Comprehensive method for controlling non-stress cracks of long concrete wall structure

Abstract

The invention relates to a comprehensive method for controlling non-stress cracks of a long concrete wall structure. The comprehensive method comprises the steps that S1, a construction flow section is divided; s2, low-early-stage elastic modulus concrete is poured at the bottom of the long wall to form a concrete transition layer, so that constraint on wall body concrete is reduced; s3, low-hydration-heat concrete is poured, and the temperature of the concrete entering a mold is controlled, so that upper concrete is formed; the low-early-stage elastic modulus concrete poured in the step S2 has the same strength grade as the low-hydration-heat concrete poured in the step S3, but the elastic modulus does not exceed 50% of the upper concrete poured at the same time within 48-72 h and does not exceed 70% in 7 d, the elastic modulus in 28 d is 90%-110% of the elastic modulus of the upper concrete, and the elastic modulus in 28 d is 90%-110% of the elastic modulus of the lower concrete. The low-hydration-heat concrete poured in the step S3 is prepared from moderate-heat cement or low-heat cement or by doping 35%-55% of fly ash into ordinary Portland cement, and the adiabatic temperature rise of the low-hydration-heat concrete is controlled to be not larger than 35 DEG C.

Description

Technical Field

[0001] The invention relates to the technical field of building construction, and in particular to a comprehensive method for controlling non-stress cracks in a concrete long wall structure. Background Art

[0002] At present, the problem of non-stress cracks in long walls of reinforced concrete structures is difficult to control. In severe cases, vertical cracks will appear every 1 to 2 meters. The through concrete cracks reduce the integrity of the structure and seriously affect the durability of the structure. Especially for long wall structures with waterproof functions underground (such as subway station side walls, basement side walls, etc.), the leakage caused by cracks directly affects the normal use function of the building and even affects the safe operation of the subway. Therefore, controlling long wall cracks is one of the key problems of construction quality that the engineering community has been committed to solving. A relatively high price has been paid for this, but it has never been completely solved.

[0003] The reason why long concrete walls are prone to cracking is that there are many factors in their structure, design, materials and construction that are not conducive to crack control. In terms of structure, long concrete walls are usually strip-shaped and will be subject to strong constraints from the first cast parts such as the bottom plate. In terms of design, due to the increase in concrete strength grade, concrete will shrink more in the early stage, and the rapid increase in strength will bring high elastic modulus and small creep capacity. The stress level generated by concrete under constraint conditions is high. In terms of concrete materials, the usual mix ratio uses more cement and mineral powder. Due to high fineness and high activity, the hydration reaction rate is fast, which causes large shrinkage; in terms of construction, the long flow section and the high mold temperature will cause the concrete hydration heat to rise too high. Temperature difference stress is often the main factor causing cracks. If the moisture retention and thermal insulation maintenance after demolding cannot control the cooling rate of concrete well, it is also easy to cause cracks after demolding or affect the strength development of the concrete entity structure.

[0004] The early shrinkage of concrete mainly comes from the continuous increase in temperature caused by the hydration of cementitious materials (mainly cement), and then the temperature continues to decrease, and the temperature changes from high to low, resulting in temperature shrinkage. During this temperature change process, the strength and elastic modulus of concrete continue to increase, and the stress generated exceeds the tensile strength of concrete, and the concrete will crack. Before demolding, the second reason is the self-shrinkage of concrete, which is more significant for high-strength concrete; after demolding, the second reason is drying shrinkage. From the perspective of engineering practice, the most important thing for long wall structures is to control temperature shrinkage.

[0005] CN111484295A discloses a construction method for preventing temperature cracks in pier wall concrete, and its main technical feature is to first pour ductile super slow setting fine stone concrete with an initial setting time of 48h to 72h as a transition layer at the root of the pier wall, and then continue to pour ordinary concrete on the transition layer. The preparation method of ductile super slow setting fine stone concrete with an initial setting time of 48h to 72h is: first mix fine aggregate, rubber fine particles, coarse aggregate and fiber for 10 to 30 seconds, then add cement, fly ash, slag powder, reinforcing densifier, magnesium oxide expansion agent and the first mixing water, and then mix for 10 to 30 seconds, then add the second mixing water, polyacrylate water reducer, fatty alcohol sodium sulfate air entraining agent and retarder, and then mix evenly. However, this method only proposes an anti-cracking method from the perspective of reducing constraints, and uses special materials such as rubber fine particles, which will affect the strength development of concrete in practical applications, and the implementation conditions are difficult, so it is difficult to use it as an effective method for controlling cracks that can be used in actual engineering projects. Moreover, the crack control effect achieved by its technical measures is relatively poor, and it is difficult to stably control the development of long wall cracks.

[0006] In addition, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the applicant studied a large number of documents and patents when making the present invention, but due to space limitations, not all details and contents are listed in detail. However, this does not mean that the present invention does not have the characteristics of these prior arts. On the contrary, the present invention already has all the characteristics of the prior art, and the applicant reserves the right to add relevant prior art to the background technology. Summary of the invention

[0007] In view of the deficiencies of the prior art, the present invention provides a comprehensive method for controlling non-stress cracks in a concrete long wall structure to solve at least part of the above-mentioned technical problems.

[0008] The invention discloses a comprehensive method for controlling non-stress cracks in a concrete long wall structure, which comprises:

[0009] S1. Divide the construction flow sections;

[0010] S2. Pour low early elastic modulus concrete at the bottom of the long wall to form a concrete transition layer, thereby reducing the restraint on the wall concrete;

[0011] S3 pouring low hydration heat concrete, and controlling the concrete mold temperature to form the upper concrete;

[0012] S4. After demoulding, moisturizing and heat preservation are carried out, including:

[0013] The low early elastic modulus concrete cast in step S2 has the same strength grade as the low hydration heat concrete cast in step S3, but has an elastic modulus of no more than 50% of the upper concrete cast at the same time within 48 to 72 hours, no more than 70% at 7 days, and close to the elastic modulus of the upper concrete at 28 days, and the low hydration heat concrete cast in step S3 adopts 42.5-grade medium-heat cement with a hydration heat of no more than 250 kJ / kg at 3 days and a hydration heat of no more than 290 kJ / kg at 7 days, or 42.5-grade low-heat cement with a hydration heat of no more than 230 kJ / kg at 3 days and a hydration heat of no more than 260 kJ / kg at 7 days, or adopts 42.5-grade ordinary Portland cement with a hydration heat of no more than 280 kJ / kg at 3 days and a hydration heat of no more than 315 kJ / kg at 7 days to prepare concrete, and fly ash with a total cementitious material (cement and fly ash) mass ratio of 35% to 55% is added to the concrete. Control the adiabatic temperature rise of low hydration heat concrete to no more than 35℃.

[0014] 2. Further, in step S1, the one-time pouring length of the construction flow section ranges from 15 to 20 m.

[0015] 3. Further, in step S2, the thickness of the transition layer poured at the bottom is 300 to 600 mm, wherein, when pouring low early elastic modulus concrete, the elastic modulus development of the concrete is determined and controlled through the previous concrete mix ratio test to meet the requirements in step S2.

[0016] 4. Further, in step S2, the low early elastic modulus concrete is mixed with early elastic modulus regulating materials and organic synthetic fibers during preparation, wherein the early elastic modulus regulating materials include one or more combinations of the following components: sodium citrate, sodium gluconate, sodium tartrate, polyethylene glycol, diacetylaminoethyl dihydrogen phosphate; and the organic synthetic fibers are polypropylene fibers and / or polyacrylonitrile fibers.

[0017] 5. Furthermore, the early elastic modulus regulating material can be made of the following components in parts by weight: 5-10 parts of sodium citrate, 10-15 parts of sodium gluconate, 5-8 parts of sodium tartrate, 0-5 parts of polyethylene glycol, and 6-12 parts of diacetylaminoethyl dihydrogen phosphate; the initial modulus of the organic synthetic fiber is not more than 10 GPa.

[0018] 6 Furthermore, the amount (mass) of early elastic modulus control material added is 1% to 3% of the mass of cementitious materials (cement and fly ash), and the amount (volume) of organic synthetic fiber added is 0.05% to 0.2% of the volume of concrete.

[0019] 7. Furthermore, measures should be taken to ensure that the temperature of low-hydration heat concrete entering the mold is 10℃-28℃ during pouring. If the detected temperature of concrete entering the mold during pouring cannot meet the requirements, the temperature of cement, mixing water and sand and gravel aggregates during concrete mixing should be controlled within the range of 5-30℃.

[0020] 8. The technical measures for moisture retention and heat preservation include the use of concrete water-saving and moisture-retaining curing membrane, and the use of covering insulation materials according to the temperature conditions. The insulation materials include one or more layers of geotextiles, quilts, etc. to ensure that the temperature difference between the center temperature and the surface temperature of the wall concrete does not exceed 20°C, and the daily cooling rate of the concrete is not more than 3°C.

[0021] 9. When implementing the technical measures of moisture retention and heat preservation, the temperature difference between the center temperature and the surface temperature of the wall concrete should be controlled to not exceed 20°C, and the daily average drop in the center temperature of the wall should not exceed 2°C or 3°C.

[0022] The present invention adopts a comprehensive method to control non-stress cracks in concrete long wall structures, and significantly reduces the risk of cracks caused by temperature shrinkage by accurately controlling the elastic modulus development of low early elastic modulus concrete and the adiabatic temperature rise of low hydration heat concrete. By adjusting the elastic modulus and hydration heat of concrete, the mechanical properties and thermal stability of concrete are optimized, thereby achieving a significant improvement in crack control effect in this field.

[0023] In a preferred embodiment, in step S1, the one-time pouring length of the construction flow section is 15-20m. The longer the one-time pouring length of the construction flow section is, the greater the risk of cracking. However, if the flow section is too short, the number of construction joints will increase and the construction efficiency will be reduced. The present invention sets the one-time pouring length of the construction flow section to 15-20m, which greatly reduces the risk of cracking in the long concrete wall, while ensuring that the construction personnel can complete the pouring, vibration and other necessary processes within a reasonable time limit to ensure the continuity and high efficiency of the construction, thereby taking into account the requirements of construction efficiency and quality control. The setting of this length takes into account the balance between the thermodynamic properties of concrete and the actual construction operation, and is an optimization of construction efficiency and crack control.

[0024] A preferred implementation manner, in step S2, low early elastic modulus concrete is poured at the bottom of the long wall to form a concrete transition layer of 300 to 600 mm, wherein, when pouring the low early elastic modulus concrete, the elastic modulus development of the concrete is determined and controlled through the previous concrete mix ratio test: within 48 to 72 hours, the elastic modulus does not exceed 50% of the upper concrete poured at the same time, does not exceed 70% at 7d, and the elastic modulus at 28d is 90%-110% of the elastic modulus of the upper concrete.

[0025] In step S2, a concrete transition layer of 300 to 600 mm is formed by using low early elastic modulus concrete. The present invention sets a concrete transition layer with a low elastic modulus at the root of the bottom of the long wall, thereby reducing the bottom constraint received by the upper concrete when shrinking, effectively reducing the generation of non-stress cracks in the concrete long wall structure, thereby ensuring the stability and durability of the wall. The elastic modulus development of the transition layer concrete needs to be tested by trial mixing concrete before pouring, and can only be implemented if it meets the requirements.

[0026] In a preferred embodiment, in step S2, the low early elastic modulus concrete is mixed with early elastic modulus regulating materials and organic synthetic fibers during preparation, wherein the early elastic modulus regulating materials include one or more combinations of the following components: sodium citrate, sodium gluconate, sodium tartrate, polyethylene glycol, diacetylaminoethyl dihydrogen phosphate; and the organic synthetic fibers are polypropylene fibers and / or polyacrylonitrile fibers.

[0027] The present invention incorporates early elastic modulus regulating materials and organic synthetic fibers when preparing low early elastic modulus concrete. The addition of these materials can ensure that the strength of the transition layer concrete develops slowly and the early elastic modulus is at a low level. The addition of organic synthetic fibers can improve the crack resistance of the transition layer concrete.

[0028] In a preferred embodiment, the early elastic modulus regulating material can be made of the following components in parts by weight: 5 to 10 parts of sodium citrate, 10 to 15 parts of sodium gluconate, 5 to 8 parts of potassium sodium tartrate, 0 to 5 parts of polyethylene glycol, and 6 to 12 parts of diacetylaminoethyl dihydrogen phosphate; the initial modulus of the organic synthetic fiber is not greater than 10 GPa.

[0029] In a preferred embodiment, the volume percentage of the early elastic modulus regulating material added is 1% to 3% of the cementitious material (cement and fly ash), and the volume percentage of the organic synthetic fiber added is 0.05% to 0.2% of the cementitious material (cement and fly ash).

[0030] The present invention further defines the parameters such as the ratio of the early elastic modulus control material and the organic synthetic fiber, the initial modulus, and the mixing ratio (volume percentage), so that the low early elastic modulus concrete prepared under the above parameters can achieve the early elastic modulus control and the crack control of the transition layer concrete itself to the greatest extent. In other words, not all low early elastic modulus concrete can achieve the high crack control rate of the present invention.

[0031] A preferred implementation manner is to take measures to ensure that the mold entry temperature of low-hydration heat concrete during pouring is 10°C-28°C. If the detected mold entry temperature of concrete during pouring cannot meet the requirements, the temperature of cement, mixing water and sand and gravel aggregates during concrete mixing should be controlled within the range of 5-30°C.

[0032] By controlling the mold temperature during low-heat concrete pouring, the final maximum temperature of the concrete is effectively reduced, the temperature difference strain and temperature difference stress during cooling are reduced, and the crack resistance of the concrete structure is significantly improved. When the mold temperature during concrete pouring is too high or too low, the temperature of the main raw materials of the concrete needs to be regulated.

[0033] In a preferred embodiment, the technical measures for moisture retention and heat preservation include using a concrete water-saving and moisture-retaining curing film, and using a covering insulation material according to the temperature conditions, wherein the insulation material includes one or more layers of geotextiles, quilts, etc., to ensure that the temperature difference between the center temperature and the surface temperature of the wall concrete does not exceed 20°C, and the daily cooling rate of the concrete is not greater than 3°C.

[0034] In a preferred embodiment, when implementing the technical measures of moisture retention and heat preservation, the temperature difference between the center temperature and the surface temperature of the wall concrete is controlled to be no more than 20°C, and the daily average drop in the center temperature of the wall is no more than 2°C or 3°C.

[0035] By adopting the moisture-keeping and heat-insulating technical measures and using the curing film and the heat-insulating materials in combination, the internal and surface temperatures of the concrete are effectively controlled, and the temperature stress is reduced. In addition, the present invention further defines the temperature difference between the center temperature and the surface temperature of the wall concrete and the daily average drop in the center temperature of the wall, so as to ensure the uniformity and stability of the concrete during the hardening process by strictly controlling the temperature difference and the cooling rate, and significantly improve the long-term performance and reliability of the concrete structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of the steps of a comprehensive method for controlling non-stress cracks in a concrete long wall structure according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0037] The following is a detailed description with reference to the accompanying drawings.

[0038] Concrete long walls usually refer to long strips of walls made of concrete materials. They can be part of a building, such as the side walls of a basement, retaining walls, soundproof walls, side walls of a subway station, etc., or they can be independent structures, such as the supporting walls of a dam or bridge. Concrete long walls have multiple functions in engineering, including load-bearing, retaining, soundproofing, and anti-seepage. They can bear loads independently or work in conjunction with other structural elements. Concrete long walls generally have larger sizes and heights, and the size in the length direction is much larger than the height or thickness. This structural form gives the long wall a higher stiffness perpendicular to the length direction. Due to factors such as concrete shrinkage, temperature changes, and foundation settlement, concrete long walls are prone to cracks, especially non-stress cracks, which may affect the durability and waterproof performance of the structure.

[0039] Based on this, Figure 1 As shown, the present invention discloses a comprehensive method for controlling non-stress cracks in a concrete long wall structure, which comprises:

[0040] S1. Divide the construction flow sections;

[0041] S2. Pouring low early elastic modulus concrete to form a concrete transition layer, thereby reducing the restraint on the wall concrete;

[0042] S3 pouring low hydration heat concrete, and controlling the concrete mold temperature to form the upper concrete;

[0043] S4. After demoulding, carry out moisturizing and heat preservation maintenance.

[0044] Preferably, in step S1, the one-time pouring length of the construction flow section can be set to 15-20m, so that the risk of cracking in the concrete long wall is greatly reduced, while ensuring that the construction personnel can complete the pouring, vibration and other necessary processes within a reasonable time limit to ensure the continuity and high efficiency of the construction. Further, shortening the one-time pouring length of the construction flow section can reduce the risk of cracks, but it will affect the progress of the construction work and increase the setting of construction joints, which is a link in the construction quality that is difficult to control, thereby taking into account the needs of construction efficiency and quality control. This length setting takes into account the balance between the thermodynamic properties of concrete and the actual construction operation, and optimizes the construction efficiency and crack control.

[0045] Preferably, in step S2, a certain height of concrete with the same strength grade as the upper concrete of the wall but with a low early elastic modulus (elastic modulus) can be pre-cast at the bottom of the long wall, wherein the elastic modulus of the concrete does not exceed 50% of the elastic modulus of the upper concrete cast at the same time within 48 to 72 hours, does not exceed 70% at 7 days, and the elastic modulus at 28 days is 90%-110% of the elastic modulus of the upper concrete. Preferably, the above-mentioned certain height can be set to 300 to 600 mm. Further preferably, the low early elastic modulus concrete is characterized by having a lower (i.e., lower than ordinary concrete) elastic modulus during the early hardening process (usually within 48 hours to 7 days after casting), which helps to reduce the stress caused by constraints. Further, reducing the constraints from the bottom can effectively reduce the stress level of the long wall, thereby controlling the occurrence of cracks. Preferably, the low early elastic modulus concrete has the same strength grade as the upper concrete to avoid structural safety problems.

[0046] Preferably, the low early elastic modulus concrete of the present invention can be prepared in the same mix ratio as the upper concrete, and the early elastic modulus regulating material and the organic synthetic fiber are added during stirring, and mixed together with the concrete material. Optionally, the mixing time of the concrete material, the early elastic modulus regulating material and the organic synthetic fiber can be 10 to 30 seconds. Such a setting can ensure that the constraints on the upper concrete are reduced while also enhancing the crack resistance of this part of the concrete itself.

[0047] Preferably, the above-mentioned early elastic modulus regulating material can be made of the following components in parts by weight: 5-10 parts of sodium citrate, 10-15 parts of sodium gluconate, 5-8 parts of sodium tartrate, 0-5 parts of polyethylene glycol, and 6-12 parts of diacetylaminoethyl dihydrogen phosphate.

[0048] Preferably, the organic synthetic fiber may be a fiber material with a low initial modulus, wherein the low initial modulus may refer to an initial modulus of no more than 10 GPa. Further preferably, the organic synthetic fiber may be a polypropylene fiber and a polyacrylonitrile fiber.

[0049] Preferably, the amount (mass) of the early elastic modulus regulating material added is 1% to 3% of the mass of the cementitious material (cement and fly ash).

[0050] Preferably, the amount (volume) of organic synthetic fibers added is 0.05% to 0.2% of the volume of concrete.

[0051] Preferably, the present invention uses elastic modulus as a control index to measure the deformation capacity of concrete under external force. Preferably, in step S2, in order to measure the elastic modulus development of low early elastic modulus concrete, the present invention can adopt the following method: at the construction site, strain gauges and pressure sensors are installed to measure deformation and stress, and the elastic modulus is calculated by applying static loads and measuring the corresponding strains and stresses. Preferably, in step S2, in order to meet the requirements of the elastic modulus of concrete in different periods, the present invention can control the elastic modulus development by the following method: select a suitable water-cement ratio and additives to control the early strength and elastic modulus development of concrete, wherein, especially for low early elastic modulus concrete, adding an appropriate amount of glucose retarder can effectively control the early elastic modulus.

[0052] Preferably, in step S3, low hydration heat concrete can be prepared by using 42.5 grade medium heat cement with 3d hydration heat not exceeding 250 kJ / kg and 7d hydration heat not exceeding 290 kJ / kg, or 42.5 grade low heat cement with 3d hydration heat not exceeding 230 kJ / kg and 7d hydration heat not exceeding 260 kJ / kg, or using 42.5 grade ordinary Portland cement with 3d hydration heat not exceeding 280 kJ / kg and 7d hydration heat not exceeding 315 kJ / kg, and adding fly ash with a total cementitious material (cement and fly ash) mass ratio of 35% to 55% into the concrete. Preferably, low hydration heat concrete can be cast as upper concrete on the concrete transition layer formed by low early elastic modulus concrete. Further, the use of medium heat cement or low heat cement, or the use of ordinary Portland cement with a large amount of fly ash, the purpose is to obtain a concrete with low hydration heat, the control requirement of which is that the adiabatic temperature rise of the concrete is not more than 35 ° C. Concrete with low hydration heat can reduce the temperature rise and temperature gradient of the concrete after pouring. Preferably, the low hydration heat concrete of the present invention generates relatively less heat during the hydration reaction to reduce the temperature gradient inside the concrete. The temperature gradient is one of the main causes of concrete cracking, in which the temperature caused by the hydration of the cementitious material (mainly cement) continues to rise, and then continues to decrease, and the temperature shrinks from high to low. In this process, the elastic modulus of the concrete continues to increase, and the stress generated exceeds the tensile strength of the concrete, and the concrete will crack. Further, when the present invention uses ordinary Portland cement, due to the high hydration heat, it is necessary to add a large amount of fly ash to reduce the amount of cement, thereby reducing the hydration heat of the concrete, effectively reducing the risk of concrete cracks, and improving the durability of the structure.

[0053] Preferably, in step S3, controlling the temperature of concrete entering the mold means taking measures to ensure that the temperature of low-heat concrete entering the mold is 10°C-28°C during pouring. Furthermore, a thermometer or infrared thermometer can be used to regularly detect the temperature of concrete during pouring. Too high a temperature will increase the temperature difference between the internal temperature of the concrete and the ambient temperature, thereby increasing the risk of cracking. Too low a temperature will affect the strength development of concrete and seriously affect construction efficiency. If the detected temperature of concrete entering the mold during pouring does not meet the requirements, the temperature of cement, mixing water and sand and gravel aggregates should be controlled within the range of 5-30°C during concrete mixing.

[0054] Preferably, in step S4, after demolding, the technical measures of moisture retention and heat preservation can be used for curing, wherein the technical measures of moisture retention and heat preservation can include the use of concrete water-saving and moisture-retaining curing membrane, and the use of one or more layers of geotextiles, quilts and other thermal insulation materials according to the temperature conditions to ensure that the temperature difference between the center temperature and the surface temperature of the wall concrete does not exceed 20°C, and the daily cooling rate of the concrete is not greater than 3°C. Further preferably, the temperature difference between the center temperature and the surface temperature of the wall concrete does not exceed 20°C, and the daily average drop in the center temperature of the wall does not exceed 2°C or 3°C.

[0055] Example 1

[0056] In a project for crack control of the long wall construction at the bottom of a subway station, the long wall is 700 mm thick, 4.95 m high, and the concrete design strength grade is C40. Preferably, the comprehensive method of the present invention can be adopted in the project. Preferably, according to the construction conditions and / or needs, the construction flow section is controlled at 18 m.

[0057] Preferably, the low hydration heat concrete mix ratio in this embodiment is as shown in Table 1, and the low early elastic modulus concrete mix ratio is as shown in Table 2.

[0058] Table 1 Low hydration heat concrete mix ratio (kg / m 3 )

[0059]

[0060] Table 2 Early low elastic modulus concrete mix proportion (kg / m 3 )

[0061]

[0062] Preferably, the composition of the early elastic modulus regulating material is as follows: the mass ratio of sodium citrate, sodium gluconate, sodium tartrate and diacetylaminoethyl dihydrogen phosphate is 10:15:5:12.

[0063] Preferably, during the construction of the engineering project of this embodiment, the development control of the elastic modulus of concrete is as shown in Table 3.

[0064] Table 3 Control of the development of elastic modulus of concrete

[0065] Concrete Type 60h elastic modulus (GPa) 7d elastic modulus (GPa) 28d elastic modulus (GPa) Low hydration heat concrete 17.4 28.9 34.6 Low early elastic modulus concrete 0 12.6 33.9 Proportion 0％ 43.6％ 98％

[0066] It can be seen from Table 3 that for the low early elastic modulus concrete of this embodiment, the elastic modulus, a control index, meets the control requirements of not exceeding 50% of the elastic modulus of the upper concrete poured simultaneously within 48 to 72 hours, not exceeding 70% at 7 days, and 90%-110% of the elastic modulus of the upper concrete at 28 days.

[0067] Preferably, the following construction method can be performed in this embodiment:

[0068] (1) Formwork: First, clear away debris and obstacles on the construction site to ensure that the formwork area is flat. Then, install the prefabricated formwork on the supporting structure to ensure that the formwork is flat, firm and meets the design requirements.

[0069] (2) Casting: After the formwork is supported, low early elastic formwork concrete with a height of 400 mm is first cast on the bottom of the long wall, and then low hydration heat concrete is cast until the wall reaches the predetermined height of 4.95 m. The concrete is ensured to flow evenly and is compacted with a vibrator to eliminate voids and air. The temperature entering the mold is controlled at 22 °C.

[0070] (3) Moisture-preservation and heat-insulating maintenance and demolding: After 3 days of maintenance, the upper concrete formwork is removed and covered with a concrete water-saving and moisture-preserving maintenance film, which helps prevent the concrete surface from drying out too quickly and keeps its relative humidity greater than or equal to 90% to reduce the moisture loss and temperature change of the concrete. At the same time, a quilt is used to cover the concrete surface, which can effectively slow down the heat dissipation of the concrete and reduce the daily cooling rate, thereby maintaining the relative stability of the temperature inside and outside the wall. During this period, the temperature was monitored. The highest temperature in the center of the wall concrete was 53°C, the difference between the center temperature and the surface temperature of the wall concrete did not exceed 18°C, and the daily cooling rate of the concrete was 2°C. After 14 days, the lower formwork was removed. Be careful when removing the formwork to avoid damage to the concrete or deformation.

[0071] For example, the crack development of an engineering project with a structure similar to that of the present embodiment using a traditional construction method is shown in Table 4.

[0072] Table 4 Crack development in similar structural projects using traditional construction methods

[0073] Case Number of cracks / root Total length of cracks / m Average crack width / mm Total crack area / mm <![CDATA[Crack area ratio mm 2 / m 2 > 1Pool wall 15 15.2 0.62 9424 102 2Pool wall 13 12.7 0.75 9525 132 3Basement exterior wall 12 13.4 0.6 8040 98 4 Basement exterior wall 9 11.2 0.81 9072 113

[0074] The cracking phenomenon of the traditional concrete long wall structure is relatively common, and it is difficult to control the cracks. The main reason for the serious cracking is that the wall is subject to the constraints of the foundation and the end. In the case shown in Table 4, the severity of the cracking of the exterior wall is closely related to the degree of constraint at the end of the wall. Therefore, when the wall thickness increases or the constraint at the corner of the wall is strengthened, the cracking of the wall is also aggravated. Different from this, this embodiment adopts the comprehensive method of the present invention, by pouring low early elastic modulus concrete to form a concrete transition layer for reducing non-stress cracks in the wall caused by foundation settlement, thereby controlling the occurrence of early non-stress cracks; at the same time, low hydration heat concrete is used on the upper part of the concrete transition layer to reduce the release of hydration heat, reduce the temperature gradient, and thus reduce the formation of cracks; and in the later stage, the technical measures of moisture retention and heat preservation are taken for maintenance to prevent the surface from drying and cracking and reduce the temperature gradient, reduce the shrinkage stress of the concrete, thereby reducing the cracks and non-stress cracks caused by surface drying.

[0075] Preferably, the upper formwork is removed 3 days after the long wall is poured. Only slight cracks are seen in the early stage. The cracks are distributed vertically and nearly linearly, with a spacing of 1.5 to 2.0 m, a width of only 0.2 to 0.3 mm, and a depth of 30 to 50 mm. The cracks start at about 0.5 m from the bottom plate and end at about 0.5 m from the top of the wall. Compared with the crack results treated by traditional methods, the number of cracks is reduced by up to 70% and the crack width is reduced by up to 75%. After the lower formwork is removed on the 14th day, and then after thermal insulation and moisture maintenance, the number of cracks is significantly reduced, the crack width is also effectively controlled, and the cracks remain basically stable. In the end, there are no vertical through cracks in the long wall, and no non-stress cracks. After the completion of the project, in order to evaluate the effectiveness of the temperature crack control technology of the concrete wall, we use the cracking risk of concrete as an evaluation indicator to evaluate the temperature crack condition ψ of the concrete wall after the construction is completed. The evaluation is based on the formula:

[0076]

[0077] Where: η(t)——the maximum tensile force of the concrete wall at time t;

[0078] f t (t)——tensile strength of concrete wall at time t.

[0079] The assessment criteria for concrete cracking risk are defined as follows: if the value of ψ reaches or exceeds 1, it means that temperature cracks will definitely occur in the concrete wall; when the value of ψ is between 0.7 and 1, it indicates that there is a potential risk of temperature cracks in the concrete wall; and when the value of ψ does not exceed 0.7, it is considered that temperature cracks are unlikely to occur in the concrete wall.

[0080] In order to understand the effect of temperature crack control on the concrete wall in this project, we calculated the ψ values ​​at different locations of 9 concrete walls according to the above formula (1). The calculation results are listed in Table 5 below.

[0081] Table 5 Calculation results of temperature cracking of concrete wall

[0082] Location 1 2 3 4 5 6 7 8 9 Temperature cracking calculation results 0.69 0.62 0.53 0.64 0.62 0.51 0.58 0.57 0.68

[0083] According to the data in Table 5, we can conclude that after applying the concrete wall temperature crack control technology proposed in this paper, the temperature crack risk assessment value ψ of all walls did not exceed 0.7, and the highest ψ value was only 0.69. This is consistent with the actual results, which shows that the implementation effect of the temperature crack comprehensive control technology of the present invention is significant and can effectively prevent the cracking problem of concrete walls.

[0084] Example 2

[0085] In a project for crack control of a long wall of a certain building, the long wall is 450mm thick, 5.2m high, and the concrete design strength grade is C45. Preferably, the comprehensive method of the present invention can be adopted in the project. Preferably, according to the construction conditions and / or needs, the length of the construction flow section is controlled at 20m.

[0086] Preferably, the low hydration heat concrete mix ratio in this embodiment is shown in Table 6, and the low early elastic modulus concrete mix ratio is shown in Table 7.

[0087] Table 6 Low hydration heat concrete mix ratio (kg / m 3 )

[0088]

[0089] Table 7 Early low elastic modulus concrete mix proportion (kg / m 3 )

[0090]

[0091] Preferably, the composition of the early elastic modulus regulating material is as follows: the mass ratio of sodium citrate, sodium gluconate, potassium sodium tartrate, polyethylene glycol, and diacetylaminoethyl dihydrogen phosphate is 5:10:5:3:8.

[0092] Preferably, during the construction of the engineering project of this embodiment, the development control of the elastic modulus of concrete is as shown in Table 8.

[0093] Table 8 Control of the development of elastic modulus of concrete

[0094] Concrete Type 60h elastic modulus (GPa) 7d elastic modulus (GPa) 28d elastic modulus (GPa) Low hydration heat concrete 19.3 31.2 36.6 Low early elastic modulus concrete 5.2 19.6 36.2 Proportion 27％ 62.8％ 99％

[0095] It can be seen from Table 8 that for the low early elastic modulus concrete of this embodiment, the elastic modulus, a control index, meets the requirement of not exceeding 50% of the elastic modulus of the upper concrete poured simultaneously within 48 to 72 hours, not exceeding 70% at 7 days, and 90%-110% of the elastic modulus of the upper concrete at 28 days.

[0096] Preferably, the following construction method can be performed in this embodiment:

[0097] (1) Formwork: When performing formwork operations, the construction site must first be cleaned and all debris and obstacles removed to ensure the flatness of the formwork area. Subsequently, the prefabricated formwork is placed on the pre-built support structure. This step requires that the formwork must remain flat and stable and fully comply with the specifications and requirements of the engineering design.

[0098] (2) Casting: After the formwork is completed, the next step is casting. First, a 450mm high layer of low early elastic modulus concrete is cast at the bottom of the long wall. Then, low hydration heat concrete is cast until the wall reaches the predetermined height. During this process, it is necessary to ensure that the concrete can flow evenly. In order to eliminate voids and bubbles in the concrete, a vibrator is required to compact it. In addition, the temperature of the concrete entering the mold needs to be controlled within 28 degrees Celsius to ensure the casting quality.

[0099] (3) Moisture-preservation and heat-insulating maintenance and demolding: After pouring concrete and completing the formwork, the next step is moisture-preservation and heat-insulating maintenance and demolding. First, the concrete is maintained with the formwork for the first three days after pouring, and then the upper concrete formwork is removed. Subsequently, two layers of geotextile and quilt are covered on the concrete surface. The purpose of this is to prevent the concrete surface from losing moisture too quickly, reduce moisture evaporation and temperature fluctuations, slow down the heat loss of concrete, reduce the daily cooling rate of concrete, and maintain the temperature balance inside and outside the wall. During this process, the temperature needs to be monitored to ensure that the maximum temperature of the center of the wall concrete does not exceed 60°C, and the temperature difference between the center and the surface of the wall concrete is controlled within 20°C, and the daily cooling rate of the concrete does not exceed 2.6°C. After 14 days of maintenance, the bottom formwork can be removed. Be extremely careful during the removal process to avoid damage to the concrete or deformation.

[0100] For example, in the engineering project of this embodiment, a side wall to be cast is selected, which is 24m long, 0.7m thick, and 5.9m high. The traditional concrete scheme is used for casting based on steel formwork. The formwork is removed after 3 days, and then an insulation blanket is used for insulation. After the formwork is removed, 3 cracks appear, and eventually 14 cracks appear.

[0101] Correspondingly, in the engineering project of this embodiment, the comprehensive method of the present invention is used for pouring based on steel formwork, and a 45cm thick low elastic modulus concrete layer is set at the bottom. The upper formwork is removed after 3 days. Only small cracks appear in the early stage. The cracks are distributed in a vertical and almost straight line with the ground, with a spacing of about 2.0-2.5m, a width of only 0.1-0.2mm, and a depth of about 20-30mm. The cracks start at about 0.3m near the bottom plate of the wall and end at about 0.4m near the top plate of the wall. Compared with traditional construction, the number of cracks is reduced by about 80% and the width of the cracks is reduced by about 85%. After the lower formwork is removed on the 14th day, after heat preservation and moisture maintenance, the number of cracks is significantly reduced, the crack width is effectively controlled, the cracks are stable, no vertical through cracks occur, and no non-stress cracks are observed. No cracks were detected from the demoulding to the completion, and no leakage has been found since the project was used. In order to test the technical effect of concrete walls in controlling cracks caused by temperature, we selected the risk of concrete cracking as the measurement standard. Based on formula (1), the temperature cracking of the concrete wall after construction was evaluated, and the ψ values ​​at different positions of 9 concrete walls were calculated. The calculation results are listed in Table 9 below.

[0102] Table 9 Calculation results of temperature cracking of concrete wall

[0103]

[0104] According to the calculation results provided in Table 9, we can determine that after adopting the temperature crack control technology recommended by the present invention, the temperature crack risk assessment value ψ of all concrete walls did not exceed the threshold value of 0.7, and the highest assessment value was only 0.68. This result is consistent with the actual observation data, thus confirming the significant effect of the present invention in reducing the risk of concrete wall cracking and showing its effectiveness in preventing wall cracking.

[0105] It should be noted that the above-mentioned specific embodiments are exemplary, and those skilled in the art can come up with various solutions inspired by the disclosure of the present invention, and these solutions also belong to the disclosure scope of the present invention and fall within the protection scope of the present invention. Those skilled in the art should understand that the present invention specification and its drawings are illustrative and do not constitute a limitation of the claims. The scope of protection of the present invention is defined by the claims and their equivalents. The present invention specification contains multiple inventive concepts, such as "preferably" or "a preferred implementation method" both indicate that the corresponding paragraph discloses an independent concept, and the applicant reserves the right to file a divisional application based on each inventive concept. Throughout the text, the features guided by "preferably" are only an optional method and should not be understood as a must-have setting. Therefore, the applicant reserves the right to abandon or delete the relevant preferred features at any time.

Claims

1. A comprehensive method for controlling non-stress cracks in a concrete long wall structure, characterized in that include: S1. Divide the construction flow sections; S2. Pour low early elastic modulus concrete at the bottom of the long wall to form a concrete transition layer; S3 pouring low hydration heat concrete, and controlling the concrete mold temperature to form the upper concrete; S4. After demoulding, moisturizing and heat preservation are carried out, including: The low early elastic modulus concrete poured in step S2 has the same strength grade as the low hydration heat concrete poured in step S3, but the elastic modulus is not more than 50% of the upper concrete poured at the same time within 48 to 72 hours, not more than 70% at 7 days, and the elastic modulus at 28 days is 90%-110% of the elastic modulus of the upper concrete, and the low hydration heat concrete poured in step S3 adopts 42.5% hydration heat of not more than 250 kJ / kg at 3 days and not more than 290 kJ / kg at 7 days. The concrete shall be prepared with 42.5-grade medium-heat cement or 42.5-grade low-heat cement with a hydration heat of no more than 230 kJ / kg in 3 days and 260 kJ / kg in 7 days, or 42.5-grade ordinary Portland cement with a hydration heat of no more than 280 kJ / kg in 3 days and 315 kJ / kg in 7 days, and fly ash in a mass ratio of 35% to 55% of the total cementitious materials; the total cementitious materials are cement and fly ash, and the adiabatic temperature rise of the low-hydration-heat concrete shall be controlled to be no more than 35°C.

2. The integrated method according to claim 1, characterized in that In step S1, the one-time pouring length of the construction flow section ranges from 15 to 20 m.

3. The integrated method according to claim 1, characterized in that: In step S2, low early elastic modulus concrete is poured at the bottom of the long wall to form a concrete transition layer of 300 to 600 mm.

4. The integrated method according to claim 1 or 3, characterized in that In step S2, low early elastic modulus concrete is mixed with early elastic modulus regulating materials and organic synthetic fibers during preparation, wherein the early elastic modulus regulating materials include one or more combinations of the following components: sodium citrate, sodium gluconate, sodium tartrate, polyethylene glycol, diacetylaminoethyl dihydrogen phosphate; the organic synthetic fibers are polypropylene fibers and / or polyacrylonitrile fibers.

5. The integrated method according to claim 1, characterized in that: The early elastic modulus regulating material can be made of the following components in parts by weight: 5-10 parts of sodium citrate, 10-15 parts of sodium gluconate, 5-8 parts of sodium tartrate, 0-5 parts of polyethylene glycol, and 6-12 parts of diacetylaminoethyl dihydrogen phosphate; the initial modulus of the organic synthetic fiber is not greater than 10Gpa.

6. The integrated method according to claim 1, characterized in that: The amount (mass) of early elastic modulus control material added is 1% to 3% of the mass of cementitious materials, namely cement and fly ash, and the amount (volume) of organic synthetic fiber added is 0.05% to 0.2% of the volume of concrete.

7. The integrated method according to claim 1, characterized in that: Measures should be taken to ensure that the temperature of low-hydration hot concrete entering the mold is 10℃-28℃ during pouring. If the detected temperature of concrete entering the mold during pouring cannot meet the requirements, the temperature of cement, mixing water and sand and gravel aggregates during concrete mixing should be controlled within the range of 5-30℃.

8. The integrated method according to claim 1, characterized in that: The technical measures for moisture retention or heat preservation are to use concrete water-saving and moisture-retaining curing membrane, and according to the temperature conditions, cover it with one or several layers of geotextile or quilt to ensure that the temperature difference between the center temperature and the surface temperature of the wall concrete does not exceed 20°C, and the daily cooling rate of the concrete is not more than 3°C.

9. The integrated method according to claim 1, characterized in that: When implementing technical measures for moisture retention or heat preservation, the temperature difference between the center temperature and the surface temperature of the wall concrete should be controlled to be no more than 20°C, and the daily average drop in the center temperature of the wall should not exceed 2°C or 3°C.

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