A high anti-cracking concrete structure for high altitude and low humidity environment and its preparation method

Abstract

The present invention discloses a high anti-cracking concrete structure in a high-altitude and low-humidity environment and a preparation method thereof, belonging to the technical field of civil engineering. The present invention proposes to use the frozen concrete technology to propose a new type of concrete structure form, that is, to pour high-ductility concrete on the outer layer of the frozen concrete and pour normal-flowing ordinary concrete on the inner layer of the frozen concrete. This structure form has high-ductility concrete only within the protective layer, and the inside is still ordinary concrete, which has the effect of significantly reducing the construction cost, solves the engineering problem that high-ductility concrete cannot be used in the whole section due to its too high cost, and realizes the technical effect of high anti-cracking of the outer concrete. This technology has the effect of combining and pouring different types of concrete, and the hydration is mutually interactive without generating durability problems induced by the interface of different concretes.

Description

Technical Field

[0001] The present invention belongs to the technical field of civil engineering, and particularly relates to a high anti-cracking concrete structure in a high-altitude and low-humidity environment and a preparation method thereof. Background Art

[0002] China has complex geographical conditions. In some areas such as western Sichuan, the altitude is generally high, the climate conditions are poor, accompanied by low humidity and large temperature differences. The environmental conditions are severe, which is not conducive to the formation and development of concrete. The concrete structures poured under such environmental conditions have serious cracking problems, which is not conducive to their long-term durability and safety development, and may even induce huge social and economic losses.

[0003] Low humidity, large temperature differences and strong radiation in high-altitude areas are the main reasons for the common cracking of concrete structures in this special environment. In a low-humidity environment, the internal hydration of concrete causes the relative humidity in its pores to drop rapidly, and the pore tensile stress is relatively large, resulting in a relatively large autogenous shrinkage deformation of the concrete, thus causing cracks. Secondly, when the concrete is in a low-temperature environment below -5~-6°C for a long time, the pore water in its cement stone structure will freeze and cause volume expansion, generating expansion stress and osmotic pressure in the internal microstructure of the concrete, further leading to the generation and development of microcracks and causing freeze-thaw cracking of the concrete structure. At the same time, under the environment of hydration heat effect, solar radiation and large temperature differences, the temperature stress of the concrete is also relatively large, and some temperature cracks will also occur. Once the concrete structure shows serious cracking, it will have a greater impact on the overall durability of the structure and the safety during use.

[0004] Regarding the cracking problem of concrete structures in high-altitude cold regions, the current common methods include optimizing the concrete mix ratio, surface heat preservation and moisture preservation, etc. However, for the construction of concrete structures in high-altitude areas, due to the high altitude and harsh construction conditions, it is inconvenient to transport construction equipment and materials, and many anti-cracking measures are difficult to be effectively implemented. The method commonly used at the construction site at present is to strengthen the maintenance of the concrete and extend the wet maintenance time to ensure that the concrete is fully hydrated and improve the anti-cracking ability. However, in the special environment of high-altitude areas, once the maintenance measures are removed, the cracking caused by environmental impact will occur immediately. This method can only treat the symptoms but not the root cause, mainly because the tensile strength of the concrete itself is too low to resist such a special environment.

[0005] Regarding the above-mentioned cracking problem, there is currently a type of high-ductility concrete, which is a fiber-reinforced cement-based composite material. Compared with traditional concrete, it is characterized by high ductility and strong crack width control ability. A large number of fine fibers with high elastic modulus are incorporated into the high-ductility concrete. These fibers are evenly distributed in the cement matrix, forming a dense micro-crack control network, which can effectively prevent the generation and development of cracks, and improve the overall toughness and crack resistance of the material. Using this kind of concrete can effectively reduce the cracking problem of concrete structures in alpine regions. However, the cost of high-ductility concrete is too high, and it does not meet the conditions for full-section application of concrete structures. Summary of the Invention

[0006] In order to solve the above-mentioned deficiencies of the existing technology, the purpose of the present invention is to provide a high crack-resistant concrete structure and its preparation method in a high-altitude and low-humidity environment, so as to solve the technical problem that the existing concrete structures are prone to cracking in special environments.

[0007] The technical solution of the present invention to solve the above technical problems is as follows: Provide a high crack-resistant concrete structure in a high-altitude and low-humidity environment, characterized in that the outer layer of the high crack-resistant concrete structure is high-ductility concrete, the middle layer is frozen concrete, and the inner layer is flowing ordinary concrete.

[0008] Furthermore, the thickness of the high-ductility concrete is 20 - 50 mm; the thickness of the frozen concrete is 80 - 120 mm.

[0009] Furthermore, the thickness of the high-ductility concrete is 30 mm; the thickness of the frozen concrete is 100 mm.

[0010] Furthermore, the high-ductility concrete is a fiber-reinforced cement-based composite material.

[0011] Furthermore, the fibers in the fiber-reinforced cement-based composite material are at least one of steel fibers and polyvinyl alcohol fibers.

[0012] The present invention also provides a preparation method of a high crack-resistant concrete structure in a high-altitude and low-humidity environment, including the following steps:

[0013] (1) Freeze the flowing concrete to obtain frozen concrete, and then fix it with a steel reinforcement cage;

[0014] (2) Pour high-ductility concrete on the outer layer of the frozen concrete obtained in step (1), and pour flowing concrete on the inner layer to obtain it.

[0015] Furthermore, in the pouring process of step (2), the heights of the outer high-ductility concrete and the inner flowing ordinary concrete are kept the same.

[0016] The present invention has the following beneficial effects:

[0017] (1) The present invention proposes to utilize the frozen concrete technology to propose a new type of concrete structure, that is, to pour high-ductility concrete on the outer layer of frozen normal concrete and pour normal-flowing normal concrete on the inner layer of frozen normal concrete. Only the high-ductility concrete is within the protective layer range of this structural form, and the inside is still normal concrete, which can significantly reduce the construction cost, solve the engineering problem that the high-ductility concrete cannot be used in the whole section due to its high cost, and further achieve the technical effect of high crack resistance of the outer concrete. This technology has the effect of combining and pouring different types of concrete, and they interact with each other during hydration without causing durability problems induced by the interface between different concretes.

[0018] (2) The frozen concrete is not only the structural concrete of the column itself but also serves as a barrier to isolate the outer high-ductility concrete from entering the normal concrete, and at the same time has the function of reducing the hydration heat of the outer high-ductility concrete to prevent the thermal stress caused by excessive hydration heat. The frozen concrete will melt under the combined action of the inner and outer layer concretes, and at this time it acts together with the inner and outer concretes, so there is no interface that affects the strength or durability.

[0019] (3) The outer high-ductility concrete itself has high crack resistance, which can significantly reduce the crack width, avoid frequent curing when the whole section is normal concrete, improve the formwork turnover efficiency, reduce the curing water, etc., and can also prevent the problem that normal concrete is prone to cracking in special environments such as low humidity and large temperature difference. At the same time, this high-ductility layer concrete has high durability and can resist freeze-thaw, large temperature difference deformation, etc. during its service life. Specific embodiments

[0020] The following examples are only used to explain the present invention and are not used to limit the scope of the present invention. For those not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0021] Example 1

[0022] A high anti-cracking concrete structure for high altitude and low humidity environment, with a high ductility concrete outer layer, a frozen concrete middle layer, and a normal flowing ordinary concrete inner layer, is prepared by the following method: In this embodiment, a cylindrical concrete short column with a diameter of 500 mm and a height of 500 mm is prepared. The thickness of the high ductility concrete protective layer on the outer layer is 30 mm. First, a frozen concrete ring with an inner diameter of 240 mm, an outer diameter of 440 mm, a ring width of 100 mm, and a height of 500 mm is prepared. P.O 42.5 Portland cement is used, and the concrete type is ordinary concrete with a designed strength of C30. After pouring, it is directly placed in a liquid nitrogen freezer, and the heat is absorbed by the evaporation of liquid nitrogen to produce a cooling effect to test the freezing effect. When the concrete specimen reaches -40°C, it is taken out and placed inside the short column mold, ensuring that the center of the ring coincides with the center of the plane of the cylindrical mold during the process. Ordinary concrete with the same ratio as the frozen ring is poured at the internal center, and high ductility concrete is poured simultaneously on the outside, and the internal and external heights are kept consistent during the pouring process. Among them, the ratio (mass ratio) of ordinary concrete is water:cement:fly ash:water reducer:sand:stone = 45:100:25:1.25:144:289; the ratio (mass ratio) of high ductility concrete is Portland cement P.O42.5:sand:steel fiber:polyvinyl alcohol fiber:water:water reducer:early strength agent = 1400:2800:190:30:530:10:35.

[0023] After removing the mold, the surface cracks of the concrete are detected. It is placed in a laboratory simulation environment with a humidity of 30% and a day-night temperature difference of 30°C (the daytime period is from 7:00 to 19:00, the temperature is 30°C from 11:00 to 15:00, and the temperature is 25°C in the remaining daytime periods; the night period is from 19:00 to 7:00 the next day, and the temperature is 0°C) for 28 days of curing. The crack width and quantity of the concrete are evaluated, and the visual inspection method is used to determine the crack position and a crack width gauge is used to measure the specific width. The high anti-cracking concrete structure prepared in this embodiment has no visible cracks after testing.

[0024] Example 2

[0025] A high crack-resistant concrete structure for high-altitude and low-humidity environments, with a high-ductility concrete outer layer, a frozen concrete middle layer, and a normal-flow ordinary concrete inner layer, is prepared by the following method: In this embodiment, a concrete structure with a diameter of 500 mm, a height of 3000 mm, and a high-ductility concrete protective layer thickness of 50 mm is prepared. First, a frozen concrete ring with an inner diameter of 200 mm, an outer diameter of 400 mm, a ring width of 100 mm, and a height of 3000 mm is prepared. P.O 42.5 Portland cement is used, the concrete type is ordinary concrete, the designed strength is C30. After pouring, it is directly placed in a liquid nitrogen freezer, and the heat is absorbed by the evaporation of liquid nitrogen to generate a cooling effect for freezing. When the concrete specimen reaches -40 °C, it is taken out and placed inside a column mold, ensuring that the center of the ring coincides with the center of the plane of the cylindrical mold during the process. Ordinary concrete with the same mix ratio as the frozen ring is poured at the internal center, and high-ductility concrete is poured simultaneously on the outside. During the pouring process, the internal and external heights are kept consistent. Among them, the mix ratio (mass ratio) of ordinary concrete is water:cement:fly ash:water reducer:sand:stone = 45:100:25:1.25:144:289; the mix ratio (mass ratio) of high-ductility concrete is Portland cement P.O 42.5:sand:steel fiber:polyvinyl alcohol fiber:water:water reducer:early strength agent = 1400:2800:190:30:530:10:35.

[0026] After the pouring is completed, the curing is carried out immediately by covering with soaked geotextile. During the curing period, water is sprinkled 5 times a day, and 8 times a day in windy weather to ensure that the covering is always kept in a moist state (20% humidity environment). After 7 days of moisture curing, the formwork is removed, and then it is naturally cured until the age of 28 days. Then, the high crack-resistant concrete structure prepared in this embodiment is placed in an actual high-altitude and low-humidity environment for surface crack detection (the detection method is the same as that in Example 1). The specific detection location is Meigu County, Sichuan Province. The local geographical location is relatively remote, with a high altitude, relatively harsh environmental conditions, low humidity, and large temperature differences between day and night. The detection result is that no visible cracks appear in the high crack-resistant concrete structure prepared in this embodiment after testing. This embodiment and Example 1 better illustrate that the concrete pouring using the new structural form can effectively avoid the cracking of the concrete structure.

[0027] Comparative Example 1: Ordinary concrete

[0028] In Comparative Example 1, a concrete short column with a diameter of 500 mm and a height of 500 mm is prepared. The selected cement is Portland cement P.O 42.5, the concrete type is ordinary concrete, and the designed strength is C30. Among them, the mix ratio (mass ratio) of ordinary concrete is water:cement:fly ash:water reducer:sand:stone = 45:100:25:1.25:144:289.

[0029] After pouring the prepared concrete slurry into the test mold, place it in a laboratory simulation environment with a humidity of 80% and a temperature of 20°C for 28 days of curing. After removing the mold, detect the cracks on the concrete surface (the detection method is the same as that in Example 1). After testing, the results are as follows: There are no cracks on the surface of the concrete structure prepared in Comparative Example 1. The results of this comparative example indicate that under normal curing conditions, no visible cracks will appear on the concrete after removing the mold.

[0030] Comparative Example 2: Ordinary concrete

[0031] Prepare a concrete short column with a diameter of 500 mm and a height of 500 mm in Comparative Example 2. Select Portland cement P.O 42.5 as the cement. The type of concrete is ordinary concrete, and the designed strength is C30. Among them, the mix ratio (mass ratio) of ordinary concrete is water:cement:fly ash:water reducer:sand:stone = 45:100:25:1.25:144:289.

[0032] After pouring the prepared concrete slurry into the test mold, place it in a laboratory simulation environment with a humidity of 30% and a day-night temperature difference of 30°C (the daytime period is from 7:00 to 19:00, the temperature is 30°C from 11:00 to 15:00, and the temperature is 25°C in the remaining daytime periods; the night period is from 19:00 to 7:00 the next day, and the temperature is 0°C) for 28 days of curing. After removing the mold, detect the cracks on the concrete surface (the detection method is the same as that in Example 1). After testing, the results are as follows: There are obvious cracks in the concrete structure prepared in Comparative Example 2. The number of cracks with a length greater than 1 mm is 7, the longest crack length is 15 mm, and the maximum crack width is 0.45 mm.

[0033] The curing environment of this comparative example simulates the climatic conditions in the alpine regions of Tibet Autonomous Region. The highest daytime temperature is about 30°C, and it drops to 0°C at night, accompanied by long-term sunlight. The average humidity is 30%. Comparing with Comparative Example 1, it is found that there are obvious cracking phenomena in this specimen after removing the mold. The reason is that under the curing conditions of low humidity, the moisture on the surface of the concrete loses quickly, resulting in dry shrinkage cracks; at the same time, under the condition of large temperature difference, the temperature drops quickly, resulting in temperature cracks. The curing environment of Example 1 also simulates the alpine region. Comparing with Comparative Example 2, it is found that under the same curing conditions of low humidity and large temperature difference, when using the new concrete structure form, no visible cracks will appear. Even if there are cracks, the crack width is within the allowable crack width value specified in the Chinese code.

[0034] In summary, the concrete with the novel structure of the present invention can reduce the cracking problem of concrete in alpine regions.

[0035] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high anti-cracking concrete structure for high altitude and low humidity environment, characterized in that, The outer layer of the high crack-resistant concrete structure is high-ductility concrete, the middle layer is frozen concrete, and the inner layer is flowing concrete; wherein, the frozen concrete is obtained by freezing the flowing concrete.

2. The high crack-resistant concrete structure in a high-altitude and low-humidity environment according to claim 1, wherein The thickness of the high-ductility concrete is 20-50 mm; the thickness of the frozen concrete is 80-120 mm.

3. The high crack-resistant concrete structure in a high-altitude and low-humidity environment according to claim 2, wherein The thickness of the high-ductility concrete is 30 mm; the thickness of the frozen concrete is 100 mm.

4. The high crack-resistant concrete structure in a high-altitude and low-humidity environment according to claim 1, wherein The high-ductility concrete is a fiber-reinforced cement-based composite material.

5. The high crack-resistant concrete structure according to claim 4, characterized in that, The fiber in the fiber-reinforced cement-based composite material is at least one of steel fiber and polyvinyl alcohol fiber.

6. The preparation method of the high crack-resistant concrete structure in a high-altitude and low-humidity environment according to any one of claims 1-5, comprising the following steps: (1) Freeze the flowing concrete to obtain frozen concrete, and then fix it with a steel reinforcement cage; (2) Pour high-ductility concrete on the outer layer of the frozen concrete obtained in step (1), and pour flowing concrete on the inner layer to obtain.

7. The preparation method according to claim 6, characterized in that, In the pouring process of step (2), the heights of the outer high-ductility concrete and the inner flowing concrete are kept consistent.