RU2369575C1 - Dry building mixture for maintenance and repair work - Google Patents

Abstract

FIELD: construction industry.

SUBSTANCE: dry mixture includes crushed stone with particle size of 3-10 mm, sand M_{size modulus}=2.4, cementing material - standard portland cement of the grade not less than 500, superplasticisng agent C-3, ultrahigh early-strength cement on the basis of calcium sulfoaluminate, steel fibre, at the following component ratio, wt %: portland cement - 8.75-13.75%; ultrahigh early-strength cement - 16. 25-11.25%; sand - 44.85%; crushed stone -25.9%; superplasticisng agent C-3 - 0.25%; and fibre - 4.0%.

EFFECT: speeding up material hardening.

4 cl, 2 tbl

Description

The invention relates to building materials, namely to multicomponent dry construction mixtures, and can be used in the repair and restoration of load-bearing structures, in particular for the repair of concrete and reinforced concrete coatings of airfields, roads, parking areas, as well as structural elements of bridges, tunnels etc.

An analysis of the current state of the art in this area showed that the Progress-II dry mix is known, including Portland cement, sand, a mineral expanding additive, and a hardening accelerator (RF patent for the invention No. 2144908, IPC С04В 28/02, publ. 01.27.2000, Bulletin No. 3).

The inability to achieve a technical result provided by the inventive mixture is due to the fact that concrete made from the specified cement-sand mixture of the analogue has low compressive and tensile strength in bending due to the absence of crushed stone in it.

Known dry mixture, including mineral binder based on Portland cement, sand, superplasticizer C-3, hardening accelerator (RF Patent for invention No. 2259964, IPC С04В 28/02 // С04В 111: 20, publ. 09/10/2005, bull. No. 25 )

The inability to achieve a technical result provided by the claimed mixture is due to the fact that concrete made from the specified dry mixture has an insufficient tensile strength in compression and tension during bending at an early age (1 day).

Of the known technical solutions, the closest to the claimed one is the mixture, on the basis of which a solution is used to restore the paving of the road surface, including crushed stone, sand, mineral binder, additive, cement-based hardening accelerator (Patent DE No. 19848437, IPC E01C 23/09, publ. 04.05.2000, bulletin “Inventions of the World”, issue 57 No. 5/2001, p. 3).

The inability to achieve the specified technical solution of the prototype of the technical result achieved by the inventive mixture is due to insufficient tensile strength in compression and tensile bending at an early age. The use of ultrafine crushed cement as a part of the prototype provides a high-speed set of strength at the age of concrete hardening of 1-3 days, which leads to an extension of the start-up time of the repair products.

The task to which the claimed technical solution is directed is to create a dry building mix that can be used in a limited time, for example, when repairing cement-concrete coatings of airfields with a strict schedule of aircraft movements, and which contains widely available constituent components that allow to ensure increase in strength characteristics during compression and tension during bending in a shorter time, which allows to accelerate the start of repair products depending on customer requirements.

In solving this problem, a technical result was achieved due to the use of a binder in the dry mixture as a hardening accelerator based on ultrahigh-hardening cement based on calcium sulfoaluminate, in combination with rated Portland cement of at least 500 grade, the presence of which together with other components affected the reduction the time of curing and the ability to control the kinetics of curing by varying the crystallization time of the structural lattice due to I proportions of components administered to the mixture in the following proportions intervals that are associated with a corresponding expansion of the cement stone, shrinkage compensating deformation in said range.

The introduction of fiber and superplasticizer S-3 also allowed to increase the strength of the material.

The specified technical result is achieved due to the fact that the specified dry repair mixture includes crushed stone, sand, mineral binder, additive, cement-based hardening accelerator.

New in the composition of the dry mix is that it additionally contains fiber, normalized Portland cement of a grade of at least 500 is used as a mineral binder, C-3 superplasticizer is used as an additive, and ultrahigh-hardening cement based on calcium sulfoaluminate is used as a hardening accelerator in the following ratio components, wt.%:

Specified Portland cement 8.75-13.75 Specified Ultrahardening Cement 16.25-11.25 Crushed stone 25.9 Sand 44.85 Superplasticizer S-3 0.25 Fiber 4.0

In addition, crushed stone of fraction 3-10, sand M _cr = 2.4 can be used in the mixture, and steel fibers can be used as fiber.

In addition, the dry mixture can be closed with water in a ratio of 74 g of water per 1 kg of dry mixture.

For the preparation of dry building mixes for repair and restoration work of the specified composition of the brand "RM-26F-B" are used:

- natural quartz sand with M _cr = 2.4 Petrovsky quarry GOST 8736-93;

- normalized Portland cement ПЦ 500, ПЦ 600 of the Starooskolsky cement plant GOST 10178-85;

- granite crushed stone fraction 3-10 mm Pavlovsky quarry GOST 8267-93;

- steel fiber manufactured by CJSC "VOLVEK" Chelyabinsk;

- S-3 superplasticizer based on the sodium salt of naphthalene sulfonic acid with formaldehyde (TU 6-36-0204229-625-90), manufactured by Ural-Plast LLC, Pervouralsk GOST 24211-91;

- ultrafast hardening cement based on calcium sulfoaluminate.

Normalized Portland cement is used in the dry mix, that is, Portland cement, not containing active mineral additives, with a content of tricalcium aluminate in an amount of not more than 8% by weight. The use of normalized Portland cement at a specified dosage of 8.75-13.75 wt.% Allows you to provide the declared compressive and tensile strength in bending at an early age of hardening (2-6 hours), and the use of the specified normalized Portland cement brand of at least 500 increases the strength of the material. With a brand of less than 500, Portland cement activity decreases, which accordingly reduces its strength.

The use of crushed granite in wt.% 25.9 as a large aggregate allows you to create a "skeleton" of concrete, which allows to increase the compressive strength.

The use of sand in wt.% 44.85 with M _cr = 2.4 as a fine aggregate ensures optimal packing density of concrete.

The use of C-3 superplasticizer as an additive in the indicated proportion of 0.25 wt.% Helps to reduce the ratio of water / cement (W / C) at given costs of Portland cement and hardening accelerator while maintaining the necessary mobility. The mechanism of action of the S-3 superplasticizer is based on adsorption by its polar groups on the surface of hydrating cement particles with the formation of a monomolecular layer that reduces internal friction in the cement-water system, which increases the plasticity of the concrete mixture while reducing water consumption.

However, it was found that, adsorbing on the surface of cement minerals and their hydration products, the addition of C-3 superplasticizer slows down the hydration process in the early stages of hardening, and this change relates mainly to the silicate component of cement clinker. In the future, the process of hydration of cement stone with the addition of C-3 normal hardening is equal to the control without additives. The observed effect of the increase in the strength of cement stone while slowing down the process of cement hydration is explained by obtaining a denser stone in the presence of an additive.

Additive C-3, having dispersing properties, promotes the formation of a more uniform microstructure of cement stone, at the same time it has an air-absorbing ability, promotes the formation of a large-pore structure of cement stone with a constant water-cement ratio, as well as increasing the ductility of the repair material while reducing the water demand of the repair cement-concrete mixtures.

The use of ultrahardening cement based on calcium sulfoaluminate in the range of 16.25-11.25 as a hardening accelerator based on cement can significantly increase the time required for curing. Moreover, an increase in a given dosage within a given interval will allow to gain strength even more efficiently (30 MPa in less than 2 hours), and a decrease in a given dosage in the same interval will increase the rate of curing.

и двухкальциевый силикат C₂S, характеризуется низкими усадочными деформациями, высокой ранней (2-6 час) прочностью, стойкостью к воздействию агрессивных сред, т.е. отвечает основным требованиям сверхбыстротвердеющего вяжущего.Ultrafast hardening cement based on calcium sulfoaluminate with a low content of tricalcium aluminate C ₃ A, the main components of which are calcium sulfoaluminate C ₄ A ₃

and dicalcium silicate C ₂ S, characterized by low shrinkage deformation, high early (2-6 hours) strength, resistance to aggressive environments, i.e. Meets the basic requirements of an ultrafast hardening binder.

, получаемого путем обжига при температуре 1370°С смеси известкового, глиноземистого компонента и гипса, в результате которого первоначально образуются алюминаты кальция, при взаимодействии которых с гипсом получается сульфоалюминат кальция. Было обнаружено, что присутствие ограниченного количества извести необходимо для быстрого нарастания прочности и что требуется создать условия, чтобы весь СO₃ был связан в виде С₄А₃

, во избежание атмосферного загрязнения. В качестве глиноземистого компонента применяются высокоалюминатные глины, золы, шлаки вторичной переплавки алюминия, бокситы, причем содержание в данных компонентах Аl₂O₃ должно быть не менее 30%, а количество SiO₂ устанавливается в зависимости от количества в сырье Аl₂O₃.The acceleration of the hardening of this binder in the early stages is based on the hydration of calcium sulfoaluminate C ₄ A ₃

obtained by calcination at a temperature of 1370 ° C of a mixture of a calcareous, aluminous component and gypsum, as a result of which calcium aluminates are initially formed, which interact with gypsum to produce calcium sulfoaluminate. It was found that the presence of a limited amount of lime is necessary for a quick increase in strength and that it is necessary to create conditions so that all CO ₃ is bound in the form of C ₄ A ₃

, to avoid atmospheric pollution. As an aluminous component, high aluminate clays, ashes, slags of secondary remelting of aluminum, bauxite are used, moreover, the content of these components Al ₂ O ₃ should be at least 30%, and the amount of SiO _{2 is} set depending on the amount of Al ₂ O ₃ in the feed.

The presence of calcium sulfoaluminate, obtained by calcining a mixture of calcareous, aluminous components and gypsum, leads to the formation of high-water hydrates and high exotherm of their hydration processes, that is, to conditions that facilitate the removal of water from the reaction zone, accelerate the formation and increase the number of contacts of the crystalline type with a twisted mesh through needles 1-2 microns in length ettringite, that is, neoplasms during cement hydration, providing an ultrafast set of strength, which leads to a particularly fast a set of strength cements.

The main contribution to the formation of strength in the early stages is made by the aluminate component, and in the later ones by the silicate component of ultrahardening cement.

Also noteworthy is the equally important quality of calcium sulfoaluminate - sulfoaluminate expansion of cement stone during hydration. The main compound, the formation of which causes expansion, is ettringite, that is, the process of increasing the linear and volume sizes occurring under the influence of the formation of calcium hydrosulfoaluminates. Sulfoaluminate expansion of cement stone occurs during the first two days of hardening and can provide a change in linear dimensions up to 4-5%.

Thus, low shrinkage deformations of ultrahard-hardening cement based on calcium sulfoaluminate are achieved by compensating for the controlled linear expansion of the cement stone, which occurs during the first two days of hydration during the formation of ettringite, by shrinkage deformations that occur during the further formation of the strength of the silicate component.

It was experimentally established that the above properties of the repair area of the coating of the proposed mixture appear when a combination of these components and in the proposed proportions.

The introduction of the above substances into the composition of the dry construction mixture in the proposed ranges of the ratios of the components of the mixture, wt.% Allows to provide the following properties of the mixture, shown in table 2 for the ratios of the compositions of the compositions listed in table 1.

The technology for the production of dry mix, called RM-26F-B, includes a dosage of finished components. Mixing and packaging of moisture-proof components of the dry construction mixture into moisture-proof bags is carried out at the installation of dry mixes according to the standard technological scheme or similar installations.

Dry mortar is used in the following way.

At the preparatory stage, marking the defective area, for example, airfield cover, removing the old sealant and sealing cord from the seams, cutting grooves, is carried out.

The lines of the defective coating area are marked with paint in compliance with the following condition: the marked lines must be parallel to the existing seams of the coating.

Sealant and sealing cord are removed by special machines or steel hooks, followed by purging of the groove of the seam with compressed air.

Concrete removal from defective areas during the repair of surface damage is carried out by milling or using a percussion instrument. In accordance with the existing regulatory requirements, to prevent the formation of microcracks in the repaired coating and to observe the depth of cutting during the work of the percussion instrument, it is necessary to outline the defective area and cut additional grooves.

The grooves are cut with diamond blades in longitudinal strips to the depth of the removed defective concrete layer (but not less than 50 mm).

During repair work on partial or complete replacement of concrete slabs, for example, airfield or pavement, cutting grooves in defective slabs is carried out to the entire depth of the coating.

The sizes of blocks on which defective plates should be sawn are set in each case by calculation depending on the thickness of the plates and the characteristics of the existing hoisting mechanisms.

After completion of the preparatory phase, they proceed directly to the repair work: concrete is removed from the defective area. Concrete felling from the defective area in order to avoid cracking in the concrete of the repaired coating is carried out using a low-power impact power tool.

The walls of the felling should be vertical, and the bottom of the felling is horizontal. The depth of felling should be not less than the depth of the cleavage.

Then they clean and dust the surface of the cavity of the site freed from concrete. Surface cleaning from sludge is performed with metal brushes, followed by washing the surface with water under pressure and blowing with compressed air.

After cleaning, a gasket (soft formwork) is installed with a thickness equal to the width of the existing seam, if the chips are removed, the surface of the site is moistened and treated with brushes or brushes with cement glue with a flow rate of 0.8-1.2 l / m ² . At the same time, the surface of the concrete should be moist, but there should not be free water on it. Cement glue should be prepared in containers with a volume of 10 ... 15 liters. The required water consumption for the preparation of glue is 3 ... 3.5 liters per 10 kg of dry mix. In the presence of reinforcement in the place of cleavage, it is usually stored, cleaning from concrete residues.

After cleaning, washing with water and applying glue, the bags with the dry mixture are cut, repair material is prepared by mixing it with water based on, for example, 74 g of water per 1 kg of dry mixture, mix and the resulting solution is placed in the formed cavity. Preparation of concrete mix due to the short shelf life of its workability (see table 2) should begin immediately before laying, i.e. not later than 15 minutes after applying the cement cement to be repaired on the concrete surface.

Repair material is prepared manually by mixing the dry repair mixture with the required amount of water in the pan with shovels. At the same time, depending on the deadlines set by the customer for commencement of operation of the repaired area, ultrahardening cement varies with various values of wt.% At specified intervals.

After laying, the repair material is compacted by using a platform vibrator or vibrorails in 1-2 passes along one track. For small amounts of work, manual tamping is performed.

Next, care is taken for the laid repair material by applying a roughness and film-forming material on its surface, as well as, if necessary, heat treating the freshly laid concrete mixture, remove the gasket (soft formwork) from the seam and seal the seam.

Heat treatment is carried out at ambient temperature.

air less than 15 ° C, while the repaired coating area must be preheated before applying cement glue to the prepared concrete surface.

The heat treatment of the freshly laid concrete mixture should be carried out immediately after the final surface treatment of the coating by covering the laid concrete mixture with mineral wool heat-insulating mats.

Unloading concrete mixture to the repaired area, its distribution over the area of the site, compaction and surface finishing should be carried out as soon as possible.

When repairing chipped edges of concrete slabs, if the chipped width is less than 1.5 times its height, anchors made of reinforcing steel of a periodic profile with a diameter of 10 ... 12 mm should be installed in the horizontal and vertical shelves.

Anchors should be installed in holes pre-drilled by a puncher with a diameter of 1 ... 2 mm larger than the diameter of the anchor. Anchors should be glued to the inside of the holes throughout their depths.

For testing, control samples are made.

Determination of the density of concrete from repair material is carried out in accordance with the requirements of GOST 12730.1-78 by hydrostatic weighing on electronic scales GP 6100-G. Weighing of samples is carried out with an accuracy of 0.1 g.

Bending tensile strength testing for 40 × 40 × 160 mm beam samples is carried out according to GOST 310.4-81 on the IM-4a testing machine, and for 70 × 70 × 280 mm beam samples according to GOST 10180-90, on a hydraulic press IP 100-1.

Tests to determine the compressive strength of samples are carried out in accordance with GOST 10180-90 on a hydraulic press IP 1000.0.

Shrinkage deformations of the repair material are determined on samples-beams with a size of 40 × 40 × 160 mm using an optical strain gauge IZV-1 (fission price - 0.001 mm). Tests are carried out in accordance with the requirements of GOST 24544-81.

Determination of frost resistance of samples is carried out in accordance with the requirements of GOST 10060.0-95 and GOST 10060.2-95.

Adhesive properties (adhesion strength of the repair material to old concrete) are determined according to GOST 10180-90.

The mobility of the repair mixture was evaluated by the cone spread on the shaking table according to GOST 310.4-81.

The persistence of workability of the repair mixture was evaluated by comparative tests to determine the cone spread according to GOST 310.4-81 immediately after preparation of the repair composition and then after 5, 10, 15 ... 30 minutes after the initial determination. The assessment of the persistence of workability was characterized by the time at which the melt cone of the repair mixture with the sealed water decreases by 10% compared with the initial determination.

The ability to carry out the inventive dry mix for repair and restoration is confirmed by the use of inexpensive building materials in it, having optimal performance characteristics with properties that ensure high-quality restoration of cement concrete coatings existing and used in the field of construction repair and restoration works, including at the level of functional generalization, with the achievement of the technical result, which consists in accelerating the hardening of the material in the early rock solidification.

Table 1 Name of components Compositions, wt.% one 2 3 Portland cement 8.75 12.5 13.75 Superfast hardening cement 16.25 12.5 11.25 Sand 44.85 44.85 44.85 Crushed stone 25.9 25.9 25.9 Superplasticizer S-3 0.25 0.25 0.25 Fiber four four four table 2 Characteristics Compositions one 2 3 The consistency of the mixture (cone spread), mm at a flow rate of water:
-74 g per 1 kg of dry mix 120-130 120-130 120-130 Preservation of workability, min, at least 10 fifteen twenty Tensile strength in bending, MPa not less than: at the age of 2 hours 4,5 - - 4 h 5,0 4,5 - 6 h 6.0 5,0 4,5 1 day 7.5 7.5 7.5 28 days 10.5 10.5 10.5 Compressive strength, MPa not less than: at the age of 2 hours thirty - - 4 h 45 thirty - 6 h fifty 45 thirty 1 day 55 55 fifty 28 days 60 60 60 Adhesion to concrete, MPa not less than: at the age of 6 hours 1,2 1,2 1,2 1 day 1.8 1.8 1.8 28 days 2.5 2.5 2.5 Relative shrinkage deformation, mm / m no more than: at the age of 28 days. 0.25 0.32 0.35 Frost resistance, cycles not less 200 200 200

Claims (4)

1. Dry building mixture for repair and restoration work, including crushed stone, sand, mineral binder, additive, cement-based hardening accelerator, characterized in that it additionally contains fiber, and normalized Portland cement of a grade of at least 500 is used as a mineral binder as an additive, superplasticizer C-3, as a hardening accelerator, ultrahard-hardening cement based on calcium sulfoaluminate, in the following ratio of components, wt.%:
Specified Portland cement 8.75-13.75 Specified Ultrahardening Cement 16.25-11.25 Sand 44.85 Crushed stone 25.9 Superplasticizer S-3 0.25 Fiber 4.0 2. The dry building mixture according to claim 1, characterized in that it uses crushed stone of a fraction of 3-10 mm, sand M _cr = 2.4. 3. The dry building mix according to claim 1, characterized in that steel fibers are used as fiber. 4. The dry building mix according to claim 1, characterized in that the mixture is shut with water in a ratio of 74 g of water per 1 kg of dry mix.