RU2725559C1 - Cast and self-sealing concrete mixture for production of monolithic concrete and prefabricated articles from reinforced concrete - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to construction materials, in particular to cast and self-packing concrete mixtures, and can be used in production of monolithic and prefabricated concrete and reinforced concrete construction articles and structures of wide application. Cast and self-sealing concrete mixture for production of monolithic concrete and prefabricated articles from reinforced concrete, which includes nanocement of one of types 30, 35, 45, 55, construction sand, crushed stone, water, contains granite fraction crushed stone 5–10 mm and additionally granite crushed granules screening. 2–5 mm, with the following ratio of components, wt. %: said nanocement 12–20; construction sand 20–35; screening of granite chips of 2–5 mm fraction 15–21; granite fraction crushed stone 5–10 mm 20–29; water is the balance. Cast and self-compacting concrete mixture, in which nanocement has specific surface area of 600–900 m²/kg, additionally contains antifreeze additive in amount of 1 to 2 wt. %.

EFFECT: high mobility of the concrete mixture with preservation thereof for one to two hours at a minimum water content.

3 cl, 1 dwg, 6 tbl

Description

The invention relates to building materials, in particular, to cast and self-compacting concrete mixtures, and can be used in the manufacture of monolithic and prefabricated concrete and reinforced concrete building products and structures for general purposes, including densely reinforced structures, as well as massive concrete and reinforced concrete structures, and structures with increased crack resistance, low heat, high hardening rate, required strength, water resistance, frost resistance and durability.

At present, the production of cast and self-compacting concrete mixtures is considered the most promising direction in concrete technology, since it allows you to feed and lay concrete mixtures that penetrate well between reinforcement into the interdeck space (1-3).

The main technological task is to ensure high mobility of the concrete mixture with its preservation for one to two hours with a minimum water content by introducing various additives into the mixture.

However, the prepared cast concrete mixture / according to 1, Fig. 18) with P5 mobility, even in the presence of a wide range of modern additives, within 30-60 minutes already loses, on average, a third of mobility, despite the initial H / C of the mixture of 0.5. This circumstance complicates the transportation and laying of cast concrete mixtures, negatively affects the stratification of the mixture, crack resistance and frost resistance of concrete.

With the advent of new chemical additives and fibers, various technical solutions have been developed to eliminate these shortcomings. So, the patent of the Russian Federation No. 26565633 provides for the compilation of cast concrete mixtures of ingredients,% wt.: Portland cement 15.0-19.0; crushed stone of granite fraction 5-10 - 35.2-36.9; medium-sized quartz sand - 26.5-28.0; silica fume - 3.6-4.8; basalt fiber - 5.1-6.0; Glenium ACE 40 polycarboxylate ether superplasticizer in the form of an aqueous solution with a density of 1.04-1.08 g / cm - 0.38-0.42 and mixing water - 8.78-9.82.

Such a multicomponent composition of the concrete mixture according to the proposed invention required multi-stage mixing of the ingredients in dry form, after which they were mixed with half the water and mixed again, and in the third stage this concrete mixture was mixed with the remaining half of the water with superplasticizer. This composition of the concrete mix greatly complicates its preparation and significantly increases its cost. Unfortunately, the authors did not indicate in the patent description the retention time of the mobility of the cast concrete mixtures.

Even more difficult is the problem of obtaining modern self-compacting concrete mixtures, since the mobility required for them is characterized by even higher values of the cone spread (Table 1).

Known concrete mixture, including cement, a mixture of different types of sand from calcined bauxite with different particle size distribution, the thinnest sand with an average particle size of less than 1 mm and the largest sand with an average particle size of less than 10 mm, white soot, 90% of which are sized less than 1 μm with an average diameter of about 0.5 μm, an antifoam agent, superplasticizer, if necessary fibers and water, and in addition it additionally contains ultrafine particles of calcium carbonate with a specific surface equal to or more than 10 m ² / g (see, for example, patent RF №2359936 "Self-compacting concrete with ultra-high properties. The method of its preparation and use", 2005)

The disadvantage of this concrete mixture is also the presence of a multicomponent composition with expensive components, the high consumption of white cement CPA 52.5 Teil, which complicates and increases the cost of obtaining concrete and limits its scope.

Also known is a concrete mixture containing Portland cement, crushed stone, sand, bentonite and mixing water, and additionally, fly ash and superplasticizer on a polycarboxylate ether base in the following ratio of components, wt. %: Portland cement - 12.5-16.5, crushed stone - 39-40, sand - 27-29.3 bentonite - 0.15-0.25, fly ash - 7.5-8.5, superplasticizer on polycarboxylate the base - 0.3-0.35, mixing water - 9.5-10 (see, for example, RF patent No. 2307810 "Concrete mixture and method of preparation", 2007).

The disadvantage of this concrete mixture is also the presence of seven components, which complicates the preparation of concrete mixtures, the high cost, as well as low crack resistance and low frost resistance of the resulting concrete.

Known concrete mixture, including Portland cement, quartz sand with a particle size of 2.7-3.2, filler - chemical water treatment slurry (SHHVO), Melflux 2651 F hyperplasticizer, water-holding additive in the form of silica fume and water in the following ratio of components, wt. %: Portland cement 16.7-18.4, quartz sand 68.4-70.0, ShHVO 1.2-2.5, silica fume 0.8-2.8, Melflux 2651 F hyperplasticizer 0.08-0 , 09, water 8.91-10.11, while the specific surface area of the ShVHVO is from 1200 to 1300 m ² / kg (see, for example, RF patent No. 2566947 "CONCRETE SAND", 2014).

The disadvantage of this concrete mixture is its multicomponent composition and significant consumption of high-grade cement GSH 500 D0, low frost resistance due to the presence of carbonate filler SHHVO, as well as the need for additional grinding of ShHVO, which leads to a significant increase in energy consumption and, as a result, a high total cost of concrete mixture.

Closest to the proposed technical essence and the achieved result is a concrete mixture (prototype) for the manufacture of various types of cast monolithic building products containing nanocement of one of types 30, 35, 45 or 55 (Table 1). For example, in a concrete mix there can be the following component consumption in kg / m ³ (Table 2): nanocement - 380, quartz sand of the Ramenskoye deposit - 887, crushed stone and limestone quarry Kamensky - 887 and water (see, for example, Bikbau M article . I. Nanocements - the future of the cement industry and concrete technology. - Bulletin of the Russian Academy of Natural Sciences. - 2015. V. 5. - P. 32-41). The strength (grade) of the obtained concrete when using nanocement 30 - B50 (grade 600), and the density of concrete on nanocement 40 - 2455-2465 kg / m3.

The following is a comparison of the cost of a cube. m concrete mixes for ordinary, cast self-compacting concrete for the conditions of the Russian Federation at the present time.

The purpose of the present invention is to increase the mobility and shelf life of the cast and self-compacting concrete mixture while maintaining high compressive strength, water resistance and frost resistance of the prototype.

This goal is achieved by the fact that the cast and self-compacting concrete mixture for the production of monolithic concrete and precast concrete products, including nanocement of one of types 30, 35, 45, 55, building sand, crushed stone, water, contains crushed stone granite fractions of 5-10 mm and additionally - screening of granite crushed stone fr. 2-5 mm in the following ratio of components, wt. %:

Specified Nanocement 12-20; Building sand 20-35; Screening of crushed granite fraction 2-5 mm 15-21; Granite crushed stone fractions of 5-10 mm 20-29; Water rest.

In addition, in the cast and self-compacting concrete mixture, nanocement has a specific surface area of 600-900 m ² / kg, and this mixture additionally contains an anti-frost additive in an amount of from 1 to 2 wt. %

The essence of the claimed invention consists in the use of the proposed concrete mixtures with a protected ratio of ingredients to create a mobile highly dispersed rheological matrix of finely ground rounded dispersions in the form of grains of nanocapsulated Portland cement and particles of quartz sand (in nanocement ** (** - National preliminary standard 19-2014. Portland cement nano-modified . Technical conditions.) Particles of quartz sand are also crushed to the nanoscale - Table 3) with a reduced water content. This matrix is characterized by high rheological properties of the composition with minimal air entrainment and may include larger particles of quartz sand, as well as particles of screening of rubble and gravel up to 10 mm in size with the required mobility and preservation of self-compacting concrete mixtures.

It is a highly dispersed rheological matrix with an increased density (due to the content of highly dispersed particles of silica sand in its volume) with a minimum water content that allows the free movement of particles of sand and gravel and provides the required mobility (fluidity) of the concrete mixture. At the same time, it becomes possible to significantly reduce the amount of water in self-compacting concrete mixtures and thereby reduce shrinkage phenomena, cracking, provide the specified strength and other characteristics of concrete.

For a better understanding of the invention, the following examples of its implementation.

When performing embodiments of the invention, low-clinker nanocements with quartz sand from the KAZNANOCEMENT plant, Nur-Sultan (7) were used. The characteristics of the used industrial batches of nanocements in the table. 3.

An analysis of the granulometry determinations showed that very small particles of dispersions prevail in the produced nanocements, which is not typical for Portland cements. Joint grinding of Portland cement with quartz sand in ball mills in the presence of a modifier provides a very high specific surface area of materials with a significant predominance (more than 25% of the total amount) of dispersions of particles smaller than microns and more than 90% of particles smaller than 30 microns.

For the preparation of concrete mixtures were also used:

- 1) building sand of the Ramenskoye field with a particle size of 1.9 and clay content of less than 2% wt .;

- 2) screening of granite crushed stone fraction 2-5;

- 3) granite crushed stone of fraction 5-10;

- 4) tap water;

- 5) target additive: antifrosty - calcium chloride nitrite or sodium formate or calcium chloride.

Concrete mixtures were prepared in the Experimental Workshop of the International IMET, Moscow, on a forced concrete mixer BS-1, manufactured by 268 mechanical plant, Ivanovo, with a capacity of 1 cubic meter.

The components of the mixture were loaded into the concrete mixer after weighing, and after stirring dry for 1 min, the required volume of water was supplied, after which the mixture was stirred for 3 min.

The mobility of concrete mixtures was determined by the spread of the mixture according to GOST R 58002-2017, part 8 (corresponding to EN 12350-8: 2010).

The mobility retention rate of concrete mixtures was determined similarly - also by the spread of the mixture - every 30 minutes. The density of concrete mixtures was determined according to GOST 10181.2-81, strength indicators and density of concrete were determined according to standard methods GOST 10180-90.

The compositions of the cast and self-compacting concrete mixture are given in table. 4.

The water resistance of concrete samples was determined according to GOST 12730.5-84, frost resistance - according to GOST 10060.1-95. The basic method for determining frost resistance and according to GOST 10060.2-95. Accelerated methods for determining frost resistance, methods 2 and 3.

The characteristics of the mobility persistence of concrete mixtures based on the obtained compositions of concrete mixtures - according to table. 4 (given in table. 5.

In small-clinker nanocements among particles less than one micron in size, both Portland cement grains with modifier nanocapsules and particles of quartz sand with a size of about 100 nm or less are observed. FIG. Figure 1 shows electron-microscopic images of the lumen (scale - in the photographs) of nano-shells (light border) on Portland cement grains from a structured modifier in nanocements and quartz sand grains (according to diffraction results), and small particles without nanoshells are silica sand grains crushed to a nanolevel . Moreover, in FIG. 1 "a" shows particle sizes of 18, 19, 42, and 103 nm, and in FIG. 1 "b" also shows the thickness of the shells in nm.

In this case, the sand particles do not have modifier nanoshells and actively participate in mixing with water to ensure high mobility of cement-sand mixtures with low water content and structural formation reactions of cement stone, changing the established and written out of the old textbooks about quartz sand as an inert aggregate.

The proposed compositions of concrete mixtures by their properties, despite the exclusion of expensive polymer additives and other highly dispersed fillers, as was shown in the analysis of the prior art of the invention and, in particular, presented in the prototype, have very high rheological properties and mobility.

The developed technical solution largely corresponds to the ideas developed in the Russian Federation by prof. Kalashnikov V.I. and his school (4-6) on the rational rheology of concrete mixtures as the future technology of concrete. The present invention with a significant simplification of the composition of concrete mixtures provides "high" according to Kalashnikov V.I. rheology and mobility of concrete mixtures for high-quality concrete with significant water reduction of the fluid matrix.

The test results of the proposed concrete mixture for self-compacting concrete indicate that the concrete obtained from the proposed concrete mixture is not inferior to most concrete indicators by analogs and prototype at a significantly lower cost ...

Cast self-compacting concrete is used in the construction of structures with increased strength; in the construction of structures that consist of a large number of fittings; in the construction of hydraulic structures; in the manufacture of seamless floors without seams and the construction of buildings and structures of various geometries. One of the main advantages of cast and self-compacting concrete is the speed of concreting, since after pouring it does not require any additional efforts to compact the mixture.

Cast self-compacting concrete made according to the invention fills the formwork without any additional efforts, and the concrete mass has high mobility and density, it is easy and convenient to work with.

Literature

1. Dvorkin L.I., Kizima V.P. Effective cast concrete. Lviv., “Vishka school”, 1986 - 144 p.

2. Komarinsky MV, Smirnov SI, Burtseva DE, Cast and self-compacting concrete mixes // Construction of unique buildings and structures. 2015, No. 11 (38). S. 106-118

3. Kaprielov S.S., Smirnov S.I., Kardumyan G.S. New modified concrete - M. Paradise Printing House, 2010 - 258 p.

4. Kalashnikov V.I. Through rational rheology into the future of concrete. Part 1: Types of rheological matrices in concrete mix and the strategy of increasing the strength of concrete and saving it in structures // Concrete Technologies. 2007. No5. S. 8-10.

5. Kalashnikov V.I. Through the rational rheology of the future of concrete. Part 2: Finely dispersed rheological matrices and powder concretes of a new generation // Concrete Technologies. 2007. No.6. S. 8-11.

6. Kalashnikov V.I. Through the rational rheology of the future of concrete. Part 3: From high-strength and especially high-strength concrete of the future to superplasticized general-purpose concrete of the present // Technology of Concrete. 2008. No. 1. S. 22-26.

7. Bikbau M.Ya., Nefedov A.S., Adilbekov K.M., Karsybaev E.B. Industrial production of nanocements in the Republic of Kazakhstan // Magazine Dry building mixtures., 2019, No. 3, P. 14-19.

Claims (4)

1. Cast and self-compacting concrete mixture for the production of monolithic concrete and prefabricated reinforced concrete, including nanocement of one of types 30, 35, 45, 55, construction sand, gravel, water, characterized in that it contains granite fractions of 5-10 mm and additionally - screening of granite crushed stone fr. 2-5 mm in the following ratio of components, wt. %: Specified Nanocement 12-20 Building sand 20-35 Screening of crushed granite fraction 2-5 mm 15-21 Granite crushed stone fractions of 5-10 mm 20-29 Water rest. 2. Cast and self-compacting concrete mixture according to claim 1, characterized in that the nanocement in it has a specific surface area of 600-900 m ² / kg. 3. Cast and self-compacting concrete mixture according to claim 1, characterized in that it contains an anti-frost additive in an amount of from 1 to 2 wt. %

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