RU2516473C1 - Concrete mix - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: concrete mix includes portland cement, filler, tempering water and additive - complex solution with pH=4-5 with H₄SiO₄ sol base, besides, the specified complex solution is prepared at the following ratio of mixture components, wt %: microsilica 0.113-0.227, superplasticiser Relamix type 2 with pH=9±1 0.076-0.15, concentrated hydrochloric or acetic acid, or sulphuric acid 0.011-0.023, water 3.58-7.16 at the following ratio of concrete mix components, wt %: portland cement 22.63-22.68; filler 67.91-68.04; specified additive 3.78-7.56; tempering water 1.9-5.5.

EFFECT: higher strength of concrete during compression and reduced consumption of expensive additives of microsilica and superplasticiser.

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Description

The invention relates to building materials and can be used for the manufacture of concrete products for both civil and industrial construction.

The composition of the fine-grained concrete mixture (cement-sand mortar) is known, in the USSR author's certificate No. 675029, Mcl. C04B 31/40. In the above method of preparing a mortar, the qualitative composition of the mixture is reflected, including cement, quartz-containing fine aggregate and 5-15% by weight of sand, a solution of mineral or organic acids is introduced with a concentration of 2 · 10 ^-3 -2 · 10 ^-5 mol / l for strong and 2 · 10 ^-1 -2 · 10 ^-3 mol / l for weak acids. The disadvantages include the complication of the activation process of quartz sand, because After acid treatment, rinsing with water is recommended to prevent corrosion of metal equipment.

The known composition of the concrete mixture with the use of a complex additive with the base of sol of metacilic acid H ₂ SiO ₃ , given in the Russian patent "High-strength concrete" No. 2256630 IPC ⁷ C04B 28/04, published on March 26, 2004, in the following ratio, wt.%:

Portland cement 43.58-47.08 sand 14.43-15.69 silica-containing component represented by sol H ₂ SiO ₃ with a density of 1.014 g / cm ³ and pH = 5-6 0.25-0.27 additive - potassium ferruginous K ₄ Fe (CN) ₆ 0.44-0.47 water 12,1-12,15

Along with the advantages, there are also disadvantages:

1) a relatively high specific consumption of cement per unit of strength of 0.64-0.68% PC / MPa;

2) high water-cement ratio to obtain molding ability, i.e. W / C = 0.77-0.83;

3) ferruginous potassium is a scarce and expensive supplement.

Closest to the technical nature of the claimed invention is high-strength concrete (Yu.M. Bazhenov. Concrete technology. Publishing house of the Association of construction universities (DIA), M., 2002, p.377) containing Portland cement, silica-containing component, sand, gravel silicate flour, additive and water in the following ratio of components, wt.%

Portland cement 3.5-4.5 silica-containing component represented by silica fume 3.5-4.5 silicate flour 7.5-8.5 sand 35.9-37.8 crushed stone 41.9-43.8 superplasticizer additive 0.3-0.5 water 3,5-4,3

The advantages of the mixture include the low specific consumption of binder per unit of concrete strength of 0.35% / MPa. Along with the advantages, there are also disadvantages:

1) high consumption (3.5-4.5%) of expensive silica fume, superplasticizer (0.3-0.5%), the cost of which is higher than the cost of cement, and also requires large energy costs for fine grinding of silicate flour, which increases the cost concrete.

2) high water demand (W / C = 0.95-1.0) associated with the use of a relatively large amount of silicate flour of 7.5-8.5%;

3) low compressive strength at the age of 28 days - 54 MPa.

The objective of the invention is to improve the quality, increase the compressive strength of concrete and reduce the consumption of expensive additives of silica fume and superplasticizer per 1 ton of concrete mix.

A concrete mixture including Portland cement, aggregate, mixing water and an additive is a complex solution with pH = 4-5 with a base of H ₄ SiO ₄ sol _. The specified complex solution was prepared in the following ratio of mixture components, wt.%:

silica fume 0.113-0.227 Relamix type 2 superplasticizer with pH = 9 ± 1 0,076-0,15 concentrated hydrochloric or acetic acid or sulfuric 0.011-0.023 water 3.58-7.16,

the following content of the components of the concrete mixture, wt.%:

Portland cement 22.63-22.68 aggregate 67.91-68.04 specified additive 3.78-7.56 mixing water 1.9-5.5

Characteristics of concrete mix components:

1. Portland cement, grade M500 “ПЦ-Д0” (GOST 10178-85, GOST 30515-97) (OJSC “Mikhailovcement”, Ryazan Region, Mikhailovsky District, Oktyabrsky Village).

2. Dusty waste of ferroalloy production of Kuznetsk Ferroalloys OJSC. This dust from electrostatic precipitators produced by ferrosilicon has a particle size of 0.1-1 microns. Under the action of high temperature, silica microparticles turn into vitreous amorphous dust.

The specific surface of microparticles is 14000-30000 m ² / kg, which is 3-10 times higher than the specific surface of cement. The bulk density in the compacted state is 0.8 t / m ³ .

Chemical composition, wt.%: SiO ₂ = (91-97)%; Al ₂ O ₃ = (1.0-1.4)%; Fe ₂ O ₃ = (0.2-0.4)%; CaO = (0.2-0.4)%.

3. The plasticizer of the mixture. In the experiments, the Relamix type 2 superplasticizer GOST 24211-2008, obtained by dissolving naphthalene in sulfuric acid with the addition of polymer resins, which are an analogue of C-3 superplasticizer, was adopted. This plasticizer is produced in LLC Polyplast, Novomoskovsk. The additive has a slightly alkaline medium pH = 9 ± 1. It is applied in the form of liquid or powder. The basis of the composition is naphthenic sulfonic acid in the form of a salt of Na ₂ SO ₃ and radicals - CH ₂ .

4. Properties of acids:

4.1. Hydrochloric acid (HCl)

- concentration of 40%, i.e. 13.4 mol / l;

- density 1.198 g / cm ³ .

4.2. Sulfuric acid (H ₂ SO ₄ )

- concentration of 95.72%, i.e. 17.91 mol / L;

- density 1.84 g / cm ³ .

4.3. Acetic acid (CH ₃ CaOH)

- concentration of 99.9%, i.e. 17.5 mol / l;

- density 1.05 g / cm ³ .

5. Placeholders:

- small, i.e. quartz sand - class 1, meets the requirements of GOST 8736-93 (Atlantida LLC, Serpukhov.) The size module is 2.25.

- large - granite crushed stone of a fraction from 5 to 20 mm, meets the requirements of GOST 8267-93 (Pavlovskgranit OJSC, Voronezh Region). Gravel of crushed stone according to crushability 1200.

6. Water for mixing corresponds to the technical conditions of GOST 23732-79.

Realization of the task by experiments.

The implementation of the task consisted of two parts.

Part number 1

First, three types of solutions were prepared - modifiers (1 kg each), the same in terms of the quantitative composition of the components and the technical solution, but differing in the type of one of the components, i.e. concentrated acid. The solution was prepared in three stages in compliance with the sequence of operations, with the rationale for the choice of components:

Stage number 1. Dosage by weight:

1.1. 30 g (3% by weight of solution) of silica fume "MK" containing 92% amorphous SiO ₂ and 8% impurities of the type: Cao, Fe ₂ O ₃ ;

1.2. 20 g (2% by weight of the solution) of a superplasticizer having an alkaline medium in water with a pH of at least 8, because Superplasticizer in this technical solution should fulfill not only the direct role of the plasticizer of the concrete mixture, but also the role of an acid neutralizer up to pH = 4-5. In this case, Relamix type 2 superplasticizer with pH = 9 ± 1 was adopted;

1.3. 3 g (0.3% by weight of the solution) of any concentrated acid capable of dissolving the amorphous part of silica fume, i.e. 92% to the initial state of metasilicic acid H ₂ SiO ₃ followed by polymerization to orthosilicic H ₄ SiO ₄ . (experimental data of chemistry scientists GD Chukin, recedent: Prof. BK Nefedov, “Chemistry of the surface and structure of dispersed silica”). In addition, acids should not give a precipitate with impurities of silica fume; therefore, such acids as acetic, hydrochloric, and sulfuric were taken in the experiment.

Do not use hydrofluoric acid - HF and phosphoric H ₃ PO ₄ , because with SiO _2, HF forms a gas - SiF ₄ , and with H ₃ PO ₄ an admixture of silica fume - CaO interacts, forming a precipitate of the type Ca ₃ (PO ₄ ) ₂ .

For example:

SiO ₂ (amorphous) + 4HF = SiF (ra) + 2H ₂ O,

3CaO + 2H ₃ PO ₄ = Ca ₃ (PO ₄ ) ₂ (precipitation) + 3H ₂ O.

Thus, stabilization of the prepared solution depends on the choice of acid.

1.4. 947 g (94.7% by weight of the solution) of distilled water.

Stage number 2.

Dilution with distilled water of concentrated acid (3 g), for example hydrochloric acid, to a certain concentration, followed by mixing with 30 g of silica fume.

Water for dilution, in the required amount, was taken into account part of the solution water. For a full-fledged chemical reaction of the amorphous component of silica fume silica 92% with acid, an exposure of 10 minutes was carried out. Amorphous silica ultimately passes into colloidal particles (sol) of orthosilicic acid. Microsilica admixtures reacted simultaneously with the acid, for example: CaO, Fe ₂ O ₃

2CaO + 4HCl = 2CaCl ₂ + 2H ₂ O;

Fe ₂ O ₃ + 6HCl = 2FeCl ₃ + 3H ₂ O.

As a result of the hydrolysis of salts of CaCl ₂ , FeCl _{3, the} semi-finished product acquires an acidic environment with a pH of less than 4, which leads to corrosion of metal equipment and fittings.

Therefore, at the next stage, neutralization of the semi-finished product was carried out.

Stage number 3.

Relamix type 2 superplasticizer with pH = 9 + -1, which was placed in powder form (20 g) in the remaining distilled solution water, was adopted as a neutralizer. The resulting slightly alkaline solution with pH = 9.5 was mixed with the acidic semi-finished product obtained in step No. 2.

Thus, 1 kg of a suspension solution with pH = 4-5 was obtained, consisting predominantly (at least 92%) of suspended sols of orthosilicic acid sol and a true solution of salts of metal cations and acid anions formed during the reaction of silica fume impurities and the above acids, as well as Relamix type 2 molecules. The resulting solution acquired a slightly acidic medium with pH = 4-5, which is allowed for mixing water of dry concrete mixtures and ensures the stability of the solution up to 5 days. The name "suspension solution" was first given to Russian scientists by Zhukov (D. A. Friedrichsberg, "The Course of Colloid Chemistry" ed. 2 Leningrad, Chemistry, 1984, p.16).

The prepared solution was used as part of concrete mixtures as a modifier and chemical activator of quartz sand.

Part number 2

To develop the composition of the proposed concrete mixture, for example, composition No. 2, shown in table 1, it was necessary to prepare 13.2265 kg of such a mixture to form six samples 10 × 10 × 10 cm in size.

Initially, 1.8 kg (13.61% by weight of the concrete mixture) of quartz sand was dosed, which was mixed with the prepared modifying solution, taken in an amount of 0.5 kg (3.78% by weight of the concrete mixture) and having an acidic medium with pH = 4-5, which according to the technical solution is consistent with the adopted analogue No. 1 in the USSR copyright certificate No. 675029, Mcl. C04B 31/40.

This solution contains:

- 0.015 kg (0.113% by weight of the concrete mix) of silica fume;

- 0.01 kg (0.076% of the mass of the concrete mixture) Relamix type 2 with PH = 9 ± 1;

- 0.0015 g (0.011% by weight of the concrete mixture) of concentrated hydrochloric acid;

- 0.4435 kg (3.58% of the weight of the concrete mix) of the solution water.

The quartz sand activated with an acid solution was mixed with 7.2 kg of granite crushed stone (54.43% of the concrete mass).

Total aggregate taken 9.0 kg (68.04%).

Then 3 kg of Portland cement (22.68% by weight of the concrete mixture) and the missing water were added until W / C = 0.4, i.e. 0.727 kg (5.5% by weight of concrete mix).

After 28 days of normal hardening, the samples were tested for compressive strength. The test results are shown in table 1. In a similar way prepared the test mixture No. 1, No. 3, No. 4, No. 5.

The preparation of the composition No. 6 of the prototype was carried out in the traditional way, i.e. by mixing dry components and subsequent mixing with water.

Analysis of these results for the implementation of tasks. From the data shown in table 1, the conclusions follow:

1. Compositions No. 1 and No. 5 are transcendent, since concrete from a mixture of No. 1 has a compressive strength lower than the strength of the concrete prototype, and composition No. 5 has lower strength in comparison with compositions No. 2, 3, 4 at lower cost additives.

2. The compressive strength of concrete from mixtures No. 2, 3, 4 exceeds the strength of the concrete prototype by 13.9-20.9%, which corresponds to the task.

The essence of the reasons for achieving the task is as follows:

1. The pozzolanic reaction of hydration of calcium silicate (CaO · SiO ₂ · nH ₂ O) increases due to the sequential activation of MC by an acid-base medium and the corresponding conversion, first, to the colloidal state of the H ₂ SiO ₃ gel, and then to the H ₄ SiO ₄ sol, then there is MK from solid particles of 0.1-1 microns turned into H ₄ SiO ₄ sol nanoparticles, which significantly increased the reactivity of MK as an active mineral additive and Relamix type 2 superplasticizer.

It should be noted that, unlike the sol of H ₂ SiO ₃ (see analog No. 2), the sol of H ₄ SiO ₄ introduced into the proposed composition of the concrete mix contributes to a larger increase in the yield of CSH, which can be seen from the following reaction: Ca (OH) ₂ + H ₂ SiO ₃ = CaO · SiO ₂ · 2H ₂ O - the molecular weight of calcium hydrosilicate is 156 mass units (for the composition of analogue No. 2); Ca (OH) ₂ + H ₄ SiO ₄ = CaO · SiO ₂ · 3H ₂ O — molecular weight of calcium hydrosilicate 174 mass units (for the claimed composition, that is, 11.54% more CSH hydration product relative to the analogue composition.

2. A complex (suspension) solution containing MK 0.5-1% by weight of cement with a base of microcoloid particles of H ₄ SiO ₄ sol and the Relamix type 2 alkaline stabilizer performs the role of not only an active mineral additive, but also an electrolyte, which helps to reduce the water-cement ratio due to the separation of the second (upper diffusion) layer of water from colloidal SiO ₂ nanoparticles and its transition to a free, increasing mobility and uniformity of the mixture with stirring. Thinning of the double water layer on the surface of H ₄ SiO ₄ nanoparticles to the size of colloidal SiO ₂ particles increases their negatively charged zetapotential and electrostatic attraction with positively charged cations of the mixture, i.e., nanoparticles in the form of MK sol participate in the structuring of concrete stone, which positively affects the strength of concrete . Modification of MK from the state of solid microparticles to smaller microcolloid ones up to H ₄ SiO ₄ sol allowed to sharply reduce its consumption and consumption of superplasticizer relative to the composition of the concrete mixture of the prototype.

Representation of MK in the composition of the concrete mixture in the form of a sol of orthosilicic acid suspension solution is the main, according to the authors, element of the novelty of the qualitative composition of the proposed concrete mixture.

Table 1 The composition of the concrete mix, the corresponding strength of concrete and some parameters No. p / p Concrete components The numbers of concrete mixtures and composition, depending on the amount of silica fume (MK) introduced, are from 0.25 to 1.1% by weight of cement, mass composition in%. No. 1 (0.25% MK) Number 2
(0.5% MK) Number 3
(0.75% MK) Number 4
(1% MK) Number 5
(1.1% MK) No. 6 (prototype) one Portland cement 22.7 22.68 22.66 22.63 22.62 4.0 2 Aggregate 68.1 68.04 67.98 67.91 67.89 79.7 3 Complex solution with pH = 4-5 1.9 3.78 5.66 7.56 8.3 - / - four Mixing water 7.3 5.5 3,7 1.9 1.19 - / - Total in the mixture one hundred one hundred one hundred one hundred one hundred - / - 3-1 Silica fume 0,057 0.113 0.17 0.227 0.249 4.0 3-2 Relamix superplasticizer type 2 pH = 9 ± 1 0,038 0,076 0.113 0.150 0.116 - / - 3-3 Acids (hydrochloric, or acetic, or sulfuric) 0.005 0.011 0.017 0,023 0,025 - / - 3-4 Water in complex solution 1.8 3,58 3.36 7.16 7.86 - / - 5 Silicate flour - / - - / - - / - - / - - / - 8.0 6 Superplasticizer C-3 - / - - / - - / - - / - - / - 0.4 Total water in concrete mix 9.1 9.08 9.06 9.06 9.05 3.9 7 W / C 0.4 0.4 0.4 0.4 0.4 0.975 8 Compressive strength, MPa 51 62.5 63.1 65.3 60 54 9 Specific binder consumption per 1 MPa (binder / 1 MPa) 0.447 0.366 0.396 0.353 0.384 0,303

Claims (1)

A concrete mixture comprising Portland cement, aggregate, mixing water and an additive is a complex solution with pH = 4-5 with a base of H ₄ SiO ₄ sol, characterized in that the complex solution is prepared in the following ratio of mixture components, wt.%:
Silica fume 0.113-0.227 Relamix type 2 superplasticizer with pH = 9 ± 1 0,076-0,15 concentrated hydrochloric acid, or acetic acid, or sulfuric 0.011-0.023 water 3.58-7.16,
the following content of the components of the concrete mixture, wt.%:
Portland cement 22.63-22.68 aggregate 67.91-68.04 specified additive 3.78-7.56 mixing water 1, 9-5.5