High-strength large-volume low-shrinkage anti-crack concrete and production method thereof

Abstract

The invention discloses high-strength large-volume low-shrinkage anti-crack concrete, which is characterized in that each cubic meter of the concrete comprises the following materials: 353 to 394 kg of medium and low heat cement, 63 to 84 kg of mineral powder, 40 to 70 kg of fly ash, 733 to 900 kg of fine aggregate, 900 to 1020 kg of coarse aggregate, 4.45 kg of additive and 135 to 160 kg of water, the mixing amount of the water-retaining and viscosity-regulating agent accounts for 0.2-0.4% of the mass of the admixture, the use amount of the gel material in each cubic meter of concrete does not exceed 500kg / m < 3 >, and the sum of the mass of the admixture in the gel material is not less than 20% of the mass of the gel material. The concrete can comprehensively prevent shrinkage cracking of the high-strength mass concrete caused by various reasons, and the construction quality of the high-strength mass concrete is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete materials, and particularly relates to a high-strength, large-volume, low-shrinkage and crack-resistant concrete and a production method thereof. Background Art

[0002] High-strength, large-volume concrete refers to concrete materials with a strength grade of C50 or above and a relatively large single-pouring volume. In existing infrastructure, super high-rise buildings, large bridge projects, hydropower and nuclear power plants, transportation hubs and underground projects all require high-strength, large-volume concrete. Once high-strength, large-volume concrete cracks, its harm not only affects the short-term safety of the structure, but may also cause long-term durability problems and even lead to catastrophic consequences. Thermal shrinkage is the core reason for the cracking of high-strength, large-volume concrete. In order to make high-strength, large-volume concrete have low shrinkage and crack resistance, the conventional method is to use medium- and low-heat cement as the raw material of high-strength, large-volume concrete to reduce the heat of hydration of the cement, thereby reducing the shrinkage rate of high-strength, large-volume concrete and avoiding concrete cracking. However, the reasons for the shrinkage of high-strength, large-volume concrete not only include thermal shrinkage, but also include plastic shrinkage during the setting and hardening stage of concrete, autogenous shrinkage after the setting and hardening stage of concrete, and drying shrinkage. How to comprehensively prevent the shrinkage and cracking of high-strength, large-volume concrete caused by various reasons is an urgent problem to be solved in the field of concrete materials. Summary of the Invention

[0003] Aiming at the defects existing in the prior art, the present application provides a high-strength, large-volume, low-shrinkage and crack-resistant concrete.

[0004] In order to achieve the purpose of the above-mentioned invention, the technical solution provided by the present invention is as follows:

[0005] For a high-strength, large-volume, low-shrinkage and crack-resistant concrete, the dosage of each material per cubic meter of concrete is as follows: 353 - 394 kg of cement, 63 - 84 kg of mineral powder, 40 - 70 kg of fly ash, 733 - 900 kg of fine aggregate, 900 - 1020 kg of coarse aggregate, 4.45 kg of admixture, and 135 - 160 kg of water;

[0006] The cement is medium- and low-heat cement, the admixture is a modified high-performance polycarboxylate water reducer, and a water retention and viscosity-adjusting agent is internally incorporated in the polycarboxylate water reducer, and the dosage of the water retention and viscosity-adjusting agent in the admixture is 0.2 - 0.4% by mass; the dosage of the gel material per cubic meter of concrete does not exceed 500 kg / m 3 , and the sum of the masses of the various admixtures in the gel material is not less than 20% of the mass of the gel material.

[0007] In one implementation, the fly ash is low-calcium grade I ash, and the mineral powder is S95 grade mineral powder.

[0008] In one embodiment, the fineness modulus of the fine aggregate is 2.4 - 2.8, the mud content of the fine aggregate does not exceed 2.0%, the lumps content is less than 0.5%, and the fine aggregate is natural medium sand with continuous gradation and porosity not exceeding 40%.

[0009] In one embodiment, the coarse aggregate is crushed stone with a particle size of 5 - 20 mm, the crushing index does not exceed 5%, and it is high-quality crushed stone with continuous gradation and porosity not exceeding 40%.

[0010] In one embodiment, the dosage of the water-retaining viscosity-adjusting agent in the admixture is 0.3% by mass.

[0011] In one embodiment, the temperature of the water is controlled within 10°C, the temperatures of the coarse aggregate and the fine aggregate are controlled within 30°C, and the temperature of the concrete is lower than 30°C.

[0012] This application also provides a production method for high-strength, large-volume, low-shrinkage, and crack-resistant concrete. The concrete is the above-mentioned high-strength, large-volume, low-shrinkage, and crack-resistant concrete. The production method includes: at the mixing plant, placing condensing fans around the aggregate yard, placing ice cubes in the water, wrapping the outer surface of the silo containing the gel material with a light-colored geotextile soaked in water, wrapping the tank body of the concrete mixer truck with canvas, wetting the tank body of the concrete mixer truck before it leaves the mixing plant, and wetting the tank body of the concrete mixer truck for the second time when it enters the construction site; at the construction site, cooling the steel bars and steel sections before concrete pouring, mixing the concrete for no less than 120 s. After the concrete is poured, a second surface finishing operation is carried out before the initial setting, and the surface of the concrete pouring is covered with a wet gunny bag. After the concrete is poured, the formwork of the concrete is removed at noon. After removing the formwork, a plastic film is covered on the surface of the concrete, and a heat-insulating material is included outside the plastic film.

[0013] Compared with the prior art, this application has at least the following beneficial effects:

[0014] 1. In the concrete of the present invention, by adjusting the dosage of the gel material in the mix proportion, optimizing the gel material system, and combining with the temperature control of the raw materials, the hydration heat in the concrete is reduced through the synthesis effect, thereby controlling the shrinkage cracks caused by the hydration heat.

[0015] 2. In the concrete of the present invention, an aggregate system with continuous gradation and low porosity is selected to minimize the dosage of the gel material per unit volume of the concrete, improve the paste-aggregate ratio, reduce the dry shrinkage value of the concrete, and control the late cracks caused by the dry shrinkage.

[0016] 3. In the concrete of the present invention, by compounding an admixture with water-retaining viscosity-adjusting function in the admixture, the plastic shrinkage cracks caused by water loss are effectively reduced, and the risk of early cracking is reduced.

[0017] 4. The concrete of the present invention takes into account various cracking factors, comprehensively analyzes and designs the concrete mix ratio in combination with the actual engineering conditions, improves the cracking resistance of the concrete, and ensures the construction quality of high-strength mass concrete. Specific embodiments

[0018] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0019] The terms used in this disclosure are only for the purpose of describing specific embodiments and are not intended to limit this disclosure. The singular forms "a", "the" and "said" used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0020] It should be understood that although the terms first, second, third, etc. may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this disclosure, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "when" or "while" or "in response to a determination".

[0021] In the description of the present invention, unless otherwise specified and defined, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it may be a mechanical connection, or it may be the communication inside two components. It may be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0022] To better understand the technical solution of the present invention, the present invention will be described in detail below in conjunction with specific embodiments.

[0023] The control of cracks in high-strength mass concrete is a systematic project. All links such as the selection and preparation of the cementitious material of mass concrete, the production and pouring construction of concrete, and the maintenance will affect the quality of the final concrete project.

[0024] Example 1:

[0025] In this embodiment, taking the high-strength mass concrete with a strength of C60 used in the construction of Shanghai East Station as an example, a high-strength mass low-shrinkage crack-resistant concrete is provided. The dosage of each material per cubic meter of concrete is as follows: 385 kg of cement, 69 kg of mineral powder, 40 kg of fly ash, 733 kg of fine aggregate, 990 kg of coarse aggregate, 4.45 kg of admixture, and 158 kg of water. The cement is medium-low heat cement with a model of P.II 52.5. The fly ash is low-calcium grade I ash, the mineral powder is S95 grade mineral powder, and the admixture is a modified high-performance polycarboxylate water reducer. A water retention and viscosity-adjusting agent is internally incorporated in the polycarboxylate water reducer, and the dosage of the water retention and viscosity-adjusting agent is 0.2 - 0.4% by mass in the admixture. The dosage of the gel material per cubic meter of concrete is 494 kg / m 3 , and the sum of the masses of the admixtures in the gel material is 22% of the mass of the gel material. The temperature of the water is lower than 10°C. The fineness modulus of the fine aggregate is 2.4 - 2.8, the mud content of the fine aggregate does not exceed 2.0%, the lump content is less than 0.5%, and it is natural medium sand with continuous gradation and a porosity not exceeding 40%. The temperature of the fine aggregate does not exceed 30°C. The coarse aggregate is crushed stone with a particle size of 5 - 20 mm, the crushing index does not exceed 5%, the gradation is continuous, and the porosity does not exceed 40% of the high-quality crushed stone. The temperature of the coarse aggregate does not exceed 30°C.

[0026] Comparative Example 1

[0027] The difference between Comparative Example 1 and Example 1 is that the dosage of the gel material per cubic meter of concrete is 565 kg / m 3 , and the dosage of the gel material per cubic meter of concrete can be changed by changing the dosages of cement, mineral powder, and coal ash powder in the gel material. The dosages of other materials in the concrete except the gel material remain unchanged.

[0028] Comparative Example 2

[0029] The difference between Comparative Example 2 and Example 1 is that the dosage of the gel material per cubic meter of concrete is 515 kg / m 3 , and the dosage of the gel material per cubic meter of concrete can be changed by changing the dosages of cement, mineral powder, and coal ash powder in the gel material. The dosages of other materials in the concrete except the gel material remain unchanged.

[0030] The comparison of the working performance and mechanical performance indexes of the concrete tested under different gel material dosages is shown in Table 1 as follows:

[0031] Table 1:

[0032]

[0033] As can be seen from Table 1, through the tests on the workability and mechanical properties of concrete with different amounts of cementitious materials, it can be known that the slump of concrete decreases with the reduction of the amount of cementitious materials, and the inverted emptying time also increases due to the reduction of the amount of cementitious materials. The meshing effect of the aggregate affects the inverted emptying time, but all meet the production standard requirements; from the perspective of the compressive strength at each age, the reduction of the total amount of cementitious materials has no obvious effect on its mechanical properties and meets the standard and the acceptance requirements of the project department.

[0034] The comparison of the shrinkage rates of concrete tested with different amounts of cementitious materials is shown in Table 2 as follows:

[0035] Table 2:

[0036]

[0037] The drying shrinkage of high-strength mass concrete mainly occurs within 28 days. The shrinkage rate of concrete decreases in the later stage. As can be seen from Table 2, the reduction of the total amount of cementitious materials reduces the shrinkage value of concrete. The shrinkage rate of high-strength mass concrete with a total cementitious material ratio of 494 kg / m 3 is lower than that of high-strength mass concrete with a total cementitious material ratio of 565 kg / m 3 by 11.1%. The reduction of the total amount of cementitious materials can inhibit the cracks caused by drying shrinkage.

[0038] Comparative Example 3

[0039] The difference between Comparative Example 3 and Example 1 is that the mass percentage of the water retention and viscosity adjusting agent in the admixture is 0%, and the amounts of other concrete materials remain unchanged.

[0040] Example 2

[0041] The difference between Example 2 and Example 1 is that the mass percentage of the water retention and viscosity adjusting agent in the admixture is 0.2%, and the amounts of other concrete materials remain unchanged.

[0042] Example 3

[0043] The difference between Example 3 and Example 1 is that the mass percentage of the water retention and viscosity adjusting agent in the admixture is 0.3%, and the amounts of other concrete materials remain unchanged.

[0044] Example 4

[0045] The difference between Example 4 and Example 1 is that the mass percentage of the water retention and viscosity adjusting agent in the admixture is 0.4%, and the amounts of other concrete materials remain unchanged.

[0046] Example 5

[0047] Example 5 is different from Example 1 in that the mass percentage of the water retention and viscosity adjusting agent in the admixture is 0.5%, and the dosages of other concrete materials remain unchanged.

[0048] The comparison of the concrete performance indexes tested under different dosages of the water retention and viscosity adjusting agent in the admixture is shown in Table 3 as follows:

[0049] Table 3:

[0050]

[0051]

[0052] By adding water retention aids to the concrete, the time-dependent loss of the concrete is controlled, and the bleeding rate is also improved. When 20 - 40 kg / T of water retention agent is incorporated into the water reducer, the workability requirements of the concrete can be met. However, when the dosage of the water retention aid is too high (>40 kg / T), the fluidity of the concrete will be affected and the construction requirements cannot be satisfied. Considering comprehensively, a dosage of 0.3% of the water retention aid is selected, and its influence on plastic shrinkage is verified through the flat plate anti-cracking test. It can be seen from the test that the incorporation of the water retention agent significantly reduces the number of early shrinkage cracks. After incorporating the water retention and viscosity adjusting agent, the shrinkage crack index is reduced by 86.9%, significantly inhibiting the shrinkage cracks caused by water loss.

[0053] Comparative Example 4

[0054] Comparative Example 4 is different from Example 1 in that the sum of the masses of various admixtures in the gel material is 0% of the mass of the gel material, and the dosages of other concrete materials remain unchanged.

[0055] Comparative Example 5

[0056] Comparative Example 4 is different from Example 1 in that the sum of the masses of various admixtures in the gel material is 11.2% of the mass of the gel material, and the dosages of other concrete materials remain unchanged.

[0057] Example 5

[0058] Example 5 is different from Example 1 in that the sum of the masses of various admixtures in the gel material is 20% of the mass of the gel material, and the dosages of other concrete materials remain unchanged.

[0059] Example 6

[0060] Example 6 is different from Example 1 in that the sum of the masses of various admixtures in the gel material is 22.1% of the mass of the gel material, and the dosages of other concrete materials remain unchanged.

[0061] The comparison of the concrete performance indexes tested under different sums of the masses of various admixtures in the gel material is shown in Table 3 as follows:

[0062] Table 4:

[0063]

[0064] Regarding the control of the hydration temperature rise of mass concrete in summer, according to the characteristics of mass concrete and the structure of this project, firstly, rationally utilize the advantages of aggregate gradation to reduce the amount of cementitious materials and adopt a cementitious material system with a large proportion of admixtures; secondly, control the raw materials. For the cementitious material system after adding 11.2% (<20%, adding 22.1%) of mineral powder and fly ash, the degree of reduction in the heat of hydration is relatively low, and the heat of hydration at 3 days and 7 days is only reduced by 2.6% and 3.6%; when adding 20% of mineral powder and fly ash to the cementitious material system, the heat of hydration at 3 days and 7 days is reduced by 20.6% and 10.6% respectively.

[0065] In Example 6, for the cementitious material system after adding 22.1% (>20%) of mineral powder and fly ash to the C60 mix proportion, the heat of hydration at 3 days and 7 days is reduced by 23.4% and 11.5% respectively, and the hydration rate is also improved accordingly. The temperature at the time of placing into the mold is 7°C lower than that of conventional concrete under the same conditions. Based on the above thermal shrinkage control measures, the adiabatic temperature rise can be reduced, and the probability of generating thermal shrinkage cracks can be decreased.

[0066] Example 6:

[0067] This example discloses a production method of high-strength mass concrete with a strength of C60. The dosage of each material per cubic meter of concrete is 385 kg of cement, 69 kg of mineral powder, 40 kg of fly ash, 733 kg of fine aggregate, 990 kg of coarse aggregate, 4.45 kg of admixture, and 158 kg of water. The cement is medium-low heat cement with a model of P.II 52.5, the fly ash is low-calcium grade I ash, the mineral powder is S95 grade mineral powder, the admixture is a modified high-performance polycarboxylate water reducer, and a water retention and viscosity-adjusting agent is internally added to the polycarboxylate water reducer. The dosage of the water retention and viscosity-adjusting agent in the admixture is 0.2 - 0.4% by mass. The cementitious material dosage per cubic meter of concrete is 494 kg / m 3 , and the sum of the masses of each admixture in the cementitious material is 22% of the mass of the cementitious material. The temperature of the water is lower than 10°C. The fineness modulus of the fine aggregate is 2.4 - 2.8, the mud content of the fine aggregate does not exceed 2.0%, the mud lump content is less than 0.5%, and it is natural medium sand with continuous gradation and a porosity not exceeding 40%. The temperature of the fine aggregate does not exceed 30°C. The coarse aggregate is crushed stone with a particle size of 5 - 20 mm, the crushing index does not exceed 5%, the gradation is continuous and the porosity does not exceed 40% of high-quality crushed stone. The temperature of the coarse aggregate does not exceed 30°C.

[0068] The production method includes: Before the production and preparation of C60 concrete, each unit needs to do a good job in the production and pouring preparation of C60. To cope with the temperature stress caused by hydration heat and reduce the generation of temperature difference cracks, it is necessary to cool down the raw materials before concrete production. Place ice cubes in water, and use the melting of ice cubes to absorb a large amount of heat to reduce the temperature of mixing water and aggregates. In addition, install cool air blowers around the aggregate yard in advance, wrap the silos of cementitious materials with light-colored geotextiles in advance, and moisten them with water. Use the evaporation of water to take away heat. Wrap the concrete mixer truck with canvas, moisten the tank body before leaving the factory, and conduct a second moistening when entering the construction site to prevent the temperature rise of concrete during transportation. During production, the temperature of each raw material is controlled according to the predicted value of the concrete discharge temperature, so that the concrete discharge temperature does not exceed 30°C. Among them, the temperature of water is recommended to be controlled within 10°C, the temperature of coarse aggregate and fine aggregate is recommended to be controlled within 30°C, and the temperature of cementitious materials depends on the situation. If the temperature is too high and the concrete discharge temperature exceeds 30°C, certain cooling measures shall be taken for it;

[0069] At the construction site, before the concrete pouring construction, do a good job in the acceptance of steel bars, submit the pouring plan in advance, determine the concrete pouring volume, and ensure the efficient and high-quality pouring of concrete. In the face of high-temperature environment, cool down the steel bars and steel sections in advance, and try to choose the cooler night for pouring time;

[0070] When producing C60 concrete, it is stirred by a fully automatic production and mixing integrated equipment, accurately weighed by an electronic weighing system, and fed; the stirring time is not less than 120s to ensure full stirring of the concrete mixture. After the concrete pouring is completed, carry out the second surface troweling work before the initial setting to avoid the development of cracking cracks. At the same time, do a good job in heat preservation and moisture preservation to prevent plastic shrinkage caused by water loss, and cover the surface with wet gunny bags to prevent water loss;

[0071] After the production and pouring of concrete are completed, monitor the hydration heat of the structural column. According to the test results, the maximum temperature rise is 47°C, meeting the requirements of mass concrete for temperature rise; after the concrete reaches the peak temperature, it begins to gradually cool down, and the cooling rate < 2°C / d, meeting the standard requirements.

[0072] The form removal of C60 concrete columns needs to be determined according to the temperature difference. At the same time, the form removal order needs to be issued by the technical department. To ensure that the surface temperature of the concrete is closer to the atmospheric temperature, the form removal is selected to be carried out at noon when the temperature is relatively high. After the form removal, record whether cracks occur and the number of cracks. At the same time, immediately carry out the curing work. Cover its surface with a plastic film and wrap thermal insulation materials outside to prevent adverse effects caused by too rapid temperature drop. Remove it after curing for no less than 14 days according to the project requirements. After removing the curing device, conduct the second observation of cracks and the number, and statistically analyze the development of the number and length of cracks. Through the whole-process tracking of a large number of C60 concrete structural columns at the construction site, the overall apparent quality of the concrete is good.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that it is still possible to modify the specific implementation manners of the invention or make equivalent replacements for some technical features without departing from the spirit of the technical solutions of the present invention, and they should all be covered within the scope of the technical solutions claimed by the present invention.

Claims

1. A high-strength, large-volume, low-shrinkage and crack-resistant concrete, characterized in that, Dosage of each material per cubic meter of concrete: Cement 353 - 394 kg, blast furnace slag powder 63 - 84 kg, fly ash 40 - 70 kg, fine aggregate 733 - 900 kg, coarse aggregate 900 - 1020 kg, admixture 4.45 kg, water 135 - 160 kg; The cement described is medium-low heat cement, the admixture is a modified high-performance polycarboxylate water reducer, and a water retention and viscosity adjusting agent is internally doped in the polycarboxylate water reducer, and the dosage of the water retention and viscosity adjusting agent is 0.2-0.4% by mass percentage in the admixture; the dosage of the gel material in each cubic meter of concrete does not exceed 500 kg / m 3 , and the sum of the masses of each admixture in the gel material is not less than 20% of the mass of the gel material.

2. The high-strength large-volume low-shrinkage crack-resistant concrete according to claim 1, wherein The fly ash used is low-calcium grade-I ash, and the blast furnace slag powder is S95 grade blast furnace slag powder.

3. The high-strength, large-volume, low-shrinkage and crack-resistant concrete according to claim 1, wherein The fineness modulus of the fine aggregate is 2.4 - 2.

8. The mud content of the fine aggregate does not exceed 2.0%, and the lumps content is less than 0.5%. The fine aggregate adopts natural medium sand with continuous gradation and porosity not exceeding 40%.

4. The high-strength, large-volume, low-shrinkage and crack-resistant concrete according to claim 1, characterized in that The coarse aggregate adopts high-quality crushed stone with particle size of 5 - 20 mm, crushing index not exceeding 5%, continuous gradation and porosity not exceeding 40%.

5. The high-strength, large-volume, low-shrinkage and crack-resistant concrete according to claim 1, characterized in that, The mass percentage of the water retention and viscosity adjusting agent in the admixture is 0.3%.

6. The high-strength, large-volume, low-shrinkage and crack-resistant concrete according to claim 1, characterized in that The temperature of the water is controlled within 10°C, the temperature of the coarse aggregate and the fine aggregate is controlled within 30°C, and the temperature of the concrete is lower than 30°C.

7. A production method of high-strength, large-volume, low-shrinkage and crack-resistant concrete, characterized in that The concrete is the high-strength, large-volume, low-shrinkage and crack-resistant concrete according to any one of claims 1 - 6. The production method includes: at the mixing plant, placing condensation fans around the aggregate yard, placing ice cubes in the water, wrapping the outer surface of the silo containing the gel material with a light-colored geotextile soaked in water, wrapping the tank body of the concrete mixer truck with canvas, wetting the tank body of the concrete mixer truck before it leaves the mixing plant, and wetting the tank body of the concrete mixer truck for the second time when it enters the construction site; at the construction site, cooling the steel bars and steel sections before concrete pouring, mixing the concrete for not less than 120 s. After the concrete pouring is completed, carry out the second screeding work before the initial setting, and cover the surface of the concrete pouring with wet gunny bags. After the concrete pouring is completed, remove the formwork of the concrete mold at noon. After form removal, cover the surface of the concrete with a plastic film, and include a heat-insulating material outside the plastic film.

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