RU2833755C1 - Method of preparing concrete mixture - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: invention relates to the technology of preparing concrete mixtures with organic and mineral additives used for concreting monolithic structures, particularly in road construction. Method of concrete mixture preparation includes two stages. At the first stage, mixed are: crushed stone, sand and a mineral additive in the form of tyrsa crushed to 2,000 cm²/g, which is a kind of shell limestone, which is introduced into the mixture at rate of 60-100 kg/m³. At the second stage, binder is added in form of portland cement, water and plasticising additive in form of polycarboxylate superplasticizer ST 5.0 in amount of 1% of weight of portland cement and all components are finally mixed until a concrete mixture of given workability is obtained.

EFFECT: increased strength of concrete at three-day age, which enables to reduce the period of commissioning of the facility under construction.

1 cl, 5 tbl

Description

The invention relates to the technology of preparing concrete mixtures with organic and mineral additives for concretes that harden primarily under natural conditions, including road concretes.

A method for preparing concrete mix is known (see RU No. 1760981 A3, C04B40/00, published 09/07/1992). According to this method, water with highly active superfine microsilica with a specific surface area of 20,000-40,000 ^cm2 /g is first mixed in a turbulent high-speed concrete mixer (600-700 rpm), then sand is added, after which cement is introduced, then a complex chemical additive including MF-AR superplasticizer and sodium or calcium nitrate. Final mixing is carried out in a low-speed mixer (40-60 rpm). The method ensures an increase in the strength of concrete.

The main disadvantage of this method is the need to use a high-speed turbulent concrete mixer at the first stage, which is not available in existing concrete mixing units, which hinders its use.

The closest to the claimed method is the method for preparing a building mixture (see RU 2535321, C04B40/00, published on 10.12.2014), which includes two stages, using a mineral filler, a plasticizing additive, sand and a binder, characterized in that at the first stage the binder - Portland cement M500 D20, the mineral filler - carbonate-siliceous opoka, 55-65% sand and 60-70% mixing water are mixed until a homogeneous mixture is obtained, and at the second stage the remaining sand, the plasticizing additive - superplasticizer SP-1 and the remaining water are added to the resulting mixture and they are finally mixed until a homogeneous mixture of the specified workability is obtained.

The disadvantage of this method is the slow growth of concrete strength during the initial stages of hardening, which affects the timing of commissioning of construction projects.

The objective of the invention is to accelerate the strength gain of concrete at an early age.

The technical result achieved by the proposed invention is an increase in the strength properties of concrete at an early age without increasing the consumption of cement and the use of additional technological equipment for the preparation of concrete mixture.

The essence of the invention is that the method for preparing a concrete mixture includes two stages using sand, a binder, a plasticizing and mineral additives, wherein at the first stage crushed stone, sand, and also a mineral additive in the form of sawdust crushed to 2000 ^cm2 /g, which is a type of shell limestone, introduced into the mixture at a rate of 60-100 kg/ ^m3 , are mixed, then, at the second stage Portland cement, water and polycarboxylate superplasticizer ST 5.0 are added in an amount of 1% of the cement weight, and all components are finally mixed until a concrete mixture of a given workability is obtained.

The concrete mixture, according to the proposed invention, is prepared as follows. In accordance with the recipe, crushed stone, sand and sawdust are dosed by weight and loaded into the mixer. The said components are mixed in a dry state until a homogeneous mixture is obtained. After this, cement, water, and also polycarboxylate superplasticizer ST 5.0 are loaded into the mixer and all components are finally mixed until a concrete mixture of the specified workability is obtained.

The invention is illustrated by the following example.

Concrete mixtures for road concrete with regulatory requirements - concrete strength class B35 and concrete tensile strength class in bending Btb 4.0 were prepared by the proposed method using the following materials.

Portland cement produced by the cement plant of the Voronezh branch of JSC EUROCMENT group. The used Portland cement CEM 1 42.5 N meets the requirements of GOST 31108-2020,

Fine aggregate - ordinary quartz sand of Priazovye LLC, which meets the requirements of GOST 8736-2017. The characteristics and granulometric composition of the sand are given in Tables 1 and 2.

Table 1 - Characteristics of sand of Priazovye LLC

Indicators, units of measurement Meanings Bulk density, t/ ^m3 1.36 True density, g/ ^cm3 2.4 Module of fineness 1.29 Content of dust and clay particles, % 2,2 Content of organic impurities, % 0

Table 2 - Granulometric composition of sand of Priazovye LLC

Residues on sieves Size of sieve cells, mm 5 2.5 1.25 0.63 0.315 0.16 Private, % 0 0 0 2 7 9 Full, % 0 0 0 2 9 18

Large aggregate - crushed stone of 5-20 mm fraction from dense sandstone of Prokhorovskoye deposit in Rostov region, meeting the requirements of GOST 8267-93. The characteristics of crushed stone are given in Table 3.

Table 3 - Characteristics of crushed stone

Indicators, units of measurement Meanings Strength grade M1200 Content of lamellar and needle-shaped grains, % 14 Bulk density, kg/ ^m3 1380 Frost resistance grade F200 Clay content in lumps, % 0 Content of dust and clay particles, % 0.9

Tap water from city networks, which meets the requirements of GOST 23732-2011, was used to mix the concrete mixture.

To plasticize the concrete mixture, a superplasticizer based on polycarboxylate ST 5.0 manufactured by BSR LLC, St. Petersburg, was used.

Table 4 - Characteristics of the additive ST 5.0

Indicators, units of measurement Meanings Appearance Brown liquid Smell Weak Total solids content, % 25 Solution density, g/ ^cm3 1.070 ± 0.03 pH value (undiluted product) 9 ± 1.5

Carbonate mineral additive - sawdust, which is a type of shell limestone from the Kamenskoye deposit in the Rostov region.

Tirsa is a yellow-brown rock consisting mainly of weakly cemented shell fragments of varying sizes. The calcium carbonate content in Tirsa is within 87-97%. The average density of rock pieces is in the range of 1.5-2.2 t/ ^m3 , porosity is up to 45%, and compressive strength is 25 MPa.

The concrete mixture according to the invention was prepared as follows. At the first stage, crushed stone, sand and sawdust crushed to a state of 2000 ^cm2 /g were loaded into the concrete mixer. The specified materials were mixed until a homogeneous mixture was obtained. After this, at the second stage, portland cement, water and a superplasticizer were added to the resulting mixture and all components were finally mixed until a concrete mixture of the required workability was obtained.

The initial composition of the concrete mixture was taken to be 500 kg/ ^m3 of Portland cement with the following ratio between the components (by weight) C:P:Sh = 1:1.42:2.31.

The consumption of superplasticizer additive (aqueous solution of 25% concentration) was 1% of the mass of Portland cement. The consumption of sawdust additive varied from 40 to 120 kg/ ^m3 and was introduced into the mixture due to a corresponding reduction in sand consumption. The amount of mixing water in each case

were selected based on the condition of obtaining equally mobile mixtures of grade P1.

From the prepared concrete mixtures, beam samples measuring 100x100x400 mm were formed, which were tested for bending, and the halves were tested for compression at the age of 3 and 28 days of normal hardening using the standard method.

The test results are shown in Table 5.

Table 5

composition Method of preparation
concrete mix production Material consumption, kg/ ^m3 Concrete strength at age port
land
this
cop crushed stone sand water Supplements 3 days 28 days mineral plasticizer Rizg,
MPa / %B _tb 4.0 Rszh,
MPa /
% B35 Rizg,
MPa /
%В _tb 4.0 Rszh,
MPa /
% B35 tyrsa flask ST5.0 SP-1 1 Suggested 500 1150 670 143 40 - 5 - 2.7
58 27.9
62 4.7
91 42.3
95 2 500 1150 650 145 60 - 5 - 3.6
71 32.8
73 5.1
100 45.9
102 3 500 1150 630 147 80 - 5 - 3.8
74 34.2
76 5.2
102 46.8
104 4 500 1150 610 150 100 - 5 - 3.7
73 32.0
71 5.3
104 47.2
105 5 500 1150 590 153 120 - 5 - 3.4
67 31.1
69 4.9
96 45.6
101 6 Patent RU
2535321 500 1150 610 160 - 100 - 5 2.6
51 24.3
54 4.7
92 43.7
97

The test results showed that the proposed method of preparing a concrete mixture with the introduction of 60-100 kg/ ^{m3 of} sawdust crushed to 2000 ^cm2 /g, which is a type of shell limestone, into the mixture instead of part of the sand, in combination with the addition of polycarboxylate superplasticizer ST 5.0 in an amount of 1% of the cement weight (compositions Nos. 2, 3, 4) ensures the design indicators of concrete at the age of 28 days of normal hardening (B35 and Btb 4.0) and at least 70% of the design compressive and tensile strength in bending at the age of three days.

Moreover, the specified strength indicators were achieved without increasing cement consumption and costs for technical re-equipment of concrete mixing units.

Claims (1)

A method for preparing a concrete mixture that includes two stages, wherein at the first stage crushed stone, sand and a mineral additive in the form of sawdust crushed to 2000 ^cm2 /g, which is a type of shell limestone, are mixed, introduced into the mixture at a rate of 60-100 kg/ ^m3 , then at the second stage a binder in the form of Portland cement, water and a plasticizing additive in the form of polycarboxylate superplasticizer ST 5.0 in an amount of 1% of the weight of Portland cement are added and all components are finally mixed until a concrete mixture of a given workability is obtained.