RU2530812C1 - Fine-grained cement concrete based on modified basalt fibre - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: fine-grained cement concrete is composed of cement, sand, water, plasticizing agent and basalt fibre, introduced into the mixture by the hydraulic opening method, at the following ratio of components, wt %: cement - 34, sand - 64, water - 1.4, plasticizing agent - 0.3, basalt fibre - 0.3.

EFFECT: increase of fracture toughness, strength, resistance of micro-reinforcing component to the influence of aggressive alkaline environment of the cement stone.

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Description

The invention relates to structural materials and can be used in various industries, for example, in road and civil engineering.

The prior art method for modifying the surface of an inorganic fiber, a modified fiber and composite material [RF patent No. 2475463 RU]. However, this method does not indicate properties that reflect the influence of aggressive media on the surface of the fiber, which characterizes this method as weakly effective for solving the tasks to achieve high strength characteristics of cement concrete. When this technology is applied to the specified fiber (basalt fiber), a shell of solid carbon material forms on the surface of the fiber, which can lead to the formation of a brittle surface, thereby changing the category of material from elastic to solid. Thus, this method does not allow to achieve high adhesion of the hydration products of clinker minerals on the surface of the fiber. The disadvantages include the fact that when applying the individual elements of the modifications specified in this method, there is no technique for monitoring changes in the structure and surface of the modified fiber.

There is a method of using basalt fiber based on a melt of basalt rocks, designed for three-dimensional hardening and several times increase the resistance of fiber-reinforced concrete (compared with reinforced concrete) to cracking, bending and tensile loads, creates the necessary safety margin and helps maintain structural integrity with through cracks, and also allows to significantly reduce the total weight of building structures [RF patent No. 2418752 RU]. However, in this method, insufficient attention is paid to the problems of alkali resistance of basalt fiber. Given the specifics of the operation of the fiber in an aggressive alkaline environment of cement concrete, due attention should be paid to the problems of corrosion resistance of basalt fiber during operation. Thus, the proposed method does not meet all the requirements necessary for using the specified fiber as a micro-reinforcing component in fiber-reinforced concrete.

It is known concrete reinforcement with basalt fiber [Vasilovskaya N.G. Cement compositions dispersed reinforced with basalt fiber / N.G. Vasilovskaya, I.G. Endzhievskaya, I.G. Kalugin // Bulletin of TGASU No. 3, 2011]; [Saraikina K.A. Dispersed concrete reinforcement / K.A. Saraikina, V.A. Shamans // Bulletin of the Perm State Technical University. Urban Studies 2011. No. 2] and others. However, with the specified ratio of components, it is not possible to achieve effective three-dimensional hardening of the structure of cement concrete.

The closest technical solution adopted for the prototype is a method of preparing a modified fiber-reinforced concrete mixture and a modified fiber-reinforced concrete mixture [RF patent No. 2433038 RU], including mixing in the mixer Portland cement, steel fiber, aggregate, plasticizing and modifying additives and mixing water, as steel fiber use "Mixarm" -fibre made of steel wire with conical anchors at the ends, as a plasticizing additive - plasticizer "D-11", as modifying additives - multilayer carbon nanotubes with a diameter of 8-40 nm and a length of 2-50 μm, preliminarily disperse Portland cement, the specified plasticizer and modifying additives and mix them with fiber in a linear induction rotator for 5-7 minutes, and the resulting product is mixed in a mixer with the sequential introduction of aggregate and mixing water. However, this method uses an irrational sequence of input of raw materials, and also in the process of mixing the fiber, it comes into contact with the solid particles of the cement-concrete mixture, which leads to mechanical damage and abrasion of the fiber. A rational method for introducing a micro-reinforcing component is not described, which is an important component for obtaining a composite of a given strength. As a result, the effectiveness of the application of this method is reduced. Another disadvantage is the weak degree of reinforcement, since with the specified ratio of the reinforcing component, lumps and unevenness in the composite structure are possible. Given the ratio of length to diameter, the fibers are long enough, which will also adversely affect the uniformity of distribution. It is known that in a cement medium there is an aggressive alkaline medium that can cause corrosion. In this prototype, the question of the corrosion resistance of the microreinforcing component has not been studied.

The aim of the invention is to improve the mechanical characteristics of concrete: increasing their crack resistance, tensile strength during bending, increasing the resistance of the micro-reinforcing component to the effects of an aggressive alkaline environment of cement stone.

This goal is achieved due to the fact that the fine-grained cement concrete, consisting of cement, sand, water, a plasticizing agent and basalt fiber according to the invention contains a modified basalt fiber, introduced into the mixture by the method of hydrofusion, in the following ratio, wt.%:

cement 34 sand 64 water 1.4 plasticizer 0.3 basalt fiber 0.3

To increase the efficiency of using basalt fiber in cement concrete, the possibility of increasing the alkali resistance of the fiber by heat treatment was adopted.

The process of heat treatment of the fiber was as follows: the fiber was subjected to heating at a temperature of 500 ° C, the time of isothermal exposure was 30 minutes. Cooling occurred at room temperature in air.

To confirm the effectiveness of the use of basalt fiber in cement concrete, the samples were tested for alkali resistance by holding the fiber in a solution of cement milk (pH 12.9).

Fluffy fiber was introduced into the solution. The concentration of basalt fiber in the solution was chosen taking into account the maximum fiber content in cement composites (3-12% of the binder mass), established on the basis of the analysis of literature data and empirically. Thus, the optimal fiber concentration, allowing to achieve maximum strength characteristics was 7%.

After the expiration of the exposure time to remove residual cement component, the fiber was washed with a weak solution of hydrochloric acid (0.1%) through filter paper. To remove impurities, the sample was subsequently washed with 1 L of distilled water. Then, the basalt fiber remaining on the filter paper was dried at room temperature. The solubility of the fiber was determined by the difference in mass of the initial sample and the dry residue as a result of exposure in an alkaline environment. Mass loss was expressed as a percentage. Possible fiber losses during washing (the so-called technological losses) are assumed to be comparable for each experiment. The test results are presented in table 1.

Table 1 The dependence of alkali resistance of the fiber from heat treatment No. Test time, days Weight after exposure, g Mass loss% pH of the solution after exposure Color Source fiber one 3 2.77 7.7 11.9 the norms 2 7 2.46 18.8 11.5 weakly lightened. 3 fourteen 2.15 28,4 10.3 brightened four 28 2.1 34 10.1 lightened Heat-treated fiber at 300 ° C 5 3 2.91 3.3 11.9 the norms 6 7 2.84 5,4 11.5 the norms 7 fourteen 2.74 8.57 10.3 the norms 8 28 2.66 11.39 10.1 s.-clarified Heat treated fiber at 400 ° C 9 3 2.89 2.9 11.9 the norms 10 7 2.82 6.1 11.5 the norms eleven fourteen 2.77 7.8 10.3 the norms 12 28 2.73 9.04 10.1 s.-clarified Heat-treated fiber at 500 ° C 13 3 2.95 one 11.9 the norms fourteen 7 2.88 2.1 11.5 the norms fifteen fourteen 2.87 4.11 10.3 the norms 16 28 2.84 5.5 10.1 s.-clarified

An increase in temperature from 300 to 500 ° C enhances the alkali resistance of the fiber. The weight loss during aging in an alkaline solution after 28 days in this case is about 5%, while the initial fiber during this time loses more than 30% of the initial fiber mass.

To achieve a rational input method, the hydro-fluffing method was used. With this method, the fiber is mixed in the mixing water, which contributes to a more uniform distribution. Next, the suspension is added to the mixture of cement and sand.

The desired mobility was achieved using the plasticizer SP-1 manufactured by Polyplast. A significant effect of the method of introducing fiber and the type of plasticizer on the physicomechanical properties of fine-grained concrete was established (table 2).

The preliminary fluffing of the fiber in the mixing water in the presence of naphthalene formaldehyde plasticizer (SP-1) leads to an increase in compressive strength by 24% and in bending by 30% compared with compositions obtained by simultaneous mixing of all components (traditional method). This is due to the adsorption of the plasticizer on the surface of the basalt fiber and its hydrophilization, which leads to the formation of a solvate shell on the surface of the fiber and its uniform distribution, first in water and subsequently in the mortar mixture.

Characteristics of the components used.

1. Cement produced by CJSC Oskolcement CEM I 42.5 P.

2. Sand of the Novo-Tovolzhansky deposit, Belgorod region.

3. Plasticizing additives, SP-1 (made by Polyplast).

4. Basalt fiber: LLC Mashzavod BASK.

Density - 2.7 g / cm ³ ;

tensile strength - 1600-3600 MPa;

modulus of elasticity - 80-110 MPa;

elongation at break - 1.4-3.6%;

diameter is 3-12 microns.

To obtain cement concrete with specified strength characteristics, an integrated approach to the method of introducing basalt fiber with a plasticizing additive is proposed. So, in the work we used a method of introducing a pre-distributed fiber in mixing water (fluffing) in the presence of an additive with the further introduction of a suspension into the molding mixture.

The preliminary fluffing of the fiber in the mixing water in the presence of naphthalene formaldehyde plasticizer (SP-1) leads to an increase in compressive strength by 24% and in bending by 30% compared with the compositions obtained by simultaneous mixing of all components. This is due to the adsorption of the plasticizer on the surface of the basalt fiber and its hydrophilization, which leads to the formation of a solvate shell on the surface of the fiber and its uniform distribution, first in water, and, subsequently, in the mortar mixture.

The selection of the rational composition of fine-grained cement was carried out according to GOST 26633-91. As the calculated parameters, the mobility of the concrete mixture, compressive and bending strength, and also the design grade for frost resistance were taken into account.

The composition of fine-grained cement concrete was determined by calculation and experimental methods according to GOST 27006-86 and GOST 7473-94. At the first stage, the preliminary composition of concrete was calculated, which provided the given mobility of the cement-sand mixture and the given concrete strength.

The plasticizer was selected based on the given mobility of the concrete mixture, which was selected according to the standard method, according to GOST 24211-2008.

table 2 Composition and properties of fine-grained cement concrete No. of composition p / p Consumption of materials, wt.% The amount of additive, wt.% W / C, wt.% The number of micro-reinforcing component, wt.% The limit of compressive strength, MPa Bending Strength, MPa Concrete compressive strength class Concrete strength class Concrete frost resistance class Cement sand one 32.22 66.27 0.24 1.27 0.25 47.3 5.09 B35 B _tb 4.0 F300 2 35.3 63.08 0.27 1.35 0.23 56.31 6.2 B40 B _tb 4.4 F300 3 32,2 66.32 - 1,57 - 42.11 3.77 B30 B _tb 3.2 F300 four 36.17 62.13 - 1.7 - 45.81 4.3 B35 B _tb 3.6 F300

Claims (1)

Fine-grained cement concrete, consisting of cement, sand, water, a plasticizing agent and basalt fiber, characterized in that it contains a modified basalt fiber, introduced into the mixture after preliminary hydrofusion in the presence of naphthalene formaldehyde plasticizer (SP-1), in the following ratio of components, wt.%% :
cement 34 sand 64 water 1.4 plasticizer 0.3 basalt fiber 0.3