RU2724631C1 - Fiber-concrete mixture for centrifuged concrete - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to compositions of concrete mixtures for making centrifuged reinforced concrete articles of annular cross-section used in prefabricated reinforced concrete production. Invention contains a fiber-concrete mixture for centrifuged concrete. Fiber-concrete mixture for centrifuged concrete includes granite chips, expanded clay gravel, quartz fractionated sand, portland cement, basalt fiber, metal fiber. Granite crushed stone and expanded-clay gravel are coarse aggregates of one fraction of 5–10 mm. Weight ratio of components is, wt%: granite chips – 28–38; expanded clay – 8–13; quartz fractionated sand – 12–18; portland cement – 20–25; basalt fiber – 1–2; metal fiber – 3–5; water – 9–18.EFFECT: high homogeneity of the mixture, ultimate tensile strength during bending, plasticity of the concrete mass, reduced formation of shrinkage cracks in the concrete.1 cl, 3 tbl

Description

The invention relates to compositions of concrete mixtures for the manufacture of centrifuged reinforced concrete products of annular cross section, used in enterprises for the production of precast concrete.

Known fiber-reinforced concrete mixture for the production of centrifuged concrete (see RU 242333 C1, C04B 28/04, C04B 111/20, publ. 07/10/2011) containing Portland cement, basalt fiber, plasticizer, sand and water, and also as a chemical additive superplasticizer C-3 or Melflux 2651F hyperplasticizer. The composition of the fiber concrete mix includes, mass. %:

- fractionated quartz sand 55–60;

- Portland cement 25-30;

- silica fume 3-4;

- the addition of super- or hyperplasticizer in a dosage of 0.3-0.9;

- basalt fiber (fiber) 1.5–2.0.

The closest technical solution is the composition of the concrete mixture, selected on the basis of the calculation and experimental method (Akhverdov I.N. Reinforced concrete pressure centrifuged pipes. - M., 1967, Stroyizdat. 165 S.). Containing the following components, mass. %:

Granite crushed stone - 38 - 42;

Sand quartz fractioned - 30 - 32;

Portland cement - 16 - 20;

Water - 8 - 10.

The most significant drawback of the known concrete mixture is the use of granite coarse aggregate fractions of 10-20 mm, since in this case the concrete mixture is divided into zones according to grain size. A coarse-grained conglomerate with a larger mass moves to the outer surface of the product, and with a smaller mass, respectively closer to the inner one, which leads to heterogeneity of the centrifuged reinforced concrete products of the ring section in strength.

The task of the invention is to obtain centrifuged concrete with higher uniformity and increased tensile strength in bending based on the developed composition of the fiber-reinforced concrete mixture.

The essence of the invention lies in the fact that the fiber-reinforced concrete mixture for centrifuged concrete, including two types of coarse aggregate of one fraction of 5-10 mm - granite crushed stone and expanded clay gravel, fractionated quartz sand, Portland cement, basalt fiber, metal fiber and water in the following ratio of components, masses . %:

Granite crushed stone - 28 - 38;

Expanded clay gravel - 8 - 13;

Sand quartz fractioned - 12 - 18;

Portland cement - 20 - 25;

Basalt fiber (fiber) - 1 - 2;

Metal fiber (fiber) - 3 - 5;

Water - 9 - 18.

The technical result is obtained by introducing into the concrete mix two types of coarse aggregate (granite crushed stone and expanded clay gravel) of one fraction of 5-10 mm, which reduces the heterogeneity of centrifuged reinforced concrete products of a circular cross section along the wall thickness.

Lightweight aggregate made of expanded clay gravel helps to reduce the average density of products while maintaining the strength characteristics of concrete and serves as a damping additive. A reinforcing component of basalt and metal fiber at a dosage of 1.5 + 5%, respectively, of the weight of the dry components of the concrete mixture increases the tensile strength during bending due to microreinforcement of cement stone (basalt fiber) and macroreinforcement of concrete (metal fiber) at the level of coarse aggregate. In addition, dispersed reinforcement with basalt fiber increases the ductility of the concrete mass and reduces the formation of shrinkage cracks in concrete.

For experimental verification of the claimed composition were developed and tested several compounds with the addition of combined fibers, which are shown in table 1.

Table 1

Fiber concrete components consumption

No. Consumption of materials per 1 m ³ Granite Expanded clay Sand Cement Water Fiber basalt metal 1 1120–1380 - 580–730 325-480 125–250 - - 2 604-820 173–280 258-388 431–539 216–323 21.5–43.1 64.7-108 3 - 123–246 445–1300 615-740 320-440

Characteristics of the starting components:

1. Large and small aggregate:

- crushed granite of Pavlovsk Nerud OJSC of fraction 5-10 mm with a grade for crushability Dr1400;

- expanded clay gravel;

- quartz sand of the Grushevsky deposit (M _k = 2.0).

The physical properties of coarse and fine aggregate (sand) are presented in table 2.

table 2

Physical properties of coarse and fine aggregate

Name
material Density, kg / m ³ Voidness,% Porosity,% bulk average true Granite crushed stone 1510 2690 2700 43.8 0.37 Expanded clay gravel 510 1610 2400 68.3 33.0 Quartz sand 1260 - 2600 51.5 -

2. Metal fiber

Metal fiber is introduced into the concrete mix usually in an amount of 1–2.5% of the concrete volume (3–9% by weight, which is 80–170 kg of fiber per 1 m ^{3 of the} mixture). To improve adhesion to concrete, fiber is produced in a wave form, specially profiled or straight with curved ends. Diameter 1 ± 0.075 mm, length 50 ± 2.0, density 7800 kg / m ³ . The elastic modulus of the fiber is within 200 GPa, tensile strength 0.3–2.0 GPa.

3. Basalt fiber

Basalt fiber has a very high chemical resistance. Fibers with a diameter of 10 microns, a density of 2600 kg / m ³ , tensile strength from 1.62 to 3.2 GPa. The elastic modulus of the fiber is in the range from 7 to 60 GPa, tensile strength from 600 to 3500 MPa.

From the compositions indicated in Table 1, prism samples with sizes of 10 × 40 cm and cubes with a rib size of 10 cm were formed. After 1 day of preliminary aging, all samples were placed in a normal hardening chamber, in which they hardened for 27 days.

Prismatic strength is the main characteristic of concrete used in the calculations. Therefore, to switch from cubic to prismatic strength, the coefficient K _{b is used} , which is equal to the ratio of the normative prismatic strength to the normative cubic strength.

According to the joint venture 63.13330.2018 “Concrete and reinforced concrete structures. Fundamentals "the value of concrete strength under axial tension R _{bt is} included in a number of formulas that determine the strength, stiffness and crack resistance of reinforced concrete elements. Also, this value significantly affects the determination of the size and reinforcement of some concrete and reinforced concrete structures.

To determine the tensile strength of concrete under bending, the methodology described in GOST 10180 was used.

The data obtained (table 3) indicate that the values of the prismatic strength coefficients of concrete on a combined aggregate are within the range of K _b for ordinary lightweight concrete.

The values of tensile strength in bending for the developed composition is higher than that of other compositions

Table 3

Compositions and properties of products

No. sos
tava Granite.
crushed stone,% Keram
zit gravel,% Sand quartz. fraction.,% Port-
land
cement,% Basal.
fiber,% Metal
fiber.% Water% Avg prisms. durable., MPa Durable, MPa Raft-
nost, kg / m ³ 1 24 15 20 28 2,5 5.5 five 41.1 3,1 2410 2 28 13 18 25 2 five nine 43.5 3.2 2405 3 34 12 15 23 1.3 4 10.7 45.3 3,7 2153 4 38 8 12 20 1 3 18 40.1 3.0 1799 five 42 7 ten 17 0.8 2,5 20.7 38.9 2.7 1752 Ahver
Dov 40 - 31 18 - - eleven 40.5 2.2 -

Thus, analyzing the results obtained, we can conclude that for the manufacture of reinforced concrete products of annular cross section, the developed compounds No. 2 and No. 4 on a combined aggregate with the addition of fiber are most suitable.

Claims (8)

Fiber-concrete mix for centrifuged concrete, including two types of coarse aggregate of one fraction 5-10 mm - granite crushed stone and expanded clay gravel, fractionated quartz sand, Portland cement, basalt fiber, metal fiber and water, with the following ratio of components, wt.%: Granite crushed stone - 28–38; Expanded clay gravel - 8–13; Sand quartz fractioned - 12–18; Portland cement - 20–25; Basalt fiber (fiber) - 1-2; Metal fiber (fiber) - 3-5; Water - 9–18.