Crack control process in mass concrete construction period

Abstract

The invention discloses a crack control process during mass concrete construction. The process comprises the following five key steps: firstly, predicting temperature stress and tensile strength of each age by adopting a temperature stress calculation formula according to geometric dimensions and constraint conditions of a concrete member, and calculating a preservation coefficient to judge the possibility of crack occurrence; secondly, whole-process moisturizing maintenance is carried out after concrete pouring, and measures of preventing wind and avoiding direct sunlight are taken; arranging no thermal insulation layer in the heating stage, and dynamically arranging multiple layers of thermal insulation materials according to a calculation result in the cooling stage; meanwhile, temperature measuring points are set for real-time monitoring, and when the preservation coefficient is smaller than 1, heat preservation measures are adjusted immediately; and finally, when the temperature difference is reduced to a safe range, dismantling the insulating layer in stages. Engineering application shows that the process can reduce the crack occurrence rate of the mass concrete structure by more than 80%, shortens the maintenance period by about 30%, remarkably reduces the construction cost while ensuring the engineering quality, and has good economic benefits and popularization values.

Description

Technical Field

[0001] The present invention relates to the technical field of building engineering construction, in particular to a crack control process during mass concrete construction. Background Art

[0002] Massive concrete structures are widely used in modern high-rise buildings, nuclear power plants, large-scale infrastructure, and other important projects. Massive concrete refers to cast-in-place concrete whose specifications and dimensions require measures to properly handle temperature fluctuations, reasonably reduce or eliminate stress caused by deformation, and minimize cracking. Due to the large cross-sectional dimensions of mass concrete structures, the heat of cement hydration causes the internal temperature to rise sharply after pouring. As the temperature gradually decreases, considerable tensile stress will be generated under restraint conditions. Furthermore, the tensile strength of concrete is only about one-tenth of its compressive strength, and the ultimate tensile strain is very small. Therefore, the restraining stress caused by temperature and humidity fluctuations often exceeds the tensile capacity of the concrete, leading to cracks and seriously affecting the integrity, durability, and impermeability of the structure.

[0003] Currently, crack control methods for large-volume concrete, both domestically and internationally, primarily rely on empirical temperature control indicators, such as limiting the cooling rate to no more than 1.5°C / day and limiting the internal and external temperature difference to no more than 25°C. This approach is passive, "fixing the fold after the horse has bolted," subject to significant human factors, and carries a degree of risk and randomness. Existing technologies are unable to scientifically and accurately predict the temperature field dynamics of large-volume concrete, hindering the prior validation of specific design and material selection, construction measures, and curing strategies. This often leads to unintended insulation measures, prolonged curing cycles, or suboptimal crack control. While researchers domestically and internationally have made some progress in theoretical research on the temperature field and temperature stresses of large-volume concrete, including methods such as finite element numerical simulation and artificial neural network prediction, these findings remain largely theoretical, focusing on qualitative analysis and scant quantitative guidance. Practical technical solutions that closely integrate theoretical calculations with on-site construction are lacking.

[0004] With the development of information technology and the continuous improvement of project quality requirements, there is an urgent need to develop a large-volume concrete crack control technology that can proactively prevent cracks and scientifically guide construction. This technology should be able to predict the occurrence of temperature cracks in advance through computer calculations based on historical data on concrete temperature and humidity changes and changes in environmental conditions. Based on the predicted results, insulation measures and cooling rates can be promptly determined to achieve proactive crack control. This technology not only improves the reliability of crack control but also optimizes insulation measures, shortens maintenance cycles, and reduces construction costs while ensuring quality. It is of great significance to promoting the advancement of large-volume concrete construction technology. Summary of the Invention

[0005] Based on the above objectives, the present invention provides a crack control process during mass concrete construction: The following steps are involved: Step 1: Based on the geometric dimensions, constraints, and ambient temperature of the concrete component, the temperature stress calculation formula is used to predict the temperature stress σxmax(τ) and tensile strength Rf(τ) at each age, and the preservation coefficient K=Rf(τ) / Σσi(τ)Hi(t,τ) is calculated, where Hi(t,τ) is the stress relaxation coefficient; Step 2: Cover the concrete with plastic film within 4 to 6 hours after pouring and sprinkle water regularly for moisturizing and curing. At the same time, take measures to prevent wind and avoid direct sunlight. Step 3: No insulation layer is set during the concrete heating stage. After entering the cooling stage, multiple layers of insulation material are dynamically set according to the temperature monitoring results and the calculation results of step 1. The thickness of the insulation layer is calculated and determined according to the formula δx=KbλjH(Tb-Tq) / 2λ(Tmax-Tb); Step 4: Set temperature measuring points at key locations of the concrete for real-time temperature monitoring. When the preservation coefficient K value is less than 1, immediately increase the thickness of the insulation layer or adjust the cooling rate. Step 5: When the temperature difference between the center of the concrete and the ambient temperature drops to within 25°C, remove the insulation layer layer by layer in stages.

[0006] Furthermore, for the rectangular raft foundation structure, the temperature stress calculation formula in step 1 is σxmax(τ)=-αΔTiEi(τ)βi(τ)Hi(t,τ) / (1-μ), where βi=ChL² / (8Ei(τ)H), Ch is the horizontal resistance coefficient of the foundation, L is the length of the component, and H is the thickness of the component.

[0007] Furthermore, for the truncated cone raft foundation structure, in step 1, it is necessary to calculate the hoop stress σθ(r)=αEΔTmax(r / R-r² / R²) / (1-μ) caused by the temperature difference between the center and the edge, the stress caused by the temperature difference between the center and the surface, and the external constraint stress caused by cooling, and perform superposition analysis.

[0008] Furthermore, the multi-layer insulation material in step three uses insulation felt with a thickness of 8-15 mm. Initially, a single layer of insulation is set, and it is gradually increased to 2-3 layers according to calculation needs, with air gaps left between each layer.

[0009] Furthermore, the temperature measuring points in step 4 are arranged in an "X" shape, with 3-4 temperature measuring tubes set in each monitoring area to monitor the center temperature, edge temperature and surface temperature respectively.

[0010] Furthermore, the cooling rate of concrete is controlled in stages according to its age: 2.0-5.0℃ / day in the first 7 days and 1.5-2.0℃ / day after 7 days. The temperature difference between inside and outside is controlled at 15-20℃ in the initial stage of cooling, and is allowed to reach 25℃ in the later stage.

[0011] Furthermore, for the annular wall structure, a differentiated maintenance method is adopted. Layered insulation measures are set up on the outside, and moisturizing maintenance is carried out on the inside through surface atomized water spraying to control the equivalent temperature difference between the inside and the outside to within 10°C.

[0012] Furthermore, the moisturizing measures in step 2 include covering with plastic film to prevent water evaporation, sprinkling water every 2-4 hours to keep the surface moist, and setting up fences in dry and windy environments to reduce the impact of wind speed.

[0013] Furthermore, the following optimization measures are adopted before concrete pouring: a sliding layer material with a thickness of 5-10 mm is set at the bottom of the raft foundation, a reinforcement scheme with a diameter of no more than 25 mm and a spacing of no more than 200 mm is adopted, and the thickness of the steel bar protective layer is controlled within the range of 30-50 mm.

[0014] Furthermore, the insulation layer in step five is removed layer by layer, and each time a layer of insulation material is removed, it is observed for 24 hours to confirm that the temperature change is stable and the increase in the temperature difference between the inside and outside does not exceed 5°C before removing the next layer.

[0015] Beneficial effects of the present invention: The present invention has achieved a fundamental shift from passive control to active prevention. Traditional methods mainly rely on on-site measurements and empirical judgments to control cracks. They are remedial measures after the problem is discovered and involve great uncertainty and risk. By establishing a dynamic equilibrium relationship between temperature stress and tensile strength, the present invention can accurately predict the possibility of crack occurrence at various periods after concrete pouring and take targeted preventive measures in advance. This active control method fundamentally eliminates the occurrence of harmful cracks and significantly improves the quality reliability of large-volume concrete structures. Actual engineering applications have shown that the crack incidence rate of large-volume concrete structures using the process of the present invention has been reduced by more than 80%, effectively solving the quality problems that have long plagued construction companies.

[0016] The present invention has good economic benefits and engineering practicality. By scientifically calculating the optimal cooling rate and insulation layer thickness, the problem of excessive or insufficient insulation measures in traditional methods is avoided. Engineering practice has proven that the present invention can shorten the maintenance cycle by approximately 30% while ensuring crack control, significantly reducing the cost of insulation materials and labor expenses. At the same time, the reduced crack repair workload further saves on subsequent maintenance costs. For large-scale engineering projects, this economic benefit is very considerable and can create substantial value for construction units and construction companies.

[0017] The present invention provides a technical solution with strong scientificity and wide applicability. The process is based on the basic physical and mechanical properties of concrete materials and the principles of heat transfer, and a complete theoretical calculation system has been established to avoid the limitations of empirical methods. By developing corresponding temperature stress calculation formulas for different structural forms, the present invention is applicable to various types of large-volume concrete structures such as rectangular raft foundations, truncated cone raft foundations, floor slabs, annular walls, etc., and has good versatility. The process implementation process is highly standardized, and technical personnel can master it through training, which is convenient for promotion and application in different regions and different types of projects, providing strong support for the standardization and standardization of large-volume concrete construction technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is a schematic diagram of the implementation process of the concrete crack control technology of the present invention; Figure 2 A schematic diagram showing the relationship between temperature stress and tensile strength of concrete according to an embodiment of the present invention, plotted at a concrete cooling rate of 1.5°C / d; Figure 3 A schematic diagram showing the relationship between temperature stress and tensile strength drawn for a concrete cooling rate of 3.0°C / d according to an embodiment of the present invention; Figure 4 For the embodiment of the present invention ≤7d concrete cooling rate 5.0℃ / d, Schematic diagram of the relationship between temperature stress and tensile strength drawn from the results of cooling rate of 2.0℃ / d when the temperature is >7d; Figure 5 For the embodiment of the present invention ≤7d concrete cooling rate 2.0℃ / d, Schematic diagram of the relationship between temperature stress and tensile strength drawn from the results of cooling rate of 5.0℃ / d when the temperature is >7d; Figure 6 This is a schematic diagram of the relationship between temperature difference stress and tensile strength at different ages when the internal and external temperature difference is 20°C from the third day onwards in an embodiment of the present invention; Figure 7 Schematic diagram of the relationship between stress and tensile strength at various ages when the temperature difference is 15°C on the third day, 20°C on the fourth day, and 25°C after the fifth day according to an embodiment of the present invention; Figure 8This is a schematic diagram of an "X"-shaped arrangement of temperature measurement points according to an embodiment of the present invention; Figure 9 Schematic diagram of the measured temperature curve in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It is also noted that, to provide a more detailed description, the following embodiments are best and preferred embodiments, and those skilled in the art may employ alternative methods for implementing certain known technologies. Furthermore, the accompanying drawings are intended only to provide a more detailed description of the embodiments and are not intended to limit the present invention.

[0021] It should be noted that references in the specification to "one embodiment," "an embodiment," "exemplary embodiments," "some embodiments," etc. indicate that the described embodiments may include specific features, structures, or characteristics, but not necessarily every embodiment will include such specific features, structures, or characteristics. Furthermore, when specific features, structures, or characteristics are described in conjunction with an embodiment, it is within the knowledge of persons skilled in the relevant art to implement such features, structures, or characteristics in conjunction with other embodiments (whether or not explicitly described).

[0022] In general, terms can be understood, at least in part, from their use in context. For example, depending at least in part on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in the singular sense, or can be used to describe a combination of features, structures, or characteristics in the plural sense. Additionally, the term "based on" can be understood as not necessarily intended to convey an exclusive set of factors, but can instead, depending at least in part on the context, allow for the presence of other factors that are not necessarily explicitly described.

[0023] See Figures 1 to 9 The present invention provides a crack control process for mass concrete during construction. This process proactively controls cracks during construction by combining temperature stress calculation and prediction, dynamic adjustment of thermal insulation and moisture retention measures, and full-process monitoring. The core technical principle of this process is based on the dynamic equilibrium between concrete's temperature stress and tensile strength. Specifically, the process aims to maintain the concrete's tensile strength at or above the shrinkage stress during construction, thereby preventing cracks.

[0024] This process is based on an in-depth analysis of the temperature and humidity variations in concrete. Cement generates heat during the hydration reaction, causing the initial temperature of large-volume concrete to rise due to its low surface modulus and slow heat dissipation. As curing progresses, the heat gradually dissipates, causing the temperature to drop. Simultaneously, the cement hydration reaction continuously produces gel, causing the concrete's elastic modulus and tensile strength to increase with curing time. As concrete hardens, it continuously loses water, leading to deformations such as autogenous shrinkage, water loss and drying shrinkage, and carbonization shrinkage. When internal and external constraints within the concrete hinder its natural deformation, expansion and contraction stresses are generated internally and on the surface. When these stresses exceed the concrete's tensile strength, cracks will form.

[0025] Step 1: Preliminary preparation and design optimization. Before pouring concrete, select the appropriate cement type and mix ratio based on the structural characteristics. Adopt a small-diameter, closely spaced reinforcement scheme, and minimize the thickness of the steel bar protective layer. For large structures such as raft foundations, a sliding layer should be installed on the base layer to reduce the horizontal resistance coefficient. Utilize the later strength of concrete, such as the 60-day and 90-day strength, as the design strength, and reduce cement usage to lower the hydration heat. Add diagonal steel bars to stress-concentrated areas such as openings, and employ structural measures such as angle protection steel frames to improve crack resistance.

[0026] Step 2: Calculation and prediction of temperature stresses. Based on the concrete component's geometric dimensions, constraints, and ambient temperature, the corresponding temperature stress calculation formula is used for predictive analysis. For rectangular raft foundations, the external constraint stress is σxmax(τ)=-αΔTiEi(τ)βi(τ)Hi(t,τ) / (1-μ), where βi=ChL² / (8Ei(τ)H). For long wall structures, the stress calculation formula is σxmax(τ)=-αΔTiEi(τ)(1-βi(τ))Hi(t,τ). For truncated cone-shaped raft foundations, the temperature difference between the center and edge, the temperature difference between the center and surface, and the external constraint stress caused by cooling must be calculated separately. By calculating the temperature stress and tensile strength at each age, the preservation factor K=Rf(τ) / Σσi(τ)Hi(t,τ) is determined. A K value greater than 1 indicates that cracks will not occur.

[0027] Step 3: Moisture-proof measures throughout the entire process. Immediately after concrete pouring and vibration, take windproof measures and avoid direct sunlight throughout the process. Within 4 to 6 hours after pouring, begin covering with plastic film and watering frequently. A small amount of insulation layer can be added as needed. Moisture-proof measures are based on the concrete shrinkage value εy(τ) = 3.24×10⁻ 4 (1-e⁻ 0 · 0 The correction factor Mn includes the effect of ambient humidity. When the ambient humidity drops from 90% to 25%, the shrinkage value can increase by about 3 times. Therefore, the change of ambient humidity must be strictly controlled.

[0028] Step 4: Dynamically adjust the multi-layer insulation layer. The insulation layer is constructed using multiple layers of thin insulation material. During the concrete heating phase (typically the first three days), the insulation layer should be left uncovered as much as possible to facilitate heat dissipation and reduce the maximum internal temperature. During the cooling phase, a single layer of insulation is initially applied, and the thickness of the insulation layer is dynamically increased based on temperature monitoring and stress calculations. The insulation layer thickness is calculated based on heat transfer principles. When the cooling rate needs to be controlled, the insulation material thickness δx can be adjusted using the formula δx = KbλjH(Tb-Tq) / 2λ(Tmax-Tb), where λj is the thermal conductivity of the insulation material and λ is the thermal conductivity of the concrete.

[0029] Step 5: Temperature Monitoring and Real-Time Control. Temperature measurement points are set up at key locations on the concrete, arranged in an "X" pattern, for comprehensive monitoring. Based on the measured temperature data, a spreadsheet-based calculation program is used, with formulas and preset cooling rates pre-entered to determine whether cracks will appear in the future. If the preservation factor K value does not meet the requirements, the cooling rate and corresponding insulation thickness are reset. As actual temperature data is collected, the preset data is continuously replaced, enabling dynamic verification and cumulative calculation of temperature stresses.

[0030] Step 6: Remove the insulation layer in stages. When the temperature difference between the concrete center and the ambient temperature is within 25°C, begin removing the insulation layer. However, this must be done in stages, layer by layer, to prevent a sudden increase in the internal and external temperature difference from causing excessive surface tensile stress. Continue to monitor temperature changes during the removal process to ensure that the cooling rate meets the calculated requirements.

[0031] Key technical parameter control The implementation of this process requires strict control of several key technical parameters. The concrete cooling rate should be high initially and low later. Generally, it can be controlled at 2.0-5.0°C / day during the first seven days, and then reduced to 1.5-2.0°C / day after seven days. The temperature difference between the inside and outside should be controlled within 15-20°C during the initial cooling period, and can reach 25°C later. The concrete pouring temperature should be minimized. When the ambient temperature is high, measures such as aggregate pre-cooling can be implemented. Cement usage should be controlled at 350-400 kg / m³, and 10-15% fly ash or mineral admixtures can be added to replace some of the cement.

[0032] Example 1: Controlling Cracks in Large Raft Foundation Concrete: Taking a high-rise building raft foundation project as an example, the raft foundation has plan dimensions of 100 x 90 m, a thickness of 1.7 m, and concrete strength grade C30 (90 days). Layered and segmented pouring was used. According to the process described in this invention, a temperature stress calculation and analysis was first performed to determine the key control parameters under the design conditions. The concrete was placed at a temperature below 25°C. 525 ordinary Portland cement was used at a cement dosage of 380 kg / m³, with 10% stone powder added as a mineral admixture.

[0033] During implementation, 12 groups of temperature measurement points, totaling 36 temperature measuring tubes, were installed in an "X" pattern at key locations on the raft foundation. Immediately after concrete pouring, plastic film was applied for wind protection. On the third day, as the concrete began cooling, a single layer of insulation, 10mm thick insulation felt, was implemented. Temperature stress calculations were performed based on measured temperature data. When it was discovered that a 5°C temperature drop on the seventh day would result in a preservation coefficient (K) of 0.87, less than 1, the insulation layer thickness was immediately increased to 21mm (by adding two layers of 11mm felt), keeping the cooling rate within 4°C and increasing the preservation coefficient to K=1.12, meeting crack resistance requirements.

[0034] After 23 days of temperature-controlled curing, the core temperature of the concrete gradually dropped from a peak of 62°C to 47°C, with an average cooling rate of approximately 0.65°C per day, and the temperature difference between inside and outside the concrete was kept within 20°C. After removing the insulation layer, no visible cracks were found on the concrete surface, demonstrating effective temperature control. Compared to the traditional cooling rate of 1.5°C per day, this process shortens the curing cycle by approximately 30% while maintaining quality.

[0035] Example 2: Optimizing Crack Control in a Nuclear Power Plant's Truncated Conical Raft Foundation: For example, the raft foundation of a nuclear power plant's reactor building is a truncated conical structure with a diameter of 19.6m and a thickness of 1.8m. The concrete strength grade is equivalent to C50 (28 days). This structure is unique in that it requires consideration of the combined effects of three temperature stresses: the temperature difference between the center and the edge, the temperature difference between the center and the surface, and the external restraint stress caused by cooling.

[0036] Pre-implementation theoretical calculations revealed that when the temperature difference between the center and the edge reaches 25°C, the circumferential tensile stress σθ(R) = 1.03 MPa at the edge at 3 days of age exceeds the tensile strength Rf = 0.98 MPa, potentially leading to vertical cracks. Therefore, during implementation, special efforts were made to strengthen the side insulation, wrapping the sides with a double layer of insulation felt to keep the temperature difference between the center and the edge within 20°C. Furthermore, φ8 steel mesh (mesh spacing 150×150mm) was added to the upper surface to enhance crack resistance.

[0037] Temperature monitoring showed that optimized insulation measures kept the maximum center temperature below 75°C, with a cooling rate of 3.5°C / day for the first five days, then dropping to 2.0°C / day after five days. After 14 days of curing, the insulation layer was removed and inspection revealed a significant reduction in surface cracks, with only a few localized microcracks less than 0.2mm wide. This represents a reduction of over 80% compared to the original process.

[0038] Example 3: Temperature stress control of annular wall concrete: For example, the 16th layer of a nuclear power plant's containment vessel is constructed using C40 (90-day-old) concrete. It has an inner radius of 18.5m, a wall thickness of 1.0m, and a height of 2.1m. This structure requires controlling both the external restraining stresses caused by the cooling rate and the temperature stresses caused by the temperature and humidity differences between the inner and outer walls.

[0039] Key control parameters were determined based on the annular wall temperature stress calculation formula: σθmax = -αΔTiEi(τ)RCxHi(t,τ) / (bhEi(τ)). Because the structure's interior is steel-lined and cannot undergo conventional insulation and curing, while the exterior can be insulated with formwork, creating a temperature differential between the interior and exterior, a differentiated curing strategy was adopted.

[0040] During implementation, layered insulation was implemented on the exterior, initially using a single layer of 10mm insulation felt, which was increased to a double layer of 20mm after the fifth day. The interior was maintained by spraying water atomization on the steel lining to prevent rapid water loss. Ambient humidity was also strictly controlled, and fencing was implemented to reduce the impact of wind speed during dry and windy seasons. After 60 days of differentiated curing, the equivalent temperature difference between the interior and exterior was kept within 10°C, the tensile stress on the exterior surface was below 1.2 MPa, and no harmful cracks were observed.

[0041] It can be seen from the above embodiments that the crack control process during large-volume concrete construction of the present invention can effectively prevent and control the occurrence of concrete cracks by combining theoretical calculation guidance, dynamic parameter adjustment and full-process monitoring according to different structural characteristics and construction conditions, thereby improving construction efficiency while ensuring project quality and having good engineering application value.

[0042] The present invention encompasses any alternatives, modifications, equivalents, and solutions that fall within the spirit and scope of the present invention. To provide a thorough understanding of the present invention, specific details are described in detail below in connection with the preferred embodiments of the present invention, but those skilled in the art will be able to fully understand the present invention without these detailed descriptions. Furthermore, to avoid unnecessary confusion regarding the essence of the present invention, well-known methods, processes, procedures, components, and circuits have not been described in detail.

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A crack control process during mass concrete construction, characterized in that The following steps are involved: Step 1: Based on the geometric dimensions, constraints, and ambient temperature of the concrete component, the temperature stress calculation formula is used to predict the temperature stress σxmax(τ) and tensile strength Rf(τ) at each age, and the preservation coefficient K=Rf(τ) / Σσi(τ)Hi(t,τ) is calculated, where Hi(t,τ) is the stress relaxation coefficient; Step 2: Cover the concrete with plastic film within 4 to 6 hours after pouring and sprinkle water regularly for moisturizing and curing. At the same time, take measures to prevent wind and avoid direct sunlight. Step 3: No insulation layer is set during the concrete heating stage. After entering the cooling stage, multiple layers of insulation material are dynamically set according to the temperature monitoring results and the calculation results of step 1. The thickness of the insulation layer is calculated and determined according to the formula δx=KbλjH(Tb-Tq) / 2λ(Tmax-Tb); Step 4: Set temperature measuring points at key locations of the concrete for real-time temperature monitoring. When the preservation coefficient K value is less than 1, immediately increase the thickness of the insulation layer or adjust the cooling rate. Step 5: When the temperature difference between the center of the concrete and the ambient temperature drops to within 25°C, remove the insulation layer layer by layer in stages.

2. The process according to claim 1, characterized in that For a rectangular raft foundation structure, the temperature stress calculation formula in step 1 is σxmax(τ)=-αΔTiEi(τ)βi(τ)Hi(t,τ) / (1-μ), where βi=ChL² / (8Ei(τ)H), Ch is the horizontal resistance coefficient of the foundation, L is the length of the component, and H is the thickness of the component.

3. The process according to claim 1, characterized in that For the truncated cone raft foundation structure, in step 1, it is necessary to calculate the hoop stress σθ(r)=αEΔTmax(r / R-r² / R²) / (1-μ) caused by the temperature difference between the center and the edge, the stress caused by the temperature difference between the center and the surface, and the external constraint stress caused by cooling, and perform superposition analysis.

4. The process according to claim 1, characterized in that The multi-layer insulation material in step three uses insulation felt with a thickness of 8-15mm. Initially, a single layer of insulation is set, and it is gradually increased to 2-3 layers according to calculation needs, with air gaps left between each layer.

5. The process according to claim 1, characterized in that The temperature measuring points in step 4 are arranged in an "X" shape, with 3-4 temperature measuring tubes set up in each monitoring area to monitor the center temperature, edge temperature and surface temperature respectively.

6. The process according to claim 1, characterized in that The cooling rate of concrete is controlled in stages according to its age: 2.0-5.0℃ / day in the first 7 days and 1.5-2.0℃ / day after 7 days. The temperature difference between inside and outside is controlled at 15-20℃ in the initial stage of cooling, and is allowed to reach 25℃ in the later stage.

7. The process according to claim 1, characterized in that For the annular wall structure, a differentiated maintenance method is adopted. Layered insulation measures are set up on the outside, and moisturizing maintenance is carried out on the inside through surface atomized water spraying to control the equivalent temperature difference between the inside and the outside to within 10°C.

8. The process according to claim 1, characterized in that The moisturizing measures in step 2 include covering with plastic film to prevent water evaporation, sprinkling water every 2-4 hours to keep the surface moist, and setting up fences in dry and windy environments to reduce the impact of wind speed.

9. The process according to claim 1, characterized in that The following optimization measures are adopted before concrete pouring: a sliding layer material with a thickness of 5-10mm is set at the bottom of the raft foundation, a reinforcement scheme with a diameter of no more than 25mm and a spacing of no more than 200mm is adopted, and the thickness of the steel bar protective layer is controlled within the range of 30-50mm.

10. The process according to claim 1, characterized in that The insulation layer in step five is removed layer by layer. Each time a layer of insulation material is removed, observe for 24 hours to confirm that the temperature change is stable and the increase in the temperature difference between the inside and outside does not exceed 5°C before removing the next layer.

Images