RU2096372C1 - Method of preparing multifunctional concrete modifier and multifunctional concrete modifier - Google Patents

Abstract

FIELD: manufacture of building materials. SUBSTANCE: invention relates to methods of preparing multifunctional modifiers based on microsilica supposed to improve properties of concrete mixes and concretes. Objective of invention is to develop such a process and modifier makeup that final product were more fabricable and transportable and chemical additives in modifier affected properties of concrete mix for a long time. Process of invention consists in mixing microsilica with additive followed by drying and granulation. As additive, plasticizing agent, or mixture thereof with hardening regulator, or mixture of the both with anti- frost agent and/or with air-entraining agent, or mixture of plasticizing agent with anti-frost agent and/or air-entraining agents is used. All modifier's components are mixed in amounts: 25-70 wt % microsilica, 2-10 wt % additive, and water (the balance) to produce flowing suspension. The latter is dried and granulated in air flow at 120-270 C and air flow 3.0 to 15.0 cu.m/s to form granules up to 500 mcm in size containing 77.2-94.0 wt % microsilica, 4.7-15.7 wt % additive, and water (the balance). Modifier of invention is distinguished by including, as additive, plasticizing agent or mixture thereof with hardening regulator, and/or with air-entraining agent, and/or with anti-frost agent, initial mixture having flowing consistence and contains 25-70 wt % microsilica, 2-10 wt % additive. EFFECT: improved concrete quality. 2 cl, 2 tbl

Description

A known method of producing a modifier (complex additives) based on silica fume (MK), including the introduction into an aqueous suspension of MK sodium sulfate (23 25 wt. MK) and sodium nitrite (5 wt. Sodium sulfate). In this case, a pasty product of 20-30% concentration is obtained [1] The disadvantages of the method are the tendency of the obtained pasty material to delaminate and freeze (this virtually eliminates the possibility of long-term transportation at low temperatures), as well as the need to combine such a material with the required component of concrete with MK plasticizer ( combination requires separate processing lines for the reception, storage and supply of plasticizer). The closest in technical essence and the achieved result is a method of preparing a complex modifier, including preliminary compaction of MK by passing through the rollers and subsequent mixing with a chemical additive in a drum mixer at a temperature of 0 100 ^o C [2]
The disadvantage of this method is the inefficiency of the process of mixing and drying MK with chemical additives in a drum mixer, which affects the humidity of the finished product. In particular, when drying for 15 minutes at 100 ^° C, the humidity reaches 18%, which makes the product easily susceptible to freezing and, during long-term transportation and storage, leads to self-compaction ("caking") and a decrease in the flowability of the material.

Other disadvantages of the method are the low bulk density of the finished product (within 450 kg / cm ³ ), which leads to high costs during transportation of the material, as well as the short duration of the chemical additives contained in the material on the properties of concrete mixtures, which affects, in particular, a relatively rapid loss of plasticity of mixtures.

Known complex modifier of concrete obtained from the dried, granular source mixture containing silica fume, chemical additive and water [2]
The technical problem is to develop such a method for preparing a complex modifier of concrete and its composition, in which the resulting modifier would have a low relative humidity, therefore be less susceptible to freezing, have a higher bulk density, therefore it would be more technological and transportable, and contained in the modifier chemical additives would have a lasting effect on the properties of the concrete mixture, in particular, would contribute to the long-term preservation of plasticity .

 The problem is solved in such a way that in the method of preparing a complex concrete modifier, comprising mixing silica fume with a chemical additive and water, followed by drying and granulation, a plasticizing additive or a mixture of a plasticizing additive and a hardening regulator, or a mixture of a plasticizing additive and a hardening regulator are used as an additive with an anti-frost additive and / or with a water-entraining additive, or a mixture of a plasticizing additive with an anti-frost and / or air-involving additive ami, and all components of the modifier are mixed in the ratio, wt.

Silica fume 25 70;
Chemical additive 2 10;
Water Else
to obtain a fluid suspension, and drying and granulation is carried out in a gas-air stream at a temperature of 120,270 ^o C and a flow rate of 3.0 - 15.0 m ³ / s to obtain granules up to 500 μm in size with a relative humidity of 1 8% in the following ratio of components the resulting modifier, wt.

Silica fume silica 77.2 94.0
Chemical additive 4.7 15.7
Water Else
The problem in terms of the composition of the complex modifier obtained from the dried, granular source mixture containing silica fume, a chemical additive and water is solved due to the fact that a plasticizing additive or a mixture with a hardening regulator and / or with an air-entraining additive is used as a chemical additive / or with an anti-frost additive, while the initial mixture has the consistency of a fluid suspension and contains components in the following ratio, wt.

Silica fume 25 70;
Chemical additive 2 10;
Water Else
and drying the suspension and granulation is carried out in a gas stream with a temperature of 120,270 ^o C at a flow rate of 3.0 to 15.0 m ³ / s to obtain granules up to 500 μm in size with a relative humidity of 1 8% in the following ratio of components of the complex modifier, wt.

Silica fume silica 77.2 94.0
Chemical additive 4.7 15.7
Water Else
The proposed method differs from the prototype in that the obtained modifier of the powdered tempering form has an increased bulk density of more than 600 kg / m ³ and the effect of the action of the chemical additives contained therein increases, which is expressed in preserving the plasticity of concrete mixtures for a longer time.

 The process of preparing a powdered complex modifier is a two-stage process. Pre-prepared aqueous suspension of MK and chemical additives necessary to give concrete mixtures and concretes of various properties. Molecules of chemical additives present in the suspension are adsorbed on the surface of MK particles, forming adsorption layers. At the drying stage, aggregation of MK particles surrounded by adsorption layers occurs, granules are formed, which are clumps of MK particles with dehydrated and hardened water-soluble layers of chemical additives.

 The size of the obtained granules, not exceeding 500 microns, and relative humidity in the range of 1 8% provide a relatively high bulk density of the powdery material.

 In the preparation of concrete mixtures, during the mixing of the components, the granules of the modifier are disaggregated, and chemical additives enter the liquid phase as the interlayers dissolve between the MK particles. The "batch" intake of superplasticizer and other additives in the liquid phase is the main factor ensuring the long-term preservation of the plasticity of the concrete mixture, as well as the prolongation of the effects initiated by other additives (air-entraining, hardening regulators, etc.).

 The consistency of the prepared mixtures and the properties of hardened concrete depend on the ratio of the components of the powdery modifier.

 Thus, the proposed method for preparing a complex modifier allows you to solve the problem and meets the criteria of "novelty" and "inventive step".

 A method of preparing a complex concrete modifier is carried out in the following way.

Water 20 58% chemical additives 2 10% and MK 25 70% are loaded into the mixer and mixed until a fluid and homogeneous suspension of 30 - 80% concentration is obtained. The resulting suspension is fed to a drying unit, where it is granulated and dried in a stream of hot air or gas with a temperature of 120,270 ^° C and an air or gas flow rate of 3.0 15.0 m ³ / s. This results in a powdery product with granules up to 500 microns in size and a relative humidity of 1 8%
Example
The following materials were used to prepare the complex modifier
1. As the main mineral component, silica fume (MK) grade MK-85, corresponding to TU 4325-001-02495336-96 "Condensed silica fume. Technical conditions".

2. As chemical additives, materials traditional for concrete technology of different classes:
the rheological properties regulator (plasticizing additive) is a S-3 superplasticizer (S) based on the sodium salt of the condensation product of β-naphthalene sulfonic acid and formaldehyde, corresponding to TU-6-36-0204229-625-90 ^** "S-3 plasticizer. Specifications ";
hardening regulator (retarder) nitrilotrimethylphosphonic acid (NTF), corresponding to TU 6-09-5283-83 ^** "Nitrilotrimethylphosphonic acid, heat-resistant pure. Technical conditions";
antifrosty additive sodium nitrite (NN), corresponding to GOST 1990-74 "Technical sodium nitrite. Technical conditions";
structure regulator (air entraining additive) neutralized air entrainment resin (START), corresponding to TU 13-0281078-75-90.

 The classification of the above additives is given by their effect on the properties of concrete mixtures and concrete in accordance with GOST 24211-91 "Additives for concrete. General technical requirements".

From the above materials, aqueous suspensions of a concentration of 30 to 84% were prepared in a high-speed mixer. The resulting suspensions were fed to a drying unit with a capacity of 50 m ³ with an inert carrier, in which they were sprayed using nozzles and dried in an air and gas stream. The temperature of the gas-air flow at the inlet to the drying unit 110 - 280 ^o C, and the flow rate of 2.5 15.5 m ³ / s.

 As a result, powdered materials were obtained, which are essentially complex organo-mineral concrete modifiers. The moisture content of the obtained materials varied from 1 to 10%, while the granule size was up to 600 μm.

 Samples of modifiers according to the prototype method were prepared by compaction with a force of 10 MPa, moistened up to 30% MK on a roller type roller press with drying in a drum granulator together with chemical additives.

The freezing temperature of the obtained products was determined by visual assessment of the behavior of the material with decreasing temperature by the change in flowability (angle of repose). When exceeding the angle of repose of 20 ^o , the flowability was considered unsatisfactory. Accordingly, the optimal moisture range of the material was determined: the freezing temperature and, accordingly, the angle of repose are associated with relative humidity.

 Bulk density was determined by the volumetric mass method, and the maximum size of the powder granules by sieving the material.

 The dispersion of the obtained material was considered optimal if the strength of concrete with the introduction of a powdery modifier did not decrease compared to a control sample of concrete with a modifier prepared by the prototype method.

The compositions of concrete mixtures with modifiers prepared according to the prototype and the proposed method were taken the same: cement 300 kg / m ³ ; sand 730 kg / m ³ ; crushed stone 1120 kg / m ³ ; water 165l / m ³ . Modifier samples were injected into the concrete mixture at the rate of 15% MK by weight of cement.

Concrete mixtures were prepared using Portland cement M400 (GOST 10178), quartz sand with M _cr 2.1 (GOST 8736), and crushed granite crushed stone. 5 20 mm (GOST 8267). The plasticity of the prepared mixtures was evaluated by the standard cone sludge, the strength of concrete by testing specimen cubes with a rib size of 10 cm, solidified under normal conditions.

In the table. 1 shows the ratio of the components of the suspension intended for further drying, the main technological parameters and the composition of the finished samples of the modifier according to the proposed method in comparison with the modifier obtained by the prototype method. In the table. 2 shows the basic physical properties of modifier samples and the properties of concrete mixtures and concrete. As can be seen silt table. 2 samples NN 8 10 and 12 20 have low humidity and, accordingly, low freezing temperature. Samples NN 11 and 21, having a relatively high humidity, are prone to freezing at a temperature of -8 and -10 ^o C, do not allow to solve the problem, because do not exceed the prototype and therefore are excluded from subsequent tests.

 The introduction of MK and chemical additives in the form of a complex powdery modifier prepared by the proposed method (with the exception of sample No. 16) leads to an increase in concrete strength, and the plasticity of concrete mixtures is practically not lost after 120 minutes (Table 2). The mixtures prepared with modifiers obtained by the prototype method (samples NN 1 7, table. 1), there is a sharp drop in ductility, which in 120 minutes reaches the level of OK 0 1 cm. Using a complex powdery concrete modifier with a granule size more than 500 microns (sample N 16, table. 1), along with the positive effect of preserving the plasticity of concrete mixtures after 120 minutes, leads to a decrease in concrete strength compared to sample N 5 on an analog modifier prepared according to the prototype. This is obviously due to the insufficient degree of disaggregation of relatively large particles of the modifier when mixing the components of the concrete mixture.

Thus, from the table. 1 and 2 of the results it is seen that the proposed method of preparing a complex powdery modifier has the following advantages:
the obtained powdery material at low relative humidity has a significantly low freezing point, has good flowability and does not cake even with a twice as high bulk density;
concrete mixtures of the same composition have higher ductility and practically do not lose it when stored for 2 hours;
concretes of the same composition have higher compressive strength.

 The complex concrete modifier obtained by the proposed method is called: "MB-01 brand concrete modifier". The modifier is marked as follows: MB 8-01, MB 10-01, MB 12-01, MB 14-01. The first digital index indicates the amount of plasticizing additive in the modifier, and the second (01) indicates the presence of a hardening regulator, air-entraining and anti-frost additives in the modifier.

Claims (1)

 1. A method of preparing a complex concrete modifier, comprising mixing silica fume with a chemical additive and water, followed by drying and granulating the resulting mixture, characterized in that a plasticizing additive or a mixture thereof with a hardening regulator and / or an air-entraining additive is used as a chemical additive, and / or with an anti-frost additive, while the resulting mixture contains components in the following ratio, wt. Silica fume 25 70
Chemical additive 2 10
Water Else
moreover, mixing is carried out until a fluid suspension is obtained, and the suspension is dried and granulated in an air-gas stream with a temperature of 120-270 ^{° C.} at a flow rate of 3.0 to 15.0 m ³ / s to obtain granules up to 500 μm in size with a relative humidity of 1 8% in the following ratio of components of the obtained modifier, wt. Silica fume silica 77.2 94.0
Chemical additive 4.7 15.7
Water Else
2. A complex modifier of concrete obtained from a dried granular initial mixture containing silica fume, a chemical additive and water, characterized in that a plasticizing additive or a mixture with a hardening regulator and / or with an air-entraining additive and / or with antifrosty additive, while the initial mixture has the consistency of a fluid suspension and contains components in the following ratio, wt. Silica fume 25 70
Chemical additive 2 10
Water Else
and drying the suspension and granulation is carried out in a gas-air stream with a temperature of 120,270 ^° C at a flow rate of 3.0 to 15.0 m ³ / s to obtain granules of 500 μm in size with a relative humidity of 1 8% in the following ratio of components of the complex modifier, wt. Silica fume silica 77.2 94.0
Chemical additive 4.7 15.7
Water Else1

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