Method of concreting at sub-zero temperatures

Abstract

FIELD: construction operations.SUBSTANCE: invention can be used in the construction of monolithic horizontal reinforced concrete structures: floor slabs, foundation slabs, etc., when concreting in sub-zero temperature conditions. In the method of concreting at sub-zero temperatures, which includes the preparation of a concrete mixture, expanded clay gravel in the form of granules of a fraction of up to 10 mm in an amount of 5-15 l / m2 of the concreted surface or its screenings in an amount of 10-20 l / m2 of the concreted surface is used as a mineral additive, whereas expanded clay gravel or its screenings are pre-saturated with a solution of an anti-freeze additive. The mixture is mixed, placed into the formwork, then the mixture is vibrated and compacted until the mineral additives float and a continuous upper heat-insulating layer 5-14 mm thick is created.EFFECT: creating a continuous upper heat-insulating layer of concreted monolithic reinforced concrete structures under sub-zero temperatures, preserving the heat of exothermic reactions of cement hydration to prevent freezing of concrete, and improving the sound and heat-insulating properties of concrete structures.1 cl, 1 tbl

Description

[0001] The invention relates to construction production and can be used, in particular, in the construction of monolithic horizontal reinforced concrete structures: floor slabs, foundation slabs, etc., when concreting in sub-zero temperatures.

[0002] A method for electrically heating concrete in winter conditions is known (patent RU 2250206, April 20, 2005). The method involves heating the freshly poured concrete using electrically heated mats and applying a protective coating to the surface. A disadvantage of this method is the need for several labor-intensive technological steps, including applying a protective coating of two layers of plastic film to the surface of the freshly poured concrete. Before applying the protective coating, a series of notches are made on the outer layer, with a mixture of dried fine-grained material embedded in them, which is quite difficult to achieve on the surface of freshly poured concrete.

[0003] A known method for concreting at sub-zero temperatures involves adding a conductive mineral, shungite, to the concrete mix and exposing it to an electric field (patent RU 2750883, July 5, 2021). A disadvantage of this solution is the additional technical step of activating the additive with an electric field. Furthermore, this method does not protect the concrete structure from possible freezing if the curing method is delayed.

[0004] The closest in technical essence to the proposed invention is a method of concreting at sub-zero temperatures, including covering the exposed surface of freshly placed concrete immediately after concreting with a rolled waterproofing material and a layer of insulation to protect the upper layers of concrete from early freezing. When using fine-pored aggregates, water absorption of the lightweight aggregate can be reduced by surface treatment with polymers, water-repellent substances, or saturation with water (see the textbook by S.G. Golovnev, Yu.M. Krasny, D.Yu. Krasny, "Concrete Work in Winter Conditions", "Infra-Engineering", Moscow 2012, pp. 20, 31).

[0005] The disadvantage of this technical solution is the need for additional technological steps: covering two layers in succession, and thermal insulation must be designed and prepared in advance, which requires additional labor and material costs and increases the time required to prepare freshly placed concrete for subsequent use of traditional curing methods. Lightweight aggregate treatment is used for lightweight concrete, which has relatively low strength and is practically not used for concreting load-bearing horizontal concrete and reinforced concrete structures.

[0006] The technical problem to be solved by the claimed invention is the development of a method for concreting at sub-zero temperatures, which makes it possible to prevent freezing of monolithic concrete and reinforced concrete horizontal structures made of heavy concrete by creating a continuous heat-insulating layer with the achievement of the following technical result: a reduction in energy and labor costs in subsequent standard methods of maintaining at sub-zero temperatures; an increase in the heat and sound insulation properties of concrete monolithic horizontal concrete and reinforced concrete structures; acceleration of concrete hardening and the gain of its critical strength by intensifying the processes of structure formation

[0007] cement stone; creation of a relief surface of monolithic horizontal structures for the installation of screeds and floors.

[0008] The said technical result is achieved by the fact that in the method of concreting at sub-zero temperatures, which includes the preparation of a concrete mixture, where a porous filler and an anti-freeze additive are used, placing the concrete mixture in formwork and creating an upper heat-insulating layer, according to the invention, expanded clay gravel in the form of granules of a fraction of up to 10 mm in an amount of 5-15 l / m is used as a porous filler. 2 concrete surface or its screening in the amount of 10-20 l / m 2 concrete surface, whereby expanded clay gravel or its screenings are pre-saturated with a solution of anti-freeze additive; the mixture is mixed, placed in the formwork, then the mixture is vibrated and compacted until the mineral additives float to the surface and a continuous upper heat-insulating layer 5-14 mm thick is created.

[0009] The proposed invention is implemented as follows: concrete samples are manufactured using standard forms, measuring 200x200x200 mm (GOST 10180-2012 "Methods for determining strength using control samples"), to approximate the actual thickness of monolithic reinforced concrete floors, concrete class B30 with concrete mix mobility P5 (cone slump 20-25 cm according to GOST 10181-2014 "Concrete mixtures. Test methods"). Basic composition: mineral additives are added to the concrete mix, pre-saturated with a solution of the complex, plasticizing, antifreeze additive "Polyplast KRIO-25". Composition No. 1: concrete mix with "Polyplast KRIO-25" additive; Composition No. 2: concrete mix with the additive "Polyplast KRIO-25" with the addition of a mineral additive in the form of expanded clay gravel granules with a fraction of up to 10 mm (GOST 32496-2013 "Porous fillers for lightweight concrete"), pre-saturated with a solution of the additive "Polyplast KRIO-25", in the amount of 5 l / m 2surface of the concrete top layer; composition No. 3: concrete mix with the additive "Polyplast KRIO-25" with the addition of a mineral additive in the form of expanded clay gravel granules of fraction up to 10

[0010] mm, pre-saturated with a solution of the additive "Polyplast Cryo-25", in the amount of 10 l / m 2 surface of the top layer concrete; No. 4: concrete mix with the additive "Polyplast Kryo-25" with the addition of a mineral additive in the form of expanded clay gravel granules of a fraction of up to 10 mm, pre-saturated with a solution of the additive "Polyplast Kryo-25", in the amount of 15 l / m 2 surface of the top layer concrete; compositions No. 5, No. 6, No. 7: concrete mix of base composition with the addition of a mineral additive in the form of screened expanded clay gravel (GOST 32496-2013 "Porous fillers for lightweight concrete"), pre-saturated with a solution of the additive "Polyplast KRIO-25", in the amount of 10 l / m 2 , 15 l / m 2 and 20 l / m 2 surface of the top layer concrete.

[0011] Expanded clay gravel or expanded clay gravel screenings are placed in a container with a solution of the "Polyplast KRIO-25" antifreeze additive at a concentration corresponding to the concrete mix for 1-2 hours. The gravel or screenings are then removed and added to the concrete mix. The mix is ​​mixed and placed in a mold. Cube samples measuring 200 x 200 x 200 mm are produced to approximate the actual conditions of concreting monolithic reinforced concrete floors 200 mm thick. While pouring the concrete mix into the mold, it is vibrated on a laboratory vibrating platform until the expanded clay granules float or screenings fall to the surface. The prepared concrete samples were cured in chambers with normal humidity curing conditions, at a temperature of 20°C and a relative air humidity of at least 95% (GOST 10180-2012 "Concrete. Methods for Determining Strength Using Control Samples"). After 28 days of curing, the samples were tested for thermal conductivity and compressive strength.The following samples of concrete mixture with fine-pored mineral additives were produced:

[0012] - sample No. 1, concrete mix without additive;

[0013] - samples No. 2, 3, 4, with the addition of expanded clay gravel of fraction up to 10 mm, in the amount of 5, 10, 15 l / m 2 surface of the sample respectively;

[0014] - samples No. 5, 6, 7, with the addition of expanded clay gravel screenings with a content of 10, 15, 20 l / m 2 surface of the sample, respectively.

[0015] The test results are shown in the table.

[0016] After stripping the specimens, the continuity of the mineral additive distribution on the specimen surface and the thickness of the mineral additive layer on top of the specimens were visually determined. Thermal conductivity was determined using the "through method" (GOST 7076-99 "Construction Materials and Products. Method for Determining Thermal Conductivity and Thermal Resistance under Steady-State Thermal Conditions"), and compressive strength was determined using the destructive method. Tests were conducted using an ITP-MG 4 ("Zond") device. Temperature gradient: 20°C between the hot and cold platens.

[0017]

[0018] The test results showed that samples 3 and 6 have the best thermal conductivity, while maintaining the required compressive strength of B30. The addition of expanded clay reduces λ by 15-52% (the maximum is for sample #7). Expanded clay screenings are more effective than gravel (a smaller particle size provides more air pores). Sample #7 shows the best result. Compressive strength (loading rate 0.6 MPa / s. Strength is inversely proportional to the amount of additive (the porous structure reduces density). Expanded clay gravel (Nos. 2-4) provides a smaller reduction in strength than screenings (Nos. 5-7) with an equal volume. The critical reduction in strength is 34% for sample #7 (relative to sample #1).

[0019] Visual assessment after stripping: Samples #3 and #6 have the best homogeneity (optimal amount of additive). Segregation is seen in samples #4 and #7 (excess additive and delamination during vibration). Layer thickness increases linearly with additive volume (3-13 mm). General conclusions can be drawn that expanded clay screening produces the greatest reduction in thermal conductivity (up to 52% at 20 l / m). 2 ) The optimal composition is sample No. 6 (λ = 0.95 W / (m⋅°C). All samples correspond to concrete class B30, except sample No. 7. For monolithic floors, compositions No. 3 (expanded clay gravel 10 l / m) are preferable. 2 ) and No. 6 (screening 15 l / m 2 ), combining λ≤1.3 W / (m⋅°C) and strength ≥33 MPa.

[0020] Use of fine-pored mineral additives in the form of expanded clay gravel in the form of granules with a fraction of up to 10 mm in the amount of 10 l / m 2 or its screening in the amount of 15 l / m 2The concrete surface of monolithic horizontal concrete and reinforced concrete structures allows for the creation of a continuous upper thermal insulation layer for concrete monolithic reinforced concrete structures under subzero temperatures, preserving the heat of exothermic cement hydration reactions to prevent concrete freezing before standard methods for curing concrete at subzero temperatures are used. This method also allows for the creation of a textured surface for monolithic horizontal structures for screeds and floors.

Claims

A method of concreting at sub-zero temperatures, which includes the preparation of a concrete mixture using a porous filler and an antifreeze additive, placing the concrete mixture in formwork and creating an upper heat-insulating layer, characterized in that expanded clay gravel in the form of granules of a fraction of up to 10 mm in an amount of 5-15 l / m is used as a porous filler. 2 concrete surface or its screening in the amount of 10-20 l / m 2 concrete surface, whereby expanded clay gravel or its screenings are pre-saturated with a solution of anti-freeze additive; the mixture is mixed, placed in the formwork, then the mixture is vibrated and compacted until the mineral additives float to the surface and a continuous upper heat-insulating layer 5-14 mm thick is created.

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