阅读说明：本技术 用于任选含辅助胶凝材料的水泥、砂浆或混凝土组合物的凝结硬化加速剂及该加速剂的用途 (Setting and hardening accelerator for cement, mortar or concrete compositions optionally containing supplementary cementitious materials and use of the accelerator ) 是由 沃尔弗拉姆·弗兰克 希尔德·托默森 于 2019-03-05 设计创作，主要内容包括：本申请涉及用于任选地包含水泥替代材料(CSM)的水泥、砂浆或混凝土组合物的凝结和硬化加速剂。加速剂组合物包含硝酸盐水溶液和碱性氢氧化物。特别地,含水加速剂组合物包含30至55w/w％的硝酸盐(以硝酸盐溶液的形式)以及0.02至0.1w/w％的碱性氢氧化物(其溶解在硝酸盐溶液中并且任选地作为加速剂组合物中的氢氧化物沉淀),其中加速剂组合物的pH为至少9.0。在水泥、砂浆或混凝土组合物包含CSM的情况下,加速剂组合物的pH为至少12.0。本申请还涉及根据本申请的加速剂组合物的用途,并且涉及通过使组合物与根据本申请的加速剂(特别是在低温)反应而使水泥、砂浆或混凝土组合物加速的方法。(The present application relates to setting and hardening accelerators for cement, mortar or concrete compositions optionally comprising cement replacement materials (CSM). The accelerator composition comprises an aqueous nitrate solution and an alkaline hydroxide. In particular, the aqueous accelerator composition comprises 30 to 55 w/w% of a nitrate salt (in the form of a nitrate salt solution) and 0.02 to 0.1 w/w% of an alkaline hydroxide (which is dissolved in the nitrate salt solution and optionally precipitated as hydroxide in the accelerator composition), wherein the pH of the accelerator composition is at least 9.0. Where the cement, mortar or concrete composition comprises a CSM, the pH of the accelerator composition is at least 12.0. The present application also relates to the use of the accelerator composition according to the present application and to a method for accelerating a cement, mortar or concrete composition by reacting the composition with an accelerator according to the present application, in particular at low temperatures.)

1. An aqueous setting and hardening accelerator for cement, mortar or concrete compositions comprising 30 to 55 w/w% of a nitrate salt in the form of a nitrate salt solution, and 0.02 to 0.1 w/w% of an alkaline hydroxide dissolved in the nitrate salt solution and optionally precipitated as hydroxide in the accelerator composition, wherein the accelerator composition has a pH of at least 9.0.

2. The accelerator composition of claim 1, wherein the alkaline hydroxide is selected from calcium hydroxide, sodium hydroxide, or potassium hydroxide.

3. Accelerator composition according to claim 1 or 2, wherein the nitrate salt is selected from calcium nitrate, sodium nitrate or potassium nitrate.

4. The accelerator composition according to any one of claims 1 to 3, wherein the accelerator composition has a pH of 9.0 to 14.0.

5. The accelerator composition according to any one of claims 1 to 4, comprising 44 to 55 w/w% calcium nitrate, and 0.02 to 0.1 w/w% calcium hydroxide in the form of a nitrate solution, more particularly comprising about 49.98 w/w% calcium nitrate, and about 0.04 w/w% calcium hydroxide in the form of a nitrate solution.

6. An accelerator according to any one of claims 1 to 4, consisting of: 30 to 55 w/w% of a nitrate salt, 0.02 to 0.1 w/w% of an alkaline hydroxide and water to 100 w/w%, wherein the accelerator composition has a pH of at least 9.0; more specifically, the accelerator consists of: 44 to 55 w/w% calcium nitrate, 0.02 to 0.1 w/w% calcium hydroxide and water to make up to 100 w/w%; more specifically, the accelerator consists of: about 49.98 w/w% calcium nitrate, about 0.04 w/w% calcium hydroxide and water to make up to 100 w/w%.

7. A cement, mortar or concrete composition comprising the accelerator composition according to any one of claims 1 to 6.

8. The cement, mortar or concrete composition of claim 7 comprising one or more cement replacement materials optionally including fly ash or limestone and an accelerator according to any one of claims 1 to 6 having a pH of at least 12.0.

9. Use of an accelerator composition according to any one of claims 1 to 6 for accelerating setting and hardening of a cement, mortar or concrete composition.

10. The use according to claim 9, wherein the cement, mortar or concrete composition comprises one or more cement replacement materials, optionally including fly ash, blast furnace slag or limestone, and wherein the accelerator composition has a pH of at least 12.0.

11. A method for accelerating the setting and hardening of a cement, mortar or concrete composition, optionally comprising one or more cement replacement materials, wherein the method comprises the steps of:

-preparing an accelerator composition according to any one of claims 1 to 6; and

-adding the accelerator composition to a cementitious material or one or more cement replacement materials or coarse aggregate or any combination thereof at a temperature of 5 ℃ to 20 ℃.

12. The method of claim 11, wherein the adding of the cementitious material or one or more cement replacement materials or coarse aggregate or any combination thereof is performed at a temperature of about 5 ℃.

13. A method for preparing the accelerator composition of any one of claims 1 to 6, the method comprising:

(a) dissolving 30 to 55 w/w% of a nitrate salt, more specifically solid calcium nitrate, solid sodium nitrate or solid potassium nitrate, in water, thereby obtaining an aqueous nitrate salt solution;

(b) 0.02 to 0.1 w/w% of an alkaline hydroxide, more specifically solid calcium hydroxide, solid sodium hydroxide or solid potassium hydroxide is added to the aqueous nitrate solution, thereby obtaining an accelerator composition having a pH of at least 9.0.

Technical Field

The present application relates to the acceleration of setting and hardening of cement, mortar and concrete compositions. The cement, mortar or concrete composition optionally comprises one or more cement cementitious auxiliary materials (CSM).

Background

Since cement hydration is a slow process, it is necessary to accelerate setting and hardening to accelerate the construction process. In particular, there is a need to accelerate the working process of applying fresh concrete, which is economically interesting. In addition to setting and hardening acceleration in cold climates, setting and hardening acceleration is also critical to counteract the cooling of the concrete by the environment.

Calcium chloride (CaCl)₂) Is a possible accelerator for concrete setting, but it stimulates the continued oxidation of ferrous structures or steel or aluminum tubes embedded in the concrete. CaCl₂It can also adversely affect the concrete itself, leading to chipping and weakening. When the concrete is in contact with moist soil, CaCl₂Enhancing the erosion of sulfate in the soil. Thus, even in cases where there is no metal present in the concrete or where metal corrosion in the concrete is not a serious problem, there is still CaCl that can be added to cement, mortar or concrete compositions₂Maximum value of the amount of (c). Despite CaCl₂Low cost, but the problems associated with their use deviate from their usefulness in reinforced concrete structures.

Neutral or acidic calcium nitrate (Ca (NO)₃)₂) Are common set accelerators for concrete. It is usually added as a solution after the concrete admixture has been mixed with water. It is generally necessary to add 1% to 2% by weight of cement (═ bwoc) of calcium nitrate. Calcium nitrate does not cause any corrosion when applied at levels up to 4 and 5% by weight as approved by european or ASTM mix standards, respectively. However, acceleration effectThe ability to generate calcium hydroxide to raise the pH is based on calcium nitrate, which has a pH of only 5 to 8. Therefore, the acceleration effect in cold climates is insufficient and to achieve a faster acceleration CaCl is usually added₂This can lead to the corrosion problems described in the previous paragraph.

US4897120 describes an accelerator for Portland cement (Portland cement) derived from fertilizers. More particularly, it relates to a method of chemically altering a calcium nitrate composition containing ammonium nitrate originally used as a fertilizer or additive thereto to make it useful as an additive for portland cement concrete and mortar. In this method, a calcium ammonium nitrate composition is reacted with a trimethylol glycoluril compound or a tetrakis hydroxymethyl glycoluril compound under alkaline conditions at a pH above about 7.5, preferably in the pH range of about 9 to 11. It was found that the presence of hexamethylene tetramine (urotropin) not only has a beneficial effect on the conversion of calcium ammonium nitrate hydrate compositions for use as portland cement accelerators, but also favorably affects performance due to faster setting times, with higher compressive strength properties. The resulting set accelerator is suitable for use in cold weather conditions.

Another way to improve the coagulation acceleration of calcium nitrate is to use a polyethanolamine accelerator in combination with calcium nitrate. WO1982004038 relates to an additive composition which accelerates setting times and also improves the compressive strength of portland cements, mortars and concretes, more particularly for concretes which will contain steel reinforcement. The additive composition consists essentially of a waste by-product stream of a concentrated aqueous calcium nitrate solution and a mixture of polyethanolamines to which a small amount of a polyhydroxy aliphatic compound (such as gluconic acid) or a solution of an alkali or alkaline earth metal salt of lignosulfonic acid has been added. WO1984004089 relates to a setting accelerator comprising calcium nitrate and triethanolamine. However, in fact, those amine accelerators are harmful substances which are hardly usable with respect to the environment and with respect to its users.

It can be concluded that there is still a need to improve the setting and hardening of cement, mortar or concrete compositions, especially in cold conditions. It is therefore an object of the present application to provide an accelerator for improving the setting and hardening (including at low temperatures) of cement, mortar or concrete compositions.

It is another object of the present application to improve the setting and hardening of cement, mortar or concrete compositions comprising CSM (cement aid materials).

Summary of The Invention

According to one aspect of the present application, a set and set accelerator for a cement, mortar or concrete composition is disclosed. The accelerator comprises a supernatant comprising an aqueous nitrate solution. The supernatant also contains dissolved alkaline hydroxide supernatant solids. The supernatant has a pH of at least 9.0. The accelerator may also optionally include a hydroxide precipitate. Such an alkaline supernatant is advantageous in that it provides the elevated pH required for the crystallization reaction of the cement material. It has been found that the alkaline supernatant accelerates the setting and hardening of cement, mortar or concrete compositions, which is economically interesting. Acceleration is of particular concern for applications in cold climates where cement sets and hardens slowly.

In particular, the setting and hardening accelerator for cement, mortar or concrete compositions according to the present application is an aqueous composition comprising 30 to 55 w/w% (more particularly 30 to 50 w/w%) of a nitrate in the form of a nitrate solution, and 0.02 to 0.1 w/w% of an alkaline hydroxide dissolved in the nitrate solution and optionally precipitated as hydroxide in the accelerator composition, wherein the pH of the accelerator composition is at least 9.0.

In one possible accelerator according to the present application, the alkaline hydroxide is selected from calcium hydroxide, sodium hydroxide or potassium hydroxide.

In one possible accelerator according to the present application, the aqueous nitrate solution is selected from an aqueous calcium nitrate solution, an aqueous sodium nitrate solution or an aqueous potassium nitrate solution. Thus, in one possible accelerator composition according to the present application, the nitrate is selected from calcium nitrate, sodium nitrate or potassium nitrate.

In one possible accelerator composition according to the application, the pH of the aqueous composition is from 9.0 to 14.0. In another possible accelerator composition according to the application, the pH of the aqueous composition is from 12.0 to 14.0.

In one possible accelerator according to the application, the supernatant comprises an aqueous nitrate solution obtained by dissolving 30 to 55 w/w% (more particularly 30 to 50 w/w%) of calcium nitrate salt (solid), sodium nitrate salt (solid) or potassium nitrate salt (solid) in water, and 0.02 to 0.1 w/w% of solid calcium hydroxide, solid sodium hydroxide or solid potassium hydroxide added to the resulting aqueous nitrate solution.

In one possible accelerator according to the application, the supernatant comprises an aqueous calcium nitrate solution obtained by dissolving 44 to 55 w/w% of a calcium nitrate salt in water, and 0.02 to 0.1 w/w% of solid calcium hydroxide added to the formed aqueous calcium nitrate solution, which causes the formation of a calcium hydroxide precipitate. Thus, one possible accelerator composition according to the application comprises 44 to 55 w/w% calcium nitrate, and 0.02 to 0.1 w/w% calcium hydroxide in the form of a nitrate solution.

In one possible accelerator according to the application, the supernatant comprises an aqueous calcium nitrate solution obtained by dissolving about 49.98 w/w% of a calcium nitrate salt in water and by adding about 0.04 w/w% of solid calcium hydroxide to the formed aqueous calcium nitrate solution, which causes the formation of a calcium hydroxide precipitate. Thus, one possible accelerator composition according to the present application comprises about 49.98 w/w% calcium nitrate salt in water, and about 0.04 w/w% calcium hydroxide.

Where the cement, mortar or concrete composition comprises one or more CSMs (which optionally include fly ash or limestone), the pH of the accelerator composition or accelerator composition supernatant is at least 12.0. Such a pH is advantageous in that it provides the elevated pH required for not only the crystallization reaction of the cement, mortar or concrete in the composition, but also the crystallization reaction of the CSM in the composition. It was found that at such pH values, setting and hardening of cement, mortar or concrete compositions comprising one or more CSMs is accelerated.

Another aspect of the present application provides a cement, mortar or concrete composition comprising an accelerator composition according to the present application. In certain embodiments, a cement, mortar or concrete composition is provided, wherein the cement, mortar or concrete composition comprises one or more cement replacement materials (which optionally include fly ash or limestone), and an accelerator composition as previously described and having a pH of at least 12.0.

According to another aspect of the present application, there is disclosed the use of an accelerator composition comprising an aqueous nitrate solution and dissolved alkaline hydroxide solids, and having a pH of at least 9, and optionally comprising hydroxide precipitates, for the setting and hardening acceleration of cement, mortar or concrete compositions.

More particularly, a supernatant is used which forms part of the accelerator according to the application as described above.

According to another aspect of the present application, the use of an accelerator composition according to the present application having a pH of at least 12.0 and optionally comprising a hydroxide precipitate for accelerating the setting and hardening of a cement, mortar or concrete composition comprising one or more CSMs is disclosed.

More particularly, a supernatant is used which forms part of the accelerator according to the application as described above.

According to another aspect of the application, a method for accelerating the setting and hardening of a cement, mortar or concrete composition optionally comprising one or more CSMs is disclosed. The method comprises the following steps: preparing an accelerator according to the present application as described above, and adding the accelerator to the cementitious material or to one or more CSM or coarse aggregate or any combination thereof at a temperature of 5 ℃ to 20 ℃.

In one possible method according to the application, the addition of the cement material or one or more CSM or coarse aggregate or any combination thereof is performed at a temperature of about 5 ℃.

According to another aspect of the present application, there is disclosed a method for preparing an accelerator composition as described herein, the method comprising the steps of: dissolving 30 to 55 w/w% (more particularly 30 to 50 w/w%) of a nitrate salt (more particularly calcium nitrate, sodium nitrate or potassium nitrate) in water, thereby obtaining an aqueous nitrate salt solution; and adding 0.02 to 0.1 w/w% of an alkaline hydroxide (more specifically solid calcium hydroxide, solid sodium hydroxide or solid potassium hydroxide) to the aqueous nitrate solution, thereby obtaining an accelerator composition having a pH of at least 9.0.

Brief Description of Drawings

In fig. 1, the hydration curves of cement slurry samples containing no, one, or both sodium nitrate and sodium hydroxide are shown;

in fig. 2, the hydration curves of cement slurry samples containing calcium nitrate, a combination of calcium nitrate and sodium hydroxide, or a combination of calcium nitrate and calcium hydroxide are shown; a) an environment; b) 0% CN; c) 1% CNSS; d) 1% CNSS + Ca (OH)₂；e)1％CNSS+NaOH。

In fig. 3a, the effect of calcium nitrate and alkaline calcium nitrate on setting time at 5 ℃ for various cements and CSM is shown;

figure 3b shows the effect of calcium nitrate and alkaline calcium nitrate on setting time of various cements and CSM at 20 ℃.

Detailed Description

As defined herein, the singular forms "a", "an" and "the" include both singular and plural referents unless the context clearly dictates otherwise. The term "comprising" as used below is synonymous with "including" or "containing" and is inclusive or open-ended and does not exclude additional unrecited portions, elements or method steps. Where the description refers to a product or method "comprising" a particular feature, portion or step, it is meant that the possibility exists that additional features, portions or steps may also be present, but embodiments containing only the listed features, portions or steps may also be referred to. All references cited in this specification are to be considered to be incorporated herein by reference in their entirety.

As used herein, w/w% means weight percent. When used in the context of an accelerator composition, it means weight percent relative to the total weight of the accelerator composition. Thus, the expression "dissolving X% w/w of nitrate in water" means that X% by weight of nitrate (solids) relative to the total weight of the accelerator is dissolved in water. Which is also the percentage of nitrate that will ultimately be present in the accelerator composition. Likewise, the expression "X w/w% of hydroxide solids are added to the formed nitrate solution" means that X wt% of hydroxide solids, based on the total weight of the accelerator, are added to and dissolved in the formed nitrate solution, and that they will eventually be present in the accelerator.

The present application relates to a setting and hardening accelerator for cement, mortar or concrete compositions.

Cement is used as a binder material that hardens to form a connecting material between solids. Cements used in construction are hydraulic or non-hydraulic. Hydraulic cements (e.g., portland cement) harden due to hydration, which is a chemical reaction between the anhydrous cement powder and water. Thus, they can harden in water or on constant exposure to humid weather. The chemical reaction produces hydrates that are not very soluble in water and are therefore quite durable in water. Non-hydraulic cements do not harden in water. The hydrated lime hardens, for example, by reacting with atmospheric carbon dioxide.

To date, portland cement is the most common type of cement used throughout the world. This cement is made by heating limestone (calcium carbonate) with small amounts of other materials, such as clay, in a kiln to a temperature of 1450 ℃ in a process known as calcination. During calcination, carbon dioxide molecules are released from the calcium carbonate to form calcium oxide (also known as quicklime), which is then blended with other materials already contained in the mixture. The resulting hard mass, known as ' clinker ' (clinker) ', is then ground into a powder together with a small amount of gypsum to make ' ordinary portland Cement (ordinary portland Cement) ', which is the most commonly used type of Cement (commonly known as OPC).

There are different types of cement (denoted CEM I to CEM V) with lower or higher contents of portland cement, as well as blast furnace cements, such as cement substitute materials, also known as cementitious auxiliary materials (CSM), such as limestone or fly ash, i.e.:

CEM I: OPC with up to 5% of other compounds;

CEM II: mixtures of OPC with all types of e.g. fly ash, limestone or slate, minimum 65% OPC;

CEM III: class 3 blast furnace/portland cement mix: A. b and C, wherein

CEM III/A contains the lowest (40%) amount of blast furnace slag and CEM III/C contains the highest (60%) amount of blast furnace slag;

CEM IV: pozzolan cement (Pozzolana cement) type;

CEM V: a composite cement having a mixture of OPC, blast furnace slag, and a pozzolanic compound.

The term "cement replacement material(s)" is used herein interchangeably with the term "gelling aid material(s)" (abbreviated as CSM) and generally refers to a calcium and/or silicate rich cementitious material. In particular, the CSM is selected from the group consisting of fly ash, limestone or blast furnace slag. More particularly, CSMs contemplated herein do not include alumina or aluminate materials, such as fused or tabular alumina, zircon, aluminum silicate, and the like.

Dry mortar admixtures are typically made from a mixture of aggregate (such as sand), binder (such as cement or lime), and water. Typically, dry mortar blends consist of about 25 w/w% cement and about 75 w/w% sand. Just prior to use, the dry mortar blend is mixed with water to make a workable mortar slurry that can be used as a general building material to bond building blocks together and fill the gaps between them. The mortar slurry hardens as it sets, resulting in a hard aggregate structure. The mortar may also be used to fix or masonry when the original mortar has been washed away. The dry mortar blend was stored dry in bags.

Concrete is a composite building material mainly composed of aggregate, cement and water. There are many formulations that provide various properties. The aggregate is typically coarse gravel or crushed rock, such as limestone or granite, and fine aggregate, such as sand. Cement (usually portland cement) and other cementitious materials such as fly ash and slag cement are used as binders for aggregates. Various chemical admixtures are also added to achieve various properties. Water is mixed with the dry concrete mix to enable it to be shaped (usually poured or cast) and then set and hardened (cured, set) by a chemical process known as hydration into a high strength concrete that is hard like rock. The water reacts with the cement which binds the other components together to form a strong stone-like material. Concrete is widely used in the manufacture of building structures, foundations, brick/block walls, pavements, bridges/overpasses, highways/roads, runways, parking lots, dams, ponds/reservoirs, pipes, footings for doors, fences and poles, and even ships.

Concrete can be damaged by many processes, such as freezing of water trapped in the concrete pores. Casting and curing concrete in cold weather, particularly at or below sustained freezing temperatures, is challenging. The most common problem is that the concrete freezes and/or undergoes freeze/thaw cycles before sufficient strength is achieved during curing. In said cold weather conditions, water begins to freeze in the capillaries of the concrete at-2 ℃, which water expands up to 9% of its volume as it freezes, resulting in cracks in the concrete matrix, and a reduction in compressive strength of up to 50% may occur if the concrete freezes before reaching at least a compressive strength of 500 psi.

As described in more detail above, the setting and hardening accelerator according to the present application for cement, mortar or concrete compositions comprises a supernatant or solution comprising firstly an aqueous nitrate solution and also comprising dissolved alkaline hydroxide solids. The accelerator may also comprise hydroxide precipitates depending on the composition of the aqueous nitrate solution and the nature of the solid alkaline hydroxide dissolved in the supernatant. In particular, calcium hydroxide has a solubility in water of only 1.89g/L at 0 ℃ and a solubility in water of 1.73g/L at 20 ℃. Thus, when the amount of calcium hydroxide added or formed exceeds the solubility of calcium hydroxide at the supernatant temperature, precipitation will occur as follows:

1. adding calcium hydroxide to the aqueous nitrate solution, or

2. Calcium hydroxide is formed by adding a solid alkaline hydroxide (e.g., solid sodium hydroxide or potassium hydroxide) to an aqueous solution of calcium nitrate.

Thus, the setting and hardening accelerator according to the present application generally comprises an aqueous nitrate solution and an alkaline hydroxide.

The accelerator composition or supernatant more particularly has a typical pH depending on whether the cement, mortar or concrete composition further comprises one or more CSM or does not comprise one or more CSM. If CSM is not present, the pH of the accelerator composition or supernatant is at least 9.0, whereas when CSM is present, the pH of the accelerator composition or supernatant is typically at least 12.0. As used herein, "pH" is the conventional unit of hydrogen ion activity in an aqueous solution measured at 25 ℃ and 1 atmosphere [ i.e., ISO standard state ]. A pH of at least 9.0 includes any measured pH value that would be rounded to above 9.1. A pH of at least 12.0 includes any measured pH value that would be rounded to above 12.1. A pH of 9.0 to 14.0 includes any measured pH between a pH value rounded above 9.1 and a pH value rounded below 14.1.

More particularly, the aqueous nitrate solution contained in the accelerator is selected from an aqueous calcium nitrate solution, an aqueous sodium nitrate solution or an aqueous potassium nitrate solution. Most particularly, an aqueous solution of calcium nitrate is used. This is due to the fact that: since calcium nitrate has a pH value of 5 to 8, it has accelerated setting and hardening of cement, mortar or concrete compositions by itself. However, the pH is not yet sufficiently elevated and should generally be at least 9 when CSM is not included. This pH can be obtained by adding a solid alkaline hydroxide dissolved in an aqueous nitrate solution. The solid alkaline hydroxide is in particular selected from solid calcium hydroxide, solid sodium hydroxide or solid potassium hydroxide. In the absence of CSM, the pH of the supernatant is more particularly 9.0 to 14.0, whereas in the presence of CSM, the pH of the supernatant is 12.0 to 14.0.

The accelerator composition is prepared by: the accelerator composition according to the invention is obtained by dissolving 30 to 55 w/w% (more particularly 30 to 50 w/w%) of solid calcium nitrate (salt), solid sodium nitrate (salt) or solid potassium nitrate (salt) in water to obtain an aqueous calcium nitrate, sodium nitrate or potassium nitrate solution, after which 0.02 to 0.1 w/w% of solid calcium hydroxide, solid sodium hydroxide or solid potassium hydroxide is added to the obtained aqueous nitrate solution, depending on whether the solubility of calcium hydroxide has been exceeded or not. In particular, the accelerator composition is prepared by: an aqueous calcium nitrate solution is first prepared by dissolving 44 to 55 w/w% of solid calcium nitrate in water, after which 0.02 to 0.1 w/w% of solid calcium hydroxide is added to the resulting aqueous calcium nitrate solution. Most particularly, the accelerator composition is prepared by: an aqueous calcium nitrate solution was prepared by dissolving about 49.98 w/w% of solid calcium nitrate in water, after which about 0.04 w/w% of solid calcium hydroxide was dissolved in the form of the resulting aqueous calcium nitrate solution.

Accordingly, the present application provides an aqueous accelerator composition comprising from 30 to 55 w/w% (more particularly from 30 to 50 w/w%) of a nitrate salt in water (more particularly calcium, sodium or potassium nitrate in water), and from 0.02 to 0.1 w/w% of an alkaline hydroxide (particularly a hydroxide of an alkali or alkaline earth metal, more particularly calcium, sodium or potassium hydroxide). In particular, the aqueous accelerator composition comprises 44 to 55 w/w% calcium nitrate in water, and 0.02 to 0.1 w/w% calcium hydroxide. Even more particularly, the aqueous accelerator composition comprises about 49.98 w/w% calcium nitrate in water, and about 0.04 w/w% calcium hydroxide.

In particular embodiments, the present application provides an aqueous accelerator composition consisting of: (i)30 to 55 w/w% (more particularly 30 to 50 w/w%) of a nitrate salt, more particularly calcium nitrate, sodium nitrate or potassium nitrate; (ii)0.02 to 0.1 w/w% of an alkaline hydroxide, in particular an alkali metal or alkaline earth metal hydroxide, more particularly calcium hydroxide, sodium hydroxide or potassium hydroxide; and (iii) water. In particular, the aqueous accelerator composition consists of 44 to 55 w/w% calcium nitrate, 0.02 to 0.1 w/w% calcium hydroxide and water. Even more specifically, the aqueous accelerator composition consists of about 49.98 w/w% calcium nitrate, about 0.04 w/w% calcium hydroxide, and water.

The present application also discloses the use of an accelerator according to the present application as described above for accelerating the setting and hardening of a cement, mortar or concrete composition. In particular, an accelerator as contemplated herein is used, the accelerator comprising a supernatant or solution comprising an aqueous nitrate solution and dissolved alkaline hydroxide solids, optionally comprising a hydroxide precipitate. In the absence of CSM in the cement, mortar or concrete composition, the pH of the accelerator composition is at least 9.0, whereas when CSM is present, the pH of the supernatant is at least 12.0. In the absence of CSM, the pH of the supernatant is more particularly 9.0 to 14.0, whereas in the presence of CSM, the pH of the supernatant is 12.0 to 14.0.

The present application also discloses a method for accelerating the setting and hardening of a cement, mortar or concrete composition optionally comprising one or more CSMs. The method comprises the following steps: preparing an accelerator according to the present application, and adding the accelerator to a cementitious material optionally comprising one or more CSMs at a temperature of from 5 ℃ to 20 ℃. In particular, the addition of the cement material or one or more CSM or coarse aggregate or any combination thereof is performed at a temperature of about 5 ℃.

Also disclosed is a method for preparing an accelerator composition according to the present application, the method comprising the steps of: (a) dissolving a nitrate salt, in particular 30 to 55 w/w%, more in particular 30 to 50 w/w% of the nitrate salt (more in particular solid calcium nitrate, solid sodium nitrate or solid potassium nitrate), in water, thereby obtaining an aqueous nitrate salt solution, and (b) adding 0.02 to 0.1 w/w% of an alkaline hydroxide (more in particular solid calcium hydroxide, solid sodium hydroxide or solid potassium hydroxide) to the aqueous nitrate salt solution, thereby obtaining an accelerator composition having a pH of at least 9.0.

Examples