A crack-resistant wall construction method based on gradient combination

Abstract

The present invention relates to the technical field of building engineering wall construction, and in particular to a method for constructing anti-cracking walls based on gradient combination. The method first calculates the limiting expansion index parameter ε of the intermediate wall. e , and based on this, the mix ratio was obtained. The expansive concrete mix ratio was then verified and optimized. Based on the gradient combination of anti-cracking wall dimensions, the structures of various parts of the overall anti-cracking wall were designed, and the gradient combination of anti-cracking wall casting construction was carried out, including casting the intermediate wall within 5-25 days after the reaction pier casting was completed. Finally, the overall anti-cracking wall curing construction was carried out. When the later-cast intermediate wall expanded outward, it encountered the reaction pier and was squeezed, thereby pre-establishing pre-compressive stress. This part of the pre-compressive stress can offset the tensile stress caused by the later shrinkage and temperature deformation of the concrete, effectively preventing the occurrence of structural cracks.

Description

Technical Field

[0001] The present invention relates to the technical field of building engineering wall construction, and in particular to a crack-resistant wall construction method based on gradient combination. Background Art

[0002] my country's population continues to grow, urbanization is accelerating, and urban land supply is becoming increasingly tight. The increasing development and utilization of underground spaces, such as high-rise building basements, underground garages, and underground commercial plazas, has resulted in numerous extremely long and large basement structures. Due to the unique nature of the groundwater environment and the rigid waterproofing requirements, underground projects place high demands on crack control. Once cracks appear, water seepage can occur and induce steel corrosion, compromising the durability and safety of the structure. Repairing these cracks also requires significant manpower and resources, inevitably delaying construction.

[0003] Many factors contribute to cracks in concrete structures, primarily changes in concrete surface moisture, volumetric deformation, creep, temperature, and restraint. Cracks in base and roof slabs account for approximately 10% of all cracks, while wall cracks account for over 85%. Wall concrete cracks are crucial and challenging to control. Restrained cracks caused by temperature fluctuations and concrete shrinkage are particularly common. Walls are prone to through-hole cracks during construction due to shrinkage caused by temperature drop, autogenous shrinkage, and restraint. The root cause is tensile stress in the wall exceeding its tensile strength, leading to cracks.

[0004] Crack control remains a major challenge in the construction industry. From a lifecycle perspective, achieving economic efficiency requires a certain degree of effective crack control. Therefore, crack control is a crucial technical step in underground construction. However, the material properties of concrete dictate that cracks in concrete structures are inevitable.

[0005] Wall crack control technology involves a wide range of disciplines, primarily structure, materials, construction, design, and environment. Key methods include post-cast joints, expansive concrete, optimized mix ratios, and prestressed concrete. Currently, no mature and effective crack control technology measures exist, either domestically or internationally. Several other patents and technical documents disclose wall crack control solutions. For example, patent application number CN215564429U, entitled "A Device for Improving Shrinkage Cracks in Concrete Walls of Extra-Long Basements," employs a crack prevention structure on a sealed formwork. This structure's special cross-section controls stress dispersion, but this approach compromises the integrity of the concrete structure and reduces the wall's load-bearing capacity. Another patent application, application number CN115749049A, entitled "A Method for Preventing Cracking with Bidirectional Graded Induced Joints in Extra-Long Shear Walls," discloses a method for controlling the formation of graded induced joints in the concrete structure by embedding pre-embedded induced joint formwork. This creates pre-crack locations, rationally guides crack development, reduces stress concentration, and prevents the disordered generation of cracks. However, this approach is cumbersome and significantly impacts construction progress.

[0006] Therefore, how to fundamentally control the tensile stress in the concrete so that it does not exceed the tensile strength, avoid cracks in the wall due to tension, and ensure the safety and normal use function of the ultra-long basement concrete structure is a major technical issue in the construction process of the wall of the construction project. At the same time, how to reduce construction costs, reduce construction processes, shorten construction period, and achieve better construction economy is also an issue that needs to be considered in controlling wall cracks. Summary of the Invention

[0007] At least one of the purposes of the present invention is to provide a crack-resistant wall construction method based on a gradient combination in order to overcome the problems existing in the above-mentioned prior art. This construction method can effectively reduce the deformation of the wall structure by adjusting the wall structure and the construction process sequence, thereby avoiding the cracking of the wall due to excessive external constraints. After the construction is completed, the wall has good integrity and will not produce cracks, thereby solving the crack problem that has long plagued the field of engineering technology and achieving a good crack control effect.

[0008] In order to achieve the above objectives, the technical solutions adopted by the present invention include the following aspects.

[0009] A method for constructing a crack-resistant wall based on a gradient combination, wherein the gradient combination crack-resistant wall comprises a base plate, reaction piers spaced apart on the base plate, and an intermediate wall cast on the base plate, wherein the intermediate wall is filled between two adjacent reaction piers, so that the base plate, reaction piers, and intermediate wall form an integral crack-resistant wall. The intermediate wall is cast using expansive concrete. The construction of the gradient combination crack-resistant wall comprises the following construction steps:

[0010] Step A: Calculate the expansion restriction parameter ε of the intermediate wall e , and based on this, the expansive concrete mix ratio of the middle wall was obtained by trial mixing;

[0011] Step B: Verify and optimize expansive concrete mix proportions;

[0012] Step C: Based on the gradient combination of anti-cracking wall dimensions, design the structure of each part of the overall anti-cracking wall, including the specific shapes, dimensions, and reinforcement of the bottom plate, reaction pier, intermediate wall, and top plate;

[0013] Step D: pouring construction of the gradient combination anti-cracking wall, including pouring the intermediate wall within 5-25 days after the completion of the reaction pier pouring;

[0014] Step E: Overall anti-cracking wall maintenance construction.

[0015] The wall is designed as a gradient composite structure. Different concretes are used to cast different parts of the wall. The reaction pier uses ordinary concrete, and the middle wall uses expansive concrete. By calculating the limiting expansion index parameter ε of the expansive concrete e , and then obtain the expansive concrete mix ratio, so that the expansive concrete can establish pre-compressive stress through the reaction piers poured first in the early stage of pouring, which is used to offset the tensile stress caused by the shrinkage of the wall in the later stage. It can not only ensure that the wall will not produce induced cracks in the early stage, but also avoid shrinkage cracks in the wall in the later stage. At the same time, combined with the anti-cracking wall size, pouring process and curing process, cracks in the wall are avoided. This makes this gradient combination wall have good crack resistance under the construction process steps disclosed in this solution, while reducing costs and improving construction efficiency.

[0016] Preferably, in step A, the limiting expansion index parameter ε of the middle wall is calculated e The specific steps include:

[0017] Step A1: Calculate the concrete shrinkage index parameter ε of the middle wall in the anti-cracking wall based on the gradient combination d , specifically calculated based on the concrete properties of the middle wall, including the ultimate shrinkage value of concrete under standard conditions and the correction coefficient of concrete under non-standard conditions. The concrete shrinkage index parameter is, where is the ultimate shrinkage value under standard conditions, M1, M2, ..., Mn are correction coefficients for various non-standard conditions, including cement type M1, cement fineness M2, aggregate type M3, water-cement ratio M4, cement paste amount M5, initial curing time M6, ambient humidity M7, reinforcement ratio M8, and vibration operation method M9, b is an empirical coefficient, and t is the concrete age (days);

[0018] Step A2: Calculate the concrete shrinkage index parameter ε of the middle wall t, which can be calculated based on the concrete properties of the middle wall, including the linear expansion coefficient of concrete, the highest center temperature during concrete pouring, the average ambient temperature, and the constraint coefficient of the middle wall concrete. t =a(T 温峰 -T 环境 )·R, where α is the linear expansion coefficient of concrete, T 温峰 is the maximum temperature of the concrete center (℃), T 环境 is the average ambient temperature (°C), R is the confinement coefficient of the middle wall concrete;

[0019] Step A3: Calculate the ultimate tensile index parameter ε of the concrete of the middle wall pa , calculated based on the concrete crack resistance and cross-section reinforcement conditions, the concrete ultimate tensile index parameter Where Rf is the concrete crack resistance design strength (MPa), ρ is the cross-sectional reinforcement ratio, ρ = μ × 100, μ is the reinforcement ratio, and d is the reinforcement diameter (cm);

[0020] Step A4: According to the condition that the anti-cracking wall does not crack based on the gradient combination 0<ε e- ε d -ε t <ε pa , calculate the limiting expansion index parameter ε of the middle wall e ;

[0021] Step A5: According to the indicator parameter ε required in step A4 e Carry out expansive concrete mix design and determine the expansive concrete mix ratio and limited expansion rate data for the middle wall;

[0022] The expansion limit parameter ε of expansive concrete e The detailed calculation process includes the calculation of concrete shrinkage index parameter ε d , concrete shrinkage index parameter ε t and concrete ultimate tensile index parameter ε pa , thus obtaining the limiting expansion index parameter ε of expansive concrete e , value range, and carry out limited expansion rate test, and optimize the economic expansion agent dosage according to the test structure, so as to obtain the expansive concrete mix ratio that ensures the anti-cracking performance requirements of the gradient composite wall.

[0023] Preferably, when verifying and optimizing the expansive concrete mix ratio in step B, the following steps are specifically included:

[0024] Step B1: Design the mix proportion of ordinary concrete, using a grade one level higher than the design grade, and conduct a trial mix test to ensure that all indicators meet the requirements;

[0025] Step B2: Determine the unit cementitious material dosage, adopt the internal admixture method, use the expansion agent to replace cement, fly ash, and mineral powder to conduct the limited expansion rate test, determine the expansion agent dosage based on the test results, and finally determine the expansion index parameter ε that meets the limit in step A. e Expansive concrete mix proportion;

[0026] Step B3: Substitute the obtained expansive concrete mix ratio into step A to calculate the limiting expansion index parameter ε of the middle wall e , verify and optimize the expansive concrete mix ratio of the middle wall to meet the predetermined requirements.

[0027] Preferably, in step C, when designing the structure of each part of the overall anti-cracking wall based on the anti-cracking wall size of the gradient combination, the following contents are specifically included:

[0028] Step C1: The reaction pier is a common reinforced concrete structure;

[0029] Step C2: The reaction pier has the same thickness as the anti-cracking wall structure based on the gradient combination;

[0030] Step C3: The length of the reaction pier is between 10% and 35% of the length of the entire anti-cracking wall structure;

[0031] Step C4: The height of the reaction pier is more than 40% of the length of the entire anti-cracking wall structure;

[0032] In addition, water stop strips are designed at the connection between the reaction pier and the middle wall. By arranging the water stop strips, the anti-seepage performance of the crack-resistant wall used in the basement structure is improved.

[0033] The pouring construction of the gradient combination anti-cracking wall in step D specifically includes the following steps:

[0034] Step D1: Casting the base plate and guide wall, wherein the guide wall is cast in one piece;

[0035] Step D2: After the guide wall is poured, the reaction piers are constructed within 2-4 days. The reaction piers are constructed with pre-buried steel bars and poured with ordinary concrete.

[0036] Step D3: 5-25 days after the reaction pier is poured, the intermediate wall construction is carried out, including tying the embedded steel bars and pouring the expansive concrete with the optimized mix ratio verified in Step B.

[0037] The anti-cracking wall construction method based on gradient combination in the present application is applicable to wall structures with a wall thickness of more than 0.2m and a length of more than 12m, and in the step E, the entire anti-cracking wall is cured with wooden formwork.

[0038] In summary, due to the adoption of the above technical solution, the present invention has at least the following beneficial effects:

[0039] 1. The anti-cracking wall construction method based on the gradient combination of the present invention is adopted. After the anti-cracking wall based on the gradient combination is constructed, cracks can be effectively controlled and the wall has good anti-cracking performance. The middle wall adopts expansive concrete, and the limiting expansion index parameter εe of the middle wall adopting the expansive concrete is calculated. The expansive concrete mix ratio of the middle wall is determined based on the value, ensuring that the expansive concrete adopting the mix ratio can meet the anti-cracking performance requirements. In order to ensure that it meets the anti-cracking requirements, the mix ratio of the expansive concrete is verified and further optimized;

[0040] 2. When pouring the gradient combination anti-cracking wall, the reaction pier concrete structure is poured first. After the reaction pier is finally set 5-25 days after completion, the middle wall is poured. The middle wall expands outwards and is squeezed when it encounters the reaction pier, thus pre-establishing pre-compression stress. This pre-compression stress can offset the tensile stress caused by the late shrinkage and temperature deformation of the concrete, effectively preventing the occurrence of structural cracks.

[0041] 3. First calculate the limiting expansion index parameter ε of the middle wall e , and then the expansion concrete mix ratio of the middle wall is obtained by trial mixing, and then the expansion concrete mix ratio is verified and optimized. e The relevant parameters of concrete drying shrinkage index εd, concrete cooling shrinkage index parameter εt and concrete ultimate tensile index parameter εpa include relevant parameters including construction method and concrete curing, and the parameters satisfying 0<ε e- ε d- ε t <ε pa The wall is poured with the required expansive concrete mix ratio, and the construction and maintenance are carried out according to the required construction methods and maintenance measures to ensure that no cracks appear in the gradient combination wall, and to ensure the rationality and correctness of the anti-cracking wall structure based on the gradient combination and its anti-cracking construction method. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The figure is a process flow chart of the anti-cracking wall construction method based on gradient combination of the present invention.

[0043] Figure 2 It is a structural schematic diagram of the anti-cracking wall based on gradient combination in the present invention.

[0044] Figure 3 This is a schematic structural diagram of an anti-cracking wall based on gradient combination according to another embodiment of the present invention.

[0045] Markings in the figure: 1-bottom plate, 2-reaction pier, 3-water stop, 4-middle wall, 5-top plate. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments to make the purpose, technical solutions and advantages of the present invention more clearly understood. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0047] Example 1

[0048] Figure 2 and Figure 3 The invention shows an anti-cracking wall structure based on a gradient combination of an exemplary embodiment of the present invention. The anti-cracking wall structure based on the gradient combination comprises a base plate (1), reaction piers (2) arranged at intervals on the base plate (1), and an intermediate wall (4) cast on the base plate (1). The intermediate wall (4) is filled between two adjacent reaction piers (2), so that the base plate (1), the reaction piers (2) and the intermediate wall (4) form an integral anti-cracking wall structure. The top of the integral anti-cracking wall structure is a top plate (5). The reaction piers (2) are reinforced concrete structures formed by casting ordinary concrete. The intermediate wall (4) is a reinforced concrete structure formed by casting expansive concrete. The reaction piers (2) have the same thickness as the overall anti-cracking wall structure. The length of the reaction piers (2) is between 10% and 35% of the length of the overall anti-cracking wall structure. The height of the reaction piers (2) is 40% or more of the length of the overall anti-cracking wall structure.

[0049] During the pouring process of the wall concrete, when it is first poured and initially set, a large amount of concrete hydration heat will be released. At this time, the wall concrete expands and forms tensile stress toward the outside. Then, it gradually cools and finally sets. The wall concrete will form tensile stress toward the inside due to temperature deformation. At the same time, the deformation and shrinkage of the wall concrete itself in the later stage will also form tensile stress toward the inside. In these two processes, the wall concrete will crack due to deformation and stress. However, it is only during the early stage of pouring that the temperature rises and expands. At this time, the concrete has not solidified and the elastic modulus is low, so there is only a certain probability that cracks will appear. By setting the reaction pier (2) of the reinforced concrete structure, the reaction pier (2) is first poured and finally set during the construction process, and then the middle wall structure is poured. The middle wall expands outwards and is squeezed when it encounters the reaction pier (2), thereby pre-establishing pre-compression stress. This part of the pre-compression stress can offset the tensile stress generated by the concrete's later shrinkage and temperature deformation, effectively preventing the occurrence of structural cracks.

[0050] As one of the preferred embodiments, the length of the reaction pier (2) is between 15% and 35% of the length of the overall anti-cracking wall structure, and is specifically determined according to the length of the overall anti-cracking wall structure. The longer the overall anti-cracking wall is, the longer the length of the reaction pier is. When the overall anti-cracking wall structure is between 10m and 20m, the length of the reaction pier is 3-4m. When the overall anti-cracking wall structure is between 20m and 30m, the length of the reaction pier is 4-6m. When the overall anti-cracking wall structure is greater than 30m, the length of the reaction pier is 6-8m. The length of the reaction pier can be selected based on both the length of the overall anti-cracking wall structure and the ideal length of the reaction pier.

[0051] As one preferred embodiment, the height of the reaction pier (2) is 40% or more of the length of the overall anti-cracking wall structure, and preferably the height is 60% or more of the length of the overall anti-cracking wall structure.

[0052] This anti-cracking wall is suitable for wall structures with a wall thickness of more than 200 mm and a length of more than 12 m. When the overall anti-cracking wall structure length is less than 10 m, on the one hand, conventional crack control methods can be used to control the occurrence of cracks, such as ensuring the pouring time and space, insulation measures, and maintenance measures. On the other hand, the anti-cracking wall structure and construction method using the gradient combination of this scheme no longer have advantages.

[0053] Example 2

[0054] Figure 1 A construction process flow chart of a method for constructing a crack-resistant wall based on a gradient combination according to an exemplary embodiment of the present invention is shown. When constructing the crack-resistant wall based on the gradient combination in Example 2, the following construction steps are included:

[0055] Step A: Calculate the expansion restriction parameter ε of the intermediate wall e , and based on this, the expansive concrete mix ratio of the middle wall was obtained by trial mixing;

[0056] Step B: Verify and optimize expansive concrete mix proportions;

[0057] Step C: Based on the gradient combination of anti-cracking wall dimensions, design the structure of each part of the overall anti-cracking wall, including the specific shapes, dimensions, and reinforcement of the bottom plate, reaction pier, intermediate wall, and top plate;

[0058] Step D: pouring construction of the gradient combination anti-cracking wall, including pouring the intermediate wall within 5-25 days after the completion of the reaction pier pouring;

[0059] Step E: Overall anti-cracking wall maintenance construction;

[0060] The above-mentioned construction method adopts multiple steps, and after the anti-cracking wall based on the gradient combination is constructed, cracks can be effectively controlled and the crack resistance is good. The middle wall adopts expansive concrete, and the limiting expansion index parameter ε of the middle wall adopting the expansive concrete is calculated. e , and based on this value, the determined expansive concrete mix ratio of the middle wall is adapted to ensure that the expansive concrete with this mix ratio in the middle concrete can meet the crack resistance requirements. In order to ensure that it meets the crack resistance requirements, the mix of the expansive concrete is verified and further optimized;

[0061] During the pouring construction of the gradient combination anti-cracking wall through step D, the reaction pier concrete structure is poured first. After completion, the reaction pier is finally solidified 5-25 days later, and then the middle wall is poured. The middle wall expands outwards and is squeezed when encountering the reaction pier, thereby pre-establishing pre-compression stress. This part of the pre-compression stress can offset the tensile stress caused by the late shrinkage and temperature deformation of the concrete, effectively preventing the occurrence of structural cracks.

[0062] The following is a detailed description of each construction step for designing a gradient-combined crack-resistant wall for the basement exterior wall, which has a total length of approximately 20 to 30 meters, a thickness of 0.3 meters, and a height of 3.7 meters.

[0063] Calculate the expansion restriction parameter ε of the middle wall in step A e When we first determine an initial value of the expansive concrete mix ratio, we calculate and limit the expansion index parameter ε based on this initial value. e The relevant parameter values ​​are then obtained, and the determined value of the expansive concrete mix ratio is obtained. The intermediate wall expansive concrete mix ratio that meets the requirements is prepared according to the determined value. Then, in the subsequent step (specifically step B), the expansive concrete mix ratio is verified and optimized, and the final value of the intermediate wall expansive concrete mix ratio is obtained, so as to carry out the subsequent construction steps. The expansion index parameter ε is calculated based on the initial value of the expansive concrete and the limiting expansion index parameter ε is obtained. e When calculating related parameter values, follow the steps below. The order of A1-A3 can be adjusted.

[0064] Step A1: Calculate the concrete shrinkage index parameter ε of the middle wall in the anti-cracking wall based on the gradient combination d The parameter value of this index is calculated based on the concrete properties of the middle wall, including the ultimate shrinkage value of concrete under standard conditions and the correction coefficient of concrete under non-standard conditions. Where, is the ultimate shrinkage value under standard conditions, M1, M2, …, Mn are correction coefficients for various non-standard conditions, including cement type M1, cement fineness M2, aggregate type M3, water-cement ratio M4, cement paste quantity M5, initial curing time M6, ambient humidity M7, reinforcement ratio M8, and vibration operation method M9, b is an empirical coefficient, and t is the age of concrete (days);

[0065] Specifically: Take 3.24×10 -4 ;

[0066] The values ​​of cement type M1 are: 1.25 for slag cement, 1.12 for rapid-hardening cement, 1.10 for low-heat cement, 1.00 for ordinary cement, 1.00 for pozzolanic cement, and 0.78 for sulfate-resistant cement;

[0067] The values ​​of cement fineness M2 are: 0.9 for cement fineness 1500, 0.93 for cement fineness 2000, 1.00 for cement fineness 3000, 1.13 for cement fineness 4000, 1.35 for cement fineness 5000, 1.68 for cement fineness 6000, 2.05 for cement fineness 7000, and 2.42 for cement fineness 8000;

[0068] The values ​​of aggregate type M3 are: aggregate is M3, sandstone is 1.90, gravel sand is 1.00, basalt is 1.00, granite is 1.00, limestone is 1.00, and quartzite is 0.80;

[0069] The values ​​of water-cement ratio M4 are: 0.65 for water-cement ratio 0.2, 0.85 for water-cement ratio 0.3, 1.00 for water-cement ratio 0.4, 1.21 for water-cement ratio 0.5, 1.42 for water-cement ratio 0.6, 1.62 for water-cement ratio 0.7, and 1.80 for water-cement ratio 0.8;

[0070] The values ​​of cement slurry volume M5 are: cement slurry volume 15 is 0.90, cement slurry volume 20 is 1.00, cement slurry volume 25 is 1.20, cement slurry volume 30 is 1.45, cement slurry volume 35 is 1.75, cement slurry volume 40 is 2.10, cement slurry volume 45 is 2.55, and cement slurry volume 50 is 3.03;

[0071] The values ​​of initial curing time M6 are as follows: 1 day initial curing time is 1.11, 2 days initial curing time is 1.11, 3 days initial curing time is 1.09, 4 days initial curing time is 1.07, 5 days initial curing time is 1.04, 7 days initial curing time is 1, 10-13 days initial curing time is 0.96, and 14 days or more initial curing time is 0.93;

[0072] The values ​​of ambient humidity M7 are as follows: 1.25 for ambient humidity within 25°C, 1.21 for ambient humidity between 25°C and 30°C, 1.18 for ambient humidity between 30°C and 40°C, 1.10 for ambient humidity between 40°C and 50°C, 1.00 for ambient humidity between 50°C and 60°C, 0.88 for ambient humidity between 60°C and 70°C, 0.77 for ambient humidity between 70°C and 80°C, 0.70 for ambient humidity between 80°C and 90°C, and 0.54 for ambient humidity above 90°C.

[0073] The value of reinforcement ratio M8 is: 0.00 is 1.00, 0.05 is 0.86, 0.10 is 0.76, 0.15 is 0.68, 0.20 is 0.61, and 0.25 is 0.55;

[0074] The values ​​of the vibration operation method M9 are: mechanical vibration is 1.00, manual vibration is 1.10, steam curing is 0.85, and autoclave treatment is 0.54;

[0075] b is the empirical coefficient, which is generally taken as 0.01, and 0.03 when the maintenance is poor;

[0076] For example, based on the engineering design requirements, raw material conditions, mix ratio report and other factors, the values ​​in Table 1 are used to obtain the concrete shrinkage value.

[0077] Table 1 Concrete shrinkage index parameter ε d Calculation value table

[0078] Influencing factors Actual project situation Correction factor <![CDATA[Cement variety M1]]> Ordinary cement 1.00 <![CDATA[Cement fineness M2]]> 3000 1.00 <![CDATA[Aggregate M3]]> granite 1.00 <![CDATA[Water-cement ratio M4]]> 0.4 1.00 <![CDATA[Cement slurry volume M5]]> 20 1.00 <![CDATA[Initial curing time M6]]> 14 0.93 / 0.84 <![CDATA[Environmental humidity M7]]> 50 1.00 <![CDATA[Reinforcement ratio M8]]> 0.015 0.958 <![CDATA[Operation method M9]]> Mechanical vibration 1.00

[0079] Step A2: Calculate the concrete shrinkage index parameter ε of the middle wall t , calculated based on the concrete properties of the middle wall, including the linear expansion coefficient of concrete, the highest center temperature during concrete pouring, the average ambient temperature, and the constraint coefficient of the middle wall concrete. t =a(T 温峰 -T 环境 )·R, where α is the linear expansion coefficient of concrete, which is 1×10 -5 / ℃,T 温峰 is the maximum temperature of the concrete center (℃), T 环境 is the average ambient temperature (°C), R is the confinement coefficient of the middle wall concrete;

[0080] The maximum temperature of the concrete center T 温峰 It is obtained by calculation. When calculating, T 温峰 =T 入模 +T 水化温升 , where T 入模is the average temperature of concrete entering the mold (℃), T 水化温升 is the maximum temperature at the center of concrete (℃);

[0081] Among them, the T 水化温升 =αT max , α is the heat dissipation coefficient of concrete, T max is the concrete adiabatic temperature rise (℃), the concrete adiabatic temperature rise Where W is the amount of cementitious materials used in concrete (kg / m 3 ), Q is the total hydration heat of cementitious materials, Q = k1·k2·Q0, k1 and k2 are taken according to Table 3, P·O42.5 cement Q0 = 320kJ / kg, c is the specific heat of concrete, which is taken as 0.96kJ / (kg·℃), ρ is the concrete density, which is taken as 2400kg / m 3 , m is a coefficient related to cement type, pouring temperature, etc., and is taken as 1.4d -1 , d initial curing days;

[0082] Among them, the total hydration heat of cementitious materials Q = k1﹒ k2﹒ Q0, k1 and k2 are the coefficients of fly ash and mineral powder at different dosages, and Q0 is the total hydration heat of cement;

[0083] Specifically: Based on the initial concrete mix ratio in Table 2, first use conventional concrete to calculate whether it meets the requirements;

[0084] Table 2 Initial values ​​of concrete mix ratio

[0085]

[0086] Concrete cementitious material dosage W = 360kg / m 3 , the total hydration heat of cementitious materials Q = 0.878 × 1 × 320 = 280.96 kJ / kg, the adiabatic temperature rise of concrete T max =43.9℃;

[0087] The thickness of the basement outer wall (0.3m) is much smaller than the length (between 20 and 30m). The heat dissipation in the length direction is ignored, and only the heat dissipation in the thickness direction of the bottom plate is considered. The heat dissipation coefficient α is taken as 0.6, T 水化温升 =0.6×43.9=26.34℃;

[0088] The average temperature of concrete entering the mold is 30℃, then the maximum temperature of the concrete center is T 温峰 =30+26.34=56.34℃;

[0089] Query the historical seasonal average temperature of the construction site and the average ambient temperature during the construction period T 平均=30℃, when the concrete drops from the highest temperature to the ambient temperature, it will shrink. Since it is subject to constraint during the shrinkage process, the constraint coefficient R is taken as 0.6, then the concrete shrinkage value εt=1.0×10 -5 ×(56.34-30)×0.6=1.58×10.0 -4 .

[0090] Table 3 Coefficients of fly ash and mineral powder at different dosages

[0091] Dosage 0 10％ 20％ 30％ 40％ <![CDATA[Fly ash (k1)]]> 1 0.94 0.89 0.85 0.81 <![CDATA[Mineral powder (k2)]]> 1 0.97 0.95 0.91 0.86

[0092] Step A3: Calculate the ultimate tensile index parameter ε of the concrete of the middle wall pa ; According to the concrete cracking strength and cross-section reinforcement conditions, the concrete ultimate tensile index parameter is calculated. Where Rf is the concrete crack resistance design strength (MPa), ρ is the cross-section reinforcement ratio, ρ = μ × 100, μ is the reinforcement ratio, for example, if the reinforcement ratio μ = 0.2% and 0.5%, then ρ = 0.2 and 0.5, and d is the reinforcement diameter (cm);

[0093] Specifically: Concrete ultimate tensile strength R f =1.43MPa, cross-section reinforcement ratio ρ = 1.5%, steel bar diameter d = 1.2cm, concrete ultimate tensile strength ε pa =0.5×1.43×(1+1.5 / 1.2)×10 -4 =1.61×10 -4 .

[0094] Step A4: According to the condition that the anti-cracking wall does not crack based on the gradient combination 0<ε e- ε d- ε t <ε pa , put the value into the calculation to get the limiting expansion index parameter ε of the middle wall e , which is 2.29×10 -4 <ε e <3.90×10 -4 .

[0095] Step A5: According to the indicator parameter ε required in step A4 e Carry out expansive concrete mix design and determine the expansive concrete mix ratio and limited expansion rate data for the middle wall;

[0096] Specifically, according to the limiting expansion index parameter ε e The numerical range is 2.29×10 -4 <ε e <3.90×10 -4 To design the mix ratio of expansive concrete, according to εe The numerical range of obtains the range of expansive concrete mix proportions, as shown in Table 4.

[0097] Table 4 Expansive concrete mix ratio range

[0098]

[0099] Step B: Verify and optimize the expansive concrete mix ratio, limiting the expansion index parameter ε according to step A e When the determined value of the expansive concrete mix ratio is obtained within the range of , it is first prepared, then blended, and finally verified and optimized. The specific steps include:

[0100] Step B1: Design the mix proportion of ordinary concrete, using a grade one level higher than the design grade, and conduct a trial mix test to ensure that all indicators meet the requirements;

[0101] Step B2: Determine the unit cementitious material dosage, adopt the internal admixture method, use the expansion agent to replace cement, fly ash, and mineral powder to conduct the limited expansion rate test, determine the expansion agent dosage based on the test results, and finally determine the expansion index parameter ε that meets the limit in step A. e Expansive concrete mix proportion;

[0102] Step B3: Substitute the obtained expansive concrete mix ratio into step A to calculate the limiting expansion index parameter ε of the middle wall e , verify and optimize the expansive concrete mix ratio of the middle wall to meet the predetermined requirements, and finally obtain the determined expansive concrete mix ratio and limited expansion rate data as shown in Table 5 below.

[0103] Table 5 Expansive concrete mix ratio and limited expansion rate data

[0104]

[0105] Step C: Based on the gradient combination of anti-cracking wall dimensions, design the structure of each part of the overall anti-cracking wall, including the shape, size, and reinforcement of the bottom plate, reaction pier, intermediate wall, and top plate. The specific methods are as follows:

[0106] Step C1: The reaction pier (2) is a common reinforced concrete structure, the longitudinal section of the reaction pier is 300mm×2500mm, and the cross section is 300mm×3000mm. Reinforcement is provided on the longitudinal section, the reinforcement ratio is 1.5%, and the reinforcement diameter is 12mm;

[0107] Step C2: the thickness of the reaction pier (2) is the same as that of the anti-cracking wall structure based on the gradient combination, both of which are 300 mm;

[0108] Step C3: The length of the reaction pier (2) is between 10% and 35% of the length of the overall anti-cracking wall structure. In this embodiment, it is further optimized to between 15% and 30%, and directly takes 3000 mm;

[0109] Step C4: The height of the reaction pier (2) is more than 40% of the length of the overall anti-cracking wall structure, and in this embodiment is further optimized to more than 60%, taking 67.58%, which is 2500 mm;

[0110] Step C5: A water stop strip (3) is provided in the middle of the connection portion between the reaction pier (2) and the intermediate wall (4), and the water stop strip (3) is made of a water stop steel plate or a water stop rubber strip.

[0111] The steps C1, C2, C3, C4 and C5 are all the design structural contents of the gradient combination anti-cracking wall, and do not need to be carried out in this order, and can be designed and implemented in any order.

[0112] Step D: Gradient combination anti-cracking wall pouring construction, because the one-time pouring of the exterior wall requires high construction coordination, and also requires high construction equipment, construction manpower and concrete raw material supply, so the block pouring method is adopted. For the wall structure with a length of 20 to 30 meters in this embodiment, as shown in FIG. Figure 2 As shown, reaction piers are arranged at both ends. For the entire basement structure wall, concrete reaction piers (2) are set every 20 to 30 meters on the outer wall. Figure 3 As shown, a structural form with multiple reaction piers is finally formed, and the focus is on controlling the pouring sequence and time of the reaction piers and the middle wall. That is, the reaction piers are poured at both ends of the outer wall first, and the middle wall is poured within 5-25 days after the reaction piers are poured. The reaction piers (2) are avoided as much as possible at corners and broken lines, and are arranged on both sides of the post-casting strip. The specific construction steps include:

[0113] Step D1: Casting the base plate and guide wall, wherein the guide wall is cast in one piece;

[0114] Step D2: After the guide wall is poured, the reaction pier is constructed within 2-4 days. The reaction pier adopts the form of embedded steel bars and is poured with ordinary concrete. Before pouring, a water stop strip (3) is pre-buried in the middle of the connection between the reaction pier (2) and the middle wall (4);

[0115] Step D3: 5-25 days after the reaction pier is poured, the middle wall is constructed, including tying the embedded steel bars and pouring the expansive concrete with the optimized mix ratio verified in step B. During the pouring, pay attention to keeping the water stop strip (3) straight and smooth.

[0116] After the pouring construction in step D is completed, the overall anti-cracking wall curing construction in step E is carried out. During the curing, a variety of curing schemes can be adopted, one of which is polymer curing mold + thermal insulation cotton, the second is plastic film + spray moisturizing, and the third is curing with wooden mold;

[0117] This embodiment preferably adopts curing with wooden formwork: after the concrete has finally set, loosen the formwork on both sides in time, leaving about 3 to 5 mm from the gap, pour water into the formwork and keep the concrete in a moist state. Remove the formwork after 7 days, and continue to water and cure for 14 days after demolding.

[0118] When using plastic film + spray moisturizing: the formwork can be removed 12 hours after pouring is completed. After removing the formwork, first cover the wall surface with plastic film, and then continue to spray the plastic film for maintenance. The moisturizing maintenance needs to be more than 14 days.

[0119] The anti-cracking wall construction method based on gradient combination of the present application is not only applicable to the construction process of basement walls, but also to any ultra-long concrete wall structure with a length greater than 12m in all engineering construction.

[0120] The above description is only a detailed description of the specific embodiments of the present invention, and does not limit the present invention. Various substitutions, modifications and improvements made by those skilled in the relevant art without departing from the principles and scope of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for constructing an anti-cracking wall based on a gradient combination, characterized in that: The gradient combination anti-cracking wall includes a bottom plate, reaction piers spaced apart on the bottom plate, and an intermediate wall cast on the bottom plate. The intermediate wall is filled between two adjacent reaction piers, so that the bottom plate, reaction piers, and intermediate wall form an integral anti-cracking wall. The top of the integral anti-cracking wall structure is the top plate. The reaction piers are arranged on both sides of the post-cast strip. The reaction piers are reinforced concrete structures formed by casting ordinary concrete. The intermediate wall is a reinforced concrete structure formed by casting expansive concrete. When constructing the gradient combination anti-cracking wall, the following construction steps are included: Step A: Calculate the expansion restriction parameter ε of the intermediate wall e , and based on this, the expansive concrete mix ratio of the middle wall was obtained by trial mixing; Step B: Verify and optimize expansive concrete mix proportions; Step C: Based on the gradient combination of anti-cracking wall dimensions, design the structure of each part of the overall anti-cracking wall, including the specific shapes, dimensions, and reinforcement of the bottom plate, reaction pier, intermediate wall, and top plate; Step D: pouring construction of gradient combination anti-cracking wall; Step E: Overall anti-cracking wall maintenance construction; When verifying and optimizing the expansive concrete mix ratio in step B, the following steps are specifically included: Step B1: Design the mix proportion of ordinary concrete, using a grade one level higher than the design grade, and conduct a trial mix test to ensure that all indicators meet the requirements; Step B2: Determine the unit cementitious material dosage, adopt the internal admixture method, use the expansion agent to replace cement, fly ash, and mineral powder to conduct the limited expansion rate test, determine the expansion agent dosage based on the test results, and finally determine the expansion index parameter ε that meets the limit in step A. e Expansive concrete mix proportion; Step B3: Substitute the obtained expansive concrete mix ratio into step A to calculate the limiting expansion index parameter ε of the middle wall e , verify and optimize the expansive concrete mix ratio of the middle wall to meet the predetermined requirements; In step C, the structure of each part of the overall anti-cracking wall is designed based on the anti-cracking wall size of the gradient combination, specifically including the following contents: Step C1: The reaction pier (2) is a common reinforced concrete structure, and reinforcement is provided on the longitudinal section; Step C2: the thickness of the reaction pier (2) is the same as the thickness of the anti-cracking wall structure based on the gradient combination; Step C3: The length of the reaction pier (2) is between 10% and 35% of the length of the entire anti-cracking wall structure; Step C4: the height of the reaction pier (2) is greater than 40% of the length of the entire anti-cracking wall structure; The pouring construction of the anti-cracking wall with gradient combination in step D specifically includes the following steps: Step D1: Casting the base plate and guide wall, wherein the guide wall is cast in one piece; Step D2: After the guide wall is poured, the reaction piers are constructed within 2-4 days. The reaction piers are constructed with pre-buried steel bars and poured with ordinary concrete. Step D3: 5-25 days after the reaction pier is poured, the intermediate wall is constructed, including tying the embedded steel bars and pouring the expansive concrete with the optimized mix ratio verified in Step B; The anti-cracking wall construction method based on gradient combination is applicable to wall structures with a wall thickness of more than 0.2 m and a length of more than 12 m, and in step E, the entire anti-cracking wall is cured with wooden formwork.

2. The anti-cracking wall construction method based on gradient combination according to claim 1 is characterized in that: In step A, the expansion restriction index parameter ε of the middle wall is calculated. e The specific steps include: Step A1: Calculate the concrete shrinkage index parameter ε of the middle wall in the anti-cracking wall based on the gradient combination d ; Step A2: Calculate the concrete shrinkage index parameter ε of the middle wall t ; Step A3: Calculate the ultimate tensile index parameter ε of the concrete of the middle wall pa ; Step A4: According to the condition that the anti-cracking wall does not crack based on the gradient combination 0<ε e- ε d- ε t <ε pa , calculate the limiting expansion index parameter ε of the middle wall e ; Step A5: According to the indicator parameter ε required in step A4 e Carry out expansive concrete mix design and determine the expansive concrete mix ratio and limited expansion rate data for the middle wall.

3. The anti-cracking wall construction method based on gradient combination according to claim 2 is characterized in that: In step A1, the concrete shrinkage index parameter ε of the middle wall is calculated. d The concrete shrinkage index parameter is calculated based on the concrete properties of the middle wall, including the ultimate shrinkage value of concrete under standard conditions and the correction coefficient of concrete under non-standard conditions. , where is the ultimate shrinkage value under standard conditions, M1, M2, …Mn are correction coefficients for various non-standard conditions, including cement type M1, cement fineness M2, aggregate type M3, water-cement ratio M4, cement paste quantity M5, initial curing time M6, ambient humidity M7, reinforcement ratio M8 and vibration operation method M9, b is the empirical coefficient, and t is the age of concrete (days).

4. The anti-cracking wall construction method based on gradient combination according to claim 2 is characterized in that: In step A2, the concrete shrinkage index parameter ε of the middle wall is obtained. t The calculation is based on the concrete properties of the middle wall, including the linear expansion coefficient of the concrete, the maximum center temperature during concrete pouring, the average ambient temperature, and the constraint coefficient of the middle wall concrete. , where α is the linear expansion coefficient of concrete, T 温峰 is the maximum temperature of the concrete center (°C), T 环境 is the average ambient temperature (°C), and R is the constraint coefficient of the middle wall concrete.

5. The anti-cracking wall construction method based on gradient combination according to claim 2 is characterized in that: In step A3, the ultimate tensile index parameter ε of the concrete of the middle wall is obtained. pa The concrete ultimate tensile index parameter is calculated based on the concrete crack resistance and cross-section reinforcement conditions. , where Rf is the concrete crack resistance design strength (MPa), ρ is the cross-sectional reinforcement ratio, ρ=μ×100, μ is the reinforcement ratio, and d is the reinforcement diameter (cm).

6. The anti-cracking wall construction method based on gradient combination according to any one of claims 1 to 5, characterized in that: When designing the structure of each part of the overall anti-cracking wall based on the anti-cracking wall size of the gradient combination in step C, it also includes: a water stop strip (3) is provided at the connection part between the reaction pier (2) and the middle wall (4).

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