Temperature control anti-cracking structure for mass concrete of power plant and construction method

Abstract

The invention discloses a temperature control anti-cracking structure for mass concrete of a power plant and a construction method. According to the invention, the combination of the low-heat Portland cement and the composite admixture effectively reduces early hydration heat, reduces microcracks caused by thermal stress, and improves the compactness and stability of the concrete. And secondly, the compactness of the concrete is further ensured through reasonable grading of the machine-made sand and the granite macadam, and the structural integrity is enhanced. Functional additives such as a polycarboxylate superplasticizer and a magnesium oxide expanding agent not only improve the working performance of the concrete, but also offset the shrinkage stress through the delayed expansion effect, thereby effectively preventing the generation of cracks. In addition, due to the introduction of the phase change microcapsule material, the polypropylene fiber and the steel fiber, the temperature control and crack resistance of the concrete is remarkably enhanced through hydration heat absorption and double-fiber synergistic toughening.

Description

Technical Field

[0001] The present invention belongs to the technical field of anti-cracking of concrete in power plants, and specifically relates to a temperature control anti-cracking structure and construction method for mass concrete in power plants. Background Technique

[0002] The temperature control anti-cracking structure of concrete in power plants is a professional structure designed to address the problem that concrete components in power plant buildings are prone to cracking under the influence of temperature changes. This structure effectively reduces the hydration heat of concrete and reduces temperature stress by using low-heat cement, adding admixtures and fiber reinforcement, thereby preventing the generation of cracks. At the same time, the structure also includes prestress technology, reasonable reinforcement design, and thermal insulation layers to further control the temperature deformation and internal and external temperature difference of concrete, ensuring the strength and durability of concrete. This anti-cracking structure is crucial in power plant construction. It not only extends the service life of the building but also ensures the safety and stability of power plant operation. Currently, for the temperature control anti-cracking problem of mass concrete, some measures have been taken in the industry, such as using low-heat cement, adding admixtures such as fly ash and slag, and adopting layered pouring and cooling water pipes to reduce temperature.

[0003] However, these traditional methods still have many deficiencies in practical applications: The early strength development of traditional low-heat cement is relatively slow, affecting the construction progress; a single admixture is difficult to comprehensively improve the performance of concrete; existing cooling measures are difficult to accurately control the internal temperature distribution of concrete, easily leading to crack initiation due to temperature difference stress; in addition, traditional curing methods are difficult to continuously maintain the surface humidity of concrete, affecting the curing effect. Summary of the Invention

[0004] The purpose of the present invention is to provide a temperature control anti-cracking structure and construction method for mass concrete in power plants to solve the above-mentioned problems.

[0005] The technical solution adopted by the present invention is as follows: A temperature control anti-cracking structure for mass concrete in power plants, the structure includes:

[0006] Low heat Portland cement: 280 parts by weight;

[0007] Composite admixture: Class II fly ash 80 parts by weight, S95 slag powder 60 parts by weight, nano-silica 5 parts by weight;

[0008] Aggregate: Manufactured sand 700 - 800 parts by weight, granite crushed stone 1050 - 1200 parts by weight;

[0009] Functional admixture: Polycarboxylate water reducer 2.8 parts by weight, magnesium oxide expansive agent 25 parts by weight,

[0010] Temperature control enhancement components: 8 to 10 parts by weight of phase change microcapsule material, 0.9 to 1.5 parts by weight of polypropylene fiber, and 15 to 20 parts by weight of steel fiber.

[0011] In a preferred embodiment, the construction method comprises the following steps:

[0012] S1: Pre-cool the aggregate in a low-temperature warehouse 24 hours in advance to reduce the initial temperature; dry-mix the phase change microcapsule material and nano-silicon dioxide to avoid agglomeration;

[0013] S2: Rinse the inner wall of the mixer with ice water before stirring to ensure that the stirring environment temperature is ≤15℃;

[0014] S3: Add pre-cooled aggregate, low-heat cement, composite admixture, and magnesium oxide expansion agent in sequence, and dry mix for 60 seconds until uniform;

[0015] S4: Add polypropylene fiber and steel fiber alternately three times, with an interval of 15 seconds each time to ensure that the fibers are evenly distributed;

[0016] S5: Mix the water reducer and ice water and slowly inject them into the mixer, add the phase change microcapsule mixture simultaneously, and wet mix for 120 seconds until the slump reaches 180±20 mm;

[0017] S6: Layered pouring is adopted, wireless temperature sensors are buried, and internal temperature is monitored in real time;

[0018] S7: Immediately after pouring, cover with water-retaining curing film, pass circulating cooling water pipeline, control internal temperature rise ≤70℃, and internal and external temperature difference <25℃;

[0019] S8: After 72 hours, spray the silicone penetrating curing agent and continue moisturizing and curing for 28 days. Use the delayed expansion effect of magnesium oxide to offset the shrinkage stress, and the construction process of the entire temperature-controlled and crack-resistant structure can be completed.

[0020] In a preferred embodiment, in step S1, aggregate precooling needs to be completed in a closed low-temperature warehouse: temperature ≤10°C, humidity ≤50%, and the precooling time is not less than 24 hours to ensure that the core temperature of the aggregate is ≤12°C; the machine-made sand needs to be sieved to remove particles >5mm, and the surface moisture content of the crushed stone after washing is <1%; the phase change microcapsules and nano-silica are dry-mixed with a double-helix conical mixer at a speed of 30r / min for 15 minutes, and after mixing, they are sealed and stored in a cool environment with a temperature ≤25°C to avoid moisture absorption and agglomeration.

[0021] In a preferred embodiment, in step S2, a twin-horizontal-shaft forced mixer is used, and the inner wall and blades of the mixing tank are circulated and flushed with ice water with a water temperature of ≤5°C 30 minutes before feeding, and the flushing is continued for 10 minutes until the surface temperature of the tank drops below 10°C; during the mixing process, the mixer's supporting cooling system is activated to maintain the relative humidity in the mixing chamber at <70%.

[0022] In a preferred embodiment, in step S3, the feeding order is: pre-cooled aggregate → low-heat cement → fly ash + slag powder → magnesium oxide expansion agent; a staged feeding process is adopted: first 70% of the aggregate is added and mixed with all the cementitious materials for 30 seconds, and then the remaining aggregate is added and dry mixed for 30 seconds; the mixer speed is set to a low speed gear of 15r / min, and the mixing uniformity standard is that the material color is uniform and there is no cement agglomeration.

[0023] In a preferred embodiment, in step S4, polypropylene fiber and steel fiber are added alternately at a mass ratio of 1:16: 1 / 3 polypropylene fiber is added for the first time → 1 / 3 steel fiber → repeat twice with an interval of 15 seconds; the mixer is switched to a medium speed gear of 25 r / min, and the fiber feeding port needs to be set to a vibration disperser frequency of 50 Hz to avoid fiber clumping; the mixing time is controlled within 90 seconds, and the fiber distribution uniformity detection standard is that ≥20 fibers can be seen in a random sample of 1L slurry without directional aggregation.

[0024] In a preferred embodiment, in step S5, the water reducer and ice water are premixed into a solution in a ratio of 1:10, and injected three times through a pressurized atomizing nozzle with an interval of 20 seconds. The mixer is kept at a high speed of 35r / min during the whole water injection process; the phase change microcapsule mixture is added simultaneously during the second water injection, and the capsules are evenly suspended by water flow impact; the wet mixing time is accurately controlled to 120±5 seconds, the slump of the concrete out of the machine is detected by the expansion method, and the temperature monitoring requires the concrete temperature at the outlet to be ≤18°C.

[0025] In a preferred embodiment, in step S6, the layered pouring thickness is strictly limited to 50±5cm, and the interval time between layers is ≤1.5 hours; wireless temperature sensors are arranged using GPS positioning, with a vertical spacing of 50cm and a horizontal spacing of 200cm to form a three-dimensional monitoring network; during pouring, low-temperature chutes are used to transport concrete, and the pouring speed is controlled at 20-25m 3 / h.

[0026] In a preferred embodiment, in step S7, a 3 mm thick water-retaining curing film is covered, a Φ25 mm stainless steel cooling water pipe is embedded inside, 10±1°C cooling water is introduced, the flow rate is 2.5 m / s, and the single cycle time is 6 hours; the water temperature is adjusted by a PID control system to ensure that the temperature rise rate inside the concrete is ≤2°C / h, the peak temperature is ≤70°C, and the temperature drop every 24 hours is ≤3°C; a 5 cm air interlayer is set between the curing film and the concrete surface, and a micro fan is used to force ventilation to assist heat dissipation.

[0027] In a preferred embodiment, in step S8, after the surface temperature of the concrete drops to 35°C, a high-pressure airless sprayer is used to spray an organosilicon curing agent to form a 50-80 μm thick hydrophobic film, and water is sprayed for curing 3 times a day to maintain the surface humidity ≥ 95%; the free expansion rate is tested every 3 days starting from the 7th day, and the frequency of curing agent spraying is adjusted according to the monitoring data; external loads are prohibited during the 28-day curing period to ensure that the magnesium oxide expansion agent continues to generate 0.2-0.5MPa expansion compressive stress.

[0028] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0029] 1. In the present invention, the combination of low-heat silicate cement and composite admixtures effectively reduces the early hydration heat, reduces the microcracks caused by thermal stress, and improves the density and stability of concrete. Secondly, the reasonable gradation of machine-made sand and granite crushed stone further ensures the density of concrete and enhances the integrity of the structure. Functional admixtures such as polycarboxylate water reducer and magnesium oxide expansion agent not only improve the working performance of concrete, but also offset the shrinkage stress through the delayed expansion effect, effectively preventing the generation of cracks. In addition, the introduction of phase change microcapsule materials, polypropylene fibers and steel fibers significantly enhances the temperature control and crack resistance of concrete by absorbing hydration heat and double-fiber synergistic toughening.

[0030] 2. In the present invention, strict temperature control measures and sophisticated construction techniques, aggregate precooling, mixing environment control, layered pouring and real-time temperature monitoring effectively control the internal temperature rise and internal and external temperature difference of concrete, and avoid cracks caused by temperature stress. The use of water-retaining curing membrane and circulating cooling water pipeline, as well as the subsequent spraying of organosilicon penetrating curing agent, provide continuous moisturizing curing for concrete, make full use of the delayed expansion effect of magnesium oxide, and further optimize the anti-cracking effect. The scientific design and strict implementation of the entire construction process not only improve the mechanical properties and durability of concrete, but also greatly reduce the later maintenance costs and extend the service life of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the process principle of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] Embodiment 1:

[0034] Reference Figure 1 , used for temperature control and crack resistance structure of large volume concrete in power plants, the structure includes:

[0035] Low-heat silicate cement: 280 parts by weight (to reduce early hydration heat)

[0036] Composite admixture: 80 parts by weight of grade II fly ash, 60 parts by weight of grade S95 slag powder, 5 parts by weight of nano-silicon dioxide (to improve density and reduce micro cracks)

[0037] Aggregate: machine-made sand (fineness modulus 2.6): 700 parts by weight, granite crushed stone (5-25mm continuous grading): 1050 parts by weight;

[0038] Functional admixtures: polycarboxylate water reducer (slow setting type): 2.8 parts by weight, (water reduction rate ≥ 30%), magnesium oxide expansion agent (delayed): 25 parts by weight,

[0039] Temperature control reinforcement components: phase change microcapsule material (paraffin-based): 8 parts by weight, (phase change temperature 40-50°C, absorbing hydration heat), polypropylene fiber (12mm): 0.9 parts by weight, steel fiber (30mm, end hook type): 15 parts by weight, (double fiber synergistic toughening).

[0040] The construction method includes the following steps:

[0041] S1: Pre-cool the aggregate in a low-temperature warehouse (below 10°C) 24 hours in advance to reduce the initial temperature. Dry-mix the phase change microcapsule material and nano-silicon dioxide evenly to avoid agglomeration;

[0042] S2: Rinse the inner wall of the mixer with ice water before stirring to ensure that the stirring environment temperature is ≤15℃;

[0043] S3: Add pre-cooled aggregate, low-heat cement, composite admixture, and magnesium oxide expansion agent in sequence, and dry mix for 60 seconds until uniform;

[0044] S4: Add polypropylene fiber and steel fiber alternately three times, with an interval of 15 seconds each time to ensure that the fibers are evenly distributed;

[0045] S5: Mix the water reducer and ice water and slowly inject them into the mixer, add the phase change microcapsule mixture simultaneously, and wet mix for 120 seconds until the slump reaches 180±20 mm;

[0046] S6: Layered pouring (each layer ≤ 50 cm) is adopted, and wireless temperature sensors (spacing 2 m × 2 m) are buried to monitor the internal temperature in real time;

[0047] S7: Immediately after pouring, cover with water-retaining curing film, pass circulating cooling water pipeline (water temperature 10℃), control internal temperature rise ≤70℃, and internal and external temperature difference <25℃;

[0048] S8: After 72 hours, spray the silicone penetrating curing agent and continue moisturizing and curing for 28 days. Use the delayed expansion effect of magnesium oxide to offset the shrinkage stress, and the construction process of the entire temperature-controlled and crack-resistant structure can be completed.

[0049] In step S1, aggregate precooling needs to be completed in a closed low-temperature warehouse (temperature ≤10°C, humidity ≤50%), and the precooling time is not less than 24 hours to ensure that the core temperature of the aggregate is ≤12°C. Machine-made sand needs to be sieved to remove particles >5mm, and the surface moisture content of the crushed stone after washing is <1%. Phase change microcapsules (particle size 50-100μm) and nano-silicon dioxide (specific surface area ≥200m 2 / g) Use a double-screw cone mixer at 30r / min for 15 minutes, and seal and store in a cool environment (temperature ≤ 25°C) after mixing to avoid moisture absorption and agglomeration. The pretreated material must be put into use within 4 hours to prevent the temperature from rising.

[0050] In step S2, a twin-shaft forced mixer (capacity ≥ 2m 3 ), 30 minutes before feeding, use ice water (water temperature ≤ 5℃) to circulate and flush the inner wall and blades of the mixing tank, and continue for 10 minutes until the surface temperature of the tank drops below 10℃. During the mixing process, use the mixer's supporting cold air system (air supply temperature 8-12℃) to maintain the relative humidity in the mixing chamber <70%. After precooling, use an infrared thermometer to test the inner wall temperature of the mixing tank, and only feed after confirming that it meets the requirements.

[0051] In step S3, the order of feeding is: pre-cooled aggregate → low-heat cement → fly ash + slag powder → magnesium oxide expansion agent. A staged feeding process is adopted: first 70% of the aggregate is added and mixed with all the cementitious materials for 30 seconds, and then the remaining aggregate is added and dry mixed for 30 seconds. The mixer speed is set to a low speed gear (15r / min), and the mixing uniformity standard is that the material color is uniform and there is no cement agglomeration. The magnesium oxide expansion agent needs to be sieved through a 200-mesh sieve before adding to prevent uneven expansion efficiency due to agglomeration.

[0052] In step S4, polypropylene fibers (length 12±1 mm, density 0.91 g / cm 3 ) and steel fiber (end hook type, aspect ratio 60, tensile strength ≥1000MPa) are added alternately at a mass ratio of 1:16: first add 1 / 3 polypropylene fiber → 1 / 3 steel fiber → repeat twice with an interval of 15 seconds. The mixer is switched to medium speed gear (25r / min), and a vibrating disperser (frequency 50Hz) is required to be set at the fiber feeding port to avoid fiber agglomeration. The mixing time is controlled within 90 seconds, and the fiber distribution uniformity test standard is that ≥20 fibers can be seen in a random sample of 1L slurry without directional aggregation.

[0053] In step S5, the water reducer and ice water (5±1℃) are premixed into a solution at a ratio of 1:10, and injected three times through a pressurized atomizing nozzle (20 seconds apart). The mixer is kept at a high speed (35r / min) during the whole process of water injection. The phase change microcapsule mixture is added synchronously during the second water injection, and the capsules are evenly suspended by water flow impact. The wet mixing time is precisely controlled to 120±5 seconds, and the slump of the concrete out of the machine is detected by the expansion method (target value 550±30mm), and the temperature monitoring requires the concrete temperature at the outlet to be ≤18℃.

[0054] In step S6, the layered pouring thickness is strictly limited to 50±5cm, and the interval time between layers is ≤1.5 hours (shortened to 1 hour when the ambient temperature is greater than 30°C). Wireless temperature sensors (accuracy ±0.5°C) are deployed using GPS positioning, with a vertical spacing of 50cm and a horizontal spacing of 200cm to form a three-dimensional monitoring network. During pouring, a low-temperature chute (with a cooling pipe attached to the surface and a water temperature of 10°C) is used to transport concrete, and the pouring speed is controlled at 20-25m 3 / h, avoiding cooling loss.

[0055] In step S7, a 3 mm thick water-retaining curing film (water permeability ≤ 0.01 g / (m 2 h), Φ25mm stainless steel cooling water pipes (spacing 80cm×80cm) are embedded inside, and 10±1℃ cooling water is introduced with a flow rate of 2.5m / s, and a single cycle lasts for 6 hours. The water temperature is adjusted by the PID control system to ensure that the temperature rise rate inside the concrete is ≤2℃ / h, the peak temperature is ≤70℃, and the temperature drop is ≤3℃ every 24 hours. A 5cm air layer is set between the curing membrane and the concrete surface, and a micro fan is used for forced ventilation (wind speed 0.5m / s) to assist in heat dissipation.

[0056] In step S8, after the surface temperature of the concrete drops to 35°C (about 72 hours), a high-pressure airless sprayer (pressure 20MPa) is used to spray an organosilicon curing agent (solid content ≥ 40%) to form a 50-80μm thick hydrophobic film, and water is sprayed for curing 3 times a day (water temperature 25-30°C), and the surface humidity is maintained at ≥ 95%. From the 7th day onwards, the free expansion rate is tested every 3 days (target value 150-200με), and the frequency of curing agent spraying is adjusted according to the monitoring data. It is forbidden to apply external loads during the 28-day curing period to ensure that the magnesium oxide expansion agent continues to generate 0.2-0.5MPa expansion compressive stress.

[0057] In the present invention, the combination of low-heat silicate cement and composite admixtures effectively reduces the early hydration heat, reduces the microcracks caused by thermal stress, and improves the density and stability of concrete. Secondly, the reasonable gradation of machine-made sand and granite crushed stone further ensures the density of concrete and enhances the structural integrity. Functional admixtures such as polycarboxylic acid water reducer and magnesium oxide expansion agent not only improve the working performance of concrete, but also offset the shrinkage stress through the delayed expansion effect, effectively preventing the generation of cracks. In addition, the introduction of phase change microcapsule materials, polypropylene fibers and steel fibers significantly enhances the temperature control and crack resistance of concrete by absorbing hydration heat and double-fiber synergistic toughening.

[0058] In the present invention, strict temperature control measures and sophisticated construction techniques, aggregate precooling, mixing environment control, layered pouring and real-time temperature monitoring effectively control the internal temperature rise and internal and external temperature difference of concrete, and avoid cracks caused by temperature stress. The use of water-retaining curing membranes and circulating cooling water pipelines, as well as the subsequent spraying of organosilicon penetrating curing agents, provide continuous moisturizing curing for concrete, make full use of the delayed expansion effect of magnesium oxide, and further optimize the anti-cracking effect. The scientific design and strict implementation of the entire construction process not only improve the mechanical properties and durability of concrete, but also greatly reduce the later maintenance costs and extend the service life of the structure.

[0059] Embodiment 2:

[0060] Reference Figure 1 , used for temperature control and crack resistance structure of large volume concrete in power plants, the structure includes:

[0061] Low-heat silicate cement: 280 parts by weight (to reduce early hydration heat)

[0062] Composite admixture: 80 parts by weight of grade II fly ash, 60 parts by weight of grade S95 slag powder, 5 parts by weight of nano-silicon dioxide (to improve density and reduce micro cracks);

[0063] Aggregate: machine-made sand (fineness modulus 2.6): 800 parts by weight, granite crushed stone (5-25mm continuous grading): 1200 parts by weight;

[0064] Functional admixtures: polycarboxylate water reducer (slow setting type): 2.8 parts by weight, (water reduction rate ≥ 30%), magnesium oxide expansion agent (delayed): 25 parts by weight,

[0065] Temperature control reinforcement components: phase change microcapsule material (paraffin-based): 10 parts by weight, (phase change temperature 40-50°C, absorbing hydration heat), polypropylene fiber (12mm): 1.5 parts by weight, steel fiber (30mm, end hook type): 20 parts by weight, (double fiber synergistic toughening).

[0066] The construction method includes the following steps:

[0067] S1: Pre-cool the aggregate in a low-temperature warehouse (below 10°C) 24 hours in advance to reduce the initial temperature. Dry-mix the phase change microcapsule material and nano-silicon dioxide evenly to avoid agglomeration;

[0068] S2: Rinse the inner wall of the mixer with ice water before stirring to ensure that the stirring environment temperature is ≤15℃;

[0069] S3: Add pre-cooled aggregate, low-heat cement, composite admixture, and magnesium oxide expansion agent in sequence, and dry mix for 60 seconds until uniform;

[0070] S4: Add polypropylene fiber and steel fiber alternately three times, with an interval of 15 seconds each time to ensure that the fibers are evenly distributed;

[0071] S5: Mix the water reducer and ice water and slowly inject them into the mixer, add the phase change microcapsule mixture simultaneously, and wet mix for 120 seconds until the slump reaches 180±20 mm;

[0072] S6: Layered pouring (each layer ≤ 50 cm) is adopted, and wireless temperature sensors (spacing 2 m × 2 m) are buried to monitor the internal temperature in real time;

[0073] S7: Immediately after pouring, cover with water-retaining curing film, pass circulating cooling water pipeline (water temperature 10℃), control internal temperature rise ≤70℃, and internal and external temperature difference <25℃;

[0074] S8: After 72 hours, spray the silicone penetrating curing agent and continue moisturizing and curing for 28 days. Use the delayed expansion effect of magnesium oxide to offset the shrinkage stress, and the construction process of the entire temperature-controlled and crack-resistant structure can be completed.

[0075] In step S1, aggregate precooling needs to be completed in a closed low-temperature warehouse (temperature ≤10°C, humidity ≤50%), and the precooling time is not less than 24 hours to ensure that the core temperature of the aggregate is ≤12°C. Machine-made sand needs to be sieved to remove particles >5mm, and the surface moisture content of the crushed stone after washing is <1%. Phase change microcapsules (particle size 50-100μm) and nano-silicon dioxide (specific surface area ≥200m 2 / g) Use a double-screw cone mixer at 30r / min for 15 minutes, and seal and store in a cool environment (temperature ≤ 25°C) after mixing to avoid moisture absorption and agglomeration. The pretreated material must be put into use within 4 hours to prevent the temperature from rising.

[0076] In step S2, a twin-shaft forced mixer (capacity ≥ 2m 3), 30 minutes before feeding, use ice water (water temperature ≤ 5℃) to circulate and flush the inner wall and blades of the mixing tank, and continue for 10 minutes until the surface temperature of the tank drops below 10℃. During the mixing process, use the mixer's supporting cold air system (air supply temperature 8-12℃) to maintain the relative humidity in the mixing chamber <70%. After precooling, use an infrared thermometer to test the inner wall temperature of the mixing tank, and only feed after confirming that it meets the requirements.

[0077] In step S3, the order of feeding is: pre-cooled aggregate → low-heat cement → fly ash + slag powder → magnesium oxide expansion agent. A staged feeding process is adopted: first 70% of the aggregate is added and mixed with all the cementitious materials for 30 seconds, and then the remaining aggregate is added and dry mixed for 30 seconds. The mixer speed is set to a low speed gear (15r / min), and the mixing uniformity standard is that the material color is uniform and there is no cement agglomeration. The magnesium oxide expansion agent needs to be sieved through a 200-mesh sieve before adding to prevent uneven expansion efficiency due to agglomeration.

[0078] In step S4, polypropylene fibers (length 12±1 mm, density 0.91 g / cm 3 ) and steel fiber (end hook type, aspect ratio 60, tensile strength ≥1000MPa) are added alternately at a mass ratio of 1:16: first add 1 / 3 polypropylene fiber → 1 / 3 steel fiber → repeat twice with an interval of 15 seconds. The mixer is switched to medium speed gear (25r / min), and a vibrating disperser (frequency 50Hz) is required to be set at the fiber feeding port to avoid fiber agglomeration. The mixing time is controlled within 90 seconds, and the fiber distribution uniformity test standard is that ≥20 fibers can be seen in a random sample of 1L slurry without directional aggregation.

[0079] In step S5, the water reducer and ice water (5±1℃) are premixed into a solution at a ratio of 1:10, and injected three times through a pressurized atomizing nozzle (20 seconds apart). The mixer is kept at a high speed (35r / min) during the whole process of water injection. The phase change microcapsule mixture is added synchronously during the second water injection, and the capsules are evenly suspended by water flow impact. The wet mixing time is precisely controlled to 120±5 seconds, and the slump of the concrete out of the machine is detected by the expansion method (target value 550±30mm), and the temperature monitoring requires the concrete temperature at the outlet to be ≤18℃.

[0080] In step S6, the layered pouring thickness is strictly limited to 50±5cm, and the interval time between layers is ≤1.5 hours (shortened to 1 hour when the ambient temperature is greater than 30°C). Wireless temperature sensors (accuracy ±0.5°C) are deployed using GPS positioning, with a vertical spacing of 50cm and a horizontal spacing of 200cm to form a three-dimensional monitoring network. During pouring, a low-temperature chute (with a cooling pipe attached to the surface and a water temperature of 10°C) is used to transport concrete, and the pouring speed is controlled at 20-25m 3 / h, avoiding cooling loss.

[0081] In step S7, a 3 mm thick water-retaining curing film (water permeability ≤ 0.01 g / (m 2 h), Φ25mm stainless steel cooling water pipes (spacing 80cm×80cm) are embedded inside, and 10±1℃ cooling water is introduced with a flow rate of 2.5m / s, and a single cycle lasts for 6 hours. The water temperature is adjusted by the PID control system to ensure that the temperature rise rate inside the concrete is ≤2℃ / h, the peak temperature is ≤70℃, and the temperature drop is ≤3℃ every 24 hours. A 5cm air layer is set between the curing membrane and the concrete surface, and a micro fan is used for forced ventilation (wind speed 0.5m / s) to assist in heat dissipation.

[0082] In step S8, after the surface temperature of the concrete drops to 35°C (about 72 hours), a high-pressure airless sprayer (pressure 20MPa) is used to spray an organosilicon curing agent (solid content ≥ 40%) to form a 50-80μm thick hydrophobic film, and water is sprayed for curing 3 times a day (water temperature 25-30°C), and the surface humidity is maintained at ≥ 95%. From the 7th day onwards, the free expansion rate is tested every 3 days (target value 150-200με), and the frequency of curing agent spraying is adjusted according to the monitoring data. It is forbidden to apply external loads during the 28-day curing period to ensure that the magnesium oxide expansion agent continues to generate 0.2-0.5MPa expansion compressive stress.

[0083] In the present invention, the combination of low-heat silicate cement and composite admixtures effectively reduces the early hydration heat, reduces the microcracks caused by thermal stress, and improves the density and stability of concrete. Secondly, the reasonable gradation of machine-made sand and granite crushed stone further ensures the density of concrete and enhances the structural integrity. Functional admixtures such as polycarboxylic acid water reducer and magnesium oxide expansion agent not only improve the working performance of concrete, but also offset the shrinkage stress through the delayed expansion effect, effectively preventing the generation of cracks. In addition, the introduction of phase change microcapsule materials, polypropylene fibers and steel fibers significantly enhances the temperature control and crack resistance of concrete by absorbing hydration heat and double-fiber synergistic toughening.

[0084] In the present invention, strict temperature control measures and sophisticated construction techniques, aggregate precooling, mixing environment control, layered pouring and real-time temperature monitoring effectively control the internal temperature rise and internal and external temperature difference of concrete, and avoid cracks caused by temperature stress. The use of water-retaining curing membranes and circulating cooling water pipelines, as well as the subsequent spraying of organosilicon penetrating curing agents, provide continuous moisturizing curing for concrete, make full use of the delayed expansion effect of magnesium oxide, and further optimize the anti-cracking effect. The scientific design and strict implementation of the entire construction process not only improve the mechanical properties and durability of concrete, but also greatly reduce the later maintenance costs and extend the service life of the structure.

[0085] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. Temperature control and crack resistance structure for large volume concrete in power plants, characterized by: The structure comprises: Low heat Portland cement: 280 parts by weight; Composite admixture: 80 parts by weight of grade II fly ash, 60 parts by weight of grade S95 slag powder, and 5 parts by weight of nano silicon dioxide; Aggregate: 700-800 parts by weight of machine-made sand, 1050-1200 parts by weight of granite crushed stone; Functional admixture: 2.8 parts by weight of polycarboxylate water reducer, 25 parts by weight of magnesium oxide expansion agent, Temperature control enhancement components: 8 to 10 parts by weight of phase change microcapsule material, 0.9 to 1.5 parts by weight of polypropylene fiber, and 15 to 20 parts by weight of steel fiber.

2. The construction method for the temperature control and crack resistance structure of the large volume concrete of the power plant according to claim 1, characterized in that: The construction method comprises the following steps: S1: Pre-cool the aggregate in a low-temperature warehouse 24 hours in advance to reduce the initial temperature; dry-mix the phase change microcapsule material and nano-silicon dioxide to avoid agglomeration; S2: Rinse the inner wall of the mixer with ice water before stirring to ensure that the stirring environment temperature is ≤15℃; S3: Add pre-cooled aggregate, low-heat cement, composite admixture, and magnesium oxide expansion agent in sequence, and dry mix for 60 seconds until uniform; S4: Add polypropylene fiber and steel fiber alternately three times, with an interval of 15 seconds each time to ensure that the fibers are evenly distributed; S5: Mix the water reducer and ice water and slowly inject them into the mixer, add the phase change microcapsule mixture simultaneously, and wet mix for 120 seconds until the slump reaches 180±20 mm; S6: Layered pouring is adopted, wireless temperature sensors are buried, and internal temperature is monitored in real time; S7: Immediately after pouring, cover with water-retaining curing film, pass circulating cooling water pipeline, control internal temperature rise ≤70℃, and internal and external temperature difference <25℃; S8: After 72 hours, spray the silicone penetrating curing agent and continue moisturizing and curing for 28 days. Use the delayed expansion effect of magnesium oxide to offset the shrinkage stress, and the construction process of the entire temperature-controlled and crack-resistant structure can be completed.

3. The construction method for the temperature control and crack resistance structure of the large volume concrete of the power plant according to claim 1, characterized in that: In the step S1, the aggregate is pre-cooled in a closed low-temperature warehouse: temperature ≤10°C, humidity ≤50%, and the pre-cooling time is not less than 24 hours to ensure that the core temperature of the aggregate is ≤12°C; the machine-made sand is sieved to remove particles >5mm, and the surface moisture content of the crushed stone is <1% after washing; the phase change microcapsules and nano-silicon dioxide are dry-mixed with a double-helix conical mixer at a speed of 30r / min for 15 minutes, and after mixing, they are sealed and stored in a cool environment with a temperature ≤25°C to avoid moisture absorption and agglomeration.

4. The construction method for the temperature control and crack resistance structure of the large volume concrete of the power plant according to claim 1, characterized in that: In step S2, a twin-shaft forced mixer is used, and the inner wall and blades of the mixing tank are circulated and flushed with ice water with a water temperature of ≤5°C 30 minutes before feeding, and the flushing is continued for 10 minutes until the surface temperature of the tank drops below 10°C; during the mixing process, the mixer's supporting cooling system is activated to maintain the relative humidity in the mixing chamber <70%.

5. The construction method for the temperature control and crack resistance structure of the large volume concrete of the power plant according to claim 1, characterized in that: In the step S3, the feeding sequence is: pre-cooled aggregate → low-heat cement → fly ash + slag powder → magnesium oxide expansion agent; a staged feeding process is adopted: first 70% of the aggregate is added and mixed with all the cementitious materials for 30 seconds, and then the remaining aggregate is added and dry mixed for 30 seconds; the mixer speed is set to a low speed gear of 15r / min, and the mixing uniformity standard is that the material color is uniform and there is no cement agglomeration.

6. The construction method for the temperature control and crack resistance structure of the large volume concrete of the power plant according to claim 1, characterized in that: In the step S4, polypropylene fiber and steel fiber are added alternately at a mass ratio of 1:16: 1 / 3 polypropylene fiber is added for the first time → 1 / 3 steel fiber → repeat twice with an interval of 15 seconds; the mixer is switched to a medium speed gear of 25 r / min, and the fiber feeding port needs to be set with a vibration disperser frequency of 50 Hz to avoid fiber agglomeration; the mixing time is controlled within 90 seconds, and the fiber distribution uniformity detection standard is that ≥20 fibers can be seen in a random sample of 1L slurry without directional aggregation.

7. The construction method for the temperature control and crack resistance structure of the large volume concrete of the power plant according to claim 1, characterized in that: In the step S5, the water reducer and ice water are premixed into a solution in a ratio of 1:10, and injected three times through a pressurized atomizing nozzle with an interval of 20 seconds. The mixer is kept at a high gear of 35r / min during the whole water injection process; the phase change microcapsule mixture is added synchronously during the second water injection, and the capsules are evenly suspended by water flow impact; the wet mixing time is accurately controlled to 120±5 seconds, the slump of the concrete out of the machine is detected by the expansion method, and the temperature monitoring requires the concrete temperature at the outlet to be ≤18°C.

8. The construction method for the temperature-controlled anti-cracking structure of large-volume concrete in a power plant according to claim 1, characterized in that: In step S6, the layered pouring thickness is strictly limited to 50±5cm, and the interval time between layers is ≤1.5 hours; wireless temperature sensors are arranged using GPS positioning, with a vertical spacing of 50cm and a horizontal spacing of 200cm to form a three-dimensional monitoring network; during pouring, low-temperature chutes are used to transport concrete, and the pouring speed is controlled at 20-25m 3 / h.

9. The construction method for the temperature control and crack resistance structure of the large volume concrete of a power plant according to claim 1, characterized in that: In step S7, a 3 mm thick water-retaining curing film is covered, a Φ25 mm stainless steel cooling water pipe is embedded inside, 10±1°C cooling water is introduced, the flow rate is 2.5 m / s, and the single cycle time is 6 hours; the water temperature is adjusted by a PID control system to ensure that the temperature rise rate inside the concrete is ≤2°C / h, the peak temperature is ≤70°C, and the temperature drop range is ≤3°C every 24 hours; a 5 cm air interlayer is set between the curing film and the concrete surface, and a micro fan is used for forced ventilation to assist in heat dissipation.

10. The construction method for the temperature control and crack resistance structure of the large volume concrete of the power plant according to claim 1, characterized in that: In the step S8, after the surface temperature of the concrete drops to 35°C, a high-pressure airless sprayer is used to spray an organosilicon curing agent to form a 50-80 μm thick hydrophobic film, and water spraying is performed three times a day to maintain surface humidity ≥ 95%; the free expansion rate is tested every 3 days starting from the 7th day, and the frequency of curing agent spraying is adjusted according to the monitoring data; external loads are prohibited during the 28-day curing period to ensure that the magnesium oxide expansion agent continues to generate 0.2-0.5MPa expansion compressive stress.

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