alkoxylated phosphates, 1,3-propylene glycol, carboxylic acids, sulfonated amino alcohols, boric acid, borates, borax, phosphonates or phosphates, gluconates, iron sulfate, tin sulfate, antimony salts, glycerol, water-absorbing substances, especially in the form of superabsorbent polymers or sheet silicates such as vermiculite, bentonite, sugars, sugar acids, sugar alcohols, tall oil, polysaccharides such as starch, diutan gum, xanthan gum, gellan gum, guar gum, welan gum or carrageenan, cellulose ethers, polyvinyl alcohol, proteins, especially gelatin and / or casein, and mixtures thereof.

[0047] In another aspect, the present invention relates to a method for promoting a mineral binder composition, the method comprising the steps of:

[0048] 1) providing a mineral binder composition,

[0049] 2) providing a promoter, which comprises

[0050] a) an aqueous suspension of calcium hydroxide, and

[0051] b) at least one material I selected from alkanolamines, sodium thiocyanate, sodium nitrate, sodium nitrite, calcium nitrate, calcium silicate hydrate, sodium silicate, aluminum sulfate, sodium sulfate, sodium aluminate, alkali metal carbonates, especially lithium carbonate, alkali metal bicarbonates, especially sodium bicarbonate, organic acids or mixtures thereof, and

[0052] 3) Mixing the mineral binder composition and the at least one material I.

[0053] The embodiments described above also apply to this aspect.

[0054] Particularly suitable materials I that can be used for the process of the present invention are in particular mixtures of sodium nitrate and alkanolamines, in particular mixtures of sodium nitrate and triethanolamine (TEA), triisopropanolamine (TIPA) or N-methyldiethanolamine (MDEA). Another particularly suitable material I for the process of the present invention is a mixture of sodium nitrate and sodium thiocyanate. Another particularly suitable material I for the process of the present invention is a mixture of sodium nitrate, calcium nitrate and sodium thiocyanate. Another particularly suitable material I for the process of the present invention is a mixture of sodium nitrate, calcium nitrate, sodium thiocyanate and alkanolamines, in particular triethanolamine (TEA), triisopropanolamine (TIPA) or N-methyldiethanolamine (MDEA). Another particularly suitable material I that can be used for the process of the present invention is a mixture of sodium nitrate, calcium nitrate, sodium thiocyanate, formic acid and alkanolamines, in particular triethanolamine (TEA), triisopropanolamine (TIPA) or N-methyldiethanolamine (MDEA).

[0055] The mineral binder composition may be a mineral binder, such as cement or a binder comprising cement. The mineral binder composition may also be a formulated product, such as dry mortar or wet mortar or concrete.

[0056] The mineral binder composition is therefore characterized in that it comprises at least one mineral binder. The mineral binder in this context is especially cement.

[0057] According to an embodiment, in the method of the invention, the mineral binder composition comprises or consists of ordinary Portland cement, blended cement, aluminate cement and / or calcium sulphoaluminate cement.

[0058] Ordinary Portland cement is in particular CEM I according to standard EN 197-1. The term "blended cement" is intended to include mixtures of cement, in particular Portland cement, with supplementary cementitious materials, such as limestone, pozzolans and latent hydraulic materials. Blended cement is in particular CEM I, CEM I, CEM IV or CEM V according to standard EN 197-1 or CEM I or CEM VI according to standard EN 197-5. Blended cements according to other standards, such as ASTM C595, are also suitable. Blended cement is in particular a mixture of ordinary Portland cement with at least one of the following substances: limestone, slag, fly ash, silica fume, clay (calcined clay or raw clay), trass, marl, pumice, pozzolan, zeolitized tuff, diatomaceous earth, kiln dust, microsilica, pyrogenic silica, precipitated silica, burnt oil shale and combustion residues of organic matter. Gypsum is often additionally present as part of the ordinary Portland cement, or may be added additionally.

[0059] According to an embodiment, in the method of the present invention, the mineral binder comprises a blend of Portland cement and limestone.

[0060] Particularly suitable admixture cements comprise or consist of ordinary Portland cement, limestone, clay (preferably calcined clay) and optionally gypsum.

[0061] According to an embodiment, in the process of the invention, the accelerator is metered in an amount of calcium hydroxide providing an amount of 0.01-1.0 wt. %, preferably 0.1-0.2 wt. %, relative to the dry weight of the mineral binder.

[0062] According to an embodiment, in the process of the invention, the accelerator is metered in an amount of the at least one material I to provide an amount of not less than 0.1 wt.-%, preferably not less than 0.44 wt.-%, more preferably not less than 0.7 wt.-% relative to the dry weight of the mineral binder.

[0063] According to an embodiment, in the process of the invention, the accelerator is metered in an amount providing an amount of not more than 5 wt.-%, preferably not more than 2.66 wt.-% of the at least one material I, relative to the dry weight of the mineral binder.

[0064] According to an embodiment, the accelerator is metered in an amount to provide calcium hydroxide in an amount of 0.01-1.0 wt.-%, preferably 0.1-0.2 wt.-% and the at least one material I in an amount of not less than 0.1 wt.-%, preferably not less than 0.44 wt.-%, more preferably not less than 0.7 wt.-% and not more than 5 wt.-%, preferably not more than 2.66 wt.-%, relative to the dry weight of the mineral binder.

[0065] When material I consists of or comprises MDEA, it is preferred that the total dosage of MDEA is not greater than 0.2 wt. %, more preferably not greater than 0.16 wt. %, relative to the mineral binder.

[0066] When material I consists of or comprises sodium thiocyanate, it is preferred that the total dosage of sodium thiocyanate is not more than 3.0 wt. %, more preferably not more than 1.5 wt. %, relative to the mineral binder.

[0067] The dosage of calcium hydroxide and / or the at least one material I below the lower limit as defined above generally results in a low, often insufficient, promotion effect. The dosage of calcium hydroxide and / or the at least one material I above the upper limit as defined above generally does not bring about a further improvement in the promotion effect, but increases costs or even leads to a reduction in the promotion effect.

[0068] According to an embodiment, in the process of the invention, the accelerator is added to the mineral binder composition before or during grinding of the mineral binder composition.

[0069] In this case, the mineral binder composition is a dry mineral binder composition. It may advantageously be ordinary Portland cement, a blended cement or a component of a blended cement as defined above.

[0070] According to an embodiment, in the process of the invention, the accelerator is added to the mineral binder composition together with any mixing water or shortly after any mixing water.

[0071] Further advantageous embodiments of the invention are apparent from the following working examples. DETAILED DESCRIPTION

[0072] Example

[0073] Particle size measured by Nanophox

[0074] The particle size of the calcium hydroxide nanoparticles in the aqueous suspension was determined by dynamic light scattering using photon cross-correlation spectroscopy. The instrument used for the measurement was the Nanophox from Sympatec GmbH, Germany. The aqueous suspension was analyzed without further dilution. Prior to the measurement, the sample was homogenized for 1 minute with an ultrasonic probe.

[0075] chemicals used

[0076] Unless otherwise stated, chemicals were purchased from Sigma Aldrich at high purity and used as received.

[0077] Preparation of aqueous suspension of calcium hydroxide

[0078] The first solution was prepared by dissolving 174.4 g of Ca(NO3)2·4H2O (0.739 mol) and 10 g of a comb polymer (copolymer of acrylic acid and polyethylene glycol methacrylate; Mw of polyethylene glycol: 5000 g / mol) in 82 g of water. The second solution was prepared by dissolving 59.1 g of NaOH (1.478 mol) in 220 g of water. The first solution was loaded into a 1 liter round-bottom flask. The second solution was added via a dropping funnel over 5 minutes under vigorous stirring with a propeller stirrer. The resulting suspension was stirred for another 60 minutes. The resulting suspension was purified by ultrafiltration using a polyethersulfone membrane with a size exclusion limit of 30 KDa. In this procedure, NaNO3 was removed and the suspension was concentrated. Thereafter, the suspension was diluted with purified water to a Ca(OH)2 content of 10% by weight in the form of nanoparticles. The resulting suspension S1 had a Ca(OH)2 content of 10% by weight in the form of nanoparticles. The particle size D50 measured as described above was 163 nm.

[0079] Preparation and testing of mortar

[0080] 750 g of cement (CEM I 52.5R or CEM I A-LL as shown in Tables 1-4 below), 738 g of sand (0-1 mm), 1107 g of sand (1-4 mm) and 1154 g of sand (4-8 mm) were dry mixed on a Hobart mixer at 25° C. for 1 minute. Superplasticizer (polycarboxylate ether; 1% by weight relative to cement) and water were then added in an amount such that the weight ratio of water to cement (w / c ratio) was 0.39. The water from suspension S1 was taken into account in the calculation of the w / c ratio. Mixing was then continued for 30 seconds. The mixing was stopped, the mixing bowl was scraped and an accelerator of the type and amount shown in Table 1 below was added. Mixing was then continued for another 1 minute.

[0081] The compressive strength of the resulting mortar mixes was tested according to standard EN 12190 on 4×4×16 cm prisms after the times indicated in Tables 1 to 4 below.

[0082] Table 1: Example 1 (reference) and Examples 2-5 (present invention)

[0083]

[0084] *Methyldiethanolamine

[0085] **Triethanolamine

[0086] ***Ca(OH)2 suspension as above

[0087] Table 2: Example 6 (reference) and Examples 7-10 (present invention)

[0088]

[0089] Table 3: Example 11 (reference) and Examples 12-14 (present invention)

[0090] Example 11 12 13 14 cement CEM I CEM I CEM I CEM I <![CDATA[Na(NO3)2[g]]]> 3.3 3.3 3.3 NaSCN[g] 3.8 18.8 S1***[g] 15 15 15 Compressive strength@6h[MPa] 2.9 5.3 6.7 6.1 Compressive strength@8h[MPa] 8.2 14.4 16.6 15.2 Compressive strength@24h[MPa] 43.7 44.8 48 48

[0091] Table 4: Example 15 (reference) and Examples 16-19 (present invention)

[0092]

[0093] It can be seen from the above examples that the accelerator according to the present invention improves the early strength of the mineral binder composition.

Claims

1. An accelerator for a mineral binder composition, the accelerator comprising: a) an aqueous suspension of calcium hydroxide, and b) at least one material I selected from alkanolamines, sodium thiocyanate, sodium nitrate, sodium nitrite, calcium nitrate, calcium silicate hydrate, sodium silicate, aluminum sulfate, sodium sulfate, sodium aluminate, alkali metal carbonates, especially lithium carbonate, alkali metal bicarbonates, especially sodium bicarbonate, organic acids or mixtures thereof.

2. The accelerator according to claim 1, characterized in that The at least one material I is a mixture of sodium nitrate, calcium nitrate and sodium thiocyanate.

3. The accelerator according to claim 1, characterized in that The at least one material I is a mixture of sodium nitrate, calcium nitrate, sodium thiocyanate and an alkanolamine, in particular triethanolamine (TEA), triisopropanolamine (TIPA) or N-methyldiethanolamine (MDEA).

4. The accelerator according to at least one of claims 1 to 3, characterized in that The aqueous suspension comprises calcium hydroxide in the form of nanoparticles, in particular calcium hydroxide having a particle size D90 measured by dynamic light scattering using photon cross-correlation spectroscopy according to standard ISO 22412:2017 below 800 nm, preferably below 600 nm, more preferably below 400 nm and in particular below 200 nm.

5. Accelerator according to at least one of claims 1 to 4, characterized in that The accelerator is in the form of a single component comprising the aqueous suspension of calcium hydroxide and the at least one material I in one container.

6. Accelerator according to at least one of claims 1 to 5, characterized in that The accelerator is in the form of a two-component agent, wherein the aqueous suspension of calcium hydroxide and the at least one material I are stored in spatially separate containers and are combined only during or shortly before use.

7. Accelerator according to at least one of claims 1 to 6, characterized in that Calcium hydroxide is present in an amount of 5 to 65% by weight, preferably 8 to 15% by weight, and the at least one material I is present in an amount of 20 to 66% by weight, in each case relative to the total weight of the accelerator.

8. A method for promoting a mineral binder composition, the method comprising the steps of: 1) providing a mineral binder composition, 2) providing a promoter, which comprises a) an aqueous suspension of calcium hydroxide, and b) at least one material I selected from alkanolamines, sodium thiocyanate, sodium nitrate, sodium nitrite, calcium nitrate, calcium silicate hydrate, sodium silicate, aluminum sulfate, sodium sulfate, sodium aluminate, alkali metal carbonates, especially lithium carbonate, alkali metal bicarbonates, especially sodium bicarbonate, organic acids or mixtures thereof, and 3) Mixing the mineral binder composition and the at least one material I.

9. The method according to claim 8, characterized in that The mineral binder composition comprises or consists of ordinary Portland cement, blended cement, aluminate cement and / or calcium sulfoaluminate cement.

10. The method according to claim 9, characterized in that The mineral binder comprises a blend of Portland cement and limestone.

11. The method according to at least one of claims 8 to 10, characterized in that The accelerator is metered in an amount of calcium hydroxide that provides an amount of 0.01 to 1.0% by weight, preferably 0.1 to 0.2% by weight, relative to the dry weight of the mineral binder.

12. The method according to at least one of claims 8 to 11, characterized in that The accelerator is metered in an amount of the at least one material I that provides an amount of not less than 0.1 wt. %, preferably not less than 0.44 wt. %, more preferably not less than 0.7 wt. %, relative to the dry weight of the mineral binder.

13. The method according to at least one of claims 8 to 12, characterized in that The accelerator is metered in such an amount that an amount of not more than 5% by weight, preferably not more than 2.66% by weight, of the at least one material I is provided, relative to the dry weight of the mineral binder.

14. The method according to at least one of claims 8 to 13, characterized in that The accelerator is added to the mineral binder composition before or during grinding of the mineral binder composition.

15. The method according to at least one of claims 8 to 13, characterized in that The accelerator is added to the mineral binder composition together with any mixing water or shortly after any mixing water.

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