RU2771347C1 - Method for creating a concrete composite reinforced with a dry vegetable additive - Google Patents

Abstract

FIELD: construction industry.SUBSTANCE: invention relates to the field of industrial and civil engineering, in particular to building materials that can be used for enclosing structures in the construction of energy-efficient buildings. The main purpose of creating a concrete composite is to use a vegetable additive (dry hogweed) to improve the thermal and mechanical properties of concrete. A method for creating a concrete composite, including the preparation of a mixture of cement, sand, water, a chemical additive and a vegetable additive in the form of crushed hogweed, followed by molding and curing for 28 days. For preparation, a cement-sand mixture of the M300 Petrolit Profi brand is used, containing cement and sand with a grain size of up to 2.5 mm in a ratio of 1:2, which is mixed with water and a chemical additive (plasticizer) to improve the plasticity of the concrete mixture, and hogweed is used in an amount of 2% of the volume of the cement mixture in the form of chipped wood of 50×5 mm in size consisting of tree bark and a porous part, while adding hogweed to the cement mixture during molding at the stage of pouring it into the formwork.EFFECT: additive in the form of hogweed increases the normal strain, increases thermal resistance, reduces thermal conductivity and density, which makes the structure lighter.1 cl, 5 dwg, 2 tbl

Description

The method relates to the field of industrial and civil construction, in particular to building materials that can be used for enclosing structures in the construction and construction of energy-efficient buildings.

The main purpose of creating a concrete composite is the use of a plant additive (dry hogweed) to improve the thermal and mechanical properties of concrete.

To date, there are concrete composites reinforced with various additives, including vegetable origin (wood), which reduce the volume of cement to create a concrete composite and improve its properties.

The complex use of modified low-thermal-conductive concretes in enclosing and load-bearing structures contributes to an increase in the energy efficiency of the building.

Known concrete mix, which relates to the building materials industry, in particular to the concrete mix for the manufacture and production of concrete and reinforced concrete products with extended service life by reducing the water permeability of concrete, for high-rise construction, to increase the bearing capacity of facades (RU 2532816 C1). The concrete mixture includes cement from clinker of normalized composition PC500D0-N, barite concentrate of various fractions, fly ash (powder from production waste), as well as complex chemical additives based on polycarboxylates and lignosulfonates.

Wood additives are presented in the following form: chips, sawdust, shavings, wood dust, ash, which have shown positive effects on the strength properties of concrete. In addition to its low density, wood has high strength. The physical and chemical characteristics of wood are unique: low heat and sound conductivity, corrosion resistance in aggressive environments, the ability to dampen vibrations, easy workability and shaping.

The invention RU 92000575 relates to building materials and can be used as a raw material for the manufacture of structural material, namely wood concrete. Purpose: to increase the compressive strength of the structural material (arbolite), as well as the use of local resources.

Known wood-cement mixture for the manufacture of thermal insulation and structural building materials according to the patent RU 2568445.

A known method of creating a concrete composite, taken as a prototype, including the preparation of a mixture of cement, sand, water, chemical additives and vegetable additives in the form of crushed hogweed, followed by molding and curing for 28 days (MUSIKHIN P.V. and others, wood concrete blocks from Sosnovsky's hogweed, Collection of materials, Scientific and practical conference of the faculty of the Syktyvkar Forest Institute based on the results of research work in 2016, Syktyvkar, Syktyvkar Forest Institute, February 20-28, 2017, pp. 356-358). In this work, the disadvantage is that the work does not indicate the values that the authors obtained in the course of the research, the obtained properties are listed without numerical indicators. The authors studied the samples for compression; it is not clear from the thermal properties which parameter the authors studied. It is not indicated in what percentage the hogweed was added to the concrete sample, only the width, length and thickness of the fragments are indicated. Portland cement and slaked lime were also added to the mixture.

Sosnowsky's hogweed (BS) (Heracleum sosnowskyi Manden) is a large herbaceous plant of the Apiaceae family. In the middle of the 20th century, it was widely introduced into the fields of the European part of the USSR and Eastern Europe as a fodder crop. Due to the ability to self-sow at the end of the 20th century, it began to spread intensively beyond the lands on which it was cultivated. All parts of the plant contain furocoumarins - substances that, when in contact with the skin, dramatically increase its sensitivity to ultraviolet light. Lesions with plant sap and pollen can form not only when unprotected skin comes into contact with it, but also through clothing. Plants are easy to identify by their huge size, often 3-5 m tall. Leaves 1 m or more wide. They are divided and sharply pointed with soft hairs on the lower surface. The stiff, hollow stem is at least 10 cm in diameter. It is furrowed and green with dark reddish-purple spots. The leaf stalks are marked so that each spot has bristles that release juice when broken.

It is advisable to use hogweed as a herbal supplement, since in our country large areas of fields and roadsides are occupied by this weed. When dry, it is safe (does not emit any harmful substances) and, given the structure of the stem, is of interest as a cheap additive. For this, studies have been carried out on the use of hogweed in construction as an additive to concrete.

The technical result is an improvement in the thermal and mechanical properties of the concrete composite. This is achieved by the fact that this additive reduces the thermal conductivity and increases the normal stress of the concrete composite.

Today, in many enclosing structures, the bearing layer is reinforced concrete, followed by a layer of porous insulation and an outer (facing) layer. For concrete, various additives are used that improve its various properties.

There is a potential for developing constructive proposals for improving the concrete composite, in which, to improve the mechanical and thermal properties, dry hogweed is used as an additive, the share of which is 2% of the volume.

The essence of the method is explained by natural photographs.

In FIG. 1 shows the structure of hogweed chips

In FIG. 2 shows the elements of hogweed: a - a sample of wood chips; b - a sample of the trunk. The peculiarity of the structure of the hogweed is unique in that the trunk has not only a bark (bearing layer), but also a porous part (an analogue of a heater).

In FIG. 3 shows a herbal supplement of dry hogweed 50 mm long (a) and 25 mm long (b).

In FIG. Figure 4 shows dagrams of the dependence of bending stress on the deflection of the samples under study.

In FIG. 5 illustrates optical microscopy analysis.

For the manufacture of concrete, a cement mixture was used (the compressive strength at the age of 28 days is not less than 30 MPa) M300 Petrolit Profi, the aggregate is fine-grained sand with a maximum fraction of 2.5 mm. The ratio of cement and sand is 1:2. The composition of the concrete mix is shown in Table 1. The volume fraction of fiber in the samples produced was approximately 2%.

To select the optimal size of the herbal additive in the concrete composite, the results of a large addition of hogweed 50 mm and an average addition of hogweed 25 mm were compared. For the manufacture of concrete composite samples, a rectangular section with dimensions of 77 × 200 × 20 mm was used. The test specimens were stored before mechanical tests for 28 days at a temperature of 20°C and a relative humidity of 95%.

The strength gains of these concrete composites were compared with a control sample (without additive) and the most common additive for concrete composite - short polypropylene (PP) fiber with a length of 54 mm. The results are presented in figure 4.

The bending strength of the control sample is 4.5 MPa, which is the minimum among all the results obtained. Sample B-1, reinforced with hogweed chips 50 mm long, has a maximum strength of 5.8 MPa. While a similar sample with a length of 25 mm (B-2) has a bending strength of 4.7 MPa. The strength of the sample with PP fiber is 4.8 MPa.

Based on figure 4, we can conclude that the optimal length of the hogweed additive is 50 mm. This improves the mechanical properties of the concrete composite. Other concrete composites reinforced with wood admixtures have a rather small admixture, which mainly consists of tree bark or ash, which, by structure, cannot significantly improve the quality of concrete.

The thermal properties of the concrete composite were also investigated. Tests were carried out to determine the thermal conductivity of a concrete composite with a herbal additive of hogweed 50 mm. For experiments, a sample was created with parameters 25 × 25 × 3 cm, sample weight - 3.289 kg, volume fraction of the additive 2%.

The average value of the thermal conductivity of the concrete composite was 0.858 W/(m⋅K). Thermal conductivity of ordinary concrete in the region of 1.5 W / (m⋅K)

This is 1.75 times more than that of concrete with the addition of hogweed. This material is not only mechanically stable, but also has better thermal properties.

Thus, the main result is achieved - the improvement of the mechanical and thermal properties of the concrete composite due to a relatively cheap additive in the form of dry hogweed.

The use of this concrete composite makes it possible to obtain not only additional savings due to the use of a weed plant, but also to eliminate uncontrolled fields of hogweed for the cultivation of more useful crops.

There is a method for calculating thermal resistance, proposed by Professor, Doctor of Technical Sciences. Petrichenko Mikhail Romanovich and assistant Musorina Tatyana Alexandrovna, which allows you to more accurately determine the thermal resistance. To do this, it is necessary to find the active and reactive components of thermal resistance. This technique was applied to this concrete composite. Table 2 presents all the advantages of this concrete composite reinforced with a dry plant additive in the form of hogweed.

In order to reduce the negative impact of the herbal supplement, recommendations were made:

- chips should be cut from dry hogweed when the internal moisture content is low (harvest time is at the end of winter);

- the additive must be cut into strips of the same size (50×5 mm);

- it is necessary to pay attention to the fact that the bark does not separate from the porous layer of hogweed;

- to reduce formations on the surface of hogweed, the additive should be immersed in water for several days before creating a concrete composite. This will provide the necessary level of adhesion of the admixture and the concrete mixture and improve the mechanical and thermal properties.

Figure 5 shows a comparison of dry and wet concrete admixture.

Even in dry form, with the formation of sediment, the concrete composite has improved mechanical and thermal properties compared to the common additive of PP fibers.

Claims (1)

A method for creating a concrete composite, including preparing a mixture of cement, sand, water, a chemical additive and a plant additive in the form of crushed hogweed, followed by molding and curing for 28 days, characterized in that the cement-sand mixture of the M300 Petrolit Profi brand is used for preparation containing cement and sand with a particle size of up to 2.5 mm in a ratio of 1: 2, which is mixed with water and a chemical additive - a plasticizer to improve the plasticity of the concrete mixture, and cow parsnip is used in an amount of 2% of the volume of the cement mixture in the form of wood chips sized 50 × 5 mm, consisting of tree bark and a porous part, while adding hogweed to the cement mixture during molding at the stage of pouring it into the formwork.

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