Crack control method for high-impermeability mass concrete

Abstract

The invention relates to a construction technology of high-impermeability type concrete, in particular to a crack control method of high-impermeability type mass concrete, which comprises the following steps: optimizing the internal microstructure of the concrete, reducing the internal porosity of the concrete, and weakening the microsiphoning effect of the concrete on water molecules; materials are selected and optimized, so that the generation of hydration heat is reduced; the synergistic regulation effect of multiple admixtures is exerted, and the efficient water reducing agent is used, so that the water consumption is reduced, the water cement ratio is reduced, and the compactness and impermeability of the concrete are improved; a proper amount of expanding agent is added to compensate the shrinkage of the concrete; and quality control in the construction process: manufacturing a 1: 1 entity sample plate section, and performing systematic analysis on the cracking performance of the mass concrete. According to the crack control construction method for the high-impermeability mass concrete, provided by the invention, the crack resistance and impermeability of the concrete are comprehensively improved from the thought of optimizing the internal microstructure of the concrete.

Description

Technical Field

[0001] The invention relates to the technical field of mass concrete construction, in particular to the construction technology of high-impermeability concrete, and specifically to a crack control method for high-impermeability mass concrete. Background Art

[0002] With the continuous development of construction technology, high-impermeability large-volume concrete is increasingly used in various projects, such as large foundations, underground structures, etc. However, due to its large volume, high hydration heat, and complex construction conditions, it is easy to crack, affecting the safety and durability of the structure.

[0003] The use of traditional construction methods to operate high-impermeability large-volume concrete is prone to cracks. The main reasons include the following aspects 1. Influence of cement hydration heat: Cement releases a large amount of heat during the hydration process. Due to the large volume of large concrete structures, the heat inside the concrete is not easy to dissipate, causing the internal temperature to rise rapidly. The concrete surface dissipates heat quickly, resulting in a large temperature difference between the inside and outside. This temperature difference will produce temperature stress. When the temperature stress exceeds the tensile strength of the concrete, it will cause cracks.

[0004] 2. Influence of concrete shrinkage: Concrete will shrink in volume during the hardening process, including drying shrinkage and chemical shrinkage. For large-volume concrete, due to its large volume, shrinkage is constrained and shrinkage cracks are prone to occur.

[0005] 3. The construction technology is unreasonable. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects and to provide a crack control construction method for high-impermeability large-volume concrete.

[0007] In order to achieve the above object, the present invention is achieved in the following ways: A crack control method for high-impermeability mass concrete, comprising: S1. Optimization of concrete internal microstructure: filling, repairing and controlling multi-scale defects from micron to macro inside concrete; taking into account the optimization of multiphase interface transition zone (ITZ), reducing the internal porosity of concrete, and weakening the microscopic siphoning effect of concrete on water molecules; S2. Material selection and optimization: A) Cementitious materials: cement with low hydration heat and low fineness is preferred to reduce the activity and hydration degree of cementitious materials and reduce the generation of hydration heat; B) Admixtures: In-depth research on the optimal blending ratio of high-performance waterproofing agents, give full play to the synergistic regulatory effect of multiple admixtures, so that the concrete's working performance, impermeability, and early crack resistance can achieve the best results; use high-efficiency water reducers to reduce water consumption, lower the water-cement ratio, and improve the compactness and impermeability of concrete; at the same time, add an appropriate amount of expansion agent to compensate for the shrinkage of concrete; C) Cement: cement with low hydration heat is preferred; D) Aggregate: Coarse aggregate should be gravel with good continuous grading and larger particle size, and fine aggregate should be medium sand; the mud content and mud block content of aggregate should be strictly controlled; S3. Quality control during construction: A) Make a 1:1 solid sample section and conduct a systematic analysis of the cracking performance of large-volume concrete, including the crack development state, ductility performance, and residual deformation index of concrete; B) Evaluate the interfacial bond strength of cracks in high-impermeability mass concrete and characterize its mechanics; C) Analyze the causes of crack resistance through simulation and solve the problem of large-volume concrete crack resistance from the aspects of material and mechanism analysis and improvement.

[0008] The crack control method for the high-impermeability large-volume concrete mentioned above, in S1, improves the performance of cement paste by using high-quality admixtures so that it can better fill the gaps between aggregate and paste, thereby optimizing ITZ; adopts a more reasonable mix ratio, reduces the amount of cement, increases mineral admixtures, and reduces the internal porosity of concrete; selects appropriate aggregate grading and particle size to reduce the interconnected pores inside the concrete, thereby weakening the microscopic siphon effect.

[0009] Based on the above crack control method, the present invention further proposes a construction method for high-impermeability large-volume concrete, comprising: Step 1: When pouring the foundation slab concrete, the slab construction sections are constructed separately and poured in sequence; Step 2: Concrete pouring is carried out in sections with fixed points and thin layers, with a slope and circular advancement, and the pouring sequence is from low to high, starting from the lowest sump position in the order of pouring the bottom plate; Step 3: Before pouring concrete, set layered poles inside the foundation according to the thickness of the concrete layers. The poles are made of steel bars and placed at the concrete placement area with a spacing of 10m. Step 4: When pumping concrete, pour it at a natural flow slope of 1:6-1:10. The pouring thickness of each layer of concrete shall not exceed 500mm, and the upper layer of concrete shall be poured before the initial setting of the lower layer of concrete. When pouring the upper layer of concrete, it must be inserted into the lower layer of concrete by 50-100mm. At the same time, a special person shall be assigned to check to avoid cold joints. The concrete truck pump shall pour from one side of the post-casting belt backwards. Step 5: The free fall height of concrete shall not be greater than 2000mm. If it is greater than 2000mm, use a tube chute to discharge the concrete; Step 6. Strictly follow the construction sequence of the operating procedures, insert quickly and remove slowly, and arrange the insertion points evenly without omission; each concrete pump truck has 3 to 4 vibrators at the ash outlet, with 1 spare; when vibrating concrete, the moving distance of the vibrator should not be greater than 500mm, and the vibration time should be controlled between 20 and 30 seconds, which can make the concrete surface gray-yellow without bubbles; Step 7: When pouring concrete, the formwork, brackets, steel bars and reserved holes should be frequently observed. If any deformation or displacement is found, pouring should be stopped immediately; and the poured concrete should be repaired before it solidifies. Step 8, seepage treatment: At the end of concrete pouring, a sump is set outside the foundation pit, and the seepage water and slurry are made to flow into the sump through the cushion layer slope, and then the filtered seepage water is pumped out of the pit with a small submersible pump. If it is impossible to set up a sump, the seepage water can be sucked out with a sponge or a self-priming pump; when the concrete pouring is basically completed and the material is discharged, the material discharge route should be controlled well, and attention should be paid to consciously drive the seepage water to a corner of the foundation pit to facilitate the timely discharge of the seepage water; Step 9: Rub the concrete surface: Step 9.1, after the concrete is poured and vibrated, make a standard sample rod according to the 500mm line of the structure on the wall column dowel, draw the line to make it flat, make a ash cake on the bottom plate, scrape it flat according to the elevation control line with a scraper, and then use a wooden rubber to smooth it. Before the concrete surface is about to be final set, use a wooden rubber to rub it flat. During the whole operation, the elevation must be strictly controlled and accurate to ensure that the concrete surface is flat and free of cracks or other defects; Step 9.2, during the concrete pouring process, each section must be scraped flat with a scraper according to the elevation control point, then rubbed flat with a wooden rubber, and smoothed with an iron trowel. The entire pouring process requires three rounds of finishing. Before final setting, each section must be assigned a full-time worker to level and smooth. The construction workers are required to master the time of leveling and smoothing, and must strictly control the pouring height of the concrete according to the elevation control point. It is required to pour, vibrate, hang the line with a small white line, and scrape with a scraper, then use a wooden rubber to level and smooth with an iron trowel, and so on, as the basis for leveling the foundation concrete pouring until the foundation concrete pouring is completed. Step 10: Pouring and vibrating of wall concrete: Step 10.1, before pouring the wall concrete, evenly pour 30mm thick cement mortar with the same strength as the concrete at the bottom to make the new and old concretes completely combined. The wall concrete should be poured continuously, and the interval time should not exceed 2h. The pouring height of each layer should be controlled at about 500mm. The whole section adopts the construction process of circular pouring; reasonably arrange the location of the unloading point and the number of operators; Step 10.2: When pouring wall concrete, the self-use height from a high place shall not exceed 2m. When the vertical height of pouring exceeds 2m, use a series of buckets or chutes to make the concrete fall, and the concrete on both sides of the door and window openings shall be evenly poured; Step 10.3, when pouring concrete, the moving distance of the vibrator should be less than 500mm. In order to combine the upper and lower layers of concrete into a whole, the vibrator should be inserted into the lower concrete by about 50mm. The pouring time interval of each layer should not be more than 2h. In addition to the upper vibration, the mold carpenter should check at any time. If there is any abnormal phenomenon, contact the upper vibrator in time and report it to the on-duty management staff to take measures to deal with it. Step 10.4, the wall concrete is poured using the "rushing slurry method", pouring the concrete about 450mm high at a time at the unloading point, and then pouring forward according to the slope and flow direction formed when the concrete flows, and vibrating as it pours; until the entire wall section is poured; the wall pouring must be vibrated twice, and the time for the second vibration to be completed must be within the initial setting time of the concrete; after the pouring is completed, the protruding steel bars should be put in place in time.

[0010] Further, in the above-mentioned high-impermeability large-volume concrete construction method, in step 10, 1) Each flow section is constructed by casting walls, columns, top plates and beams separately; 2) In order to avoid concrete quality defects such as leakage, expansion of the formwork and poor joint quality at the root of the hanging formwork, a grouting plate with a width of not less than 300mm is added at the root of the hanging formwork.

[0011] Furthermore, the above-mentioned high-impermeability large-volume concrete construction method also includes temperature control measures. After each concrete pouring, in addition to the conventional curing of ordinary concrete, the thermal insulation curing should meet the following conditions: (1) A dedicated person should be responsible for thermal insulation maintenance and test records should be kept; the duration of moisture preservation maintenance should not be less than 14 days, the integrity of the plastic film or curing agent coating should be checked frequently, and the concrete surface should be kept moist; (2) The insulation cover should be removed layer by layer. When the temperature difference between the concrete surface and the maximum ambient temperature is less than 20°C, it can be completely removed. (3) After the concrete is poured, it should be covered or sprayed for maintenance immediately before initial setting; (4) Concrete insulation materials can be plastic films, geotextiles, sacks, flame-retardant insulation blankets. If necessary, windproof insulation sheds or sunshade cooling sheds can be set up. During insulation maintenance, the temperature difference between the inside and outside of the concrete casting and the cooling rate should be monitored on site. When the measured results do not meet the temperature control index requirements, the insulation maintenance measures should be adjusted in time. (5) After the large-volume concrete formwork is removed, the underground structure should be backfilled in time, and the above-ground structure should not be exposed to the natural environment for a long time.

[0012] The above-mentioned high-impermeability large-volume concrete construction method proposed by the present invention also includes the following parts maintenance methods: 1) Raft slab and top slab: water sprinkling and moistening curing shall be started within 8-12 hours after concrete pouring, and the curing surface shall be covered with a layer of plastic film + two layers of geotextile or quilt; the curing shall adopt the water storage method, and water storage bags shall be set around the raft slab and top slab after pouring. As the concrete hydrates and releases heat, the water temperature in the water storage bags rises, and the curing can achieve the effect of warm water to avoid cracking of the concrete surface; during the laying-out period, the film shall be partially opened and implemented in small sections, and the covering shall be restored in time after the laying-out is completed; the curing time shall not be less than 14 days; 2) Frame column: Curing with formwork for 7 days, after removing the formwork, brush with water-based curing liquid and wrap with two layers of plastic film, and fix the plastic film with transparent tape, one layer every 300mm; 3) Shear wall: Curing with formwork for 7 days. After removing the formwork, use the intelligent sprinkler pipe system to carry out moisture-retaining and heat-insulating curing for 14 days. If necessary, cover the wall surface with quilts, straw mats, or geotextiles.

[0013] Furthermore, in the above-mentioned high-impermeability large-volume concrete construction method proposed by the present invention, step 11, maintenance, concrete temperature measurement and monitoring measures are also included, specifically including: Step 11.1, clarify monitoring content and early warning indicators: During the concrete pouring and curing process, the monitoring content should include monitoring time, instantaneous temperature of concrete hydration heat, internal and external temperature difference, temperature drop rate and atmospheric temperature; in, Step 11.2: When the temperature difference between the surface temperature and the center temperature of concrete after pouring, that is, the temperature difference between the inner and outer surfaces reaches 25°C or the temperature drop rate at the temperature measuring point reaches -2.0°C / day, a warning shall be issued in a written report with key marks; Step 11.3: The temperature of the concrete entering the mold should be recorded for large-volume concrete construction. The temperature of the concrete entering the mold should be measured at least twice per shift. The ambient temperature and the temperature difference between the inside and outside of the concrete measuring point should not be less than 4 times per day and night after the concrete is poured. Step 11.4, each temperature monitoring point must be arranged along the thickness direction of the concrete casting body, with the surface, bottom and center temperature measuring points, and the spacing between the other measuring points should not exceed 500mm; the surface temperature of the concrete casting body is the temperature 50mm inside the concrete surface; the bottom temperature is the temperature 50mm on the bottom surface of the concrete casting body; Step 11.5, start measuring temperature from the time concrete is put into the mold until final setting; measure temperature every 4 hours on the 1st to 4th day; measure temperature every 8 hours on the 5th to 7th day; measure temperature every 12 hours from the 7th day to the end of temperature measurement; each time the concrete temperature is measured, the rise and fall values ​​and temperature difference of each temperature measurement point should be recorded and calculated; stop measuring temperature when the difference between the surface temperature and the ambient temperature is less than 20 degrees; Step 11.6, before installing the temperature test wire, it must be immersed in water at 1m for 24 hours without damage. The temperature measuring wire joint must be installed accurately and firmly, and should be insulated from the structural steel bars and the metal body of the fixing frame. The lead wires of the temperature measuring wire should be centrally arranged and protected. The surrounding of the temperature measuring wire should also be protected. During the concrete pouring process, the temperature measuring wire and the lead wire must not be directly impacted when the material is unloaded, and the vibrator must not touch the temperature measuring element and the lead wire. Step 11.7: Dealing with large temperature differences (1) According to the construction standards for large-volume concrete, the temperature difference between the inside and outside of concrete with a thickness of ≤1500mm should not exceed 20°C. Once the temperature difference between the inside and outside is found to be close to 18°C, decisive measures should be taken (increasing the covering thickness) to ensure that the temperature difference between the inside and outside is controlled within 20°C.

[0014] (2) When the temperature difference between the inside and outside of concrete and the cooling rate exceed 1.8℃ / d, spare plastic film and geotextile should be added in time. If necessary, sacks can be purchased urgently to enhance the thermal insulation performance.

[0015] (3) When the temperature difference between the surface temperature and the atmospheric temperature is greater than 18°C, an early warning is issued. When the air temperature is too low, an iodine tungsten lamp is used to increase the atmospheric temperature. When the air temperature is too high and the concrete surface temperature is too low, the thickness of the geotextile is increased.

[0016] The crack control method and construction method of high-impermeability mass concrete proposed in the present invention have the following advantages over the prior art: 1. Improve structural safety: It effectively reduces the occurrence of cracks, enhances the integrity and stability of the concrete structure, enables it to withstand greater loads and external environmental influences, and reduces the risk of structural damage or failure due to cracks. For example, in important water conservancy projects, avoiding cracks can prevent water leakage and ensure the safe operation of the dam.

[0017] 2. Enhanced durability: Controlling cracks can reduce the intrusion of moisture, chemicals, etc., delay the deterioration of concrete, and extend the service life of the structure. For example, in projects such as underground parking lots that are in a humid environment for a long time, reducing cracks can reduce the possibility of steel corrosion.

[0018] 3. Reduce maintenance costs: As the number of cracks is reduced, the subsequent maintenance and repair work of the structure is reduced accordingly, saving a lot of manpower, material and financial resources. Taking the basement of a large commercial building as an example, reducing cracks means reducing the cost of waterproofing and structural reinforcement.

[0019] 4. Ensure waterproof performance: In projects that require waterproofing, such as underground water tanks, sewage treatment plants, etc., high-impermeability construction methods can significantly improve the waterproofing ability of concrete, avoid leakage problems, and reduce water waste and environmental pollution.

[0020] 5. Adapt to complex environment: It can better cope with complex construction environments such as temperature changes and unstable geological conditions, ensuring that the concrete structure maintains good performance under various adverse conditions.

[0021] High-performance concrete with cement-based penetrating crystallization admixtures is green and environmentally friendly due to its inorganic characteristics, which greatly reduces pollution to the environment.

[0022] Cement-based permeable crystallized high-performance concrete can not only repeatedly heal concrete cracks within 0.6mm, but also has certain improvements in improving concrete's corrosion resistance and freeze-thaw resistance, thereby improving concrete's durability and increasing building life. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The construction method of the high-impermeability large-volume concrete shown in the present invention is schematically shown. Figure 1 .

[0024] Figure 2 The construction method of the high-impermeability large-volume concrete shown in the present invention is schematically shown. Figure 2 .

[0025] Figure 3 The construction method of the high-impermeability large-volume concrete shown in the present invention is schematically shown. Figure 3 . DETAILED DESCRIPTION

[0026] The technical solutions of the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field without creative work based on the embodiments in the embodiments of the present application are within the scope of protection requested by the present application.

[0027] A crack control method for high-impermeability mass concrete, comprising: S1. Optimization of concrete internal microstructure: filling, repairing and controlling multi-scale defects from micron to macro inside concrete; taking into account the optimization of multiphase interface transition zone (ITZ), reducing the internal porosity of concrete, and weakening the microscopic siphoning effect of concrete on water molecules; S2. Material selection and optimization: A) Cementitious materials: cement with low hydration heat and low fineness is preferred to reduce the activity and hydration degree of cementitious materials and reduce the generation of hydration heat; B) Admixtures: In-depth research on the optimal blending ratio of high-performance waterproofing agents, give full play to the synergistic regulatory effect of multiple admixtures, so that the concrete's working performance, impermeability, and early crack resistance can achieve the best results; use high-efficiency water reducers to reduce water consumption, lower the water-cement ratio, and improve the compactness and impermeability of concrete; at the same time, add an appropriate amount of expansion agent to compensate for the shrinkage of concrete; C) Cement: cement with low hydration heat is preferred; D) Aggregate: Coarse aggregate should be gravel with good continuous grading and larger particle size, and fine aggregate should be medium sand; the mud content and mud block content of aggregate should be strictly controlled; S3. Quality control during construction: A) Make a 1:1 solid sample section and conduct a systematic analysis of the cracking performance of large-volume concrete, including the crack development state, ductility performance, and residual deformation index of concrete; B) Evaluate the interfacial bond strength of cracks in high-impermeability mass concrete and characterize its mechanics; C) Analyze the causes of crack resistance through simulation and solve the problem of large-volume concrete crack resistance from the aspects of material and mechanism analysis and improvement.

[0028] The crack control method for the high-impermeability large-volume concrete mentioned above, in S1, improves the performance of cement paste by using high-quality admixtures so that it can better fill the gaps between aggregate and paste, thereby optimizing ITZ; adopts a more reasonable mix ratio, reduces the amount of cement, increases mineral admixtures, and reduces the internal porosity of concrete; selects appropriate aggregate grading and particle size to reduce the interconnected pores inside the concrete, thereby weakening the microscopic siphon effect.

[0029] A high-impermeability mass concrete construction method based on the above crack control method includes: Step 1: When pouring the foundation slab concrete, the slab construction sections are constructed separately and poured in sequence; Step 2: Concrete pouring is carried out in sections with fixed points and thin layers, with a slope and circular advancement, and the pouring sequence is from low to high, starting from the lowest sump position in the order of pouring the bottom plate; Step 3: Before pouring concrete, set layered poles inside the foundation according to the thickness of the concrete layers. The poles are made of steel bars and placed at the concrete placement area with a spacing of 10m. Step 4: When pumping concrete, pour it at a natural flow slope of 1:6-1:10. The pouring thickness of each layer of concrete shall not exceed 500mm, and the upper layer of concrete shall be poured before the initial setting of the lower layer of concrete. When pouring the upper layer of concrete, it must be inserted into the lower layer of concrete by 50-100mm. At the same time, a special person shall be assigned to check to avoid cold joints. The concrete truck pump shall pour from one side of the post-casting belt backwards. Step 5: The free fall height of concrete shall not be greater than 2000mm. If it is greater than 2000mm, use a tube chute to discharge the concrete; Step 6. Strictly follow the construction sequence of the operating procedures, insert quickly and remove slowly, and arrange the insertion points evenly without omission; each concrete pump truck has 3 to 4 vibrators at the ash outlet, with 1 spare; when vibrating concrete, the moving distance of the vibrator should not be greater than 500mm, and the vibration time should be controlled between 20 and 30 seconds, which can make the concrete surface gray-yellow without bubbles; Step 7: When pouring concrete, the formwork, brackets, steel bars and reserved holes should be frequently observed. If any deformation or displacement is found, pouring should be stopped immediately; and the poured concrete should be repaired before it solidifies. Step 8, seepage treatment: At the end of concrete pouring, a sump is set outside the foundation pit, and the seepage water and slurry are made to flow into the sump through the cushion layer slope, and then the filtered seepage water is pumped out of the pit with a small submersible pump. If it is impossible to set up a sump, the seepage water can be sucked out with a sponge or a self-priming pump; when the concrete pouring is basically completed and the material is discharged, the material discharge route should be controlled well, and attention should be paid to consciously drive the seepage water to a corner of the foundation pit to facilitate the timely discharge of the seepage water; Step 9: Rub the concrete surface: Step 9.1, after the concrete is poured and vibrated, make a standard sample rod according to the 500mm line of the structure on the wall column dowel, draw the line to make it flat, make a ash cake on the bottom plate, scrape it flat according to the elevation control line with a scraper, and then use a wooden rubber to smooth it. Before the concrete surface is about to be final set, use a wooden rubber to rub it flat. During the whole operation, the elevation must be strictly controlled and accurate to ensure that the concrete surface is flat and free of cracks or other defects; Step 9.2, during the concrete pouring process, each section must be scraped flat with a scraper according to the elevation control point, then rubbed flat with a wooden rubber, and smoothed with an iron trowel. The entire pouring process requires three rounds of finishing. Before final setting, each section must be assigned a full-time worker to level and smooth. The construction workers are required to master the time of leveling and smoothing, and must strictly control the pouring height of the concrete according to the elevation control point. It is required to pour, vibrate, hang the line with a small white line, and scrape with a scraper, then use a wooden rubber to level and smooth with an iron trowel, and so on, as the basis for leveling the foundation concrete pouring until the foundation concrete pouring is completed. Step 10: Pouring and vibrating of wall concrete: Step 10.1, before pouring the wall concrete, evenly pour 30mm thick cement mortar with the same strength as the concrete at the bottom to make the new and old concretes completely combined. The wall concrete should be poured continuously, and the interval time should not exceed 2h. The pouring height of each layer should be controlled at about 500mm. The whole section adopts the construction process of circular pouring; reasonably arrange the location of the unloading point and the number of operators; Step 10.2: When pouring wall concrete, the self-use height from a high place shall not exceed 2m. When the vertical height of pouring exceeds 2m, use a series of buckets or chutes to make the concrete fall, and the concrete on both sides of the door and window openings shall be evenly poured; Step 10.3, when pouring concrete, the moving distance of the vibrator should be less than 500mm. In order to combine the upper and lower layers of concrete into a whole, the vibrator should be inserted into the lower concrete by about 50mm. The pouring time interval of each layer should not be more than 2h. In addition to the upper vibration, the mold carpenter should check at any time. If there is any abnormal phenomenon, contact the upper vibrator in time and report it to the on-duty management staff to take measures to deal with it. Step 10.4, the wall concrete is poured using the "rushing slurry method", pouring the concrete about 450mm high at a time at the unloading point, and then pouring forward according to the slope and flow direction formed when the concrete flows, and vibrating as it pours; until the entire wall section is poured; the wall pouring must be vibrated twice, and the time for the second vibration to be completed must be within the initial setting time of the concrete; after the pouring is completed, the protruding steel bars should be put in place in time.

[0030] Further, in step 10, if Figure 1 to Figure 3 As shown, 1) Each flow section is constructed by casting walls, columns, top plates and beams separately; 2) In order to avoid concrete quality defects such as leakage, expansion of the formwork and poor joint quality at the root of the hanging formwork, a grouting plate with a width of not less than 300mm is added at the root of the hanging formwork.

[0031] Furthermore, the above-mentioned high-impermeability large-volume concrete construction method also includes temperature control measures. After each concrete pouring, in addition to the conventional curing of ordinary concrete, the thermal insulation curing should meet the following conditions: (1) A dedicated person should be responsible for thermal insulation maintenance and test records should be kept; the duration of moisture preservation maintenance should not be less than 14 days, the integrity of the plastic film or curing agent coating should be checked frequently, and the concrete surface should be kept moist; (2) The insulation cover should be removed layer by layer. When the temperature difference between the concrete surface and the maximum ambient temperature is less than 20°C, it can be completely removed. (3) After the concrete is poured, it should be covered or sprayed for maintenance immediately before initial setting; (4) Concrete insulation materials can be plastic films, geotextiles, sacks, flame-retardant insulation blankets. If necessary, windproof insulation sheds or sunshade cooling sheds can be set up. During insulation maintenance, the temperature difference between the inside and outside of the concrete casting and the cooling rate should be monitored on site. When the measured results do not meet the temperature control index requirements, the insulation maintenance measures should be adjusted in time. (5) After the large-volume concrete formwork is removed, the underground structure should be backfilled in time, and the above-ground structure should not be exposed to the natural environment for a long time.

[0032] In this embodiment, the following maintenance methods are also included: 1) Raft slab and top slab: water sprinkling and moistening curing shall be started within 8-12 hours after concrete pouring, and the curing surface shall be covered with a layer of plastic film + two layers of geotextile or quilt; the curing shall adopt the water storage method, and water storage bags shall be set around the raft slab and top slab after pouring. As the concrete hydrates and releases heat, the water temperature in the water storage bags rises, and the curing can achieve the effect of warm water to avoid cracking of the concrete surface; during the laying-out period, the film shall be partially opened and implemented in small sections, and the covering shall be restored in time after the laying-out is completed; the curing time shall not be less than 14 days; 2) Frame column: Curing with formwork for 7 days, after removing the formwork, brush with water-based curing liquid and wrap with two layers of plastic film, and fix the plastic film with transparent tape, one layer every 300mm; 3) Shear wall: Curing with formwork for 7 days. After removing the formwork, use the intelligent sprinkler pipe system to carry out moisture-retaining and heat-insulating curing for 14 days. If necessary, cover the wall surface with quilts, straw mats, or geotextiles.

[0033] Furthermore, it also includes step 11, maintenance, concrete temperature measurement and monitoring measures, specifically including: Step 11.1, clarify monitoring content and early warning indicators: During the concrete pouring and curing process, the monitoring content should include monitoring time, instantaneous temperature of concrete hydration heat, internal and external temperature difference, temperature drop rate and atmospheric temperature; in, Step 11.2: When the temperature difference between the surface temperature and the center temperature of concrete after pouring, that is, the temperature difference between the inner and outer surfaces reaches 25°C or the temperature drop rate at the temperature measuring point reaches -2.0°C / day, a warning shall be issued in a written report with key marks; Step 11.3: The temperature of the concrete entering the mold should be recorded for large-volume concrete construction. The temperature of the concrete entering the mold should be measured at least twice per shift. The ambient temperature and the temperature difference between the inside and outside of the concrete measuring point should not be less than 4 times per day and night after the concrete is poured. Step 11.4, each temperature monitoring point must be arranged along the thickness direction of the concrete casting body, with the surface, bottom and center temperature measuring points, and the spacing between the other measuring points should not exceed 500mm; the surface temperature of the concrete casting body is the temperature 50mm inside the concrete surface; the bottom temperature is the temperature 50mm on the bottom surface of the concrete casting body; Step 11.5, start measuring temperature from the time concrete is put into the mold until final setting; measure temperature every 4 hours on the 1st to 4th day; measure temperature every 8 hours on the 5th to 7th day; measure temperature every 12 hours from the 7th day to the end of temperature measurement; each time the concrete temperature is measured, the rise and fall values ​​and temperature difference of each temperature measurement point should be recorded and calculated; stop measuring temperature when the difference between the surface temperature and the ambient temperature is less than 20 degrees; Step 11.6, before installing the temperature test wire, it must be immersed in water at 1m for 24 hours without damage. The temperature measuring wire joint must be installed accurately and firmly, and should be insulated from the structural steel bars and the metal body of the fixing frame. The lead wires of the temperature measuring wire should be centrally arranged and protected. The surrounding of the temperature measuring wire should also be protected. During the concrete pouring process, the temperature measuring wire and the lead wire must not be directly impacted when the material is unloaded, and the vibrator must not touch the temperature measuring element and the lead wire. Step 11.7: Dealing with large temperature differences (1) According to the construction standards for large-volume concrete, the temperature difference between the inside and outside of concrete with a thickness of ≤1500mm should not exceed 20°C. Once the temperature difference between the inside and outside is found to be close to 18°C, decisive measures should be taken (increasing the covering thickness) to ensure that the temperature difference between the inside and outside is controlled within 20°C.

[0034] (2) When the temperature difference between the inside and outside of concrete and the cooling rate exceed 1.8℃ / d, spare plastic film and geotextile should be added in time. If necessary, sacks can be purchased urgently to enhance the thermal insulation performance.

[0035] (3) When the temperature difference between the surface temperature and the atmospheric temperature is greater than 18°C, an early warning is issued. When the air temperature is too low, an iodine tungsten lamp is used to increase the atmospheric temperature. When the air temperature is too high and the concrete surface temperature is too low, the thickness of the geotextile is increased.

[0036] The above are only embodiments provided for the present application and are not intended to limit the present application. Although the present application is described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. However, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A crack control method for high-impermeability mass concrete, characterized by: include S1. Optimization of concrete internal microstructure: filling, repairing and controlling multi-scale defects from micron to macro inside concrete; taking into account the optimization of multiphase interface transition zone (ITZ), reducing the internal porosity of concrete, and weakening the microscopic siphoning effect of concrete on water molecules; S2. Material selection and optimization: A) Cementitious materials: cement with low hydration heat and low fineness is preferred to reduce the activity and hydration degree of cementitious materials and reduce the generation of hydration heat; B) Admixtures: In-depth research on the optimal blending ratio of high-performance waterproofing agents, give full play to the synergistic regulatory effect of multiple admixtures, so that the concrete's working performance, impermeability, and early crack resistance can achieve the best results; use high-efficiency water reducers to reduce water consumption, lower the water-cement ratio, and improve the compactness and impermeability of concrete; at the same time, add an appropriate amount of expansion agent to compensate for the shrinkage of concrete; C) Cement: cement with low hydration heat is preferred; D) Aggregate: Coarse aggregate should be gravel with good continuous grading and larger particle size, and fine aggregate should be medium sand; the mud content and mud block content of aggregate should be strictly controlled; S3. Quality control during construction: A) Make a 1:1 solid sample section and conduct a systematic analysis of the cracking performance of large-volume concrete, including the crack development state, ductility performance, and residual deformation index of concrete; B) Evaluate the interfacial bond strength of cracks in high-impermeability mass concrete and characterize its mechanics; C) Analyze the causes of crack resistance through simulation and solve the problem of large-volume concrete crack resistance from the aspects of material and mechanism analysis and improvement.

2. The crack control method of high-impermeability mass concrete according to claim 1 is characterized by: In S1, the performance of cement paste was improved by using high-quality admixtures, which enabled it to better fill the gaps between aggregate and paste, thereby optimizing ITZ; a more reasonable mix ratio was adopted, the amount of cement was reduced, mineral admixtures were increased, and the internal porosity of concrete was reduced; and appropriate aggregate grading and particle size were selected to reduce the interconnected pores inside the concrete, thereby weakening the microscopic siphon effect.

3. A high-impermeability mass concrete construction method based on the crack control method of claim 1 or 2, characterized in that: include Step 1: When pouring the foundation slab concrete, the slab construction sections are constructed separately and poured in sequence; Step 2: Concrete pouring is carried out in sections with fixed points and thin layers, with a slope and circular advancement, and the pouring sequence is from low to high, starting from the lowest sump position in the order of pouring the bottom plate; Step 3: Before pouring concrete, set layered poles inside the foundation according to the thickness of the concrete layers. The poles are made of steel bars and placed at the concrete placement area with a spacing of 10m. Step 4: When pumping concrete, pour it at a natural flow slope of 1:6-1:

10. The pouring thickness of each layer of concrete shall not exceed 500mm, and the upper layer of concrete shall be poured before the initial setting of the lower layer of concrete. When pouring the upper layer of concrete, it must be inserted into the lower layer of concrete by 50-100mm. At the same time, a special person shall be assigned to check to avoid cold joints. The concrete truck pump shall pour from one side of the post-casting belt backwards. Step 5: The free fall height of concrete shall not be greater than 2000mm. If it is greater than 2000mm, use a tube chute to discharge the concrete; Step 6. Strictly follow the construction sequence of the operating procedures, insert quickly and remove slowly, and arrange the insertion points evenly without omission; each concrete pump truck has 3 to 4 vibrators at the ash outlet, with 1 spare; when vibrating concrete, the moving distance of the vibrator should not be greater than 500mm, and the vibration time should be controlled between 20 and 30 seconds, which can make the concrete surface gray-yellow without bubbles; Step 7: When pouring concrete, the formwork, brackets, steel bars and reserved holes should be frequently observed. If any deformation or displacement is found, pouring should be stopped immediately; and the poured concrete should be repaired before it solidifies. Step 8, seepage treatment: At the end of concrete pouring, a sump is set outside the foundation pit, and the seepage water and slurry are made to flow into the sump through the cushion layer slope, and then the filtered seepage water is pumped out of the pit with a small submersible pump. If it is impossible to set up a sump, the seepage water can be sucked out with a sponge or a self-priming pump; when the concrete pouring is basically completed and the material is discharged, the material discharge route should be controlled well, and attention should be paid to consciously drive the seepage water to a corner of the foundation pit to facilitate the timely discharge of the seepage water; Step 9: Rub the concrete surface: Step 9.1, after the concrete is poured and vibrated, make a standard sample rod according to the 500mm line of the structure on the wall column dowel, draw the line to make it flat, make a ash cake on the bottom plate, scrape it flat according to the elevation control line with a scraper, and then use a wooden rubber to smooth it. Before the concrete surface is about to be final set, use a wooden rubber to rub it flat. During the whole operation, the elevation must be strictly controlled and accurate to ensure that the concrete surface is flat and free of cracks or other defects; Step 9.2, during the concrete pouring process, each section must be scraped flat with a scraper according to the elevation control point, then rubbed flat with a wooden rubber, and smoothed with an iron trowel. The entire pouring process requires three rounds of finishing. Before final setting, each section must be assigned a full-time worker to level and smooth. The construction workers are required to master the time of leveling and smoothing, and must strictly control the pouring height of the concrete according to the elevation control point. It is required to pour, vibrate, hang the line with a small white line, and scrape with a scraper, then use a wooden rubber to level and smooth with an iron trowel, and so on, as the basis for leveling the foundation concrete pouring until the foundation concrete pouring is completed. Step 10: Pouring and vibrating of wall concrete: Step 10.1, before pouring the wall concrete, evenly pour 30mm thick cement mortar with the same strength as the concrete at the bottom to make the new and old concretes completely combined. The wall concrete should be poured continuously, and the interval time should not exceed 2h. The pouring height of each layer should be controlled at about 500mm. The whole section adopts the construction process of circular pouring; reasonably arrange the location of the unloading point and the number of operators; Step 10.2: When pouring wall concrete, the self-use height from a high place shall not exceed 2m. When the vertical height of pouring exceeds 2m, use a series of buckets or chutes to make the concrete fall, and the concrete on both sides of the door and window openings shall be evenly poured; Step 10.3, when pouring concrete, the moving distance of the vibrator should be less than 500mm. In order to combine the upper and lower layers of concrete into a whole, the vibrator should be inserted into the lower concrete by about 50mm. The pouring time interval of each layer should not be more than 2h. In addition to the upper vibration, the mold carpenter should check at any time. If there is any abnormal phenomenon, contact the upper vibrator in time and report it to the on-duty management staff to take measures to deal with it. Step 10.4, the wall concrete is poured using the "rushing slurry method", pouring the concrete about 450mm high at a time at the discharge point, and then pouring forward according to the slope and flow direction formed when the concrete flows, and vibrating as it pours; until the entire wall is poured; the wall pouring must be vibrated twice, and the time for the second vibration to be completed must be within the initial setting time of the concrete; after the pouring is completed, the protruding steel bars must be put in place in time.

4. The high-impermeability mass concrete construction method according to claim 3 is characterized in that: In step 10, 1) Each flow section is constructed by casting walls, columns, top plates and beams separately; 2) In order to avoid concrete quality defects such as leakage, expansion of the formwork and poor joint quality at the root of the hanging formwork, a grouting plate with a width of not less than 300mm is added at the root of the hanging formwork.

5. The high-impermeability mass concrete construction method according to claim 3 is characterized by: It also includes temperature control measures. After each concrete pouring, in addition to the conventional curing of ordinary concrete, the thermal insulation curing should meet the following conditions: (1) A dedicated person should be responsible for thermal insulation maintenance and test records should be kept; the duration of moisture preservation maintenance should not be less than 14 days, the integrity of the plastic film or curing agent coating should be checked frequently, and the concrete surface should be kept moist; (2) The insulation cover should be removed layer by layer. When the temperature difference between the concrete surface and the maximum ambient temperature is less than 20°C, it can be completely removed. (3) After the concrete is poured, it should be covered or sprayed for maintenance immediately before initial setting; (4) Concrete insulation materials can be plastic films, geotextiles, sacks, flame-retardant insulation blankets. If necessary, windproof insulation sheds or sunshade cooling sheds can be set up. During insulation maintenance, the temperature difference between the inside and outside of the concrete casting and the cooling rate should be monitored on site. When the measured results do not meet the temperature control index requirements, the insulation maintenance measures should be adjusted in time. (5) After the large-volume concrete formwork is removed, the underground structure should be backfilled in time, and the above-ground structure should not be exposed to the natural environment for a long time.

6. The high-impermeability mass concrete construction method according to claim 3 is characterized by: It also includes the maintenance methods of the following parts: 1) Raft slab and top slab: water sprinkling and moistening curing shall be started within 8-12 hours after concrete pouring, and the curing surface shall be covered with a layer of plastic film + two layers of geotextile or quilt; the curing shall adopt the water storage method, and water storage bags shall be set around the raft slab and top slab after pouring. As the concrete hydrates and releases heat, the water temperature in the water storage bags rises, and the curing can achieve the effect of warm water to avoid cracking of the concrete surface; during the laying-out period, the film shall be partially opened and implemented in small sections, and the covering shall be restored in time after the laying-out is completed; the curing time shall not be less than 14 days; 2) Frame column: Curing with formwork for 7 days, after removing the formwork, brush with water-based curing liquid and wrap with two layers of plastic film, and fix the plastic film with transparent tape, one layer every 300mm; 3) Shear wall: Curing with formwork for 7 days. After removing the formwork, use the intelligent sprinkler pipe system to carry out moisture-retaining and heat-insulating curing for 14 days. If necessary, cover the wall surface with quilts, straw mats, or geotextiles.

7. The high-impermeability mass concrete construction method according to claim 3 is characterized by: It also includes step 11, maintenance, concrete temperature measurement and monitoring measures, including: Step 11.1, clarify monitoring content and early warning indicators: During the concrete pouring and curing process, the monitoring content should include monitoring time, instantaneous temperature of concrete hydration heat, internal and external temperature difference, temperature drop rate and atmospheric temperature; in, Step 11.2: When the temperature difference between the surface temperature and the center temperature of concrete after pouring, that is, the temperature difference between the inner and outer surfaces reaches 25°C or the temperature drop rate at the temperature measuring point reaches -2.0°C / day, a warning shall be issued in a written report with key marks; Step 11.3: The temperature of the concrete entering the mold should be recorded for large-volume concrete construction. The temperature of the concrete entering the mold should be measured at least twice per shift. The ambient temperature and the temperature difference between the inside and outside of the concrete measuring point should not be less than 4 times per day and night after the concrete is poured. Step 11.4, each temperature monitoring point must be arranged along the thickness direction of the concrete casting body, with the surface, bottom and center temperature measuring points, and the spacing between the other measuring points should not exceed 500mm; the surface temperature of the concrete casting body is the temperature 50mm inside the concrete surface; the bottom temperature is the temperature 50mm on the bottom surface of the concrete casting body; Step 11.5, start measuring temperature from the time concrete is put into the mold until final setting; measure temperature every 4 hours on the 1st to 4th day; measure temperature every 8 hours on the 5th to 7th day; measure temperature every 12 hours from the 7th day to the end of temperature measurement; each time the concrete temperature is measured, the rise and fall values ​​and temperature difference of each temperature measurement point should be recorded and calculated; stop measuring temperature when the difference between the surface temperature and the ambient temperature is less than 20 degrees; Step 11.6, before installing the temperature test wire, it must be immersed in water at 1m for 24 hours without damage. The temperature measuring wire joint must be installed accurately and firmly, and should be insulated from the structural steel bars and the metal body of the fixing frame. The lead wires of the temperature measuring wire should be centrally arranged and protected. The surrounding of the temperature measuring wire should also be protected. During the concrete pouring process, the temperature measuring wire and the lead wire must not be directly impacted when the material is unloaded, and the vibrator must not touch the temperature measuring element and the lead wire. Step 11.7: Dealing with large temperature differences (1) According to the construction standards for large-volume concrete, the temperature difference between the inside and outside of concrete with a thickness of ≤1500mm should not exceed 20°C. Once the temperature difference between the inside and outside is found to be close to 18°C, decisive measures should be taken (increasing the covering thickness) to ensure that the temperature difference between the inside and outside is controlled within 20°C; (2) When the temperature difference between the inside and outside of the concrete and the cooling rate exceed 1.8℃ / d, spare plastic film and geotextile should be added in time. If necessary, sacks can be purchased urgently to enhance the thermal insulation performance; (3) When the temperature difference between the surface temperature and the atmospheric temperature is greater than 18°C, an early warning is issued. When the air temperature is too low, an iodine tungsten lamp is used to increase the atmospheric temperature. When the air temperature is too high and the concrete surface temperature is too low, the thickness of the geotextile is increased.

Images