RU2835462C1 - Concrete mixture for structural lightweight concrete - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to concrete mixtures and high-strength structural light concrete. Concrete mixture contains portland cement, sand with particle size of up to 5 mm as fine aggregate, light coarse aggregate from porous material with particle size of 5 mm, at least one modifying additive and water. Mixture contains, as a light coarse aggregate, crushed stone and/or gravel from porous material with particle size of 5-10 mm with bulk density of 250-950 kg/m³ and additionally contains heavy coarse aggregate – crushed stone and/or gravel with fraction of 5-10 mm or 5-20 mm from dense rocks with true density of 2600-2750 kg/m³, with a certain ratio of components.

EFFECT: providing during hardening of concrete under normal conditions by 28 days of initial modulus of elasticity of concrete above 30 GPa, ultimate strength in compression – from 60 to 85 MPa, with average density of light concrete 1800-2000 kg/m³.

7 cl, 2 tbl

Description

The invention relates to concrete mixtures and high-strength structural lightweight concretes with an average density of 1800-2000 kg/ ^m3 (density grades D1800–D2000), with a compressive strength limit of over 60 MPa, which corresponds to classes of at least B55, and with improved deformation properties, characterized by values of the initial modulus of elasticity from 30 to 35 GPa.

Concrete mixtures and lightweight concretes with a bulk density of 1800 to 2000 kg/ ^m3 with a compressive strength of about 60 MPa and an initial modulus of elasticity of 20-25 GPa are known [1, 2]. A feature of the mixtures is that they are produced using lightweight coarse aggregate of various origins and heavy sand.

The closest to the proposed solution is a concrete mixture for obtaining lightweight concrete with a bulk density of 1800 to 2000 kg/ ^m3 with a compressive strength of 60 to 70 MPa. In its preparation, Portland cement, organomineral modifier MB10-50S, including an active mineral additive and superplasticizer, heavy natural or light expanded clay sand and porous lightweight coarse filler - expanded clay gravel are used [3].

The disadvantage of this mixture is that while providing concrete compressive strength at a level of 60–70 MPa, the values of the initial modulus of elasticity of lightweight concrete do not exceed 28 GPa.

The technical problem is to obtain a concrete mixture that ensures, during concrete hardening, the achievement of higher initial modulus of elasticity and compressive strength.

The technical result achieved by the invention consists in ensuring, during the hardening of concrete under normal conditions, by 28 days an initial modulus of elasticity of concrete greater than 30 GPa, a compressive strength limit of 60 to 85 MPa, with an average density of lightweight concrete of 1800–2000 kg/ ^m3 .

The specified technical result is achieved in that the concrete mixture containing Portland cement, sand of fraction up to 5 mm as a fine aggregate, lightweight coarse aggregate made of porous material of fraction from 5 mm, at least one modifying additive and water, according to the invention contains as lightweight coarse aggregate - crushed stone and/or gravel made of porous material of fraction 5-10 mm with bulk density of 250-950 kg/ ^m3 and additionally contains heavy coarse aggregate - crushed stone and/or gravel made of dense rocks of fraction 5-10 mm or 5-20 mm with true density of 2600-2750 kg/ ^m3 , with the following ratio of components, wt. %:

Portland cement 24.0 – 33.0 the specified sand 28.0 – 40.0 specified heavy coarse aggregate 5.0 – 38.0 specified lightweight coarse aggregate 7.0 – 25.0 at least one modifying additive 0.2 – 9.0 water rest

In special cases, the concrete mixture may contain at least one modifying additive:

- a plasticizing additive, which may be a superplasticizer based on polynaphthalene sulfonates or a superplasticizer based on modified polycarboxylate esters, or

- a combination of a plasticizing additive with at least one mineral additive, which may be microsilica, or fly ash, or blast furnace granulated slag, or

- a combination of a plasticizing additive with an organomineral modifier of the MB type, containing a plasticizing and mineral additive, or

- organomineral modifier type MB, containing plasticizing and mineral additives.

Below are examples of the materials used, preparation of concrete mixtures and test samples, methods and test results. Table 1 shows examples of concrete mixtures, and Table 2 shows the characteristics of the resulting concrete (see the graphic section).

1. Materials for the preparation of concrete mixtures

1.1 Cement:

- Portland cement grade TsEM I 52.5 (GOST 31108-2020);

1.2. Fine aggregate heavy:

- natural sand with a true density of 2600 kg/ ^m3 fractions up to 5 mm, corresponding to GOST 8736-2014;

- natural sand for construction work with a true density of 2750 kg/ ^m3 fractions up to 5 mm, corresponding to GOST 8736-2014;

- porous sand with fractions up to 5 mm, corresponding to GOST 32496-2013.

1.3. Coarse heavy aggregate from dense rocks:

- granite crushed stone from dense rock with a true density of 2750 kg/ ^m3, fraction 5-10 or 5-20 mm, corresponding to GOST 8267-96;

- gravel from dense rocks with a true density of 2600 kg/ ^m3, fraction 5-10 or 5-20 mm, corresponding to GOST 8267-96, obtained by screening a sand and gravel mixture.

1.4. Large lightweight aggregate made of porous materials:

- expanded clay gravel with a bulk density of 250 kg/ ^m3 (bulk density grade M250), compressive strength of 0.60 MPa (strength grade P35), corresponding to GOST 32496-2013; manufacturer: Keramzit CJSC;

- expanded clay gravel with a bulk density of 450 kg/ ^m3 (bulk density grade M500), compressive strength of 2.45 MPa (strength grade P100), corresponding to GOST 32496-2013; manufacturer: Aleksinsky Expanded Clay Plant LLC;

- expanded clay gravel with a bulk density of 720 kg/ ^m3 (bulk density grade M800), compressive strength of 4.10 MPa (strength grade P150), corresponding to GOST 32496-2013; manufacturer: Vinzilinsky Expanded Clay Gravel Plant LLC;

- crushed tuff stone with a bulk density of 950 kg/ ^m3 (bulk density grade M1000), compressive strength of 2.38 MPa (strength grade P200), corresponding to GOST 22263-76; Svyatogorsk deposit, Khabarovsk Territory).

1.5. Mineral additives, active according to GOST R 56196-2014:

- condensed microsilica grade MKU-85 (GOST R 58894-2020 and TU 24.10.12-005605757665-2021); manufacturer - Novolipetsk Iron and Steel Works JSC;

- fly ash, acidic (GOST 25818-2017); manufacturer - JSC Cherepetskaya GRES;

- blast furnace granulated slag (GOST 3476-2019 and TU 38.32.22-012-99126491-2017); manufacturer - Mechel JSC.

1.6. Organic additives, plasticizing according to GOST 24211-2008:

- superplasticizer SP-1 based on polynaphthalene sulfonates (GOST 24211-2008 and TU 5870-005-58042865-2005) in the form of an aqueous solution of 30% concentration; manufacturer - Polyplast LLC;

- superplasticizer based on modified polycarboxylate esters (GOST 24211-2008 and TU 5745-033-58042865-2016 with amendment No. 1) in the form of an aqueous solution of 30% concentration; manufacturer - Polyplast LLC.

1.7. Organomineral additives, modifiers of type MB according to GOST R 56178-2014:

- modifiers of the MB 2-30S A-I-4, MB 10-50S A-II-2, MB 10-01 A-I-2 brands (GOST 56178-2014 and TU 5743-083-4685090-98); EMBELITH 8-100 B-II-3 (TU 5870-176-46854090-04); manufacturer - Master Beton Enterprise LLC.

1. Preparation of concrete mixtures and concrete samples for testing.

Concrete mixtures were prepared in a forced-action mixer with the volume of each batch (the total volume of all concrete components) being 0.03 ^m3 .

The control sample of concrete mix was selected as a sample prepared according to the prototype composition [3], the other (main) samples were prepared according to the compositions corresponding to the proposed technical solution. The dosages of small and large aggregates, mineral and organomineral additives are given based on dry (relative humidity 0%) materials. The dosages of organic additives - superplasticizers are given based on the solid residue (dry product).

The components of concrete mixtures were loaded into the mixer in the following sequence:

- 2/3 of the calculated mixing water;

- cement and modifying additives with mixing for 20 seconds;

- a mixture of coarse and fine aggregates with mixing for 30 seconds;

- 1/3 of the calculated mixing water with stirring for 40 sec.

From each batch of concrete mixture, concrete samples were prepared, including: cubes measuring 100×100×100 mm – to determine the compressive strength (R) – and prisms measuring 100×100×400 mm – to determine the initial modulus of elasticity (E _b ). The samples were hardened under normal temperature and humidity conditions (relative humidity 95…100%, temperature + 18…22 ⁰ C)

2. Test methods

Testing of concrete mixtures and concrete samples was carried out according to standardized methods: properties of concrete mixtures (mobility, density) - in accordance with GOST 10181-2014, compressive strength of concrete - according to GOST 10180-2012, density of concrete - according to GOST 12730.1-2020, initial modulus of elasticity of concrete - according to GOST 24452-80.

The age of concrete at the time of testing to determine strength (R) is 28 days, at the time of testing to determine the initial modulus of elasticity (E _b ) is 28 days.

3. Test results

Table 1 shows the compositions of concrete mixtures prepared using the selected materials. The dosages of the components of concrete mixtures are given by weight (kg/ ^m3 ), volume (l/ ^m3 ) and mass percentage (wt.%).

Samples of mixtures No. 1–4, prepared according to compositions corresponding to the prototype [3], as well as samples of mixtures No. 5 – 39, prepared according to the proposed technical solution using a mixture of heavy and light coarse aggregates at different ratios and dosages, had a cone slump mobility of 3 to 26 cm, and a cone spread mobility of 55 to 70 cm.

The values of the mobility of mixtures according to the flow and slump of the cone (RK/OK) and the properties of concrete – density (D), compressive strength (R) and initial modulus of elasticity (E _b ) at the age of 28 days are given in Table 2.

As can be seen from the results, in contrast to the prototype, the combination of large aggregates (crushed stone or gravel) of different density allows, with a certain range of dosages of concrete mixture components, to solve the technical problem. The dosage thresholds at which the problem of achieving the value of the initial modulus of elasticity at a level of not less than 30 GPa with a tensile strength of not less than 60 MPa and an average density of 1800 - 2000 kg / m ³ is not solved are given in the compositions of samples No. 12, 13, 29, 30, 36, 37, 38.

4. Conclusions.

High-strength lightweight concrete with a compressive strength of 60–85 MPa, an initial elastic modulus of 30–35 GPa and an average density of 1900–2000 kg/ ^m3 was obtained. The technical solution is based on the combined use of large aggregates of 5–10 or 5–20 mm fraction made of heavy dense rocks and 5–10 mm fraction made of lightweight porous materials.

Optimization of the balance between heavy and light coarse aggregates by mass and volume, taking into account the difference in aggregate density and strength, makes it possible to control the characteristics of lightweight concrete – the modulus of elasticity and strength.

The proposed ratio of concrete mixture components allows increasing the elastic modulus to 30–35 GPa, ensuring high strength of lightweight concretes of density grades D1800 – D2000 kg/ ^m3 .

In the proposed concrete mixtures, expanded clay gravel or crushed rock from tuff with fractions from 5 to 20 mm can be used as lightweight coarse aggregate, and plasticizers or a combination of plasticizers with active mineral additives or organomineral modifiers of the “MB” type can be used as additives.

Sources of information:

1. Guide for Structural Lightweight-Aggregate Concrete. Reported by ACI Committee 213 // ACI 213R-03

2. Wilson H. S., Malhotra V. M. Development of high strength lightweight concrete for structural applications. // International Journal of Cement Composites and Lightweight Concrete. Volume 10, Number 2, May 1988, pp. 79-90; 

3. Kaprielov S.S., Sheinfeld A.V., Selyutin N.M. “Self-compacting high-strength expanded clay concrete of classes B50-B65 - a new generation of lightweight concrete for high-rise building structures”, “Construction Materials”, pp. 42-50, No. 4, 2023.

Claims (8)

1. A concrete mixture containing Portland cement, sand of fraction up to 5 mm as a fine aggregate, lightweight coarse aggregate made of porous material of fraction from 5 mm, at least one modifying additive and water, characterized in that it contains crushed stone and/or gravel of porous material of fraction 5-10 mm with a bulk density of 250-950 kg/ ^m3 as lightweight coarse aggregate and additionally contains heavy coarse aggregate – crushed stone and/or gravel of fraction 5-10 mm or 5-20 mm made of dense rocks with a true density of 2600-2750 kg/ ^m3 , with the following ratio of components, wt. %: Portland cement 24.0-33.0 the specified sand 28.0-40.0 specified heavy coarse aggregate 5.0-38.0 specified lightweight coarse aggregate 7.0-25.0 at least one modifying additive 0.2-9.0 water rest 2. A concrete mixture according to claim 1, characterized in that it contains a plasticizing additive as at least one modifying additive. 3. A concrete mixture according to item 2, characterized in that it contains a superplasticizer based on polynaphthalene sulfonates or a superplasticizer based on modified polycarboxylate esters as a plasticizing additive. 4. A concrete mixture according to claim 1, characterized in that it contains, as at least one modifying additive, a combination of a plasticizing additive with at least one mineral additive. 5. A concrete mixture according to item 4, characterized in that it contains microsilica, or fly ash, or blast furnace granulated slag as at least one mineral additive. 6. A concrete mixture according to claim 1, characterized in that it contains, as at least one modifying additive, a combination of a plasticizing additive with an organomineral modifier of the MB type, containing a plasticizing and mineral additive. 7. A concrete mixture according to claim 1, characterized in that it contains, as at least one modifying additive, an organomineral modifier of the MB type, containing a plasticizing and mineral additive.