A method for controlling early cracks in building exterior walls based on integrated design and construction

Abstract

This application relates to a method for controlling early cracks in building exterior walls based on integrated design and construction, and relates to the technical field of wall crack control. The method includes: reducing the amount of cement in concrete, optimizing aggregate gradation to reduce hydration heat and autogenous shrinkage, and regulating material temperature and deformation; designing structural reinforcement to optimize reinforcement for temperature stress and shrinkage stress in the early stages; and regulating temperature and humidity during the construction phase to control the temperature difference between the inside and outside of the concrete and the temperature difference between the surface and the atmosphere. This application can reduce the risk of early cracking in basement concrete exterior walls and control early cracks, thereby improving the durability of basement concrete exterior walls.

Description

Technical Field

[0001] The present application relates to the technical field of wall crack control, and in particular to a method for controlling early cracks in building exterior walls based on integrated design and construction. Background Art

[0002] As the depth of urban underground space development increases, and generally reaches more than 20 meters, the proportion of large-span, ultra-long continuous concrete wall structures has increased significantly. In the early stage of hardening from 3 to 14 days after pouring, when the hydration heat release is basically completed and the temperature tends to stabilize, this type of structure is exposed to complex water environments and high constraints for a long time, and early cracking problems are prominent, leading to water seepage, steel corrosion, and durability degradation. In pursuit of high strength and high fluidity, modern concrete generally adopts a mix design with high cement content and high slurry-to-aggregate ratio. Combined with problems such as poor grading of machine-made sand and fluctuations in stone powder content, this further aggravates the superposition effect of material shrinkage and temperature stress, becoming the main cause of early cracking.

[0003] Existing technologies have addressed premature cracking in exterior walls. For example, at the material level, increasing the sand content or cementitious materials to improve fluidity has been employed, but without systematically optimizing gradation and infill relationships. Structural design relies on traditional reinforcement methods, failing to quantify the effects of early non-load stresses. Construction relies on formwork insulation and conventional wet curing for temperature control, but the precision required to control the internal and external temperature differential is insufficient. While these methods can partially alleviate cracking, they fail to coordinate the entire material, structure, and construction chain, resulting in limited crack control effectiveness.

[0004] In summary, it is necessary to propose an integrated early crack control technology method for the design and construction of basement concrete exterior walls. Through experiments and simulations, technical control indicators for each stage of material design, structure and construction design, and construction are established to reduce the risk of early cracking of basement concrete exterior walls and control early cracks, thereby improving the durability of basement concrete exterior walls. Summary of the Invention

[0005] The present application provides a method for controlling early cracks in building exterior walls based on integrated design and construction, which can reduce the risk of early cracking in basement concrete exterior walls and control early cracks, thereby improving the durability of basement concrete exterior walls.

[0006] This application provides a method for controlling early cracks in building exterior walls based on integrated design and construction, which adopts the following technical solutions:

[0007] A method for controlling early cracks in building exterior walls based on integrated design and construction, with the early stage set as 3-14 days after concrete pouring, including:

[0008] By reducing the amount of cement in concrete and optimizing aggregate gradation to reduce hydration heat and autogenous shrinkage, the design is regulated based on material temperature and deformation.

[0009] Structural reinforcement design, optimizing reinforcement for temperature stress and shrinkage stress in the early stages;

[0010] During the construction phase, the temperature and humidity are controlled to ensure that the temperature difference between the inside and outside of the concrete is ≤25°C and the temperature difference between the surface and the atmosphere is ≤20°C.

[0011] By adopting the above technical solution, it is possible to reduce the amount of cement or the slurry-aggregate ratio caused by reducing the amount of water used in the concrete mixture while maintaining the water-binder ratio, thereby reducing the occurrence of cracks in the early stages. At the same time, the material temperature and deformation are regulated and designed to reduce the stress accumulation caused by temperature difference and shrinkage, thereby improving the stability of the material. At the same time, structural steel bar design is added to optimize the reinforcement for temperature stress and shrinkage stress in the early stages, enhance the wall's resistance to non-load stress, and avoid cracks caused by stress concentration as much as possible. Moreover, by regulating temperature and humidity during the construction phase, the temperature difference between the inside and outside of the concrete is strictly controlled to not exceed 25°C, and the temperature difference between the surface and the atmosphere is strictly controlled to not exceed 20°C, effectively preventing thermal stress damage caused by excessive temperature difference, and further ensuring the integrity and durability of the wall.

[0012] In a preferred example, the present application can be further configured as follows: the steps of reducing the amount of cement in concrete, optimizing aggregate gradation, reducing hydration heat and autogenous shrinkage, and regulating and designing the material temperature and material deformation include:

[0013] Dynamically adjust the proportion of stone powder replacing cementitious materials according to the stone powder content measured in the machine-made sand;

[0014] The adjusted stone powder is subjected to 45 μm negative pressure screening. When the sieve residue mass accounts for ≤20%, the stone powder is determined to have a water-reducing effect, and the water consumption is optimized based on the water demand ratio;

[0015] The water demand ratio test is conducted on the stone powder having a water-reducing effect, and the water consumption of the concrete is optimized based on the stone powder combined with the water demand ratio.

[0016] By adopting the above technical solution, the mix ratio parameters are dynamically adjusted according to the characteristics of the stone powder in the machine-made sand to replace the cementitious material, thereby increasing the stone powder content and reducing the heat release and shrinkage of the concrete; the adjusted stone powder is subjected to 45μm negative pressure screening and the weight ratio of the sieve residue is controlled. The stone powder with a water-reducing effect can be screened out, thereby optimizing the water consumption of the concrete. The water consumption is further refined in combination with the water demand ratio test results, reducing the hydration heat and shrinkage while ensuring the working performance of the concrete, thereby effectively reducing the risk of early cracking.

[0017] In a preferred example, the present application may be further configured as follows: the step of dynamically adjusting the proportion of stone powder replacing cementitious material according to the stone powder content measured in the machine-made sand includes:

[0018] Obtain the amount of stone powder, cement and fly ash measured in manufactured sand;

[0019] If the proportion of stone powder to manufactured sand does not exceed 20% of the cement content, the strength influence coefficient is introduced to adjust the concrete mix parameters, and the stone powder contained in the manufactured sand is used to replace cement;

[0020] If the proportion of stone powder in manufactured sand exceeds 20% of the cement dosage, the amount of stone powder that does not exceed 20% of the cement dosage shall replace cement, and the amount of stone powder that exceeds 20% of the cement dosage shall replace fly ash, and the excess amount of stone powder shall not be regarded as a component of manufactured sand and shall not be included in the calculation of sand ratio.

[0021] By adopting the above technical solution, when the proportion of stone powder in the machine-made sand does not exceed 20% of the cement dosage, stone powder is used to replace part of the cement, thereby reducing the cement dosage while ensuring that the strength of the concrete is not affected; when the proportion of stone powder in the machine-made sand exceeds 20% of the cement dosage, the excess part will be used to replace fly ash, optimizing the grading of various fillers, and thereby reducing the concrete's slurry-aggregate ratio or sand ratio, achieving low carbon, low temperature and low shrinkage of the concrete, and improving the concrete's crack resistance.

[0022] In a preferred example, the present application can be further configured as follows: the structural reinforcement design, the step of optimizing reinforcement arrangement based on temperature stress and shrinkage stress in the early stage, includes:

[0023] If the stress generated by the wall temperature field changing with thickness exceeds the tensile strength of concrete, the tensile stress is borne by adjusting the reinforcement area and redesigning the reinforcement spacing.

[0024] By adopting the above technical solution, when the stress generated by the wall due to the change of temperature field with thickness exceeds the tensile strength of the concrete itself, the reinforcement area is reasonably increased to make the steel bars bear the excess tensile stress, thereby avoiding cracks in the concrete due to excessive stress; at the same time, the steel bar spacing is redesigned so that the steel bars in the replaced reinforcement area are distributed more evenly, thereby enhancing the overall crack resistance of the wall.

[0025] In a preferred example, the present application may be further configured as follows: if the stress generated by the wall temperature field changing with thickness exceeds the tensile strength of concrete, the steps of adjusting the reinforcement area to bear the tensile stress and redesigning the reinforcement spacing include:

[0026] Calculating the real-time temperature stress of the concrete based on the concrete cooling rate and the wall elastic modulus value, and calculating the shrinkage stress of the concrete based on the wall elastic modulus value and autogenous shrinkage strain;

[0027] If the total stress after the real-time temperature stress and shrinkage stress of the concrete are superimposed exceeds the tensile strength of the concrete, the tensile stress is borne by adjusting the reinforcement area and redesigning the reinforcement spacing.

[0028] By adopting the above technical solution, real-time temperature stress and shrinkage stress are calculated. When the total stress after the superposition of the two exceeds the tensile strength of concrete, the reinforcement area is adjusted to bear the tensile stress, thereby achieving precise control of the internal stress state of concrete and reducing the risk of cracking. The reinforcement area and steel bar spacing are adjusted, and the steel bar layout is optimized to adapt to changes in temperature and shrinkage stress, thereby effectively preventing cracks caused by excessive stress.

[0029] In a preferred example, the present application may be further configured as follows: before the step of calculating and obtaining the real-time temperature stress of the concrete based on the concrete cooling rate and the wall elastic modulus value, and calculating and obtaining the shrinkage stress of the concrete based on the wall elastic modulus value and the autogenous shrinkage strain, the step further includes:

[0030] Select the corresponding wall temperature gradient value according to the wall thickness;

[0031] According to the mix ratio of concrete obtained by mixing cementitious materials and stone powder, the peak temperature inside the wall is calculated;

[0032] According to the temperature peak value and the wall temperature gradient value, combined with the temperature difference time-varying model and temperature monitoring data, the concrete cooling rate is calculated;

[0033] According to the empirical value of the wall elastic modulus changing with age, the wall modulus value in the early stage is calculated;

[0034] The autogenous shrinkage strain of the concrete is calculated based on the hydration characteristics of the cementitious material.

[0035] By adopting the above technical solution, the corresponding wall temperature difference gradient value is selected according to the wall thickness, which improves the pertinence and accuracy of the temperature stress calculation, thereby providing a reliable basis for subsequent stress analysis; by calculating the peak temperature inside the wall, combining the temperature difference time-varying model and temperature monitoring data, the concrete cooling rate is accurately obtained, which helps to control the internal and external temperature difference and reduce the risk of cracks caused by temperature stress; based on the empirical value of the wall elastic modulus changing with age, the wall modulus value in the early stage is calculated, which improves the scientificity and rationality of the shrinkage stress calculation; based on the hydration characteristics of the cementitious material, the autogenous shrinkage strain of the concrete is calculated, which further refines the quantitative analysis of shrinkage stress, effectively supports the optimization of reinforcement design, improves the overall crack control effect, and ultimately achieves accurate calculation of temperature stress and shrinkage stress in the early stage of concrete.

[0036] In a preferred example, the present application may be further configured as follows: if the total stress after the superposition of the real-time temperature stress and the shrinkage stress of the concrete exceeds the tensile strength of the concrete, the steps of adjusting the reinforcement area to bear the tensile stress and redesigning the reinforcement spacing include:

[0037] The reinforcement is used to meet the following requirements:

[0038] A s ·f y ≥σ 总 ·A c ,

[0039] Among them, A s is the cross-sectional area of ​​the steel bar, f y is the tensile strength of steel bars, σ 总 A is the total stress after the real-time temperature stress and shrinkage stress of the concrete are superimposed, c is the cross-sectional area of ​​concrete;

[0040] Design the steel bar spacing based on the reinforcement area and the area of ​​a single steel bar.

[0041] By adopting the above technical solution, the reinforcement satisfies the requirement that the product of the steel bar cross-sectional area and the steel bar tensile strength is greater than or equal to the product of the total stress and the concrete cross-sectional area, thereby achieving reasonable bearing of tensile stress; at the same time, the steel bar spacing is designed according to the reinforcement area and the area of ​​a single steel bar, and the steel bar layout is optimized to improve the structural crack resistance and enhance the durability of the basement exterior wall.

[0042] In a preferred example, the present application may be further configured as follows: before the step of adjusting the reinforcement area to bear the tensile stress and redesigning the reinforcement spacing if the stress generated by the wall temperature field changing with thickness exceeds the concrete tensile strength, the method may further include:

[0043] Establish a database of structural design indicators for diaphragm walls of different thicknesses, covering the cementitious material dosage range of 300-450 kg / m³ corresponding to C15-C50 concrete strength grades;

[0044] The wall thickness and steel bar arrangement parameters are matched according to the database so that the maximum adiabatic temperature rise and fall is not less than the temperature threshold and the shrinkage rate reduction is not less than a preset ratio.

[0045] By adopting the above technical solution, the coordinated control effect of temperature stress and shrinkage stress is further enhanced, effectively reducing the maximum adiabatic temperature rise to no less than the temperature threshold, and at the same time reducing the self-shrinkage rate to no less than the preset ratio, thereby comprehensively improving the crack resistance and structural stability of the basement exterior wall in the early stage.

[0046] In a preferred embodiment, the present application may be further configured as follows: the step of regulating temperature and humidity during the construction phase to control the temperature difference between the inside and outside of the concrete to be ≤25°C and the temperature difference between the surface and the atmosphere to be ≤20°C includes:

[0047] Use hydration heat inhibitor to slow down the hydration reaction rate;

[0048] The heat dissipation coefficient is adjusted to the range of 0.5~1.0 through the formwork insulation layer, and the temperature difference between the center and surface of the concrete is monitored in real time to control the cooling rate of the concrete to ≤3℃ / d.

[0049] By adopting the above technical solution, a hydration heat inhibitor is used to slow down the hydration reaction rate, which can significantly reduce the peak hydration heat of the concrete and reduce the occurrence of cracks caused by temperature stress. By adjusting the heat dissipation coefficient of the formwork insulation layer to the range of 0.5~1.0, precise control of the heat dissipation process of the concrete can be achieved, further reducing the temperature difference between the inside and outside, and avoiding cracking caused by excessive temperature gradients as much as possible. The temperature difference between the center and the surface of the concrete is monitored in real time and the cooling rate is controlled to ≤3℃ / d to ensure uniform and stable temperature changes, effectively preventing thermal shock cracks caused by sudden cooling and heating.

[0050] In a preferred embodiment, the present application may be further configured as follows: the step of regulating temperature and humidity during the construction phase to control the temperature difference between the inside and outside of the concrete to be ≤25°C and the temperature difference between the surface and the atmosphere to be ≤20°C, further includes:

[0051] Internal curing methods are used to regulate the internal humidity field of concrete during the hydration process.

[0052] By adopting the above technical solution and using internal curing methods to regulate the internal humidity field of concrete during the hydration process, the temperature difference between the inside and outside of the concrete, as well as the temperature difference between the surface and the atmosphere, can be effectively controlled, which helps to reduce stress concentration caused by temperature gradients, thereby reducing the risk of early cracking of concrete and improving the durability of the basement exterior wall.

[0053] In summary, this application has the following beneficial technical effects:

[0054] 1. This application effectively reduces hydration heat and autogenous shrinkage by reducing cement usage, optimizing aggregate gradation, and dynamically adjusting the proportion of stone powder replacing cementitious materials, thereby significantly reducing early cracks caused by temperature stress and material deformation;

[0055] 2. This application optimizes the reinforcement design based on the temperature stress and shrinkage stress in the early stage. By accurately calculating the real-time stress of the concrete and adjusting the area and spacing of the steel bars, the wall's crack resistance is enhanced.

[0056] 3. During the construction phase, this application controls the temperature and humidity to keep the temperature difference between the inside and outside of the concrete and the temperature difference between the surface and the atmosphere within a reasonable range, thereby further suppressing the risk of cracks caused by temperature stress and improving the overall durability of the basement exterior wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a flow chart of a method for controlling early cracks in building exterior walls based on integrated design and construction in one embodiment of the present application.

[0058] Figure 2 This is a flowchart of the sub-steps of step S1 in one embodiment of the present application.

[0059] Figure 3 This is a flowchart of the sub-steps of step S10 in one embodiment of the present application.

[0060] Figure 4 This is a flowchart of the sub-steps of step S2 in one embodiment of the present application.

[0061] Figure 5 This is a flowchart of the sub-steps of step S20 in one embodiment of the present application.

[0062] Figure 6 This is a flowchart of the steps added before step S200 in one embodiment of the present application.

[0063] Figure 7 This is a flowchart of the sub-steps of step S201 in one embodiment of the present application.

[0064] Figure 8 This is a flowchart of the steps added before step S20 in one embodiment of the present application.

[0065] Figure 9 This is a flowchart of the sub-steps of step S3 in one embodiment of the present application.

[0066] Figure 10 This is a flowchart of the sub-steps of step S31 in one embodiment of the present application. DETAILED DESCRIPTION

[0067] The following is combined with Figure 1-10 This application is described in further detail.

[0068] It should be noted that all actions of obtaining data or information or data in this application are carried out in compliance with the relevant data protection laws and policies of the country where they are located and with the authorization of the corresponding users.

[0069] refer to Figure 1A method for controlling early cracks in building exterior walls based on integrated design and construction, with the early stage set as 3-14 days after concrete pouring, specifically including:

[0070] S1. Reduce the amount of cement in concrete, optimize aggregate grading, reduce hydration heat and autogenous shrinkage, and regulate the design based on material temperature and material deformation.

[0071] Specifically, during the initial hardening process after concrete pouring until the release of hydration heat is essentially complete and the temperature stabilizes, the underground environment, influenced by soil quality, water levels, and the geographical environment, creates more complex conditions for concrete structures in service. This makes early cracking more likely, leading to water seepage, steel corrosion, and durability degradation, compromising the structural stability of the basement exterior walls. Therefore, this early stage, spanning three to fourteen days after pouring, is designated as the early stage. To address the potential cracking of the basement exterior walls during this early stage, based on the characteristics of modern concrete and variations in raw materials, this approach is implemented by reducing the increased cement content or mortar-to-aggregate ratio associated with high water content in modern concrete mixes while maintaining a constant water-binder ratio. This addresses the current problem of increased cement content or mortar-to-aggregate ratios, which exacerbate cracking in the material due to high water content in the mixes to meet high workability requirements under pumping and dense rebar conditions. Simultaneously, material temperature and deformation are controlled to reduce stress accumulation caused by temperature differences and shrinkage, improving material stability and preventing early cracking.

[0072] S2. Structural reinforcement design: optimization of reinforcement for temperature stress and shrinkage stress in the early stages.

[0073] Specifically, in terms of structure and construction, in order to adapt to the stress and stress concentration caused by cross-sectional mutations due to the temperature and volume stability of the material in the early hardening stage of concrete, reinforcement optimization is required to make the steel bar position design and spacing design more targeted and effective, enhance the wall's resistance to non-load stress, and avoid cracks caused by stress concentration as much as possible.

[0074] S3. Regulate temperature and humidity during the construction phase, and control the temperature difference between the inside and outside of the concrete to ≤25°C, and the temperature difference between the surface and the atmosphere to ≤20°C.

[0075] Specifically, during the construction phase, by regulating temperature and humidity, the temperature difference between the inside and outside of the concrete is strictly controlled to not exceed 25°C, and the temperature difference between the surface and the atmosphere is strictly controlled to not exceed 20°C, effectively preventing thermal stress damage caused by excessive temperature difference and further ensuring the integrity and durability of the wall.

[0076] In this embodiment, in the early stage of construction, on the basis of optimizing the concrete mix ratio for prevention and control, and optimizing the reinforcement to achieve the resistance of the wall, the temperature and humidity of the concrete wall in the construction stage are adjusted to control the temperature and humidity that are prone to cause early cracks within a reasonable range, thereby achieving the regulation of the reasonable range of values ​​of the unfavorable indicators for the generation of early cracks, reducing the probability of early cracks, and reducing early cracks in concrete of various structural forms.

[0077] refer to Figure 2 Furthermore, in one embodiment, step S1 is further divided into the following sub-steps:

[0078] S10. Dynamically adjust the proportion of stone powder replacing cementitious materials based on the stone powder content measured in the machine-made sand.

[0079] Specifically, a device for measuring the stone powder content of dry powdered manufactured sand at the construction site can quickly determine the stone powder content in the manufactured sand. This allows for the corresponding concrete mix proportion to be calculated, and the content of cement, fly ash, mineral powder, and other cementitious materials, as well as sand and stone, per cubic meter of concrete can be calculated. Then, based on the characteristics of the stone powder in the manufactured sand, the mix parameters are dynamically adjusted to replace the cementitious materials and increase the stone powder content, thereby reducing concrete heat release and shrinkage.

[0080] S11. Perform 45μm negative pressure screening on the adjusted stone powder. When the sieve residue mass accounts for ≤20%, it is determined that the stone powder has a water-reducing effect, and the water consumption is optimized based on the water demand ratio.

[0081] Specifically, when stone powder is subjected to a 45μm negative pressure screening test, if the sieve residue mass percentage does not exceed 20%, it is considered to have a water-reducing effect. If the sieve residue mass percentage exceeds 20%, it can be determined to have no water-reducing effect. After adjusting the stone powder, 45μm negative pressure screening is carried out and the sieve residue mass percentage is controlled to screen out stone powder with a water-reducing effect, thereby optimizing the water consumption of concrete.

[0082] S12. Conduct water demand ratio test on stone powder with water-reducing effect, and optimize the water consumption of concrete based on the stone powder combined with water demand ratio.

[0083] Specifically, the water requirement ratio test results are combined to further refine the water consumption, reducing hydration heat and autogenous shrinkage while ensuring concrete workability, thereby effectively reducing the risk of premature cracking. In this embodiment, the water requirement ratio is combined with the water requirement ratio to further optimize the water consumption while using admixtures and ensuring workability. Stone powder, which does not have a water-reducing effect, is not considered for water consumption optimization.

[0084] In addition, reference Figure 3 Furthermore, in one embodiment, step S10 is further divided into the following sub-steps:

[0085] S100. Obtain the amounts of stone powder, cement, and fly ash measured in the machine-made sand.

[0086] S101. If the proportion of stone powder to manufactured sand does not exceed 20% of the cement dosage, the strength influence coefficient shall be introduced to adjust the concrete mix parameters and the stone powder contained in the manufactured sand shall be used to replace the cement.

[0087] Specifically, based on the difference between the activity index of stone powder and cement, a theoretical correction model is established:

[0088] ;

[0089] Where β is the reduction coefficient of stone dust activity, which needs to be calibrated through experiments and is usually 0.2-0.3. When the stone dust activity is high (such as containing calcium carbonate), β takes a low value, and vice versa.

[0090] S102. If the proportion of stone powder in manufactured sand exceeds 20% of the cement dosage, the amount of stone powder that does not exceed 20% of the cement dosage shall replace cement, and the amount of stone powder that exceeds 20% of the cement dosage shall replace fly ash, and the excess amount of stone powder shall not be regarded as a component of manufactured sand and shall not be included in the calculation of sand ratio.

[0091] Specifically, when the proportion of stone powder in machine-made sand exceeds 20% of the cement dosage, the excess stone powder will be used to replace fly ash to optimize the grading of various fillers, and also reduce the slurry-aggregate ratio or sand ratio of concrete, achieving low-carbon, low-temperature and low-shrinkage concrete, thereby improving the crack resistance of concrete.

[0092] In addition, reference Figure 4 Furthermore, in one embodiment, step S2 is further divided into the following sub-steps:

[0093] S20. If the stress generated by the wall temperature field changing with thickness exceeds the tensile strength of concrete, the tensile stress is borne by adjusting the reinforcement area and redesigning the reinforcement spacing.

[0094] Specifically, when the stress generated by the wall due to the change in temperature field with thickness exceeds the tensile strength of the concrete itself, the reinforcement area can be reasonably increased so that the steel bars can bear the tensile stress that exceeds the concrete's bearing capacity, thereby reducing the phenomenon of concrete cracking due to excessive stress; at the same time, by optimizing the steel bar spacing design, the steel bars in the newly added reinforcement area are distributed more evenly, thereby improving the overall crack resistance of the wall.

[0095] In addition, reference Figure 5 Furthermore, in one embodiment, step S20 is further divided into the following sub-steps:

[0096] S200: Calculate and obtain the real-time temperature stress of the concrete based on the concrete cooling rate and the wall elastic modulus value, and simultaneously calculate and obtain the shrinkage stress of the concrete based on the wall elastic modulus value and the autogenous shrinkage strain.

[0097] Specifically, as the wall's temperature field changes with thickness, the resulting temperature stress also changes. Simultaneously, autogenous shrinkage stress from material volume deformation and sudden changes in wall stiffness can also lead to stress concentration. Therefore, by calculating real-time temperature and shrinkage stresses, and when the combined total stress exceeds the concrete's tensile strength, the reinforcement area needs to be adjusted to accommodate the tensile stress. This allows for precise control of the concrete's internal stress state, reducing the risk of early cracking in the exterior wall.

[0098] Furthermore, the real-time temperature stress σ in the early stage is calculated by the formula:

[0099] σ = -EαR c ,

[0100] Among them, α is set to 0.7×10 -5 ~1.4×10 -5 / ℃, E is the elastic modulus of concrete, R c is the concrete cooling rate.

[0101] Furthermore, the shrinkage stress is calculated. ) is caused by the constraint of shrinkage strain, and the core formula is:

[0102] ,

[0103] Among them, E c is the real-time wall elastic modulus value in the early stage, is the autogenous shrinkage strain, which is related to the total hydration heat Q of the cementitious material. Calculate, where is the admixture adjustment coefficient, is the total heat of cement hydration.

[0104] The R value is obtained in real time according to the following table:

[0105] Constraint Type R value Selection basis Fully constrained 1.0 Four-way constraints Moderate constraints 0.5-0.7 Upper and lower constraints Low Constraint 0.3-0.5 Unilateral constraints

[0106] S201. If the total stress after the superposition of the real-time temperature stress and shrinkage stress of concrete exceeds the tensile strength of concrete, the tensile stress shall be borne by adjusting the reinforcement area and redesigning the reinforcement spacing.

[0107] Specifically, when the temperature stress exceeds the tensile strength of concrete, the tensile stress needs to be borne by reinforcement. The reinforcement area ( ) is calculated as:

[0108] ,

[0109] in, is the design value of temperature stress (N / mm 2 ), is the concrete cross-sectional area (mm 2 ), is the design value of steel bar tensile strength (N / mm 2 ), such as HRB400, take 360N / mm 2 .

[0110] Furthermore, the steel bar spacing design is calculated using the formula:

[0111] ,

[0112] Among them, a s It is the area of ​​a single steel bar, determined by the selected steel bar diameter.

[0113] By adjusting the reinforcement area and the spacing between reinforcement bars, the reinforcement arrangement is optimized to adapt to the changing temperature and shrinkage stress, thereby effectively preventing the occurrence of cracks caused by excessive stress.

[0114] In addition, reference Figure 6 Furthermore, in one embodiment, before step S200, steps S2000, S2001, S2002, S2003, and S2004 are added:

[0115] S2000. Select a corresponding wall temperature gradient value according to the wall thickness.

[0116] Specifically, the wall temperature gradient value corresponding to the wall thickness is selected by directly looking up the table in the database to improve the pertinence and accuracy of the temperature stress calculation and provide a reliable basis for subsequent stress analysis.

[0117] S2001. Calculate and obtain the peak temperature inside the wall based on the mix ratio of concrete obtained by mixing cementitious materials and stone powder.

[0118] Specifically, the peak temperature inside the wall is calculated based on the concrete mix ratio:

[0119] ,

[0120] in, is the concrete pouring temperature (℃), is the maximum adiabatic temperature rise (°C), is the temperature reduction coefficient, which can be found in the table or fitted through the empirical formula.

[0121] The adiabatic temperature is:

[0122] ,

[0123] The specific parameter definitions are shown in the following table:

[0124]

[0125] S2002. Calculate and obtain the concrete cooling rate based on the peak temperature value and the wall temperature gradient value, combined with the temperature difference time-varying model and temperature monitoring data.

[0126] Specifically, by calculating the peak temperature inside the wall, combining the temperature difference time-varying model and temperature monitoring data, it helps to control the temperature difference between inside and outside, and minimize the risk of cracks caused by temperature stress. It is defined as the difference between the concrete core temperature and the surface temperature per unit time. The calculation requires a combination of a temperature difference time-varying model and temperature monitoring data. The core formula considering the heat dissipation effect is as follows:

[0127] ,

[0128] in, is the ambient temperature (°C), is the heat dissipation coefficient, usually ranging from 0.5 to 1.0, and is adjusted according to the thickness of the insulation layer. β is the temperature gradient value of the wall thickness.

[0129] S2003. Calculate and obtain the wall modulus value at the early stage based on the empirical value of the wall elastic modulus changing with age.

[0130] Specifically, based on the empirical value of the wall elastic modulus changing with age, the wall modulus value in the early stage is calculated, thereby improving the scientificity and rationality of the shrinkage stress calculation. The elastic modulus changes with age, and the empirical formula is:

[0131] ,

[0132] is the elastic modulus of concrete at 28 days, Calculate, where is the compressive strength of the cube.

[0133] S2004. Calculate and obtain the autogenous shrinkage strain of concrete based on the hydration characteristics of the cementitious material.

[0134] Specifically, the autogenous shrinkage strain is related to the hydration characteristics of the cementitious material and can be calculated based on the following model:

[0135] CEB-FIP model:

[0136] ,

[0137] in: is the ultimate autogenous shrinkage strain, which is related to the total hydration heat Q of the gelling material. Calculate, where is the admixture adjustment coefficient, is the total heat of cement hydration. is the age (days).

[0138] The autogenous shrinkage strain of concrete is calculated based on the hydration characteristics of cementitious materials, which further refines the quantitative analysis of shrinkage stress, effectively supports the optimization of reinforcement design, improves the overall crack control effect, and ultimately achieves accurate calculation of temperature stress and shrinkage stress in concrete in the early stage.

[0139] In addition, reference Figure 7 Furthermore, in one embodiment, step S201 is further divided into the following sub-steps:

[0140] S2010, through reinforcement to meet:

[0141] A s ·f y ≥σ 总 ·A c ,

[0142] Among them, A s is the cross-sectional area of ​​the steel bar, f y is the tensile strength of steel bars, σ 总 A is the total stress after the real-time temperature stress and shrinkage stress of concrete are superimposed, c is the cross-sectional area of ​​concrete.

[0143] Specifically, through calculation, the reinforcement is made to satisfy the requirement that the product of the cross-sectional area of ​​the steel bar and the tensile strength of the steel bar is greater than or equal to the product of the total stress and the cross-sectional area of ​​the concrete, so as to achieve reasonable bearing of the tensile stress.

[0144] S2011. Design the spacing between steel bars based on the reinforcement area and the area of ​​a single steel bar.

[0145] In addition, reference Figure 8 Furthermore, in one embodiment, before step S20, steps S202 and S203 are added:

[0146] S202. Establish a database of structural design indicators for diaphragm walls of different thicknesses, covering the cementitious material dosage range of 300-450 kg / m³ corresponding to concrete strength grades C15-C50.

[0147] Specifically, the elastic modulus of concrete can be obtained from the index database to improve the efficiency of calculation. The specific values ​​can be obtained from the following table:

[0148] C15 <![CDATA[2.2×10 4 Mpa <!-- 9 -->]]> C20 <![CDATA[2.6×10 4 Mpa]]> C25 <![CDATA[2.9×10 4 Mpa]]> C30 <![CDATA[3.0×10 4 Mpa]]> C40 <![CDATA[3.3×10 4 Mpa]]> C50 <![CDATA[3.5×10 4 Mpa]]>

[0149] S203: Match the wall thickness and steel bar arrangement parameters according to the database so that the maximum adiabatic temperature rise and fall is not less than the temperature threshold and the shrinkage rate reduction is not less than a preset ratio.

[0150] Specifically, in this embodiment, the temperature threshold is set to 10°C, that is, the maximum adiabatic temperature rise value of ordinary concrete can be reduced by more than 10°C; the preset ratio is set to 44.3%, that is, the maximum reduction in shrinkage rate is 44.3%, so as to enhance the coordinated control effect of temperature stress and shrinkage stress, thereby comprehensively improving the crack resistance and structural stability of the basement exterior wall in the early stage.

[0151] In addition, reference Figure 9 Furthermore, in one embodiment, step S3 is further divided into the following sub-steps:

[0152] S30. Use a hydration heat inhibitor to slow down the hydration reaction rate.

[0153] Specifically, the use of hydration heat inhibitors to slow down the hydration reaction rate can significantly reduce the peak hydration heat inside the concrete, forming self-regulation of the temperature inside the wall itself, and reducing the occurrence of cracks caused by temperature stress.

[0154] S31. Adjust the heat dissipation coefficient to the range of 0.5~1.0 through the formwork insulation layer, monitor the temperature difference between the center and surface of the concrete in real time, and control the cooling rate of the concrete to ≤3℃ / d.

[0155] Specifically, by adjusting the heat dissipation coefficient of the formwork insulation layer to the range of 0.5~1.0, precise control of the heat dissipation process of the concrete can be achieved, further reducing the temperature difference between the inside and outside, and reducing the occurrence of cracking caused by excessive temperature gradient.

[0156] At the same time, the temperature difference between the center and the surface of the concrete is monitored in real time and the cooling rate is controlled to ≤3℃ / d, so that the temperature changes are uniform and stable, and thermal shock cracks caused by sudden cooling and heating are avoided as much as possible. It is very effective in preventing early concrete cracks.

[0157] In addition, reference Figure 10 Furthermore, in one embodiment, step S31 is further divided into the following sub-steps:

[0158] S310. Use internal curing methods to regulate the internal humidity field of concrete during the hydration process.

[0159] Specifically, the internal curing method is used to adjust the internal humidity field of the concrete during the hydration process, forming a self-regulating humidity inside the wall to achieve the control of the temperature difference between the inside and outside of the concrete within 25°C and the temperature difference between the surface and the atmosphere within 20°C. This helps to reduce stress concentration caused by temperature gradients, thereby reducing the risk of early cracking of concrete and improving the durability of the basement exterior wall.

[0160] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

Claims

1. A method for controlling early cracks in building exterior walls based on integrated design and construction, wherein the early stage is set as 3-14 days after concrete pouring, and is characterized in that: include: By reducing the amount of cement in concrete, optimizing the aggregate gradation to reduce hydration heat and autogenous shrinkage, and regulating the design based on the material temperature and its own deformation, that is, according to the stone powder content measured in the machine-made sand, the proportion of stone powder replacing cementitious materials is dynamically adjusted, including obtaining the amounts of stone powder, cement and fly ash measured in the machine-made sand; if the proportion of stone powder in the machine-made sand does not exceed 20% of the cement amount, the strength influence coefficient is introduced to adjust the concrete mix parameters, and the stone powder contained in the machine-made sand is used to replace the cement; if the proportion of stone powder in the machine-made sand exceeds 20% of the cement amount, the amount of stone powder that does not exceed 20% of the cement amount is used to replace cement, and the amount of stone powder that exceeds 20% of the cement amount is used to replace fly ash, and the excess amount of stone powder is not considered as a component of the machine-made sand and is included in the sand ratio calculation; Structural reinforcement design optimizes reinforcement for temperature stress and shrinkage stress in the early stages. Specifically, if the stress generated by the wall temperature field varying with thickness exceeds the tensile strength of the concrete, the tensile stress is assumed by adjusting the reinforcement area. The reinforcement spacing is then redesigned based on the reinforcement area and the area of ​​a single steel bar. Specifically, the real-time temperature stress of the concrete is calculated based on the concrete cooling rate and the wall elastic modulus. The shrinkage stress of the concrete is also calculated based on the wall elastic modulus and autogenous shrinkage strain. If the total stress after the real-time temperature stress and shrinkage stress of the concrete exceeds the tensile strength of the concrete, and the reinforcement meets the following requirements: A s ·f y ≥σ 总 ·A c , where A s is the cross-sectional area of ​​the steel bar, f y is the tensile strength of steel bars, σ 总 A is the total stress after the real-time temperature stress and shrinkage stress of the concrete are superimposed, c is the cross-sectional area of ​​concrete; wherein, the corresponding wall temperature gradient value is selected according to the wall thickness; the peak temperature value inside the wall is calculated based on the mix ratio of concrete obtained by mixing cementitious materials and stone powder; based on the peak temperature value and the wall temperature gradient value, combined with the temperature difference time-varying model and temperature monitoring data, the concrete cooling rate is calculated to obtain the real-time temperature stress of the concrete; and at the same time, the shrinkage stress of the concrete is calculated based on the elastic modulus value and autogenous shrinkage strain of the wall; if the total stress after the superposition of the real-time temperature stress and shrinkage stress of the concrete exceeds the tensile strength of the concrete, the tensile stress is assumed by adjusting the reinforcement area and redesigning the steel bar spacing; During the construction phase, the temperature and humidity are controlled to ensure that the temperature difference between the inside and outside of the concrete is ≤25°C and the temperature difference between the surface and the atmosphere is ≤20°C.

2. The method according to claim 1, characterized in that The steps of reducing the amount of cement in concrete, optimizing aggregate gradation, reducing hydration heat and autogenous shrinkage, and regulating and designing the material temperature and material deformation include: The adjusted stone powder is subjected to 45 μm negative pressure screening. When the sieve residue mass accounts for ≤20%, the stone powder is determined to have a water-reducing effect, and the water consumption is optimized based on the water demand ratio; The water demand ratio test is conducted on the stone powder having a water-reducing effect, and the water consumption of the concrete is optimized based on the stone powder combined with the water demand ratio.

3. The method according to claim 1, characterized in that Before the steps of calculating and obtaining the real-time temperature stress of the concrete according to the concrete cooling rate and the wall elastic modulus value, and calculating and obtaining the shrinkage stress of the concrete according to the wall elastic modulus value and the autogenous shrinkage strain, the method further includes: According to the empirical value of the wall elastic modulus changing with age, the wall modulus value in the early stage is calculated; The autogenous shrinkage strain of the concrete is calculated based on the hydration characteristics of the cementitious material.

4. The method according to claim 3, characterized in that Before the step of adjusting the reinforcement area to bear the tensile stress and redesigning the reinforcement spacing when the stress generated by the wall temperature field changing with thickness exceeds the tensile strength of the concrete, the method further includes: Establish a database of structural design indicators for diaphragm walls of different thicknesses, covering the cementitious material dosage range of 300-450 kg / m³ corresponding to concrete strength grades C15-C50; The wall thickness and steel bar arrangement parameters are matched according to the database so that the maximum adiabatic temperature rise and fall is not less than the temperature threshold and the shrinkage rate reduction is not less than a preset ratio.

5. The method according to claim 1, characterized in that The step of regulating temperature and humidity during the construction phase to control the temperature difference between the inside and outside of the concrete to be ≤25°C and the temperature difference between the surface and the atmosphere to be ≤20°C includes: Use hydration heat inhibitor to slow down the hydration reaction rate; The heat dissipation coefficient is adjusted to the range of 0.5~1.0 through the formwork insulation layer, and the temperature difference between the center and surface of the concrete is monitored in real time to control the cooling rate of the concrete to ≤3℃ / d.

6. The method according to claim 1, characterized in that The step of regulating temperature and humidity during the construction phase to control the temperature difference between the inside and outside of the concrete to be ≤25°C and the temperature difference between the surface and the atmosphere to be ≤20°C also includes: Internal curing methods are used to regulate the internal humidity field of concrete during the hydration process.

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