SI23320A - Accelerator for setting and hardening of portland cement systems - 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 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 fluorides, fluoroaluminates, fluorosilicates, fluoroborates, borates, phosphates, sulphates, carboxylates, 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 which can be run at a room temperature.

Description

An accelerator for the bonding and curing of Portland cement systems

The subject of the invention is a liquid accelerator for the binding and hardening of Portland cement systems, which is small 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. Accelerator is characterized by simple synthesis.

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. Due to the high concentration of alkali metals and alkaline pH, alkaline accelerators that have replaced the chloride additives present a risk of handling such accelerators and create difficult working conditions, especially the unfavorable atmosphere when sprayed concrete is applied at e.g. tunnel construction.

-2In addition to the rapid bonding and curing of freshly sprayed concrete, an important feature that accelerators for sprayed concrete have is to ensure that the ultimate compressive strength of sprayed concrete does not fall by more than 15% relative to the reference concrete - standard (European Standard 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 Na ₂ O <1% equivalent) 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 quite a few 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.).

Most 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.

-3As 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 H ₃ PO ₄ 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. no fluorine compound other than HF can be found in published patent application WO 03/106375. 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 to accelerate synthesis for binding and curing, i. a liquid admixture for Portland cement systems, characterized by rapid bonding and an increase in concrete strength at low accelerator doses, in the form of liquid non-alkaline or slightly alkaline accelerators without chloride ions, for which H F is not required.

-5Description 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. Improved accelerating activity on the bonding of Portland cement systems and the favorable initial and final compressive strength of cement systems (eg injection molded concrete) favor various fluorine compounds. 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 aluminum hydroxide may be added. Fluoride compounds that can enhance the activity of a liquid accelerator are, according to the invention, fluorides, fluoroaluminates, fluorosilicates, fluoroborates and other compounds that are soluble either in water and / or in acidic aqueous solutions or in pH neutral or acidic media decompose to more basic building blocks , most often to fluoride anions. Among the fluorides, more specifically, HF, KF and other fluorides, from fluoroaluminates Na ₃ AlF6 and other alkali, earth-alkali and other fluoroaluminates, from fluorosilicates ZnSiFg and MgSiF ₆ , from fluoroborates NaBF4, etc. Some of these fluorine compounds are of natural origin, others are synthetically produced, but as a source of fluorine are technologically simpler compounds than extremely reactive and dangerous HF, which, according to published patents or patent applications, can be found as one of the components of liquid non-alkaline accelerators. 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 these compounds were not synthesized in the synthesis process. .

For non-alkaline accelerators, the requirement of European standard prEN 934-5 is that the concentration of alkali metals expressed as Na ₂ O does not exceed 1%. If the concentration of alkali metals exceeds this value we are talking about a little alkali accelerators. To satisfy the condition Na ₂ O <l%, an accelerator can be added, e.g. 2.2% Na ₃ AlF ₆ to be regarded as non-alkaline according to the European standard prEN 934-5.

-6Fluoro compounds that 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 we can highlight the concentration of aluminum sulfate (A1 ₂ (SO ₄ ) 3.14H ₂ O), which should not exceed 50%, the concentration of aluminum hydroxide and the presence of some known stabilizers, such as carboxyl 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, is a fluorine compound that is soluble either in water and / or in an aqueous solution of aluminum sulfate (eg cryolite - (Na3AlF ₆ )) or a mixture of different fluorine compounds and / or amorphous aluminum hydroxide and / or ortho phosphoric acid, another mineral, mono or dicarboxylic acid and / or a salt of these acids and / or diethanolamine.

The reaction product is a clear or slightly cloudy solution or, if the reaction is conducted at a temperature above 80 ° C, a suspension.

The liquid accelerator can be prepared by the following procedure:

A fluorine compound soluble in aqueous sulfate is introduced into an aqueous solution of aluminum sulfate, e.g. cryolite. The concentration of sulfate (as Al2 (SO ₄ ) 3.14H ₂ O) in water is usually about 40%, and the cryolite as equivalent (F ') is between 0.1 and 20%, but usually about 2%. Amorphous aluminum hydroxide can then be added and stirred at a temperature higher than room temperature, preferably at 35 ° C, until a clear or slightly cloudy liquid is obtained. The concentration of amorphous aluminum hydroxide may be between 0 and 20%, but usually about 6%. Impurities can be filtered. Phosphoric acid, a salt of this acid, or a mixture of acid and salt can then be added to the solution, thereby improving the stability of the solution. The acid concentration can be between 0 and 10%, usually about 1%. The presence of diethanolamine or triethanolamine or EDTA (0-10%, usually 2%) in the accelerator may further improve some of the characteristics of the liquid supplement.

-7The bonding enhancer of the invention may be added between 1 and 10% by weight of the cement system 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 is also called 17% AI2O3 aluminum sulfate.

A different form of water-soluble aluminum sulfate may be used in place of said sulfate.

Cryolite represents Na ₃ AlF6 - sodium hexafluoroaluminate. It is irrelevant to the invention whether this mineral is in crystalline or amorphous form, it can be both synthetic and natural. According to the invention, other fluorine compounds may be used which are soluble either in water and / or in an acidic solution of aluminum sulfate, or which decompose into more basic ions (e.g., fluorides) in aqueous or acidic media. These compounds may be fluorides, other 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.

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

Phosphoric acid accounts for 85% of H3PO4.

-8The remainder of up to 100% for each formulation is water.

-9Table 1.

Formulation Temperature synthesis Aluminum sulfate Cryolite Aluminum hydroxide Dietanol- amine Phosphorus acid 1 60 ° C 48% 4% / / / 2 85 ° C 48% 4.7% 4% / / 3 50 ° C 44% 4.3% 5.4% / / 4 30 ° C 39% 4,5% 7,8% 2% 1%

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 2'50 2 6 2 ' 3 7 Γ15 6 1'45 5 2'30 ” 4 6 T20 5 Γ40 4 3'30

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 0.5 0.7 0.8 1.3 22.3 2 6 0.6 0.9 1.1 1.5 19 3 6 0.7 1.0 1,2 1.9 19

Example 3:

The stability of the liquid additive at non-alkaline and low-alkaline accelerators is particularly important since many of the formulations presented in the patents do not have a sufficiently long stability time for successful commercial use. Usually, the shelf life of commercial accelerates, ie. stability, limited to a minimum of 3 months, which represents a minimum time for product use for efficient commercial use. In Example 3, therefore, the stability time is limited to a period of 3 months, although some formulations of the invention are also stable for a much longer period of time.

The stability information of formulation 2 as a function of time is not given in this specification, since this product is a suspension, unlike other formulations that are clear or cloudy homogeneous liquids. Suspension or suspension stability solid phase deposition can be achieved by dispersants for inorganic dispersion acids.

The stability of the samples was monitored at four different temperatures: -5 ° C, 5 ° C, 20 ° C and 30 ° C. Good stability was observed at all samples and at all temperatures, indicated in Table 4 by the expression Ok, only at formulation 4 crystals can be observed at -5 ° C. The crystals of Formula 4 are formed at 4 weeks, and in Table 4 this state is indicated by the term Ok *. Formulation 3, unlike the other two presented in Table 4, is not a clear solution, but a cloudy liquid, which is equally active, that is, has the same effect on embroidery as a clear liquid of the same formulation. The opacity of this formulation depends on the temperature and at 20 ° C it becomes cloudy after 4-6 weeks.

Crucial to the stability of the non-alkaline or low-alkaline liquid accelerator is both the concentration of the individual components in the formulation as well as the ratio between them and the temperature of the synthesis accelerator.

Table 4.

Formulation 2 weeks 4 weeks 6 weeks 8 weeks 10 weeks 13 weeks 1 Okay Okay Okay Okay Okay Okay 3 Okay Okay Okay Okay Okay Okay 4 Okay Ok * Ok * Ok * Ok * Ok *

-12The markings in Table 4 are as described above: Ok - good stability at all temperatures Ok * - crystals form on the formulation.

Liquid accelerator for the bonding and curing of Portland cement systems. formulation, characterized in that it consists of at least one fluorine compound, which may be fluoride, fluoroaluminate, fluorosilicate, fluoroborate ..., which is soluble or in water and / or in acidic solution or which decomposes in a pH neutral or acidic medium to more base ions and from at least one water-soluble sulfate that 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 previous solution and / or additionally containing stabilizers of the liquid solution acting as complexants or as a source of anions that prevent the further hydration of aluminum compounds, especially aluminum hydroxide, among these stabilizers preferably fluorides, fluoroaluminates, fluorosilicates, fluoroborates, borates, phosphates, sulfates, carboxylates, their salts, acids or mixtures of the aforementioned substances and / or additionally amines, among these preferably diethanolamine. The concentration of 17% AI2O3 aluminum sulphate in the accelerator may be between 25-55%, fluoride, fluoroaluminate, fluorosilicate, fluoroborate or other fluoro compound expressed as equivalent (F ') between 0.1-10%. The concentration of amorphous aluminum hydroxide is between 0-20% and the concentration of phosphoric acid (H3PO4) is between 0-5%. Diethanolamine can be added to the accelerator between 0-10%. The accelerator is a clear or cloudy solution or suspension depending on the synthesis temperature. The accelerator is used for bonding and curing Portland cement systems, especially injection molded concrete.

Claims (8)

Patent claims 4.Current accelerator for bonding and curing Portland cement systems formulation, characterized in that it consists of 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 in pH neutral or acidic medium to more basic ions and from at least one water-soluble sulfate that 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 previous solution and / or additionally containing stabilizers of the liquid solution acting as complexants or as a source of anions that prevent the further hydration of aluminum compounds, especially aluminum hydroxide, among these stabilizers preferably fluorides, fluoroaluminates, fluorosilicates, fluoroborates, borates, phosphates, sulfates, carboxylates, their salts, acids or mixtures of the aforementioned substances and / or additions consists of amines, preferably diethanolamine. 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 fluoride, fluoroaluminate, fluorosilicate, fluoroborate or a mixture of different fluorine compounds 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 concentration of phosphoric acid (H3PO4) is between 0-5%. The accelerator according to claim 1, wherein the diethanolamine concentration is between 0-10%. An accelerator according to the preceding claims, which is a clear or cloudy solution or 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.