RU2345969C2 - Concrete mixture and method of making objects from concrete mixture - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention pertains to production of construction material, particularly to compositions of concrete mixtures, used in making pavement elements, pedestrian and park and garden tracks, pedestrian squares and parking areas of public transport, and methods of making the given elements. The concrete mixture contains the following, in wt %: 20-30 binding substance with low water requirements, obtained from mixed grinding of 96-98 Portland cement and 2-4 C-3 plasticizer; 60-67 fine aggregate - mechanical mixture of a 0.16-5 mm fraction of natural enriched sand with M_"кр" 2.0-2.5 and sand from granite crushing residue with M_"кр" 3.6, in ratio of 1:0.25-0.67; 3-7 modifier in form of ash microspheres; 6-7 water. The method of making objects from the given concrete mixture involves preparing the concrete mixture, putting it into a press mould, compressing it at 40-60 MPa pressure by application of one or two-fold force impact onto the puncheon of the press mould, immediate release of the moulded objects and keeping then in an air-humid atmosphere. The invention is developed in subclaims.

EFFECT: improved physical and mechanical properties of concrete to be used for making paving elements, reduced expenses on energy and material and widening of the raw material base for their production.

4 cl, 1 ex, 5 tbl

Description

The invention relates to the production of building materials, in particular to compositions of concrete mixtures used for the manufacture of paving elements of sidewalks, pedestrian and garden paths, pedestrian areas and landing areas of public transport and methods for manufacturing these elements.

Known concrete mixtures for the manufacture of paving elements and facing products, including a binder, aggregate - crushed stone and (or) sand, a plasticizer and various mineral and organic (polymer) additives - property modifiers.

Portland cement is used as an astringent (RU 2131856, С04В 28/04, 06/20/1999; RU 2272860, C04B 28/04, 03/27/2006); a joint grinding product of Portland cement with a plasticizer (RU 21186236, C04B 28/04, 09/10/1998); a mixture of joint grinding of Portland cement, plasticizer and siliceous additives (RU 2147017, C04B 28/00, 03/27/2000).

However, products from the proposed concrete mixtures either have insufficient mechanical compressive and / or tensile strength when bent, frost and corrosion resistance, or relatively high abrasion, and the composition of the concrete mixture in accordance with RU 2118623 has a high cement content (up to 50 wt.%), which increases the cost of products.

To reduce cement consumption and at the same time increase the strength of concrete products in concrete mixtures, the following binders are used: low water demand (Kalashnikov V.I., Borisov A.A. et al. Modern ideas on the use of finely ground cements and VNV in concrete. // Building materials. 2000 No. 7. S.12-13; RU 2071456, C04B 28/00, 01/10/1997); fractionated aggregates with optimized grain composition (Chuykin A.E., Safina O.M. et al. Experience in the production and use of small-piece road vibropressed concrete products // Building Materials. 2003. No. 10. P.28-29).

However, the physicomechanical characteristics of the paving elements obtained from these concrete mixtures remain insufficiently high, as a result of which the paving and paving surfaces are relatively short-lived.

There is a method of increasing the mechanical strength of concrete, intended for the manufacture of driven piles and foundations of machines, based on the replacement of part of hard aggregates (crushed stone, sand) with dispersed material of reduced stiffness - with an elastic modulus (1-8) · 10 ³ MPa. Such a component of concrete is called a damping additive, and its role is associated with a decrease in intra-structural stresses in a cement stone and with the inhibition of the cracking process under loading (Babkov V.V., Mokhov V.N. et al. Technological possibilities for increasing the impact resistance of concrete. // Building materials 2003. No. 10, pp. 19-20). As such additives are proposed: expanded perlite (SU 313807, C04B 15/02, 09/07/1971); expanded vermiculite (SU 610818, C04B 15/00, 06/15/1978); composition of finely ground expanded clay, crushed rock-borne sand and finely ground lime-containing waste (SU 1255605, C04B, September 7, 1986); carbonate sludge (RU 2177920, C04B 28/02, 01/10/2002).

According to the authors, the positive effect of the introduction of a damping additive should be especially significant when the concrete mixture is intended for the manufacture of paving elements, which during operation are subjected to repeatedly repeated mechanical and thermomechanical loads. Therefore, the search for new types of damping additives is relevant.

There are various methods of manufacturing concrete products - paving elements of road and pavement. These include: the vibro-casting method, according to which the concrete mixture is placed in single or multi-place forms, subjected to vibration processing for 90-120 s, then the product is kept in molds for at least 24 hours, after which the products are stripped and aged for 5 days in vivo (RU 2147017, С04В 28/00, 03/27/2000); vibration casting method, which differs from the previous one in that the vibration processing is carried out simultaneously with laying the mixture in molds, in particular in the case when the paving elements have a relief surface (RU 2132274, С04В 40/00, 06/27/1999); filtration pressing, according to which a concrete mixture with high water content is subjected to pressure of 10-20 MPa to squeeze out excess moisture and air, and the molded products are kept for 7 days in air-wet conditions (RU 2259338, С04В 40/00, 08/27/2005 ); vibration molding with a load, when after filling the mold with concrete mixture and leveling the concrete surface, a loading plate is installed on it according to the dimensions of the product, which exerts additional force on it (7-8 kPa), and then is subjected to vibration for 60-90 s. (Production of paving slabs by vibration compaction //http://snip8.narod.ru/article/article_plitka_vibr.html); vibro-stamping, in which the working body of the molding device (vibro-stamp) has a dynamic effect on the surface of the concrete mixture to give the product the desired shape (Handbook for the production of precast concrete products. Edited by B. G. Skramtayev and P. K. Balatiev. - M .: Publishing house of literature on building., 1965; pressing of paving slabs //http://snip8.narod.ru/article/articlc_plitka_press.html); volume vibropressing in the mold on a special vibrating press under a pressure of 3-5 MPa, when not only the mold of the mold is exposed to vibration (within 3-5 s), but also a movable sealing body (punch) equipped with its own vibrator (Comparative characteristics of the methods production of paving slabs // http://piknikspb.ru/technology.htm).

However, the casting method and its varieties do not provide a strict geometry of paving elements, large-scale material costs are required to organize their mass production, and the technological process contains a significant proportion of manual labor when stripping products and preparing molds for reuse. Volumetric vibropressing requires expensive equipment, does not provide high profitability of production, and products obtained in this way have low decorative properties (Production of paving slabs and pavers by pressing // http://www.transportda.ru/article9.html). In addition, concrete products - paving elements obtained by known methods, have increased open porosity (with vibro-casting technologies - due to the relatively high water content of the concrete mixture, and when vibropressing - due to insufficient compaction of the workpieces), and therefore, low mechanical compressive strength and tensile and low frost resistance, as well as increased abrasion, and therefore are relatively short-lived.

According to published data (Chuikin A.E., Safina O.M. et al. Experience in the production and use of small-piece road vibropressed concrete products. // Building materials. 2003, No. 10. P.28-29; Production of paving slabs and wall blocks by volume vibropressing // Building materials. 2000, No. 12. P.16-17) concrete products - paving elements obtained by the method of volume vibropressing without surface hydrophobization, have the following physical and mechanical characteristics: compressive strength 20.0-45.8 MPa; ultimate tensile strength in bending 5.2-6.3 MPa; water absorption of 3-6%; frost resistance in accordance with GOST 10060.2-95 F200-F300; abrasion 0.4-0.8 g / cm ² .

The closest in composition and technical essence to the claimed invention is a concrete mixture for the manufacture of decorative and decorative plates, including a binder of low water demand (8-21 wt.%), Aggregate (72-83 wt.%), Modifier (0.2-1 , 6 wt.%) And water, and the binder of low water demand consists of Portland cement (50-67.5 wt.%), Mineral additives (25-37.5 wt.%), Pigment (5-7.5 wt.%) ) and a plasticizer (2.5-5 wt.%), as a plasticizer use a mixture of sodium and triethanolamine salts of sulfonated waste condensation product produced phenol, as a filler, use a mechanical mixture of finely ground quartz sand and fine aggregate of building sand in a ratio of 1: (0.5-2), and the fine aggregate consists of three fractions in the following ratio, wt.%: 0-0, 5 mm 15-30, 0.5-1 mm 25-35, 1.0-1.5 mm 45-50, and foam polystyrene with a content of the main fraction of 0.4-1.6 mm of at least 92 is used as a modifier % (RU 2097352, С04В 28/04, 11/27/1997).

However, the proposed composition of the concrete mixture does not allow to obtain products with increased mechanical strength and frost resistance and with reduced abrasion.

Closest to the claimed method of manufacturing paving elements is a semi-dry pressing method, in which a concrete mixture with a moisture content of 10-12%, prepared in the form of a press powder, is placed in the mold and subjected to one or two times the force of the moving part of the mold ( punch) at a pressure of 10-20 MPa for 3-5 s, then the product is immediately extruded and stored until the design accuracy is set, or subjected to heat and moisture treatment (Kaftaeva M.V. Regulation of the properties of fine-grained concrete with low water content: Dis .... Candidate of Technical Sciences Belgorod, 2000; pressing of paving slabs // http://snip8.narod.ru/article/article_plitka_press.html).

However, the compaction coefficient of the concrete mixture when using the known method of semi-dry pressing is insufficient to obtain products with high physical and mechanical characteristics.

The objective of the invention is to increase the mechanical compressive strength, mechanical tensile strength during bending and frost resistance and reduce the abrasion of concrete products - paving elements, simplifying the technology, expanding the raw material base and reducing energy and material costs in the production of paving elements.

The essence of the invention lies in the fact that the concrete mixture, including a binder of low water demand, obtained by co-grinding Portland cement and a plasticizer, fractionated fine aggregate, modifier and water, contains C-3 superplasticizer in the composition of the binder as a plasticizer in the following ratio, wt.% : Portland cement 96-98, C-3 2-4, as a fractionated fine aggregate - a mechanical mixture of a fraction of 0.16 -5 mm natural sand enriched with M _cr 2.0-2.5 and sand from granite screenings with M _cr 3.6 in a ratio of 1: 0.25-0.67, as a modifier - a damping additive in the form of ash microspheres in the following ratio of components, wt.%:

specified binder 20-30 specified placeholder 60-67 specified modifier 3-7 water 6-7

while fractionated fine aggregate contains, wt.%:

fraction 2.5-5.0 mm 18-24 fraction 0.63-2.5 mm 26-28 fraction 0.16-0.63 mm 48-56

The essence of the invention also lies in the fact that the method of manufacturing products from the proposed concrete mixture includes preparing the concrete mixture, laying it in the mold, compaction at a pressure of 40-60 MPa by applying one or two forces to the mold punch, immediately extruding the molded products and their exposure in an air-moist atmosphere, while the concrete mixture contains fractionated fine aggregate of the following composition, wt.%:

fraction 2.5-5.0 mm 18-24 fraction 0.63-2.5 mm 26-28 fraction 0.16-0.63 mm 48-56

It is known to use ash microspheres in the technology of structural and heat-insulating concrete, light concrete and foam concrete in order to reduce their density and thermal conductivity (RU 2154619, С04В 38/08, 08.20.2000; RU 2186749, С04В 38/10, 10.08.2002; RU 2277076, С04В 38/08, 05/27/2006; RU 93052682, С04В 38/10, 04/10/1996).

However, there is no information on the use of ash microspheres as a damping additive in the compositions of heavy fine-grained concrete, used, in particular, for the manufacture of paving elements.

The analysis of scientific publications and their own research allowed the authors of the invention to conclude that the method of semi-dry pressing of paving elements is the most progressive in terms of the simplicity of the technology, the content of requirements for the composition and quality of raw materials and the level of capital costs for organizing production.

However, concrete products obtained by dry pressing (Kaftaeva M.V. Regulation of the properties of fine-grained concrete with a low water content: Dis .... Candidate of Technical Sciences. - Belgorod, 2000), do not differ in high physicochemical characteristics (concrete strength class compression - B30, concrete class in terms of tensile strength in bending - B _tb 3.2, water absorption without surface hydrophobization - 5.6%, frost resistance - up to 200 cycles, abrasion - up to 0.7 g / cm ² ).

At the same time, the technological parameters used in the implementation of the existing semi-dry pressing method, namely, the moisture content of the concrete mixture 10-12% and the pressing pressure 10-20 MPa, are the maximum allowable. Thus, an increase in pressing pressure is impossible due to the appearance of transverse cracking cracks in the preforms, while at the same time it is not possible to increase the plastic properties of the press powder by increasing the water content, since the water holding capacity of the cement clinker mixture with mineral aggregate is not high enough in this case. As a result, an increase in the pressing pressure leads to an uneven "squeezing" of water from the workpiece and a decrease in the mechanical strength of the product. Thus, the task of developing new ways to improve the semi-dry pressing method of concrete products in order to increase their physical and mechanical characteristics remains relevant.

Characterization of raw materials

Portland cement ПЦ 500-ДО-Н of cement plant “Proletary” of OJSC “Novoroscement” was used as binders for the preparation of concrete mixtures, as well as a binder of low water demand (VNV), obtained by joint grinding of said Portland cement and plasticizer, which was used as the sodium salt of the product condensation of naphthalenesulfonic acid with formaldehyde - superplasticizer S-3 (Bazhenov Yu.M. Concrete technology. - M .: Publishing house ASV, 2007), in the amount of 2-4 wt.% in the MBL-1 ball mill for 1 hour.

The determination of the properties of binders was carried out according to the methods of GOST 310.1-76 “Cements. Test methods. General Provisions ”, GOST 310.2-76“ Cements. Methods for determining the fineness of grinding ", GOST 310.3-76" Cements. Methods for determining the normal density, setting time and uniformity of volume change ”, GOST 310.4-81“ Cements. Methods for determining bending and compression strengths. "

The test results of binders are shown in table 1.

Table 1. Binder Properties Name of material The properties Regulatory Compliance Portland cement non-additive cement plant "Proletarian" Fineness: 6.2%
Bulk density - 1157 kg / m ³
True density - 3100 kg / m ³
Specific surface area - 3200 cm ² / g
Normal density of cement paste - 26%
Uniformity in volume change - withstands
Activity - 46.6 MPa
Bending Strength - 5.2 MPa Conforms to GOST 10178-85 VNV (Portland cement with superplasticizer C3) Fineness: 4.6%
Bulk density - 1157 kg / m ³
True density - 3100 kg / m ³
The specific surface is 4300 cm ² / g
Normal density of cement paste - 22%
Uniformity in volume change - withstands
Activity - 55.1 MPa
Bending Strength - 7.0 MPa Conforms to GOST 10178-85

The following were used as aggregates: natural enriched sand (5.0-0.16 mm) medium OJSC “Mostovskoy Crushing and Sorting Plant”; sand from screenings of crushing of granite is very large fractionated (5.0-0.16 mm) of Pavlovskgranit OJSC; mechanical mixtures of these sands, taken in the ratio of natural sand: sand from screenings of crushing granite 1: (0.25-0.67).

The main physical properties of the aggregates were determined according to the methods of GOST 8735-88 “Sand for construction work. Test methods "and are given in table 2.

Table 2. Placeholder Properties Placeholder Type Total residues (%) on sieves, mm Fineness modulus Bulk density, kg / m ³ Intergranular voidness,% 2.5 1.25 0.63 0.315 0.16 Natural sand 11-12 24-26 35-38 63-66 one hundred 2.3-2.4 1530 41.5 Sand from granite screenings 44-45 58-60 73-76 89-93 one hundred 3.6-3.7 1560 44.0

In terms of their properties, the natural sand of Mostovskaya Crushing and Sorting Plant OJSC and sand from granite screenings of Pavlovskgranit OJSC satisfy the requirements of GOST 8736-93 “Sand for construction work. Technical conditions ”set forth in paragraphs 4.4.1, 4.4.3, 4.4.7, 4.4.8 and in sections 5, 6, which are mandatory.

As a modifier - a damping component that regulates the molding properties of concrete mixtures and the strength characteristics of concrete products - ash microspheres were used - bulk material consisting of hollow glassy particles of a spherical shape, released by reagentless flotation from ash and slag mixtures at thermal power plants and state district power plants. The physical properties of the ash microspheres were determined according to the methods of GOST 9758-87 “Inorganic porous aggregates for construction work. Test Methods. " The test results are shown in table 3.

Table 3 Ash Microsphere Properties Name of material The properties Ash microspheres from ash and slag mixtures of Novocherkasskaya state district power station The average bulk density is 390 kg / m ³
The average particle density of 580 kg / m ³
Particle Diameter - 20-200 microns
The true density of the shell is 2500 kg / m ³
Shell thickness - 5-15 microns
Compression strength in the cylinder - 1.8 MPa

Examples of the invention

1. Production of concrete mixtures and concrete products

A binder of low water demand (VNV) was obtained by co-grinding Portland cement with the addition of superplasticizer C-3 (2-4 wt.%). Then, the dosed dry components were loaded into LB-12 mixing runners and mixed for 1 min, then mixing water (5-7 wt%) was introduced into the mixture by irrigation, and stirring continued for another 4 min. Concrete samples in the form of cylinders with a diameter of 70 and a height of 70 mm were made by pressing in a metal mold on a 2PG-125 hydraulic press. The dosed press powder prepared on mixing runners was loaded into the mold, after which a single or double force corresponding to a pressure of 20-60 MPa was applied to the punch for 1-3 s, then the samples were immediately pressed and stored. Hardening of the samples took place under normal conditions at a humidity of 90-95% for 28 days.

2. Determination of the properties of concrete products

Samples were tested in accordance with the recommendations of GOST 17608-91 “Concrete paving slabs. Technical conditions ”and according to the methods of the following regulatory documents: GOST 10180-90“ Concretes. Methods for determining the strength of control samples ”- in determining the compressive and tensile strength in bending; GOST 12730.3-78 “Concretes. Methods for determining water absorption ”- in determining water absorption; GOST 10060.2-95 “Concretes. Accelerated methods for determining frost resistance during alternate freezing and thawing ”- in determining frost resistance; GOST 13087-81 "Methods for determining abrasion" - when determining abrasion.

3. Test results

3.1. The composition of the concrete mixture, which is the subject of the invention, and the properties of concrete 28 days after hardening under normal conditions are presented in table 4.

As can be seen from the table, the introduction into the mixture of ash microspheres in the amount of 3-7 wt.% Significantly increases the compressive strength of concrete in comparison with the prototype and in comparison with the known concrete mixtures used for the manufacture of paving elements. The role of the damping additive especially affects the increase in frost resistance (at least two grades according to GOST 10060. 2-95) and the tensile strength of concrete under bending (in comparison with the known concrete mixes for the manufacture of paving elements). With an increase in the ash microsphere content to 10 wt.% Or a decrease in the HVF content of less than 20 wt.%, The compressive strength of concrete decreases with a simultaneous increase in open porosity, as evidenced by an increase in concrete water absorption. An increase in the content of VNV more than 30 wt.% Is impractical for economic indicators, especially since the increase in strength is not as significant as in the range of 15-30 wt.%.

Table 4 The composition of the concrete mixture and the properties of hardened concrete Composition number The composition of the concrete mixture, wt.% Average compressive strength R, MPa The average tensile strength R _tf , MPa Water absorption W _m ,% Frost resistance according to the third method GOST 10060.2-95, cycles (brand according to MRZ) Abrasion resistance G _c , g / cm ² VNV ^* Placeholder ^** Ash Microspheres Water one 15.0 73.5 5,0 6.5 44.8 6.10 4.80 37 (F300) - 2 20,0 68.5 5,0 6.5 54,2 7.72 4.33 41 (F300) 0.28 3 22.0 67.0 5,0 6.0 54.0 7.52 3.64 59 (F400) 0.26 four 25.0 65.5 3.0 6.5 60.9 7.83 3.85 45 (F300) 0.23 5 30,0 60.0 3.0 7.0 64.1 8.27 3.20 72 (F400) 0.22 6 25.0 63.5 5,0 6.5 62.0 7.96 3,58 62 (F400) 0.24 7 25.0 61.5 7.0 6.5 60.0 8.19 3.53 74 (F400) - 8 25.0 58.5 10.0 6.5 56.2 8.75 3.61 94 (F500) - 9 25.0 67.0 - 8.0 49.5 5.41 4.90 29 (F200) 0.35 Prototype 8-21 72-83 ^*** Modifier ^**** 0.2-1.6 6.8-7.4 25-27 - 2.8-3.5 F200 ^***** 0.4-0.6 ^* - composition of VNV, wt.%: Portland cement - 97.0, thinner C-3 - 3.0 ^** - natural enriched sand: sand from screenings of crushing granite fractionated = 1: 0.67 ^*** - fine quartz sand: fractionated sand for construction work = 1: (0.5-1.2) ^**** - modifier composition: foamed polystyrene 0.4-1.6 mm ^***** - determination of the grade by frost resistance (MPE) of the concrete prototype was carried out by the basic method according to GOST 10060.1-95

Introduction to the aggregate of sand from screenings of crushing granite leads to a significant reduction in the abrasion of concrete - from the values of 0.40-0.60 g / cm ² characteristic of ordinary fine-grained concrete concrete natural sands to 0.22-0.35 g / cm ² when using fractionated aggregate, including sand from granite screenings. This, in our opinion, is associated with an increase in the grade in terms of the strength of the rock used to make sand. Thus, the strength grade of crushed stone produced from the sand and gravel mix of the Mostovskoye deposit is 1000, while the strength grade of granite crushed stone of Pavlovskgranit OJSC is 1400. In addition, when sand is introduced from crushing screenings, there is an increase in aggregate fractions of angular and lamellar particles, which also increases the wear resistance of concrete.

As you know, the main condition for using sand as a filler in the composition of fine-grained concrete is the selection of its grain composition in accordance with the requirements of GOST 26633-91 “Concrete heavy and fine-grained. Technical conditions. " The aggregate compositions used in the claimed invention contain enriched natural sand and sand from granite screenings of crushing in a ratio of 1: (0.25-0.67). In this area of compositions, the large (5.0-2.5 mm), medium (2.5-0.63 mm) and small (0.63-0.16 mm) fractions are contained in the aggregate in the following quantitative proportions, wt. %:

coarse fraction 18-24 middle fraction 26-28 fine fraction 48-56

With other ratios of natural sand and sand from granite screenings (less than 1: 0.25 and more than 1: 0.67) in the aggregate, the aggregate grain composition significantly exceeds the limits recommended by GOST 26633-91 for fine-grained concrete (Section 1.6. 12).

The influence of technological factors on the properties of concrete mix and hardened concrete are presented in table 5.

Table 5 The composition of the concrete mixture, its properties and the properties of hardened concrete No. p / p The composition of the concrete mix * Pressing Pressure, MPa ρ _St.
kg / m ³ K _y ** ρ _m , kg / m ³ R, MPa R _tf , MPa one 25 VNV without ZM twenty 2300 0.92 2270 46.7 4.91 2 25 VNV without ZM 40 2420 0.97 2380 60.3 6.65 3 25 VNV + 5 ЗМ twenty 2280 0.96 2250 48.8 7.40 four 25 VNV + 5 ЗМ 40 2325 0.98 2290 58.6 7.96 5 25 VNV + 5 ЗМ 60 2370 0.99 2340 62.3 7.60 6 25 VNV + 7 ЗМ 40 2310 0.99 2280 60.0 8.19 7 25 VNV + 10 ZM 40 2210 0.98 2180 51.6 8.75 8 25 C without ZM (prototype) twenty 2240 0.89 2210 41.7 4.30 9 25 VNV without ZM Vibro., 0.1 *** 2390 0.95 2350 54.8 5.41 10 25 VNV + 5 ЗМ Vibro., 0.1 2310 0.97 2280 51.7 6.94 * - the amount of cement (C), a binder of low water demand (VNV) and ash microspheres (ZM), indicated in wt.%; ** - coefficient of compaction of concrete mix; *** - samples are made by vibropressing at a pressure of 0.1 MPa.

When using the well-known method of dry pressing, paving elements made of cement-sand mixture at a pressure of 20 MPa have worse quality indicators than when using vibropressing methods (examples 9, 10). However, the use of the mixture of VNV significantly increases the compaction coefficient and physico-mechanical characteristics of concrete. A further increase in the pressing pressure to 40-60 MPa with the simultaneous introduction of ash microspheres into the composition of the concrete mixture further increases the compaction coefficient of the concrete mixture and, as a result, concrete quality indicators, especially mechanical bending tensile strength. An increase in pressure of more than 60 MPa is impractical, since the compressive strength increases slightly, and the tensile strength even decreases. As our studies have shown, this is due to the partial destruction of the microspheres.

The use of S-3 superplasticizer as a modifier of concrete mixtures intended for the manufacture of paving elements using semi-dry pressing technology in order to increase the pressing pressure is new, differs from the previously described action of S-3 on plastic concrete mixtures (Kalashnikov V.I., Borisov A .A. And others. Modern ideas about the use of finely ground cements and VNV in concrete // Building materials. 2000, No. 7. S.12-13) and can be considered as a new technological technique. The introduction of additive C-3 with additional dry grinding of cement hydrophilizes the surface of its particles and facilitates their relative sliding in the concrete mixture during pressing. The smooth surface of the ash microspheres also contributes to the reduction of internal friction in the press powder.

The role of ash microspheres as a new active component of semi-dry concrete mixes lies in their ability to hold mixing water in the required amount during application of pressure, ensuring its uniform distribution over the volume of the molded product and keeping it for the period of cement hydration and hardening of concrete, preventing its rapid evaporation. In addition, ash microspheres as a dispersed component with reduced stiffness help to equalize local stresses over the volume of the pressed product and thereby prevent the formation of technological cracks in it after depressurization.

Thus, the introduction of ash microspheres into the composition of a concrete mixture in semi-dry pressing technology fundamentally changes the molding properties of the mixture and makes it possible to switch to higher pressing pressures and, as a result, increase the compaction coefficient of the mixture. This in turn has a positive effect on the physicomechanical characteristics of hardened concrete.

The proposed composition of the concrete mixture and the method of manufacturing concrete products and, in particular, paving elements from it allow, on the one hand, to increase the mechanical compressive and tensile strength under bending and frost resistance, and on the other hand, to reduce the abrasion of concrete and thereby increase durability prefabricated pavement and pavement.

The strength of freshly molded products manufactured by the proposed method reaches 0.8 MPa, which allows the manufacturer to refuse to purchase and maintain in working condition a large number of plastic or metal molds, in which products obtained by known methods are usually held up to a set of stripping and technological strengths pallets intended for transportation of products to the places of storage. All this significantly reduces production costs and increases the economic efficiency of the production of concrete products - paving elements of road and pavement.

Claims (4)

1. A concrete mixture comprising a binder of low water demand, obtained by co-grinding Portland cement and a plasticizer, fractionated fine aggregate, modifier and water, characterized in that the binder contains C-3 as a plasticizer in the following ratio, wt.%: Portland cement 96- 98, C-3 2-4, as a fractionated fine aggregate, a mechanical mixture of the 0.16-5 mm fraction of natural sand enriched with M _cr 2.0-2.5 and sand from granite screenings with M _cr 3.6 in the ratio 1: 0.25-0.67, as a modifier damping additive in the form of ash microspheres in the following ratio of components, wt.%:
specified binder 20-30 specified placeholder 60-67 specified modifier 3-7 water 6-7 2. The concrete mixture according to claim 1, characterized in that the fractionated fine aggregate contains, wt.%:
fraction 2.5-5.0 mm 18-24 fraction 0.63-2.5 mm 26-28 fraction 0.16-0.63 mm 48-56 3. A method of manufacturing products from a concrete mixture according to claim 1, comprising preparing a concrete mixture, laying it in a mold, sealing at a pressure of 40-60 MPa by applying one or two forces to the mold punch, immediately extruding the molded products and holding them in air Humid atmosphere. 4. The method according to claim 3, characterized in that the fractionated fine aggregate contains, wt.%:
fraction 2.5-5.0 mm 18-24 fraction 0.63-2.5 mm 26-28 fraction 0.16-0.63 mm 48-56