SI23289A - Accelerator for setting and hardening of portland cement systems, based on cryolite bath - Google Patents

Abstract

The subject of the invention is a liquid accelerator for setting and hardening of portland cement systems, that is low or non- alkaline and does not contain chloride ions. The accelerator according to the invention is characteristic in that it consists of a cryolite bath, a waste product in the production of aluminium, and/or of at least one fluorine compound which can be fluoride, fluoroaluminate, fluorosilicate, fluoroborate etc., which is soluble either in water and/or in an acid solution, and of at least one of water soluble sulphates which lower pH of the solution, among them preferably a 17 % Al2O3 aluminium sulphate, and/or also of amorphous or crystalline aluminium hydroxide, which depends on the pH of previous solution, and/or that it contains additional liquid solution stabilizers, acting as complexants or sources of anions, to prevent further hydration of aluminium compounds, particularly of aluminium hydroxide, among these stabilizers being preferably formic acid and/or other mono- and dicarboxylates, fluorides, fluoroaluminates, fluorosilicates, fluoroborates, phosphates, sulphates, their salts, acids or mixtures of the said substances. The activity of the accelerator can be improved additionally with diethanolamine which is added to the liquid accelerator. The accelerator excels in a simple synthesis and a low price. The reaction product is a suspension which is stabilized with a stabilizer - a dispersant such as hydrated magnesium silicate.

Description

Accelerator for bonding and curing of Portland cement systems based on cryolite bath

The subject of the invention is a liquid accelerator for the bonding and curing of Portland cement systems based on cryolite bath, which is slightly or non-alkaline and does not contain chloride ions. The accelerator presented enables fast bonding and curing of cement systems and is distinguished by the rapid increase in compressive strength of fresh Portland cement systems and high ultimate compressive strength. The acceleration is mainly due to the simple synthesis and low cost of the finished product.

Liquid accelerator for bonding and curing is used in the construction industry as an adjunct to injection-molded concrete used in tunnel construction, bank consolidation, mines, subway construction, etc. Accelerators in liquid aggregate state are used in the wet process for injection molded concrete, which is well known to the expert public and in practice also the most established process for the application of sprayed concrete. In order for a successful application, that is, sprayed concrete, the following requirements must be met in particular:

- the sprayed concrete can adhere well to the substrate (eg rocky surface of the tunnel borehole), which means that the liquid accelerator must accelerate the setting of the concrete rapidly enough,

- the incremental initial strength of the sprayed concrete must be sufficiently rapid to allow thicker layers of new sprayed concrete to be applied to the freshly sprayed concrete and to prevent the layers from falling off the substrate.

The state of the art

In the past, e.g., accelerators for bonding cement systems have been used, e.g. calcium chloride, but the chloride anion promotes corrosion in concrete. Alkaline accelerators, which have replaced chloride additives, pose a high risk of alkali metal concentration and alkaline pH.

-2 handling such acceleration and create difficult working conditions, especially the unfriendly atmosphere, when sprayed concrete is applied at e.g. tunnel construction.

In addition to the rapid setting and hardening of fresh sprayed concrete, an important feature that accelerators for sprayed concrete have is to ensure that the final compressive strength of sprayed concrete does not fall by more than 15% compared to the reference concrete - standard (European proposal y> Admixtures for Sprayed Concrete-Definitions, Requirements, Conformity, Marking, Labeling, prEN 934-5). The alkaline aluminate-based alkali accelerators already mentioned do not reach the prescribed ultimate strengths as stipulated in the aforementioned standard.

The mentioned weaknesses and regulations, respectively. standards (prEN 934-5) dealing with injection molded concrete additives have led to the development of non-alkaline accelerators (alkali metal content expressed as equivalent to O <1%) or little alkaline accelerators that successfully solve some problems associated with alkali additives. Despite the accelerated development of building materials over the last decade, there are a number of shortcomings and weaknesses in liquid accelerators for cement systems that are not addressed or accessible by the available literature. does not offer adequate solutions.

In addition to the requirements that can be found in the aforementioned standard, liquid non-alkaline accelerators must also satisfy other criteria, which are determined to the greatest extent by the market. The acceleration must be stable - that is, it does not deteriorate over time, does not turn brown, does not gel, or is cloudy for at least several months. While this criterion is not a prerequisite for successful application, it is practical for the liquid to be stable or stable. that over time a reasonable period does not fall, e.g. 3 months.

The basis of most published patents dealing with non-alkaline accelerators is amorphous aluminum hydroxide and usually aluminum sulfate. The aqueous solution of these two substances mixed in an appropriate ratio, respectively. a product of the reaction between these substances, has been known to be an effective accelerator for the hardening of cement systems for over 20 years (patent US 4507152, Buerge et al.).

-3Most of the publicly available inventions report only modifications to the basic formulation that lead to improved stability of the liquid accelerator, which may be a clear liquid or suspension, better activity or higher ultimate or initial compressive strength.

As a stabilizer, ie. a component that stabilizes a solution of aluminum hydroxide and aluminum sulfate, carboxylic acids are used according to patent EP0946451, most commonly formic acid according to patent US6723163B1. Other stabilizers such as the ortho phosphoric acid H3PO4 and its non-alkaline salts are also used (Hofmann, US 6692564 B2).

In addition to aluminum sulphate, US6302954 mentions aluminum carbonate, but this formulation, despite its high concentration of 10 wt% relative to cement, exhibits excessive curing times of over 7 min.

In addition to all the above components, which can be found in various formulations, the authenticity of amines, in particular diethanolamine, can be found in all formulations, which has a positive effect on reducing the bonding time or increasing the strength of freshly sprayed concrete.

For all the formulations presented, it can be summarized that the required concentration of liquid accelerator relative to cement is high and the end times of curing are long.

The latest generation of non-alkaline accelerators have the same basis as previous non-alkaline accelerators, and they have been added with hydrofluoric acid, HF, which, according to published patents, provides more accelerator activity. Despite their good activity, some such accelerators with HF do not provide high strength of sprayed concrete, especially during the first hours of hydration (WO 2007/022852 A2). The problem with non-alkaline accelerators containing HF is also the synthesis of such a product known to the expert public as an extremely dangerous, aggressive and reactive compound.

Sommer et al. In US6537367 B2 report water-soluble fluorides which, as one of the key components in the accelerator, have a beneficial effect on the initial binding, but no fluorine compounds other than HF are found in the claims or the description of the invention. Also elsewhere in the literature, e.g. in the published patent

-4report W0 03/106375 no fluorine compound other than HF can be detected. Some patent documents report fluoroaluminates, but then no other fluoro compound other than HF can be found in the description of the invention. The author of published patent application US 2007/0044686 claims that fluoroaluminates are formed by the reaction between HF and aluminum hydroxide and aluminum sulfate.

Despite the favorable properties exhibited by HF accelerators, the synthesis of such a product is very demanding, since HF, due to its exceptional reactivity, is a dangerous component in the synthesis of such accelerators and at the same time presents a great potential environmental hazard. The HF concentration added to the accelerator varies between 5-20% according to published patents and patent applications.

The accelerator formulation in US 6537367 B2 is very similar to patent application US 2007/0044686 A1, except that the fluoride solution of the aluminum salt is formed by the reaction between aluminum sulfate and HF, or. between aluminum sulfate, HF and aluminum hydroxide and one or more lithium salts.

WO 2007/022852 A1 discloses the composition of a liquid non-alkaline accelerator as the product of a reaction between aluminum hydroxide, aluminum sulfate and HF at a temperature above 50 ° C. H3PO4 or its salts, boric acid, etc. are referred to as the stabilizer in this application.

A common feature of the latest generation of non-alkaline accelerators is the addition of HF to aluminum sulfate and hydroxide, which acts as a reaction component in the synthesis of accelerators in all formulations. No patented fluorine compound other than HF is found in any of the patents filed and published. The synthesis of accelerators, where as one of the components, i.e. reactants, HF occurs, is extremely challenging due to the aggressiveness and reactivity of this acid, especially if the HF content of such formulation is significant. The technological process and equipment in such synthesis is much more demanding than in the case where aggressive HF is not present among the reactants.

The object and object of the invention is the synthesis of accelerated binding and curing, i. a liquid additive for Portland cement systems, characterized by rapid bonding and an increase in concrete strength at low accelerations at low doses, in the form of liquid non-alkaline or slightly alkaline accelerators without chloride ions, for which HF is not required.

Description of the invention

Throughout the text,% are meant as weight%.

A formulation for liquid non-alkaline or slightly alkaline accelerators without chloride ions for which HF is not required is presented. The enhanced activity of accelerating the bonding of Portland cement systems and the favorable initial and final compressive strengths of cement systems (eg injection molded concrete) favor various fluorine compounds. Among the fluorine compounds that can be used in the synthesis of the accelerator, the cryolite bath has significant advantages over other fluorine compounds (HF, alkali fluorides, alkali fluoroaluminates and other metal fluoroaluminates). Cryolite bath is a waste product of aluminum production and contains (Al, F, Na, K). The approximate elemental composition of the cryolite bath is: w (Al) = 0.162; w (F) = 0.525; w (Na) = 0.302, where w represents the mass fraction. Cryolite bath is a powder material of metallic greyish color.

The basis of the liquid non-alkaline accelerator is an aqueous solution of aluminum sulfate (may also be another water-soluble sulfate that lowers the pH of the solution) to which a cryolite bath is added. Non-alkaline accelerators for cement binding and hardening contain a significant proportion of aluminum hydroxide, but when any of the fluorine compounds mentioned in the liquid accelerator is present, the need for amorphous aluminum hydroxide - with the same activity accelerated - is less than if the compounds were not synthesized in the synthesis process. . For good stabilization of the aluminates, a liquid accelerator can be added, e.g. monocarboxylic or dicarboxylic acid and stabilizer - a dispersant that stabilizes the suspension of the liquid phase and solids resulting from precipitation of the liquid product or unreacted reactant components.

The fluorine compounds which can be used have a beneficial effect on the activity of the accelerator and also stabilize the liquid accelerator. The stability of the product also depends on other parameters, among which

-6Aluminum sulphate (Al2 (SO4) 3.14H ₂ O) concentration not exceeding 50%, aluminum hydroxide concentration and the presence of certain known stabilizers such as carboxylic acids, dicarboxylic acids, mineral acids, e.g. H2SO4, H3PO4 etc. and various salts of these acids.

The liquid additive of the invention can be described as slightly or non-alkaline. According to the invention, the reaction product, at a temperature above room temperature, between aluminum sulfate, cryolite bath and / or various fluorine compounds and / or amorphous aluminum hydroxide and / or formic acid or other mineral, mono or dicarboxylic acid and / or salt these acids and / or diethanolamine, triethanolamine and / or a different mixture of water-soluble amines and / or a stabilizer-dispersant e.g. with hydrated magnesium silicate.

The reaction product is suspension.

The liquid accelerator can be prepared by the following procedure:

A crystallite bath is partially introduced into the aqueous solution of aluminum sulfate, which is partially soluble in an aqueous solution of sulfate or a mixture of cryolite bath and other fluoro compounds. The concentration of sulfate (as Al2 (SO ₄ ) 3.14H ₂ O) in water is usually about 40%, the cryolite bath equivalent (F) is between 0.1 and 15%, but usually about 10%. The reaction is conducted at a temperature higher than room temperature, preferably at 75 ° C. This reaction step is completed when the concentration of F 'ions reaches a constant value. Amorphous aluminum hydroxide can then be added to the solution / suspension. The concentration of amorphous aluminum hydroxide may be between 0 and 20%, but usually about 6%. This reaction step is run at 40 ° C. Then a stabilizer-dispersant is added to the reaction mixture, e.g. hydrated magnesium silicate. Mono or di-carboxylic acid, a salt of this acid or a mixture of acid and salt can be added to the solution / suspension to improve the activity and stability of the solution. The acid concentration, among these preferably formic acid (HCOOH), may be between 0 and 10%, usually about 1%. The presence of diethanolamine, triethanolamine, EDTA or other water-soluble amines (0-10%, usually 2%) in the accelerator can further improve the binding time and the increase in initial and final compressive strength.

-ΊThe bonding enhancer of the invention may be added between 1 and 10% by weight of cement depending on the type of cement.

The features of the invention are further described in the following embodiments.

Examples

Table 1 presents the various formulations of liquid accelerators, numbered 1-4, which differ in synthesis temperature and chemical composition, and have been used in the following examples.

Aluminum sulfate represents AhCSO ^ .MHiO, also called 17% AI2O3 aluminum sulfate. A different form of water-soluble aluminum sulfate may be used in place of said sulfate.

A cryolite bath is a waste product in a particular aluminum electrolysis process. It is basically cryolite (sodium hexafluoroaluminate) which changes chemically during electrolysis. The weight percentages of fluorine, aluminum and sodium are similar to those in cryolite (e.g. w (F) = 0.52; w (Al) = 0.16; w (Na) = 0.30).

According to the invention, other fluorine compounds and / or cryolite baths which are soluble or partially soluble or in water and / or in an acidic solution of aluminum sulfate, or which decompose to more basic ions (e.g., fluorides, may be used) ). These compounds may be fluorides, fluoroaluminates, fluorosilicates, fluoroborates, etc.

Aluminum hydroxide is an amorphous aluminum hydroxide, A1 (OH) 3. The crystalline form of hydroxide with a sufficiently low granulation, or a sufficiently low granulation, may also be used in the synthesis. in the presence of a sufficiently strong acid where such hydroxide melts. In the synthesis, a mixture of crystalline and amorphous hydroxide may also be used depending on the type of components used, and especially the pH.

-8Diethanolamine represents a 90% solution of diethanolamine of the empirical formula C4H11NO2.

Formic acid represents 85% aqueous HCOOH.

The remaining up to 100% for each formulation is water.

-9Table 1.

Formulation Temperature synthesis Aluminum sulfate Cryolite bath Aluminum hydroxide Dietanol- amine Ant acid Stabilizer dispersant 1 75 ° C 44% 15% / / / 2% 2 85 ° C 42% 10% 4% / / 1.5% 3 70 ° C 38% 15% 5% / / 2% 4 75 ° C 37% 10% 4% 2% 2% 1.5%

Example 1:

To test the bonding of cement mortar, i. how quickly the accelerator reacts with the mineral components of Portland cement, the Vicat method was used. The recipe for the mortar was as follows:

450 g cement (CEM II A-C, 42.5 R) Anhovo

1350 g standard sand

190 g water

3.15 g superplasticizer (Zeta Super S, TKK, Srpenica).

Table 2 shows the end times of Vicat bonding by type of accelerator and the concentration of accelerator, expressed in weight% by weight of cement. The first column in Table 2, Formulation, represents the different types of accelerators according to the invention numbered from 1 to 4. These formulations are presented more precisely in Table 1. The second column indicates the amount of accelerator added to the mortar,% means the mass of the accelerator relative to to the mass of cement. For the recipe mortar presented above, e.g. dosage accelerated 8% weight 36 g. The third column shows the end times of the binding, where (') indicates minutes and () seconds.

-10Table 2.

Formulation Accelerated dosage (%) End time of binding 1 8 3'20 2 7 3 ' 3 7 1'35 6 2Ί0 5 6'30 ” 4 6 Γ30 5 3'40 ” 4 7'30 ”

Example 2:

In Example 2, the compressive strength of the mortar was determined at different times from the beginning of the bonding, respectively. after the accelerator was added to the mortar. Compressive strengths were determined by two different methods. The strength of fresh concrete, that is up to about a few hours, respectively. up to 1.3 Mpa were determined by a pneumatic device for measuring the thrust, and strengths exceeding 1.3 MPa were determined in accordance with EN 196/1 for a sample dimension of 40 mm x 40 mm x 160 mm.

Table 3 presents the results of compressive strength in MPa at different times from the start of lure binding to 24 hours - the hour mark is h - depending on the type of formulation and dosage accelerated.

Table 3.

Formulation Dozacija accelerated (%) Compressive strength (MPa) 1 h 2h 3 h 5h 24 h 1 8 0.3 0.8 1.0 1.3 22.3 2 6 0.5 0.7 1.1 1.5 17 4 6 0.7 1.1 1.5 3.0 18

Liquid accelerator for the bonding and curing of Portland cement systems. formulation comprising a cryolite bath and / or at least one fluorine compound which may be fluoride, fluoroaluminate, fluorosilicate, fluoroborate ... soluble or partially soluble or in water and / or in an acidic solution or which in pH neutral or acidic medium decomposes to more basic ions and from at least one water-soluble sulfate which lowers the pH of the solution between these preferably 17% A1 ₂ O ₃ aluminum sulfate and / or from amorphous or crystalline aluminum hydroxide, depending on the pH of the previous solution and / or additionally containing stabilizers of liquid solution that act as complexants or as an anion source that prevent the further hydration of aluminum compounds, especially aluminum hydroxide, among these stabilizers preferably mono and / or di carboxylates and / or fluorides, fluoroaluminates, fluorosilicates, fluoroborates, borates , phosphates, sulfates, carboxylates, their salts, acids or mixtures of the foregoing and / or additionally consisting of amines, among which tannolamine, and consisting of a stabilizer dispersant (e.g. hydrated magnesium silicate) that stabilizes the resulting suspension. The concentration of 17% AI2O3 aluminum sulfate in the accelerator may be between 25-55%, cryolite baths, fluoride, fluoroaluminate, fluorosilicate, fluoroborate or other fluorine compound expressed as equivalent (F ') between 0.1-10%. The concentration of amorphous aluminum hydroxide is between 0-20% and the formic acid concentration is between 0-5%. Diethanolamine can be added to the accelerator between 0-10%. Stabilizer - dispersant is added to the accelerator between 0.5-5%. The suspension accelerated. The accelerator is used for bonding and curing Portland cement systems, especially injection molded concrete.

Claims (8)

Patent claims - (. Liquid accelerator for the binding and curing of Portland cement systems or formulations, characterized in that it consists of a cryolite bath and / or at least one fluorine compound, which may be fluoride, fluoroaluminate, fluorosilicate, fluoroborate or other fluorine compound, which is soluble or in water and / or in acidic solution or which decomposes into more basic ions in pH neutral or acidic medium, and from at least one water-soluble sulfate which lowers the pH of the solution between these preferably 17% AI2O3 aluminum sulfate and / or from amorphous or crystalline aluminum hydroxide, depending on the pH of the stock solution and / or additionally containing stabilizers of liquid solution that act as complexants or as a source of anions that prevent the further hydration of aluminum compounds, especially aluminum hydroxide, among these stabilizers, preferably mono and / or dicarboxylates and / or fluorides, fluoroaluminates, fluorosilicates, fluoroborates, borates, phosphates, sulfates, their salts, acids or mixtures thereof of these substances and / or additionally consists of amines, among which preferably diethanolamine, and consisting of a stabilizer, a suspension stabilizing dispersant. 2. The accelerator of claim 1, wherein the concentration of 17% AI2O3 aluminum sulfate is between 25-55%. The accelerator according to claim 1, wherein the concentration of the cryolite bath and / or fluorides, fluoroaluminates, fluorosilicates, fluoroborates is expressed as equivalent (F) between 0.1-10%. The accelerator according to claim 1, wherein the concentration of amorphous aluminum hydroxide is between 0-20%, The accelerator according to claim 1, wherein the formic acid concentration (HCOOH) is between 0-5%. The accelerator according to claim 1, wherein the diethanolamine concentration is between 0-10%. An accelerator according to claim 1, wherein the concentration of stabilizer dispersant (hydrated magnesium silicate) is between 0.5 and 5% 7. Accelerator according to the preceding claims being a suspension. Use of the accelerator according to the preceding claims as an adjunct to accelerate the bonding and curing of Portland cement systems, especially injection molded concrete.