RU2641676C2 - Reinforcing additive for concrete - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: additive including zinc-twisted strands twisted into a bundle with a right Z-twist is described, in the form of a strip, by extruding a melt of a mixture of polypropylene-PP and low pressure polyethylene-LPPE, where the twisting is performed at a number of 40-45 twists per one running meter of fibre at a ratio components of the mixture, wt %: PP 67-73, LPPE 27-33 with additional subsequent corrugation of the said fibre. The invention is developed in dependent claims of the invention formula.

EFFECT: bulk reinforcement of cement products with high strength characteristics.

4 cl, 2 tbl

Description

The invention relates to a technology for the production of polymer fibers, in particular polyolefin, which can be used as a reinforcing aggregate in the production of various types of concrete: bulk floors and screeds; dry mounting and repair mixtures; mortars and plasters; bridge structures; paving slabs, blind areas; elements of architectural design and other monolithic, road, architectural structures and structures.

It is known that the addition of a reinforcing component to building materials, such as cement materials, brick, asphalt, etc., improves the structural integrity of the material and reduces the likelihood of cracking. The introduction of a reinforcing component in cementitious materials reduces the effect of two main structural defects: 1) low tensile strength and 2) low level of deformation at break. The occurrence of non-structural shrinkage cracks in cement products is due to the fact that numerous microcracks are formed in them during the manufacture of cement products from cement mortar. Subsequently, when a one-time or constant load is applied to a product made of a cement product, or under the influence of its own mass, such a product, microcracks begin to propagate, their number and size increase, and they transform into larger non-structural shrinkage cracks, causing a decrease in strength and destruction of the cement product. product. By preventing the propagation of microcracks, it is possible to increase the effective strength of the cement product and contribute to increasing its durability.

To give the cement product additional physical and mechanical strength, various reinforcing components are used, such as metal reinforcement, mineral elements and synthetic fibers. It is known that it is synthetic fibers that can most effectively prevent the development of non-structural shrinkage cracks from microcracks, since they are the thinnest of the listed types of reinforcing components, and their sizes are comparable to the sizes of microcracks.

Thus, the volumetric reinforcement of the cement product with synthetic fibers can compensate for the main disadvantages of the cement product - shrinkage cracking, low tensile strength and brittleness of fracture, and, as a result, the cement product with a fiber component has a higher compressive strength, tensile strength, tensile strength shear, impact and fatigue strength, crack resistance, frost resistance and water resistance compared to a cement product that does not contain volume reinforcing its synthetic fiber.

Unlike other fibrous materials, synthetic fibers are known to reduce such cracking caused by early plastic shrinkage. For example, a fibrillated fiber formed from a polyolefin film has been successfully used to prevent or reduce cracking. The fibers are stretched several times, and then cut along the lines, at least partially transversely with respect to the orientation direction. The fibers are thus fibrillated. When mixed with cementitious material, the fibers are dispersed in the mixture, forming a network, and thereby the strength and bonding characteristics of the cement matrix are increased.

Known synthetic fibers for dispersed reinforcement of cement-based products (RF patent No. 2074153). According to this patent, bundles of synthetic fibers are introduced into the cement mortar containing 10-10000 elementary fibers per bundle. The bundles of synthetic fibers before being introduced into the cement mortar are treated with a wetting agent that increases the surface tension of the elementary fibers. To increase surface tension, corona discharge treatment of fiber bundles can also be used along with wetting agent treatment. The elementary synthetic fibers are polyolefin fibers, preferably polyethylene or polypropylene fibers, 1-30 mm long and an average transverse size of 5-50 microns.

However, although synthetic fibers can avoid the use of metal reinforcement, cement products that use such fibers still have not very high strength. This is due to the fact that the surface treatment of the fiber with hydrophilizing agents does not allow to achieve the same surface tension on the entire surface of the fiber, and, moreover, when processing fibers in a bundle, individual fibers can remain unprocessed, which further affects the dispersion of such fibers in cement product.

Known reinforcing additive (patent US 6753081, publ. 06/22/2004), which is a mixture of synthetic fibers and comprising a first fiber component formed from a polypropylene homopolymer, and a second fiber component formed from a mixture of high density polypropylene and polyethylene. The first component is fibrillated, and the second is a twisted bundle of non-fibrillated monofilament fibers.

A mixture of fibers gives improved reinforcement properties to the building materials to which they are added. In particular, synthetic fibers provide the following properties: permeability decreases, strength fatigue increases, toughness improves, and plastic shrinkage also decreases. The unique properties of the twisted second fiber component mixed with the first fiber component provides improved mixing and uniform distribution of the synthetic fiber in the cementitious material mixture.

Known fiber-reinforced material, products from them and the method of its production (patent US 7168232, publ. 02.26.2004, IPC С04В 16/06; СВВ 28/02) (prototype).

The fiber-reinforced material may include a fiber component, which is a twisted bundle consisting of many strands of non-fibrillated monofilaments, the degree of twist is more than about 0.9 revolutions / inch (about 0.36 revolutions / cm). It may also further comprise another fiber component formed from a twisted fibrillated fiber component.

In this case, the first and second components essentially have the same length in the range of 19-60 mm and are made of a copolymer of polypropylene (75-80%) and polyethylene (20-25%).

The degree of twist in the range from more than about 0.9 revolutions / inch (about 0.36 rpm) to about 1.1 revolutions / inch (about 0.43 revolutions / cm) and about 1.1 revolutions / inch (about 0.43 rpm / cm).

Known reinforced material was used as a reinforcing additive for cementitious asphalt mixture.

An object of the present invention is to provide a reinforcing additive for concrete made of synthetic fiber for bulk reinforcement of cement products, which is capable of uniformly dispersing in the volume of cement product, characterized after hardening by high strength indices, such as high compressive strength, bending strength and tensile bending strength .

The technical result of the claimed invention consists in high strength indices: high compressive strength, bending strength and tensile bending strength.

The technical result is achieved by the fact that the reinforcing additive for concrete includes twisted into a strand with a right Z-shaped torsion, fibers obtained in the form of a tape by extrusion of a melt of a mixture of polypropylene and low-pressure polyethylene, while torsion is performed at a number of 40-45 twists per linear meter of fiber when the ratio of the components of the specified mixture, wt. %: (PP) polypropylene 67-73, (HDPE) low pressure polyethylene 27-33 with additional subsequent corrugation of the specified fiber.

The implementation of the invention

A method of obtaining a reinforcing additive for concrete

1. The manufacture of polyolefin fiber-fiber

Polyolefin fibers were made from a melt of a mixture of 70% polypropylene grade 21030, produced according to GOST 26996-86, and 30% low-density polyethylene grade 276-73, manufactured according to GOST 16338-85, with the addition of dye.

The heated molten mass was passed through an extruder to obtain individual fibers, representing a tape with approximate dimensions: width - 1.15 ± 0.05 mm, thickness - 0.34 ± 0.053 mm. The obtained fibers were subjected to corrugation of the surface on the corrugator in the amount of 200-350 corrugations per 1 linear meter of fiber and a corrugation height of 0.5-1.5 mm.

The tow was made of several fibers (2-10 fibers) with a linear density of 333 tex twisted together with the right (Z) direction of torsion and a twist angle of 10 °.

The twisting of the fibers was carried out with a value of at least 40-45 twists per 1 linear meter of a bundle twisted of ten fibers.

The finished harness was strung on a bobbin and then subjected to cutting on a special guillotine into segments 30-65 mm long.

Point samples were taken to control the physicochemical properties of the obtained fiber, according to GOST 10213.0.

The main physico-chemical properties of the obtained by extrusion of fiber (corrugated) are shown in table 1.

The physicochemical properties of the extruded corrugated fiber were determined by standard methods: tensile strength and elongation at break were determined by the method of GOST 10213.2. Humidity is determined according to GOST 10213.3.

Tests of fiber - polyolefin fiber, in order to determine the assessment of its effectiveness in mixtures, concretes and solutions were carried out according to GOST 30459.

Examples of the implementation of the claimed invention:

A control sample was made of heavy concrete without fibers: Consumption of materials per 1 m ³ :

Cement ПЦ-500, OJSC "Mordovcement" 360 kg Crushed stone fractions 5-20 mm 1100 kg Enriched sand (MKR - 3.0) 850 kg Water 230 l

Other control samples of concrete compositions were also made: by introducing metal fibers into the control composition and concrete composition samples by introducing into the control composition a reinforcing additive consisting of extruded and corrugated polyolefin fibers twisted into a bundle with a right Z torsion direction.

Composition No. 1: by introducing into the control composition of metal fibers in the amount of 1/50 - 25 kg.

Composition No. 2: by introducing into the control composition of the reinforcing additive in an amount of 1 kg

Composition No. 3: by introducing into the control composition of the reinforcing additive in an amount of 1.2 kg

Composition No. 4 by introducing into the control composition of the reinforcing additives in an amount of 1.5 kg

Prism samples were made from control samples.

Production and testing of samples was carried out in accordance with the requirements of GOST 10180-2012 “Concretes. Methods for determining the strength of control samples. "

The characteristics of the samples from the control composition and compositions with the obtained obtained polyolefin fiber are shown in table 2.

1. The compressive strength test of 10 × 10 × 10 cm cubic samples, taking into account the coefficient of reducing the concrete strength to the strength of the sample of basic dimensions (0.95) at the age of 7 days:

where R _cr = F / S, where F is the breaking load, S is the working area,

showed that when a polyolefin fiber is introduced into concrete, the compressive strength of concrete does not change. Concrete samples at the age of 7 days reach a strength corresponding to concrete class B25 (M350).

2. Strength test of prism samples with a square section of 10 × 10 × 40 cm tensile when bending at the age of 7 days:

where R _izg = F × l / a (b) * 2, where F is the breaking load, N (kgf),

a, b, l - respectively, the width and height of the cross section of the prism and the distance between the supports when testing samples for tensile bending, mm ² (cm ² ),

and destructive loads: F1 = 2 kH, F2 = 12 kH, F3 = 12.5 kH.

The test results showed that the compositions with the introduced polyolefin fiber have the greatest tensile strength in bending at the age of 7 days and at the age of 28 days, which is higher than in the control sample.

The difference of the claimed reinforcing concrete additive from the prototype is a different ratio by weight of polypropylene and by weight of polyethylene in the fiber, as well as by performing a strand with right Z-shaped torsion, including at least 40-45 twists per linear meter and fiber corrugation.

According to the prototype, the copolymer is about 75-80 percent by weight of polypropylene and about 20-25 percent by weight of polyethylene.

According to the claimed copolymer is about 67-73 percent by weight of polypropylene and about 27-33 percent by weight of polyethylene.

In this case, the fibers of the polyolefin fiber are obtained by extrusion, after which the fibers are corrugated on the corrugator.

The tow is made of several fibers (2-10 fibers) with a linear density of 333 tex, twisted together with the right Z direction of torsion and a twist angle of 10 °.

The twisting of the fibers is carried out with a value of at least 40-45 twists per 1 linear meter of a bundle twisted of ten fibers.

Z - twisting of 45 per 1 linear meter gives tension in the body of the polyolefin fiber, which allows you to evenly distribute in the body of the concrete mixture, when interacting with inert components of concrete.

The advantages of the inventive reinforcing additives for concrete

Mixing polypropylene with low-pressure polyethylene in the claimed weight ratio gives flexibility and softness to the fibers obtained by extrusion, while maintaining the ability to absorb tensile loads. This allows you to twist the resulting thread into a bundle.

This property also minimizes the "sticking" of fibers on the surface.

Twisting the threads into a bundle allows you to increase the reduced diameter of the fibers introduced into the concrete mixture, which contributes to the uniform distribution of the polyolefin fiber in the concrete mixture and eliminates clumping, and allows the polyolefin fiber to be introduced directly into the mixer on the object, while achieving complete distribution of the twisted thread to the component fibers.

The use of the obtained polyolefin fiber in the composition of concrete provides:

- a significant reduction in the process of cracking;

- prevention of chips and cracking;

- increase resistance to shrinkage and kink;

- reduction of the effect of delamination of the concrete mixture;

- increase in friction resistance;

- reduction in water permeability;

- increase the overall life due to resistance to freezing and thawing;

- Improving the waterproofing properties of concrete in the arrangement of pools and other hydraulic structures.

The chemical inertness of the polyolefin fiber makes it possible to use it as a reinforcing additive in concrete structures in chemically aggressive environments (offshore structures, chemical industry enterprises, etc.).

Claims (4)

1. Reinforcing additive for concrete, including fibers twisted into a strand with right Z-shaped torsion, obtained in the form of a tape by extruding a melt of a mixture of polypropylene and low-pressure polyethylene, characterized in that the torsion is performed at a number of 40-45 twists per linear meter of fiber the ratio of the components of the mixture, wt. %: polypropylene 67-73, low pressure polyethylene 27-33 with additional subsequent corrugation of the specified fiber. 2. A reinforcing additive for concrete according to claim 1, characterized in that the tape has a width of 1.1-1.2 mm, a thickness of 0.287-0.393 mm, a length of 30-65 mm. 3. A reinforcing additive for concrete according to claim 1, characterized in that the tow is made with a linear density of 333 tex and a retinue of ten fibers. 4. A reinforcing additive for concrete according to claim 1, characterized in that said corrugation is performed on a corrugator.