Design and construction integration-based early crack control method for outer wall of building

Abstract

The invention relates to a design and construction integration-based early crack control method for a building outer wall, and relates to the technical field of wall crack control, and the design and construction integration-based early crack control method comprises the following steps: reducing hydration heat and self-constriction by reducing cement consumption in concrete and optimizing aggregate gradation, and carrying out regulation and control design aiming at material temperature and material self-deformation; steel bar design is constructed, and reinforcement optimization is conducted according to temperature stress and shrinkage stress in the early stage; temperature and humidity are regulated and controlled in the building construction stage, and concrete inside and outside temperature difference and surface and atmosphere temperature difference are controlled. The early cracking risk and early crack control of the basement concrete outer wall can be reduced, so that the durability of the basement concrete outer wall is improved.

Description

Technical Field

[0001] This application relates to the technical field of wall crack control, and particularly to an early crack control method for building exterior walls based on the integration of design and construction. Background Art

[0002] With the increasing depth of urban underground space development, which generally reaches more than 20m, the proportion of large-span and extra-long continuous concrete wall structures has increased significantly. During the initial hardening stage after concrete pouring until the heat of hydration is basically released and the temperature stabilizes, which is the early stage within the time range of 3 to 14 days after pouring, such structures are long-term under complex water environments and high restraint conditions, and the early crack problem is prominent, resulting in water seepage, steel bar corrosion, and durability deterioration. Modern concrete pursues high strength and high fluidity, and generally adopts mix proportion designs with high cement consumption and high paste-aggregate ratios. Coupled with problems such as poor gradation of manufactured sand and fluctuations in stone powder content, it further exacerbates the superposition effect of material shrinkage and temperature stress, becoming the main cause of early cracking.

[0003] The prior art has made improvements to the early cracking phenomenon of exterior walls. For example, at the material level, the fluidity is improved by increasing the sand ratio or cementitious materials, but the gradation and filling relationship are not systematically optimized; the traditional reinforcement method is still used in structural design, and the early non-load stress effect is not quantified; during the construction stage, temperature control depends on formwork insulation and conventional wet curing, but the accuracy of internal and external temperature difference regulation is insufficient. Although such methods alleviate cracks locally, they do not coordinate the entire material-structure-construction chain, resulting in limited crack control effects.

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

[0005] This application provides an early crack control method for building exterior walls based on the integration of design and construction, which can reduce the early cracking risk and early crack control of basement concrete exterior walls, thereby improving the durability of basement concrete exterior walls.

[0006] An early crack control method for building exterior walls based on the integration of design and construction provided by this application adopts the following technical solutions: An early crack control method for building exterior walls based on the integration of design and construction sets the early stage as 3 - 14 days after concrete pouring, and includes: Reducing the cement consumption in concrete, optimizing the aggregate gradation to reduce the heat of hydration and autogenous shrinkage, and conducting regulation design for material temperature and material self-deformation; Structural reinforcement design to optimize reinforcement for thermal stress and shrinkage stress in the early stages; 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.

[0007] By adopting the above technical scheme, it is possible to reduce the increase in cement consumption or mortar-aggregate ratio by reducing the amount of water used in the concrete mixture while keeping the water-cement ratio unchanged, thereby reducing the occurrence of cracks in the early stage, and 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 stage, enhance the wall's resistance to non-load stress, and try to avoid cracks caused by stress concentration; and during the construction stage, 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 not more than 20°C, effectively preventing thermal stress damage caused by excessive temperature difference, and further ensuring the integrity and durability of the wall.

[0008] 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 material temperature and material deformation include: According to the stone powder content measured in the machine-made sand, dynamically adjust the proportion of stone powder replacing cementitious materials; The adjusted stone powder is subjected to 45 μm negative pressure screening, and when the screen 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; The water demand ratio test is carried out on the stone powder with water reducing effect, and the water consumption of concrete is optimized according to the stone powder combined with the water demand ratio.

[0009] By adopting the above technical solution, the mix parameters are dynamically adjusted according to the characteristics of the stone powder in the machine-made sand to replace the cementitious material, and the content of the stone powder is increased to reduce 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, so that the stone powder with a water-reducing effect can be screened out, thereby optimizing the water consumption of the concrete, and then the water consumption is further refined in combination with the water demand ratio test results, thereby reducing the hydration heat and shrinkage while ensuring the working performance of the concrete, thereby effectively reducing the risk of early cracking.

[0010] In a preferred example, the present application can 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: Obtain the amount of stone powder, cement and fly ash measured in manufactured sand; If the proportion of stone powder in manufactured sand does not exceed 20% of the cement dosage, introduce a strength influence coefficient to adjust the concrete mix parameters, and use the stone powder contained in the manufactured sand to replace cement; If the proportion of stone powder in manufactured sand exceeds 20% of the cement dosage, replace cement with the amount of stone powder not exceeding 20% of the cement dosage, replace fly ash with the amount of stone powder exceeding 20% of the cement dosage, and the excess amount of stone powder is not regarded as a component of the manufactured sand and is included in the calculation of the sand ratio.

[0011] By adopting the above technical solutions, when the proportion of stone powder in manufactured sand does not exceed 20% of the cement dosage, use stone powder to replace part of the cement, thereby reducing the cement dosage while ensuring that the concrete strength is not affected; when the proportion of stone powder in manufactured sand exceeds 20% of the cement dosage, use the excess part to replace fly ash, optimize the gradation of various fillers, and further reduce the paste-aggregate ratio or sand ratio of the concrete, realizing low-carbon, low-temperature and low-shrinkage of the concrete and improving the crack resistance of the concrete.

[0012] In a preferred example of the present application, it can be further configured as: the step of optimizing the reinforcement for the temperature stress and shrinkage stress in the early stage in the design of the structural reinforcement includes: When the stress generated by the change of the wall temperature field with the thickness exceeds the tensile strength of the concrete, adjust the reinforcement area to bear the tensile stress and redesign the reinforcement spacing.

[0013] By adopting the above technical solutions, when the stress generated by the change of the wall temperature field with the thickness exceeds the tensile strength of the concrete itself, reasonably increase the reinforcement area to make the reinforcement bear the excess tensile stress, thereby avoiding cracks in the concrete due to excessive stress; at the same time, redesign the reinforcement spacing to make the reinforcement with the changed reinforcement area more evenly distributed and enhance the crack resistance of the overall wall.

[0014] In a preferred example of the present application, it can be further configured as: when the stress generated by the change of the wall temperature field with the thickness exceeds the tensile strength of the concrete, the step of adjusting the reinforcement area to bear the tensile stress and redesigning the reinforcement spacing includes: According to the concrete cooling rate and the wall elastic modulus value, calculate and obtain the real-time temperature stress of the concrete, and at the same time, according to the wall elastic modulus value and the autogenous shrinkage strain, calculate and obtain the shrinkage stress of the concrete; When 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, adjust the reinforcement area to bear the tensile stress and redesign the reinforcement spacing.

[0015] By adopting the above technical solution, the real-time temperature stress and shrinkage stress are calculated. When the total stress after the superposition of the two exceeds the tensile strength of the concrete, the reinforcement area is adjusted to bear the tensile stress, so as to accurately control the internal stress state of the concrete and reduce the cracking risk; the reinforcement area and the reinforcement spacing are adjusted, and the reinforcement layout is optimized to adapt to the changes of temperature and shrinkage stress, thereby effectively preventing the generation of cracks caused by excessive stress.

[0016] In a preferred example of the present application, it can be further configured that: before the step of calculating the real-time temperature stress of the concrete according to the concrete cooling rate and the wall elastic modulus value, and simultaneously calculating the shrinkage stress of the concrete according to the wall elastic modulus value and the autogenous shrinkage strain, it further includes: Select the corresponding wall temperature difference gradient value according to the wall thickness; According to the mix proportion of the concrete obtained by mixing the cementitious material and the stone powder, calculate the temperature peak value inside the wall; According to the temperature peak value and the wall temperature difference gradient value, combine the temperature-time-varying model and the temperature monitoring data to calculate the concrete cooling rate; According to the empirical value of the change of the wall elastic modulus with age, calculate the wall modulus value in the early stage; According to the hydration characteristics of the cementitious material, calculate the autogenous shrinkage strain of the concrete.

[0017] By adopting the above technical solution, selecting the corresponding wall temperature difference gradient value according to the wall thickness improves the pertinence and accuracy of the temperature stress calculation, thereby providing a reliable basis for subsequent stress analysis; by calculating the temperature peak value inside the wall, combining the temperature-time-varying model and the temperature monitoring data, accurately obtaining the concrete cooling rate helps to control the internal and external temperature difference and reduce the crack risk caused by temperature stress; according to the empirical value of the change of the wall elastic modulus with age, calculating the wall modulus value in the early stage improves the scientificity and rationality of the shrinkage stress calculation; calculating the autogenous shrinkage strain of the concrete based on the hydration characteristics of the cementitious material further refines the quantitative analysis of the shrinkage stress, effectively supports the optimization of the reinforcement design, improves the overall crack control effect, and finally realizes the accurate calculation of the temperature stress and shrinkage stress in the early stage of the concrete.

[0018] In a preferred example of the present application, it can be further configured that: when 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 step of adjusting the reinforcement area to bear the tensile stress and redesigning the reinforcement spacing includes: Satisfy through reinforcement: A s ·f y ≥σ 总 ·A c , Among them, A s is the cross-sectional area of the steel bar, f y is the tensile strength of the steel bar, σ 总 is the total stress after the superposition of the real-time temperature stress and shrinkage stress of the concrete, A c is the cross-sectional area of the concrete; Design the steel bar spacing according to the reinforcement area and the area of a single steel bar.

[0019] By adopting the above technical solution, the reinforcement is made to satisfy 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 reasonably bear the tensile stress; at the same time, design the steel bar spacing according to the reinforcement area and the area of a single steel bar, and optimize the steel bar layout to improve the crack resistance of the structure and enhance the durability of the basement exterior wall.

[0020] In a preferred example of the present application, it can be further configured that: before the step of adjusting the reinforcement area to bear the tensile stress and redesigning the steel bar spacing when the stress generated by the change of the wall temperature field with the thickness exceeds the tensile strength of the concrete, it further includes: Establish a database of construction design indexes for continuous walls with different thicknesses, covering the range of cementitious material consumption of 300 - 450 kg / m³ corresponding to the concrete strength grades of C15 - C50; Match the wall thickness and steel bar layout parameters according to the database, so that the maximum adiabatic temperature rise amplitude is not less than the temperature threshold value and the shrinkage rate reduction amplitude is not less than the preset ratio.

[0021] By adopting the above technical solution, the synergistic control effect of the temperature stress and shrinkage stress is further enhanced, the maximum adiabatic temperature rise is effectively reduced, and its reduction amplitude is not less than the temperature threshold value. At the same time, the autogenous shrinkage rate is reduced, and the reduction amplitude is not less than the preset ratio, so as to comprehensively improve the crack resistance and structural stability of the basement exterior wall in the early stage.

[0022] In a preferred example of the present application, it can be further configured that: the step of regulating the temperature and humidity during the construction stage to control the temperature difference between the inside and outside of the concrete ≤ 25°C and the temperature difference between the surface and the atmosphere ≤ 20°C includes: Adopt a hydration heat inhibitor to delay the hydration reaction rate; Adjust the heat dissipation coefficient to be in the range of 0.5 - 1.0 through the formwork insulation layer, and monitor the temperature difference between the center and the surface of the concrete in real time to control the cooling rate of the concrete ≤ 3°C / d.

[0023] By adopting the above technical solutions, using a hydration heat inhibitor to delay the hydration reaction rate can significantly reduce the peak value of the internal hydration heat of concrete and reduce the generation of cracks caused by temperature stress; by adjusting the heat dissipation coefficient of the formwork insulation layer to be in the range of 0.5 to 1.0, precise control of the heat dissipation process of concrete is achieved, further reducing the internal and external temperature difference and minimizing the cracking caused by too large a temperature gradient; the temperature difference between the center and the surface of the concrete is monitored in real time and the cooling rate is controlled ≤ 3°C / d to ensure uniform and stable temperature changes and effectively prevent thermal shock cracks caused by sudden cooling and heating.

[0024] In a preferred example of the present application, it can be further configured that: the step of regulating the temperature and humidity during the construction stage and controlling the internal and external temperature difference of the concrete ≤ 25°C and the surface - atmosphere temperature difference ≤ 20°C further includes: Using an internal curing method to regulate the internal humidity field of concrete during the hydration process.

[0025] By adopting the above technical solutions, using an internal curing method to regulate the internal humidity field of concrete during the hydration process can effectively control the internal and external temperature difference of the concrete and the surface - atmosphere temperature difference, help reduce the stress concentration caused by the temperature gradient, thereby reducing the risk of early cracking of the concrete and enhancing the durability of the basement exterior wall.

[0026] In summary, the present application has the following beneficial technical effects: 1. By reducing the cement dosage, optimizing the aggregate gradation, and dynamically adjusting the proportion of stone powder replacing the cementitious material, the present application effectively reduces the hydration heat and autogenous shrinkage, thus significantly reducing the early cracks caused by temperature stress and material deformation; 2. The present application optimizes the reinforcement design for the temperature stress and shrinkage stress in the early stage. By accurately calculating the real - time stress of the concrete and adjusting the steel bar area and spacing, the crack resistance of the wall is enhanced; 3. By regulating the temperature and humidity during the construction stage, the present application controls the internal and external temperature difference of the concrete and the surface - atmosphere temperature difference within a reasonable range, 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

[0027] Figure 1 is a flowchart of a method for controlling early cracks in a building exterior wall based on the integration of design and construction in one embodiment of the present application.

[0028] Figure 2 is a sub - flowchart of step S1 in one embodiment of the present application.

[0029] Figure 3 is a sub - flowchart of step S10 in one embodiment of the present application.

[0030] Figure 4 It is a flowchart of sub - steps of step S2 in one embodiment of the present application.

[0031] Figure 5 It is a flowchart of sub - steps of step S20 in one embodiment of the present application.

[0032] Figure 6 It is a flowchart of the step added before step S200 in one embodiment of the present application.

[0033] Figure 7 It is a flowchart of sub - steps of step S201 in one embodiment of the present application.

[0034] Figure 8 It is a flowchart of the step added before step S20 in one embodiment of the present application.

[0035] Figure 9 It is a flowchart of sub - steps of step S3 in one embodiment of the present application.

[0036] Figure 10 It is a flowchart of sub - steps of step S31 in one embodiment of the present application. Detailed implementation manners

[0037] The following is a further detailed description of the present application in conjunction with the attached Figures 1 - 10 to further illustrate the present application in detail.

[0038] It should be noted that all actions of obtaining data or all actions of obtaining information or data in the present application are carried out in accordance with the corresponding data protection regulations and policies of the country where the location is located and with the authorization of the corresponding users.

[0039] Refer to Figure 1 , a method for controlling early cracks in building exterior walls based on the integration of design and construction, setting the early stage as 3 - 14 days after concrete pouring, specifically including: S1. Reduce the cement consumption in concrete, optimize the aggregate gradation to reduce the hydration heat and autogenous shrinkage, and conduct regulation design for the material temperature and the self - deformation of the material.

[0040] Specifically, during the initial hardening process from the time when concrete is poured until the release of hydration heat is basically completed and the temperature tends to be stable, the underground environment is affected by the soil quality, water level, and geographical environment, and the environmental conditions for the service of concrete structures are more complex, which is prone to early cracks, leading to water seepage, steel corrosion, and durability degradation, affecting the structural stability of the basement exterior wall. Therefore, this time range of 3 to 14 days after pouring is set as the early stage, and for the cracking of the basement exterior wall that may occur in the early stage, based on the characteristics of modern concrete and changes in raw materials, while keeping the water-binder ratio unchanged, the water consumption of the modern concrete mixture is reduced, resulting in an increase in cement consumption or an increase in the mortar-binder ratio, which solves the current problem of increasing the amount of water used in the mixture to meet the high workability requirements under pumping and dense steel conditions, while keeping the water-binder ratio unchanged, resulting in an increase in cement consumption or an increase in the mortar-binder ratio, which further aggravates the cracks in the material. At the same time, the temperature and deformation of the material are regulated and designed to reduce the stress accumulation caused by temperature difference and shrinkage, improve the stability of the material, and achieve the prevention and control of early cracks.

[0041] S2. Structural reinforcement design: optimization of reinforcement for temperature stress and shrinkage stress in the early stages.

[0042] Specifically, in terms of structure and construction, in order to adapt to the stress caused by the temperature and volume stability of the material in the early hardening stage of concrete and the stress concentration caused by sudden changes in cross-section, reinforcement optimization is needed to make the steel bar position design and spacing design more targeted and effective, enhance the wall's resistance to non-load stress, and try to avoid cracks caused by stress concentration.

[0043] S3. Regulate temperature and humidity during the construction phase, and control the temperature difference between the inside and outside of the concrete to ≤25℃, and the temperature difference between the surface and the atmosphere to ≤20℃.

[0044] 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.

[0045] In this embodiment, in the early stage of construction, on the basis of optimizing the mix ratio of concrete 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.

[0046] refer to Figure 2, Further, in one embodiment, step S1 is refined into the following sub-steps: S10. Dynamically adjust the proportion of stone powder replacing cementitious materials according to the measured stone powder content in the manufactured sand.

[0047] Specifically, through the device for measuring the stone powder content of dry manufactured sand on the construction site, quickly measure the stone powder content in the manufactured sand, and perform the concrete mix proportion of the corresponding grade, calculate the content of each component per cubic meter of concrete such as cementitious materials (such as cement, fly ash, blast furnace slag powder, etc.) and sand, stone, etc. Then, dynamically adjust the mix proportion parameters according to the characteristics of the stone powder in the manufactured sand to replace the cementitious materials and increase the content of the stone powder, so as to reduce the heat release and autogenous shrinkage of the concrete.

[0048] S11. Conduct a 45μm negative pressure screening on the adjusted stone powder. When the mass ratio of the sieve residue ≤ 20%, it is determined that the stone powder has a water-reducing effect, and optimize the water consumption based on the water demand ratio.

[0049] Specifically, conduct a 45μm negative pressure screening experiment on the stone powder. If the mass ratio of the sieve residue does not exceed 20%, it can be considered to have a water-reducing effect. If the mass ratio of the sieve residue exceeds 20%, it can be determined that it does not have a water-reducing effect. Conduct a 45μm negative pressure screening on the adjusted stone powder and control the mass ratio of the sieve residue, and the stone powder with a water-reducing effect can be screened out, so as to optimize the water consumption of the concrete.

[0050] S12. Conduct a water demand ratio test on the stone powder with a water-reducing effect, and optimize the water consumption of the concrete based on the water demand ratio of the stone powder.

[0051] Specifically, further refine and adjust the water consumption in combination with the test results of the water demand ratio, reduce the hydration heat and autogenous shrinkage while ensuring the workability of the concrete, so as to effectively reduce the risk of early cracking. In this embodiment, the water consumption can be further optimized in combination with the water demand ratio on the basis of using admixtures and ensuring the workability, while for the stone powder without a water-reducing effect, the optimization of the water consumption is not considered.

[0052] In addition, refer to Figure 3 , Further, in one embodiment, step S10 is refined into the following sub-steps: S100. Obtain the dosages of the stone powder, cement and fly ash measured in the manufactured sand.

[0053] S101. If the proportion of the stone powder amount in the manufactured sand does not exceed 20% of the cement dosage, introduce a strength influence coefficient to adjust the concrete mix proportion parameters, and use the stone powder contained in the manufactured sand to replace the cement.

[0054] Specifically, based on the difference between the activity index of the stone powder and the cement, establish a theoretical correction model: ; Among them, β is the reduction coefficient of the activity of stone powder, which needs to be calibrated through experiments and is usually 0.2 - 0.3. When the activity of stone powder is high (such as containing calcium carbonate components), β takes a low value, and vice versa for a high value.

[0055] S102. If the proportion of stone powder in manufactured sand exceeds 20% of the cement dosage, replace the cement with the amount of stone powder not exceeding 20% of the cement dosage, replace the fly ash with the amount of stone powder exceeding 20% of the cement dosage, and the excess amount of stone powder is not included as a component of manufactured sand and is included in the calculation of the sand ratio.

[0056] Specifically, when the proportion of stone powder in manufactured sand exceeds 20% of the cement dosage, the excess part of the stone powder is used to replace the fly ash to optimize the grading of various fillers, and also reduces the paste-aggregate ratio or sand ratio of the concrete, realizes low-carbon, low-temperature and low-shrinkage of the concrete, and further improves the crack resistance of the concrete.

[0057] In addition, referring to Figure 4 , further, in one of the embodiments, step S2 is refined into the following sub-steps: S20. If the stress generated by the change of the wall temperature field with thickness exceeds the tensile strength of the concrete, adjust the reinforcement area to bear the tensile stress and re-design the reinforcement spacing.

[0058] Specifically, when the stress generated by the change of the wall temperature field with thickness exceeds the tensile strength of the concrete itself, by reasonably increasing the reinforcement area, the reinforcement bears the tensile stress exceeding the bearing capacity of the concrete, thereby reducing the phenomenon of concrete cracking due to excessive stress; at the same time, by optimizing the design of the reinforcement spacing, the reinforcement of the newly added reinforcement area is more evenly distributed, and thus the overall crack resistance of the wall is improved.

[0059] In addition, referring to Figure 5 , further, in one of the embodiments, step S20 is refined into the following sub-steps: S200. Calculate and obtain the real-time temperature stress of the concrete according to the concrete cooling rate and the wall elastic modulus value, and at the same time calculate and obtain the shrinkage stress of the concrete according to the wall elastic modulus value and the autogenous shrinkage strain.

[0060] Specifically, while the wall temperature field changes with thickness, the generated temperature stress also changes. At the same time, the autogenous shrinkage stress of the material volume deformation and the stress concentration factors brought about by the sudden change of the wall stiffness will also occur. Therefore, by calculating the real-time temperature stress and shrinkage stress, when the total stress after superimposing the temperature stress and shrinkage stress exceeds the tensile strength of the concrete, it is necessary to adjust the reinforcement area to bear the tensile stress, realize the precise control of the internal stress state of the concrete, and reduce the cracking risk of the exterior wall in the early stage.

[0061] Further, the calculation and acquisition of the real-time temperature stress σ in the early stage is through the formula: σ = -EαR c , where α ranges from 0.7×10 -5 to 1.4×10 -5 / °C, E is the elastic modulus of concrete, and R c is the cooling rate of concrete.

[0062] Furthermore, the shrinkage stress is calculated. The concrete shrinkage stress ( ) is caused by the restraint of the shrinkage strain, and the core formula is: , where E c is the real-time elastic modulus value of the wall in the early stage, is the autogenous shrinkage strain, which is related to the total heat of hydration Q of the cementitious materials and is calculated according to , where is the admixture adjustment coefficient, is the total heat of hydration of cement.

[0063] The value of R is obtained in real time according to the following table: Constraint type R value Selection basis Full constraint 1.0 Perimeter constraint Medium constraint 0.5-0.7 Vertical constraint Low constraint 0.3-0.5 Single - side constraint S201. 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 tensile stress is borne by adjusting the reinforcement area, and the reinforcement spacing is redesigned.

[0064] Specifically, when the temperature stress exceeds the tensile strength of the concrete, the tensile stress needs to be borne by the reinforcement. The reinforcement area ( ) is calculated by the formula: , where is the design value of the temperature stress (N / mm 2 ), is the cross-sectional area of the concrete (mm 2 ), is the design value of the tensile strength of the reinforcement (N / mm 2 ), such as 360 N / mm 2 for HRB400.

[0065] Furthermore, the reinforcement spacing design is calculated by the formula: , where a s is the area of a single reinforcement, which is determined according to the selected reinforcement diameter.

[0066] By adjusting the reinforcement area and the reinforcement spacing, the reinforcement layout is optimized to adapt to the changing temperature and shrinkage stress, thus effectively preventing the generation of cracks caused by excessive stress.

[0067] In addition, reference Figure 6 Further, in one embodiment, before step S200, steps S2000, S2001, S2002, S2003, and S2004 are added: S2000. Select a corresponding wall temperature gradient value according to the wall thickness.

[0068] 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.

[0069] S2001. Calculate and obtain the peak temperature value inside the wall according to the mix ratio of concrete obtained by mixing cementitious materials and stone powder.

[0070] Specifically, the peak temperature inside the wall is calculated based on the concrete mix ratio: , 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.

[0071] The adiabatic temperature is: , The specific parameter definitions are shown in the following table:

[0072] 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.

[0073] 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 center temperature and the surface temperature per unit time. The calculation needs to be combined with the temperature difference time-varying model and temperature monitoring data. The core formula considering the heat dissipation effect is as follows: , 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 difference gradient value of the wall thickness.

[0074] S2003. Calculate and obtain the modulus value of the wall in the early stage based on the empirical value of the change in the elastic modulus of the wall with age.

[0075] Specifically, calculate the modulus value of the wall in the early stage according to the empirical value of the change in the elastic modulus of the wall with age, thereby improving the scientificity and rationality of the shrinkage stress calculation. The elastic modulus changes with age, and the empirical formula is: , is the elastic modulus of concrete at 28 days, calculated by where is the cube compressive strength.

[0076] S2004. Calculate and obtain the autogenous shrinkage strain of concrete according to the hydration characteristics of the cementitious material.

[0077] Specifically, the autogenous shrinkage strain is related to the hydration characteristics of the cementitious material and can be calculated based on the following model: CEB-FIP model: , where: is the ultimate autogenous shrinkage strain, related to the total hydration heat Q of the cementitious material, calculated by where is the admixture adjustment coefficient, is the total hydration heat of cement. is the age (days).

[0078] Calculating the autogenous shrinkage strain of concrete based on the hydration characteristics of the cementitious material further refines the quantitative analysis of shrinkage stress, effectively supports the optimization of reinforcement design, improves the overall crack control effect, and finally realizes the accurate calculation of temperature stress and shrinkage stress in the early stage of concrete.

[0079] In addition, referring to Figure 7 , further, in one embodiment, step S201 is refined into the following sub-steps: S2010. Meet the requirement through reinforcement: 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 the steel bar, σ 总 is the total stress after superimposing the real-time temperature stress and shrinkage stress of the concrete, and A c is the cross-sectional area of the concrete.

[0080] Specifically, by calculation, it is ensured that the product of the cross-sectional area of the reinforcement and the tensile strength of the reinforcement is greater than or equal to the product of the total stress and the cross-sectional area of the concrete, so as to achieve the reasonable bearing of the tensile stress.

[0081] S2011. Design the reinforcement spacing according to the reinforcement area and the area of a single reinforcement bar.

[0082] In addition, referring to Figure 8 , further, in one embodiment, before step S20, steps S202 and S203 are added: S202. Establish a database of construction design indexes for diaphragm walls with different thicknesses, covering the range of cementitious material dosage of 300 - 450 kg / m³ corresponding to the concrete strength grades of C15 - C50.

[0083] Specifically, the elastic modulus of the concrete can be obtained according to the index database to improve the calculation efficiency. Specifically, it can be taken from the following table: 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]]> S203. Match the wall thickness and the reinforcement layout parameters according to the database, so that the maximum adiabatic temperature rise amplitude is not less than the temperature threshold value and the shrinkage rate reduction is not less than the preset ratio.

[0084] Specifically, in this embodiment, the temperature threshold value 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 amplitude of the shrinkage rate reaches 44.3%, so as to enhance the synergistic control effect of the temperature stress and the shrinkage stress, and thus comprehensively improve the crack resistance performance and the structural stability of the basement exterior wall in the early stage.

[0085] In addition, referring to Figure 9 , further, in one embodiment, step S3 is refined into the following sub - steps: S30. Use a hydration heat inhibitor to delay the hydration reaction rate.

[0086] Specifically, using a hydration heat inhibitor to delay the hydration reaction rate can significantly reduce the peak value of the hydration heat inside the concrete, form the self - regulation of the temperature inside the wall, and reduce the generation of cracks caused by temperature stress.

[0087] S31. Adjust the heat dissipation coefficient to be in the range of 0.5 - 1.0 through the formwork insulation layer, and monitor the temperature difference between the center and the surface of the concrete in real time, and control the cooling rate of the concrete ≤ 3°C / d.

[0088] Specifically, by adjusting the heat dissipation coefficient to be in the range of 0.5 - 1.0 through the formwork insulation layer, the precise control of the concrete heat dissipation process is realized, further reducing the internal and external temperature difference and reducing the occurrence of cracking caused by too large a temperature gradient.

[0089] Meanwhile, the temperature difference between the center and the surface of the concrete is monitored in real time, and the cooling rate is controlled to be ≤ 3°C / d, so that the temperature change is uniform and stable, and thermal shock cracks caused by sudden cooling or heating are avoided as much as possible, which has a good effect on preventing early concrete cracks.

[0090] In addition, referring to Figure 10 , further, in one embodiment, step S31 is refined into the following sub-steps: S310. Use the internal curing method to adjust the internal humidity field of the concrete during the hydration process.

[0091] Specifically, using the internal curing method to adjust the internal humidity field of the concrete during the hydration process forms the self-regulation of the humidity inside the wall, so as to control 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, which helps to reduce the stress concentration caused by the temperature gradient, thereby reducing the risk of early cracking of the concrete and improving the durability of the basement exterior wall.

[0092] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present 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 to 3-14 days after concrete pouring, and is characterized in that: include: By reducing the amount of cement in concrete, optimizing aggregate grading to reduce hydration heat and autogenous shrinkage, and regulating the design based on material temperature and material deformation; Structural reinforcement design to optimize reinforcement for thermal stress and shrinkage stress in the early stages; 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 material temperature and material deformation include: According to the stone powder content measured in the machine-made sand, dynamically adjust the proportion of stone powder replacing cementitious materials; The adjusted stone powder is subjected to 45 μm negative pressure screening, and when the screen 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; The water demand ratio test is carried out on the stone powder with water reducing effect, and the water consumption of concrete is optimized according to the stone powder combined with the water demand ratio.

3. The method according to claim 2, characterized in that 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 comprises: Obtain the amount of stone powder, cement and fly ash measured in manufactured sand; If the proportion of stone powder to machine-made sand does not exceed 20% of the cement dosage, 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 cement; If the proportion of stone powder in artificial sand exceeds 20% of the cement dosage, the stone powder that does not exceed 20% of the cement dosage shall replace cement, and the stone powder that exceeds 20% of the cement dosage shall replace fly ash. The excess amount of stone powder shall not be regarded as a component of artificial sand and shall not be included in the calculation of sand ratio.

4. The method according to claim 1, characterized in that: The structural reinforcement design includes the following steps of optimizing the reinforcement arrangement for the temperature stress and shrinkage stress in the early stage: If the stress generated by the change of wall temperature field with thickness exceeds the tensile strength of concrete, the tensile stress is borne by adjusting the reinforcement area and redesigning the reinforcement spacing.

5. The method according to claim 4, characterized in that If the stress generated by the wall temperature field changing with the thickness 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: According to the concrete cooling rate and the wall elastic modulus value, the real-time temperature stress of the concrete is calculated and obtained, and according to the wall elastic modulus value and the autogenous shrinkage strain, the shrinkage stress of the concrete is calculated and obtained; 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.

6. The method according to claim 5, characterized in that Before the step 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: Select the corresponding wall temperature gradient value according to the wall thickness; According to the mix ratio of concrete obtained by mixing cementitious materials and stone powder, the peak temperature inside the wall is calculated; 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; According to the empirical value of the wall elastic modulus changing with age, the wall modulus value obtained in the early stage is calculated; The autogenous shrinkage strain of the concrete is calculated and obtained according to the hydration characteristics of the cementitious material.

7. The method according to claim 5, characterized in that 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 step of adjusting the reinforcement area to bear the tensile stress and redesigning the spacing of the reinforcement bars comprises: The reinforcement meets the following requirements: A s ·f y ≥σ 总 ·A c , 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; Design the steel bar spacing based on the reinforcement area and the area of ​​a single steel bar.

8. The method according to claim 6, 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 the thickness exceeds the tensile strength of the concrete, the method further includes: Establish a database of structural design indicators for continuous walls of different thicknesses, covering the cementitious material dosage range of 300~450kg / m³ corresponding to C15~C50 concrete strength grades; The wall thickness and the reinforcement arrangement parameters are matched according to the database so that the maximum adiabatic temperature rise and fall amplitude is not less than the temperature threshold value and the shrinkage rate reduction amplitude is not less than the preset ratio.

9. The method according to claim 1, characterized in that: The step of controlling the 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 the surface of the concrete is monitored in real time to control the cooling rate of the concrete to ≤3℃ / d.

10. The method according to claim 1, characterized in that The step of controlling the 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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