Method for controlling cracks of high-performance mass concrete of super-thick and super-large bearing platform

Abstract

The invention discloses a high-performance mass concrete crack control method for an ultra-thick and ultra-large bearing platform. The method comprises the following steps of preparation before construction; performing optimization design on the concrete mix proportion by adopting a concrete mix proportion set intersection design method; concrete interior and surface temperature difference control; carrying out temperature and stress calculation on the concrete hydration heat by adopting analysis software; and concrete pouring, maintenance and formwork removal construction are conducted. The crack control method solves the technical problems that existing common mass concrete is short in setting time, many in temperature crack, poor in early-stage crack resistance and poor in durability, the existing mass concrete is single, limited, scientific and low in reliability in mix proportion design, and an existing mass concrete construction method is low in applicability. The whole construction process has the beneficial effects of simplicity and convenience in operation, short construction period, low construction cost and convenience in wide application.

Description

Technical Field

[0001] The present invention relates to the technical field of mass concrete construction, and in particular, to a method for controlling cracks in high-performance mass concrete of an ultra-thick and extra-large pile cap. Background Art

[0002] In civil engineering construction, mass concrete construction is often involved, such as projects like bridges, marine works, and hydraulic dams. The main characteristic of mass concrete is its large volume, with the minimum dimension in any direction of the smallest cross-section being 1 m.

[0003] In a cable-stayed bridge project in Shantou City, Guangdong Province, which is in a medium-high temperature area and near the ocean, the pile cap of the 7# main pier of the bridge is a dumbbell-shaped pile cap. The plane size of the pile cap is 63.0 m × 20.5 m, the height is 5.0 m, and the total pouring quantity of the pile cap concrete is 5377 m 3 , belonging to a dumbbell-shaped ultra-thick and extra-large pile cap structure. Due to the large number of designed reinforcement layers in the pile cap, the small spacing between adjacent reinforcements, and the area of the dumbbell-shaped pile cap being 1075 m 2 , the pouring time of each layer of concrete is long, and the initial setting time of the concrete is required to be 15 - 20 h to ensure that the upper-layer concrete of the pile cap can bond and join before the lower-layer concrete starts to set, without cold joints; also, due to the strict requirements for early anti-cracking, electric flux, and carbonation depth of the concrete in marine concrete projects, such as: the early anti-cracking C of the concrete is required to be 100 ≤ C < 400 (mm 2 / m 2 ), the electric flux Q S of the concrete is required to be 500 ≤ Q S < 1000 (C), and the carbonation depth d of the concrete is required to be 0.1 ≤ d < 10 (mm); also, due to the large total pouring volume of the pile cap concrete, existing mass concrete and its construction methods include:

[0004] (1) Ordinary mass concrete has a short setting time, a large amount of hydration heat, a fast internal temperature rise, a fast solidification speed, slow heat dissipation, and a large temperature difference between the inside and the surface, resulting in rapid evaporation of the concrete moisture, causing the concrete to be prone to temperature cracks, which affects the durability and service safety of the concrete structure.

[0005] (2) A construction method for high-strength mass concrete in hot seasons, as disclosed in Patent Application No. CN202410392699.4, includes the following steps: S1: Determine the concrete mix ratio; S2: Conduct finite element simulations based on the final concrete mix ratio, and determine the cooling water pipe layout plan through temperature distribution simulations and cooling effect simulations; S3: Arrange temperature detection points; S4: Pour the concrete; S5: After the concrete is poured, perform finishing, covering, and curing on the concrete. This construction method only designs the mix ratio of high-strength mass concrete from four influencing factors such as strength, heat of hydration, splitting, and shrinkage, and fails to analyze and experimentally verify from multiple influencing factors of concrete and its durability, making the design of the concrete mix ratio have singularity and limitations, lacking scientificity and reliability, and unable to reflect the dual characteristics of high performance and large volume of concrete.

[0006] (3) A crack-free mass concrete construction method, as disclosed in Patent Application No. CN202210311366.5, includes a comprehensive crack control technology for mass concrete through the mix ratio design stage by incorporating a large amount of special anti-cracking admixtures into the mass concrete; during the construction stage, on-site monitoring of the internal and surface temperature difference and cooling rate of the concrete; during the plastic stage of the concrete, taking measures such as covering with plastic film to moisturize and cure the concrete; during the temperature drop stage of the concrete, according to the measured results of the internal and surface temperature difference and cooling rate, timely taking measures such as covering with flame-retardant insulation blankets for heat preservation and curing. In this construction method, the mix ratio design of the concrete lacks experimental verification, making the mix ratio design of the concrete lack scientificity and reliability; this construction method only conducts research on the cracks of the concrete and lacks research on the durability aspects such as the electric flux and carbonation depth of the concrete; this construction method cannot be applied to bridge projects near or in a marine environment with strict requirements for the electric flux and carbonation depth of the concrete, and its applicability is not strong.

[0007] The above-mentioned mass concrete and its construction method no longer meet the construction technical requirements of the high-performance mass concrete of the dumbbell-shaped ultra-thick and extra-large cap of the 7# main pier of this bridge near the ocean. Summary of the Invention

[0008] The present invention provides a method for controlling cracks in high-performance mass concrete of ultra-thick and extra-large caps to solve the technical problems such as the short setting time, many temperature cracks, poor early crack resistance, and poor durability of existing ordinary mass concrete, the singularity and limitations, low scientificity and reliability of the mix ratio design of existing mass concrete, and the weak applicability of existing mass concrete construction methods.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A method for controlling cracks in high-performance mass concrete of a super-thick and super-large bearing platform, comprising the following steps: preparation before construction; optimizing the concrete mix ratio by using the intersection design method of concrete mix ratio sets; controlling the temperature difference between the inside and the surface of the concrete; calculating the temperature and stress of the concrete hydration heat by using analysis software; and constructing the concrete pouring, curing and form removal.

[0011] Further, the step of "optimizing the concrete mix ratio by using the intersection design method of concrete mix ratio sets" specifically includes the following steps: preparing raw materials and conducting quality inspection; trial-mixing multiple groups of trial-mixed concrete with different water-binder ratios and detecting; drawing the relationship curves between the performance indexes of the trial-mixed concrete and the water-binder ratio by using conventional software according to the detection results, establishing a polynomial fitting curve model and evaluating; obtaining multiple groups of optimized concrete mix ratios according to the current standard specification requirements of the concrete performance indexes and the corresponding polynomial fitting curve model; and calculating the adiabatic temperature rise of the concrete for each group of optimized concrete mix ratios to determine the best concrete mix ratio.

[0012] Further, the step of "trial-mixing multiple groups of trial-mixed concrete with different water-binder ratios and detecting" specifically includes the following steps: formulating the initial mix ratios of multiple groups of concrete with different water-binder ratios; trial-mixing the trial-mixed concrete corresponding to the initial mix ratio of each group of concrete by using the raw materials; and testing and detecting the performance indexes of each group of trial-mixed concrete.

[0013] Further, the step of "drawing the relationship curves between the performance indexes of the trial-mixed concrete and the water-binder ratio by using conventional software according to the detection results, establishing a polynomial fitting curve model and evaluating" specifically includes the following steps: drawing the relationship curves between the performance indexes of the trial-mixed concrete and the water-binder ratio; establishing a polynomial fitting curve model between the performance indexes of the trial-mixed concrete and the water-binder ratio to obtain the goodness of fit R 2 ; evaluating the obtained goodness of fit R 2 for evaluation.

[0014] Further, the step of "obtaining multiple groups of optimized concrete mix ratios according to the current standard specification requirements of the concrete performance indexes and the corresponding polynomial fitting curve model" specifically includes the following steps: establishing the water-binder ratio sets of each performance index according to the current standard specification requirements of the concrete performance indexes and the corresponding polynomial fitting curve model; fitting the water-binder ratio sets of all performance indexes to obtain multiple groups of optimized concrete water-binder ratios; and calculating and obtaining the corresponding optimized concrete mix ratios according to each group of optimized concrete water-binder ratios.

[0015] Further, the step of "controlling the temperature difference between the inside and the surface of the concrete" specifically includes the following steps: detecting and calculating the temperature at each stage of the concrete; arranging cooling water pipes and setting up a cooling system; and arranging a temperature control monitoring network.

[0016] Further, the step of "temperature detection and calculation at each stage of concrete" specifically includes the following steps: detecting the temperature of concrete raw materials and the temperature of the concrete mixing environment; calculating the temperature of the concrete mixture, the temperature at the outlet, the temperature during transportation to the pouring site, and the temperature when pouring is completed.

[0017] Further, the step of "layout of cooling water pipes and setting of cooling system" specifically includes the following steps: laying out the cooling water pipes; setting up the cooling system; controlling the temperature of the pile cap concrete.

[0018] Further, the step of "calculating temperature and stress of concrete hydration heat using analysis software" specifically includes the following steps: establishing a finite element calculation model of the pile cap; setting boundary conditions; calculating temperature; calculating stress.

[0019] Further, when performing the step of "concrete pouring, curing and form removal construction", the following steps can also be carried out: temperature monitoring during the pile cap pouring process, which specifically includes: setting monitoring contents, setting monitoring frequencies, feedback of monitoring results and analysis of monitoring data; after completing the step of "concrete pouring, curing and form removal construction", the following steps are also included: concrete quality inspection, which specifically includes: test detection of various performance indexes of concrete and on-site entity crack detection of the pile cap.

[0020] The present invention has the following beneficial effects:

[0021] The crack control method of the present invention: (1) Optimize the concrete mix ratio by using the intersection design method of concrete mix ratio sets to obtain the C40 high-performance mass concrete mix ratio. Compared with the traditional concrete mix ratio design method, it not only follows the scientific concrete mix ratio design principles and methods, but also ensures the reliability and scientificity of the C40 high-performance mass concrete mix ratio design through the analysis of multiple influencing factors such as sand ratio, slump, setting time, compressive strength, early crack resistance, electric flux, carbonation depth, etc. and experimental verification. Thus, in terms of the quality of concrete raw materials and mix ratio design, it effectively controls the temperature cracks of concrete, and further improves the durability and service safety of the pile cap concrete structure; (2) By controlling the temperature difference between the inside and the surface of the concrete, it effectively controls the temperature difference between the inside and the surface of the ultra-thick and extra-large pile cap high-performance mass concrete, making the cooling rate of the pile cap concrete ≤ 2.0 °C / d and the difference between the highest temperature inside the pile cap concrete and the surface temperature ≤ 20 °C, and further effectively reducing the generation of temperature cracks on the top and side surfaces of the pile cap concrete; (3) By using analysis software to calculate the temperature and stress of the concrete hydration heat, to theoretically master the development and change of the internal temperature and temperature stress of the concrete, and to evaluate the crack resistance safety of the high-performance mass concrete, potential crack problems can be discovered and processed in time to ensure the safety of the pile cap concrete structure during use. The technical solution of the present invention solves the technical problems such as the short setting time, many temperature cracks, poor early crack resistance and poor durability of the existing ordinary mass concrete, the singleness and limitation, low scientificity and reliability of the existing mass concrete mix ratio design, and the weak applicability of the existing mass concrete construction method, and has the beneficial effects of simple construction process operation, short construction period, low construction cost and being convenient for wide use.

[0022] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The following will refer to the drawings to further elaborate on the present invention in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0024] Figure 1 is the flowchart of the crack control method for the ultra-thick and extra-large pile cap high-performance mass concrete in the preferred embodiment of the present invention;

[0025] Figure 2 is the design flowchart of the intersection design method of the high-performance mass concrete mix ratio set;

[0026] Figure 3 is the curve of the relationship between the sand ratio and the water-binder ratio;

[0027] Figure 4 is the curve of the spread ratio versus the water-binder ratio;

[0028] Figure 5 is the curve of the setting time versus the water-binder ratio;

[0029] Figure 6 is the curve of the compressive strength of concrete versus the water-binder ratio;

[0030] Figure 7 is the curve of the early anti-cracking performance versus the water-binder ratio;

[0031] Figure 8 is the curve of the electric flux versus the water-binder ratio;

[0032] Figure 9 is the curve of the carbonation depth versus the water-binder ratio;

[0033] Figure 10 is the half-plan view of the cross-bridge direction of the cooling pipes in the 1st, 3rd, and 5th layers;

[0034] Figure 11 is the half-elevation view of the cross-bridge direction of the cooling pipes in the 1st, 3rd, and 5th layers;

[0035] Figure 12 is the half-plan view of the longitudinal-bridge direction of the cooling pipes in the 2nd and 4th layers;

[0036] Figure 13 is the half-elevation view of the longitudinal-bridge direction of the cooling pipes in the 2nd and 4th layers;

[0037] Figure 14 is the 1 / 4 model diagram of the bearing platform;

[0038] Figure 15 is the 1 / 4 model diagram of the layout of the cooling water pipes in the 1st, 3rd, and 5th layers of the bearing platform;

[0039] Figure 16 is the 1 / 4 model diagram of the layout of the cooling water pipes in the 2nd and 4th layers of the bearing platform;

[0040] Figure 17 is the temperature nephogram of the first concrete placement of the bearing platform;

[0041] Figure 18 is the temperature nephogram of the second concrete placement of the bearing platform;

[0042] Figure 19 is the stress nephogram of the first concrete placement of the bearing platform;

[0043] Figure 20 is the stress nephogram of the second concrete placement of the bearing platform;

[0044] Figure 21 is the schematic cross-sectional diagram of the layout of the temperature control monitoring points of the bearing platform;

[0045] Figure 22 It is a schematic plan view of the layout of temperature control monitoring points for the bearing platform.

[0046] Figure 22 It is a time - history curve of the characteristic values of the concrete temperature of the first monitoring layer (height 0.05m).

[0047] Figure 23 It is a time - history curve of the characteristic values of the concrete temperature of the second monitoring layer (height 1.5m).

[0048] Figure 24 It is a time - history curve of the characteristic values of the concrete temperature of the third monitoring layer (height 2.95m).

[0049] Figure 25 It is a time - history curve of the characteristic values of the concrete temperature of the fourth monitoring layer (height 4.00m).

[0050] Figure 26 It is a time - history curve of the characteristic values of the concrete temperature of the fifth monitoring layer (height 4.95m).

[0051] Legend:

[0052] 1. Bottom - sealed concrete; 2. Bearing platform; 201. Outline of the bearing platform; 202. Bounding line for layered pouring of the bearing platform; 3. Cooling water pipes; 301. Cooling water pipes of the first layer; 302. Cooling water pipes of the second layer; 303. Cooling water pipes of the third layer; 304. Cooling water pipes of the fourth layer; 305. Cooling water pipes of the fifth layer; 4. Temperature control monitoring points. Specific implementation mode

[0053] The following will detail the embodiments of the present invention with reference to the accompanying drawings. However, the present invention can be implemented in many different ways defined and covered by the following.

[0054] This application takes the construction of the 7# main pier bearing platform of a cable - stayed bridge in Shantou City, Guangdong Province, a medium - high temperature area, as an example to detail the method for controlling cracks in high - performance mass concrete of ultra - thick and large bearing platforms.

[0055] Refer to Figure 1 , the preferred embodiment of the present invention provides a method for controlling cracks in high - performance mass concrete of ultra - thick and large bearing platforms, including the following steps:

[0056] S1: Preparation before construction;

[0057] S2: Optimize the concrete mix design by using the concrete mix ratio set intersection design method;

[0058] S3: Control the temperature difference between the inside and the surface of the concrete;

[0059] S4: Use analysis software to calculate the temperature and stress of the concrete hydration heat;

[0060] S5: Concrete pouring, curing and form removal construction.

[0061] For the crack control method of the present invention, (1) The concrete mix ratio is optimized by using the concrete mix ratio set intersection design method to obtain the C40 high-performance mass concrete mix ratio. Compared with the traditional concrete mix ratio design method, it not only follows the scientific concrete mix ratio design principles and methods, but also through the analysis and experimental verification of multiple influencing factors such as sand ratio, slump, setting time, compressive strength, early cracking resistance, electric flux, carbonation depth, etc., to ensure the reliability and scientificity of the C40 high-performance mass concrete mix ratio design. Thus, in terms of the raw material quality and mix ratio design of concrete, the temperature cracks of concrete are effectively controlled, and further the durability and service safety of the pile cap concrete structure are improved; (2) By controlling the temperature difference between the inside and the surface of the concrete, the effective control of the temperature difference between the inside and the surface of the ultra-thick and extra-large pile cap high-performance mass concrete is realized, so that the cooling rate of the pile cap concrete ≤ 2.0 °C / d and the difference between the highest temperature inside the pile cap concrete and the surface temperature ≤ 20 °C, and further effectively reduce the generation of temperature cracks on the top and side surfaces of the pile cap concrete; (3) By using analysis software to calculate the temperature and stress of the concrete hydration heat, to theoretically master the development and change of the internal temperature and temperature stress of the concrete, and to evaluate the cracking safety of the high-performance mass concrete, potential crack problems can be discovered and processed in time to ensure the safety of the pile cap concrete structure during use. The technical solution of the present invention solves the technical problems of the existing ordinary mass concrete such as short setting time, many temperature cracks, poor early cracking resistance and poor durability, as well as the simplicity and limitation, low scientificity and reliability of the existing mass concrete mix ratio design, and the weak applicability of the existing mass concrete construction method, and has the beneficial effects of simple construction process operation, short construction period, low construction cost and convenient for wide use.

[0062] Optionally, step "S1: Preparation before construction" specifically includes:

[0063] 1. Preparation for pre-construction: According to the construction design drawings, complete the construction contents such as the cofferdam and foundation pit support of the pile cap foundation pit, excavation of foundation pit soil, removal of the pile head of the cast-in-place pile, the first layer of blinding concrete, the anchor reinforcement on the top of the cast-in-place pile, and lightning protection grounding;

[0064] 2. Installation of pile cap steel bars: On the top of the blinding concrete, complete the installation of pile cap steel bars according to the construction design drawings.

[0065] Optionally, step "S2: Optimize the concrete mix ratio by using the concrete mix ratio set intersection design method" specifically includes the following steps:

[0066] S201: Raw material preparation and quality inspection;

[0067] S202: Mix and test multiple groups of trial-mixed concrete with different water-binder ratios and conduct tests;

[0068] S203: According to the test results, use conventional software to plot the relationship curves between various performance indexes of the trial-mixed concrete and the water-binder ratio, establish a polynomial fitting curve model, and evaluate;

[0069] S204: According to the current standard specifications of various performance indexes of concrete and the corresponding polynomial fitting curve model, obtain multiple groups of optimized mix proportions of concrete;

[0070] S205: Calculate the adiabatic temperature rise of the concrete for each group of optimized mix proportions of concrete to determine the best mix proportion of concrete.

[0071] Compared with the traditional concrete mix proportion design method, the design method of the present invention not only follows the scientific principles and methods of concrete mix proportion design, but also analyzes and experimentally verifies from multiple influencing factors such as various performance indexes of the trial-mixed concrete (including sand ratio, slump flow, setting time, compressive strength, early cracking resistance, electric flux, carbonation depth), ensuring the scientificity, accuracy and reliability of the mix proportion design of high-performance mass concrete; at the same time, the design method of the present invention does not require the establishment of a complex mathematical model, and only needs to use conventional analysis software for analysis and modeling, which is simple to operate and easy to master, does not require a large amount of time, manpower and material resources, and is less affected by experimental conditions and operator levels, and has strong replicability and comparability in the mix proportion design of other types and various strength grades of concrete.

[0072] Optionally, step S201: Raw material preparation and quality inspection is specifically as follows:

[0073] High-performance mass concrete refers to a mixture made by mixing cement, fly ash, slag powder, manufactured sand, crushed stone, retarder and mixing water in a certain proportion. According to the types and specifications of the constituent materials of the determined high-performance mass concrete, prepare the constituent materials on-site at the mixing plant, stack them separately in bins according to categories and specifications, and mark and manage them to prevent rain. Conduct relevant quality index inspections on the component raw materials of high-performance mass concrete before entering the site. All inspection results must meet the requirements of relevant national and industrial construction technical specifications, product standards or technical documents before they can be used. Specifically as follows:

[0074] 1. Cement: Use China Resources P.O42.5 ordinary Portland cement; the test results are: density is 3.05 g / cm 3 , specific surface area is 346 m 2 / kg, the initial setting time is 242 min, the final setting time is 320 min, the soundness is qualified, the 28-day compressive strength is 51.4 MPa, and the 28-day flexural strength is 7.3 MPa. All inspection indicators meet the technical requirements of P.O42.5 in the "Common Portland Cement" (GB175) standard. The 3-day heat of hydration of China Resources P.O42.5 ordinary Portland cement is 240 kJ / kg, and the 7-day heat of hydration is 270 kJ / kg.

[0075] 2. Fly ash: Class I F fly ash from Datang Power Plant with stable quality and uniform incoming materials is used, and its dosage is 15% of the total mass of the cementitious materials. The test results are as follows: the density is 2.52 g / cm 3 , the fineness is 8.3%, the water demand ratio is 91%, the moisture content is 0.1%, the loss on ignition is 4.4%, and the strength activity index is 84%. Its quality meets the technical requirements of Class I fly ash in the "Fly Ash Used in Cement and Concrete" (GB / T1596) standard.

[0076] 3. Ground granulated blast-furnace slag: S95 grade powdered ground granulated blast-furnace slag is used, and its dosage is 20% of the total mass of the cementitious materials. The test results are as follows: the density is 2.93 g / cm 3 , the specific surface area is 422 m 2 / kg, the fluidity ratio is 96%, the moisture content is 0.6%, and the 7-day activity index is 89%. Its quality meets the technical requirements of S95 grade slag powder in the "Ground Granulated Blast-Furnace Slag Used in Cement, Mortar and Concrete" (GB / T18046) standard.

[0077] 4. Manufactured sand: Manufactured sand made from acid granite with hard, dense texture and high strength through multiple crushing processes is used. The test results are as follows: the fineness modulus is 2.83, belonging to medium sand, the apparent density is 2530 kg / m 3 , the bulk density is 1630 kg / m 3 , the mud content is 0%, the methylene blue MB value test is qualified, the mud lump content is 0.2%, and the single-stage maximum crushing value is 16.8%. All inspection indicators meet the technical requirements of Class II manufactured sand of medium sand in Zone 2 in the "Sand for Construction" (GB / T14684) standard.

[0078] 5. Crushed stone: Continuously graded crushed stone with a nominal particle size of 5 - 25 mm made from acid granite with hard, dense texture and high strength through multiple crushing processes is used. The test results are as follows: the particle size distribution is good, the mud content is 0.2%, the mud lump content is 0%, the content of needle-like and flaky particles is 6.8%, the crushing value is 8.6%, the apparent density is 2610 kg / m 3 , the bulk density is 1550 kg / m 3, its saturated compressive strength of the rock is 93.5 MPa, and all inspection indicators meet the technical requirements of Class II crushed stones in the Standard for Crushed Stones and Pebbles for Construction (GB / T 14685).

[0079] 6. Retarding agent: HPWR-R retarding type high-performance water reducer is adopted. It is a water-based agent with a water reduction rate of 25%. Its dosage is 3.0% of the total mass of cementitious materials, and its quality meets the technical requirements of retarding type high-performance water reducer in the Standard for Concrete Admixtures (GB8076).

[0080] 7. Mixing water: Drinking water is adopted. After inspection, its quality meets the requirements of the Standard for Water Used in Concrete (JGJ63) for water used in concrete.

[0081] Optionally, step "S202: Trial-mix trial-mix concrete with multiple different water-binder ratios and detect" specifically includes the following steps:

[0082] S2021: Propose initial mix ratios of concrete with multiple different water-binder ratios. The specific operation is as follows:

[0083] According to the provisions of Clause 6.15.9 in the Standard for Construction Technology of Highway Bridges and Culverts (JTG / T 3650-2020), the unit water consumption of high-performance concrete is controlled within 130 - 160 kg / m 3 regulation, and according to the provisions of Clause 7.5.3 in the Standard for Mix Proportion Design of Ordinary Concrete (JGJ55-2011) that the water-binder ratio shall not be greater than 0.55 and the water consumption shall not be greater than 175 kg / m 3 regulation, and also considering the water reduction rate of 25% of the HPWR-R retarding type high-performance water reducer and other factors, the unit water consumption of the concrete in this application is taken as 160 kg / m 3 , and it is proposed to conduct tests on 7 groups of initial mix ratios of C40 concrete with a water-binder ratio difference of 0.03 from each other. See Table 1 for details:

[0084] Table 1 Initial mix ratios of 7 groups of C40 concrete with different water-binder ratios (unit: kg / m 3 )

[0085]

[0086]

[0087] S2022: Use the raw materials to trial-mix the trial-mix concrete corresponding to each group of initial mix ratios of concrete;

[0088] S2023: Conduct test detections on the performance indicators of each group of trial-mix concrete. The specific operation is as follows:

[0089] For the 7 groups of C40 trial-mixed concrete with different water-binder ratios in Table 1, according to the determination methods in the "Code for Design of Mix Proportions of Ordinary Concrete" (JGJ55-2011), "Standard Test Method for Performance of Fresh Ordinary Concrete" (GB / T50080), "Standard Test Method for Physical and Mechanical Properties of Concrete" (GB / T 50081), and "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (GB / T50082), perform performance index tests on sand ratio, slump, spread, setting time (initial setting time and final setting time), compressive strength of concrete, early anti-cracking, electric flux, and carbonation depth. The test results are shown in Table 2.

[0090] Table 2 Test Results of Performance Indexes of 7 Groups of C40 Trial-Mixed Concrete with Different Water-Binder Ratios

[0091]

[0092] Optionally, step "S203: According to the test results, use conventional software to draw the relationship curves between the performance indexes of the trial-mixed concrete and the water-binder ratio, establish a polynomial fitting curve model, and evaluate" specifically includes the following steps:

[0093] S2031: Draw the relationship curves between the performance indexes of the trial-mixed concrete and the water-binder ratio. The specific operation is as follows: Take the water-binder ratio as the X-axis and the concrete performance indexes as the Y-axis, and draw the relationship curves between the sand ratio and the water-binder ratio, the spread and the water-binder ratio, the setting time and the water-binder ratio, the compressive strength of the concrete and the water-binder ratio, the early anti-cracking and the water-binder ratio, the electric flux and the water-binder ratio, and the carbonation depth and the water-binder ratio, as Figures 3 - 9 shown;

[0094] S2032: Establish a polynomial fitting curve model between the performance indexes of the trial-mixed concrete and the water-binder ratio to obtain the goodness of fit R 2 , and the specific operation is as follows:

[0095] According to the test results in Table 2, take the water-binder ratio as the X-axis and the concrete performance indexes as the Y-axis, establish polynomial fitting curve models between the sand ratio and the water-binder ratio, the spread and the water-binder ratio, the setting time and the water-binder ratio, the compressive strength of the concrete and the water-binder ratio, the early anti-cracking and the water-binder ratio, the electric flux and the water-binder ratio, and the carbonation depth and the water-binder ratio, and obtain the goodness of fit R 2 , as Figures 3 to 9 shown. Specifically as follows:

[0096] (1) Modeling steps of the polynomial fitting curve model: Based on the water-binder ratio and its corresponding sand ratio, slump, setting time (initial setting time, final setting time), concrete compressive strength (concrete 7-day compressive strength, concrete 28-day compressive strength, concrete 60-day compressive strength), early anti-cracking, electric flux, carbonation depth and other data in Table 2, use the conventional WPS Office XLSX worksheet to draw the relationship curve between various performance indicators of trial-mixed concrete and the water-binder ratio and establish a polynomial fitting curve model to obtain the goodness of fit R 2 .

[0097] The specific operations are as follows:

[0098] ① On the computer desktop, create a new XLSX file, double-click to open the newly created XLSX file, and input the X-axis data and Y-axis data that you need to statistically make into a curve. Among them: input the water-binder ratio data in Table 2 in the X-axis column, and input the sand ratio data in Table 2 in the Y-axis column.

[0099] ② Switch the upper menu bar to the "Insert" option, click on the small triangle below "Scatter Chart", and select the curve type with a smooth line. A smooth line scatter chart will pop up on the interface.

[0100] ③ In the area of the smooth line scatter chart, right-click and select the "Select Data" option. The "Edit Data Source" window will be displayed on the interface. Select "Series 1" and click "Edit". The "Edit Data Series" window will be displayed on the interface. In the "Series Name (N)", select the data name, which is "Sand Ratio" for this chart; in the "X-axis Series Values (X)", select the "Water-Binder Ratio" data in the X-axis column, and in the "Y-axis Series Values (Y)", select the "Sand Ratio" data in the Y-axis column. After clicking "OK", the "Sand Ratio" series curve can be successfully generated on the interface;

[0101] ④ Click on the lower X-axis in the area of the smooth line scatter chart, and enter the minimum value 0.30 and maximum value 0.50 of the X-axis in the "Axis Options" boundary; click on the left Y-axis in the area of the smooth line scatter chart, and enter the minimum value 37 and maximum value 45 of the Y-axis in the "Axis Options" boundary;

[0102] ⑤ In the area of the smooth line scatter chart, click the left mouse button and then click the "Chart Elements" icon. In the "Chart Elements" option, select "Axis", "Axis Title", and "Chart Title" to complete the X-axis name, Y-axis name, and smooth line scatter chart name of the smooth line scatter chart;

[0103] ⑥ In the "Trendline" option of the chart elements, select "Polynomial (P)", "Display Equation (E)", and "Display R-squared Value (R)". The "Polynomial Equation" and "Goodness of Fit R 2 value" will be displayed on the smooth line scatter chart interface.

[0104] ⑦ Select "Legend" in "Chart Elements", and then select the "Right" option, then the legends of "Sand Ratio Series Name" and "Polynomial Series Name" will be displayed on the right interface of the smooth line scatter plot. That is, the polynomial fitting curve model of sand ratio and water-binder ratio is completed.

[0105] ⑧ According to the above steps, complete in sequence: polynomial fitting curve models such as slump and water-binder ratio, setting time and water-binder ratio, concrete compressive strength and water-binder ratio, early cracking resistance and water-binder ratio, electric flux and water-binder ratio, carbonation depth and water-binder ratio.

[0106] ⑨ In the polynomial fitting curve models of setting time and water-binder ratio, and concrete compressive strength and water-binder ratio, when there are 2 or 3 series curves on one graph, the modeling steps of the polynomial fitting curve model: When drawing the polynomial fitting curve models of setting time and water-binder ratio, and concrete compressive strength and water-binder ratio, after completing the selection and determination of "Series Name (N)", "X-axis Series Value (X)", and "Y-axis Series Value (Y)" of "Initial Setting Time or Concrete 7-day Compressive Strength", click "Add (+)" in the "Edit Data Source" window, and the "Edit Data Series" window will be displayed. In the "Series Name (N)", continue to select the data name of "Final Setting Time or Concrete 28-day Compressive Strength or Concrete 60-day Compressive Strength", in the "X-axis Series Value (X)", continue to select the data of "water-binder ratio", and in the "Y-axis Series Value (Y)", continue to select the data of "Final Setting Time or Concrete 28-day Compressive Strength or Concrete 60-day Compressive Strength" in the Y-axis column. After clicking "OK", the series curve of "Final Setting Time or Concrete 28-day Compressive Strength or Concrete 60-day Compressive Strength" can be successfully generated on the interface, that is, the polynomial fitting curve model of drawing 2 or 3 series curves on one graph is completed.

[0107] (2) According to the above modeling steps of the polynomial fitting curve model, obtain: Polynomial fitting curve model of sand ratio and water-binder ratio: Polynomial formula Y = -3E -12 x 2 + 33.333x + 27.667, goodness of fit R 2 = 1; where: E refers to the base of the natural logarithm function, which is a natural constant. The natural constant E is an infinite non-repeating decimal, and its value is approximately 2.718281828459045;

[0108] (3) According to the above modeling steps of the polynomial fitting curve model, obtain: Polynomial fitting curve model of slump and water-binder ratio: Polynomial formula Y = -1865.1X 2 + 2502.8X - 184.7, goodness of fit R 2 = 0.9953;

[0109] (4) According to the modeling steps of the above polynomial fitting curve model, the following are obtained: Initial setting time and water-binder ratio polynomial fitting curve model: Polynomial formula Y = 476.19X 2 + 1476.2X + 437.19, goodness of fit R 2 = 0.9947; Final setting time and water-binder ratio polynomial fitting curve model: Polynomial formula Y = -1058.2X 2 + 2846.6X + 312.35, goodness of fit R 2 = 0.9974;

[0110] (5) According to the modeling steps of the above polynomial fitting curve model, the following are obtained: 7-day compressive strength of concrete and water-binder ratio polynomial fitting curve model: Polynomial formula Y = 137.57X 2 - 230.53X + 114.12, goodness of fit R 2 = 0.9998; 28-day compressive strength of concrete and water-binder ratio polynomial fitting curve model: Polynomial formula Y = -23.81X 2 - 92.619X + 91.857, goodness of fit R 2 = 0.9991; 60-day compressive strength of concrete and water-binder ratio polynomial fitting curve model: Polynomial formula Y = -70.106X 2 - 57.844X + 90.007, goodness of fit R 2 = 0.9974;

[0111] (6) According to the modeling steps of the above polynomial fitting curve model, the following is obtained: Early-age cracking resistance and water-binder ratio polynomial fitting curve model: Polynomial formula Y = -1375.7X 2 + 2229.1X - 314.87, goodness of fit R 2 = 0.9921;

[0112] (7) According to the modeling steps of the above polynomial fitting curve model, the following is obtained: Electric flux and water-binder ratio polynomial fitting curve model: Polynomial formula Y = -1719.6X 2 + 3123.3X - 38.275, goodness of fit R 2 = 0.9974;

[0113] (8) According to the modeling steps of the above polynomial fitting curve model, the following is obtained: Carbonation depth and water-binder ratio polynomial fitting curve model: Polynomial formula Y = 39.683X 2 + 0.873X + 1.4159, goodness of fit R 2 = 0.9979.

[0114] S2033: For the obtained goodness of fit R 2Evaluate; specifically, according to the trend line goodness of fit R of the polynomial fitting curve models such as the sand ratio and water-binder ratio, the slump and water-binder ratio, the setting time and water-binder ratio, the concrete compressive strength and water-binder ratio, the early cracking resistance and water-binder ratio, the electric flux and water-binder ratio, the carbonation depth and water-binder ratio, etc. 2 The value indicates that: all are greater than 0.99, and the closer the goodness of fit R 2 value is to 1, the better the model fitting effect, the higher the fitting degree of the trend line, and the higher the credibility. According to the above goodness of fit R 2 evaluation shows that: the initial mix designs of 7 groups of C40 concrete with different water-binder ratios have high credibility.

[0115] Optionally, step "S204: Obtain multiple groups of optimized concrete mix ratios according to the current standard specifications of various concrete performance indicators and the corresponding polynomial fitting curve models" specifically includes the following steps:

[0116] S2041: Establish a water-binder ratio set for each performance indicator according to the current standard specifications of various concrete performance indicators and the corresponding polynomial fitting curve models; that is, based on the performance indicators such as early cracking resistance, electric flux, carbonation depth, the trial mix strength of concrete 28-day compressive strength, initial setting time, slump, etc. in the current relevant standard specifications, the technical requirements for the water-binder ratio of mass concrete, and the polynomial fitting curve models of relevant performance indicators, and calculate respectively to obtain the water-binder ratio set A based on the early cracking resistance index, the water-binder ratio set B based on the electric flux index, the water-binder ratio set C based on the carbonation depth index, the water-binder ratio set D based on the trial mix strength of concrete 28-day compressive strength index, the water-binder ratio set E based on the initial setting time index, the water-binder ratio set F based on the slump index, and the water-binder ratio set G based on the water-binder ratio index of mass concrete. Specifically as follows:

[0117] 1. According to the technical requirement in the "Concrete Quality Control Standard" (GB 50164-2011) standard that the early cracking resistance L-IV level is 100 ≤ C < 400 (mm 2 / m 2 ), and the polynomial formula in the polynomial fitting curve model of the early cracking resistance and water-binder ratio, calculate to obtain: the water-binder ratio (X value) is 0.215 to 0.440, and establish the water-binder ratio set A, then A = {0.215, 0.216,..., 0.440}.

[0118] 2. According to the technical requirement in the "Concrete Quality Control Standard" (GB 50164-2011) standard that the electric flux Q-IV level is 500 ≤ Q S<1000(C), according to the technical requirement of electric flux ≤ 1000(C) in the "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T 3650 - 2020) standard and the polynomial formula in the polynomial fitting curve model of electric flux and water - binder ratio, it is calculated that: the water - binder ratio (X value) is 0.193 - 0.438, and a water - binder ratio set B is established, then B = {0.193, 0.194, …, 0.438}.

[0119] 3. According to the technical requirement of carbonation depth T - Ⅳ level of 0.1 ≤ d < 10 (mm) in the "Standard for Quality Control of Concrete" (GB 50164 - 2011) standard and the polynomial formula in the polynomial fitting curve model of carbonation depth and water - binder ratio, it is calculated that: the water - binder ratio (X value) is 0 - 0.454, and a water - binder ratio set C is established, then C = {0, 0.001, …, 0.454}.

[0120] 4. According to the technical requirement that the trial - mix strength of the 28 - day compressive strength of concrete ≥ 48.2 (MPa) in the "Code for Design of Mix Proportions of Ordinary Concrete" (JGJ 55 - 2011) standard and the polynomial formula in the polynomial fitting curve model of the 28 - day compressive strength of concrete and water - binder ratio, it is calculated that: the water - binder ratio (X value) is 0 - 0.424, and a water - binder ratio set D is established, then D = {0, 0.001, …, 0.424}.

[0121] 5. According to the technical requirement that the initial setting time required for the mass concrete construction of this bridge pier cap is 900 - 1200 (min), and the polynomial formula in the polynomial fitting curve model of the initial setting time and water - binder ratio, it is calculated that: the water - binder ratio (X value) is 0.287 - 0.451, and a water - binder ratio set E is established, then E = {0.287, 0.288, …, 0.451}.

[0122] 6. According to the technical requirement of slump flow of 450 - 550 (mm) in the "Evaluation Standard for High - Performance Concrete" (JGJ / T 385 - 2015) standard and the polynomial formula in the polynomial fitting curve model of slump flow and water - binder ratio, it is calculated that: the water - binder ratio (X value) is 0.340 - 0.433, and a water - binder ratio set F is established, then F = {0.340, 0.341, …, 0.433}.

[0123] 7. According to the requirement in Clause 7.5.3 of the "Code for Design of Mix Proportions of Ordinary Concrete" (JGJ 55 - 2011) standard that the water - binder ratio of mass concrete shall not be greater than 0.550, and a water - binder ratio set G is established, then G = {0, 0.001, …, 0.550}.

[0124] S2042: Fit the water-cement ratio sets of all performance indicators to obtain multiple sets of optimized concrete water-cement ratios. The specific operation is as follows: For water-cement ratio sets A, B, C, D, E, F, and G, use the set intersection principle to integrate the data to obtain water-cement ratio set H = {0.340, 0.341, …, 0.424}, and finally fit it into the optimized concrete water-cement ratios, with values of 0.34, 0.36, 0.38, 0.40, and 0.42.

[0125] S2043: Calculate the corresponding optimized concrete mix proportions based on each set of optimized concrete water-cement ratios. The specific operation is as follows:

[0126] Based on the above-fitted 5 sets of optimized concrete water-cement ratios, combined with the polynomial formula in the polynomial fitting curve model of sand ratio and water-cement ratio, calculate that the sand ratios are 39.00%, 39.67%, 40.33%, 41.00%, and 41.67% respectively, with values of 39%, 40%, 40%, 41%, and 42%, meeting the requirement of the sand ratio of 38% - 42% in Clause 7.5.3 of the "Code for Design of Ordinary Concrete Mix Proportions" (JGJ 55-2011) standard. Also, based on the unit water consumption of 160 kg / m³ of concrete per cubic meter, fly ash content of 15% of the total cementitious material mass, slag powder content of 20% of the total cementitious material mass, and retarder content of 3.0% of the total cementitious material mass, 5 sets of optimized mix proportions of C40 concrete with different water-cement ratios can be calculated, as shown in Table 3: 3 For details, see Table 3: 5 sets of optimized mix proportions of C40 concrete with different water-cement ratios (unit: kg / m³)

[0127] Table 3 5 sets of optimized mix proportions of C40 concrete with different water-cement ratios (unit: kg / m³) 3 )

[0128]

[0129] Optionally, the step "S205: Calculate the adiabatic temperature rise of the concrete for each set of optimized concrete mix proportions to determine the best concrete mix proportion" specifically includes the following steps:

[0130] S2051: Calculate the adiabatic temperature rise of the concrete for each set of optimized concrete mix proportions; the control value for the maximum temperature inside the concrete placement is: the temperature rise of the concrete placement based on the initial temperature ≤ 50°C and the maximum internal temperature ≤ 75°C.

[0131] The specific process is as follows:

[0132] 1. Known conditions: The specific heat capacity C of concrete is taken as 0.94 kJ / (kg·°C); the measured mass density ρ of concrete is 2390 kg / m³ 3;Based on the 3-day hydration heat of Huaren P.O42.5 ordinary Portland cement being 240 kJ / kg, the 7-day hydration heat being 270 kJ / kg, the fly ash dosage being 15% of the total cementitious material mass, the slag powder dosage being 20% of the total cementitious material mass, the cement being ordinary Portland cement with λ being 0.88, and the concrete pouring temperature being calculated according to the target control value of 28°C, calculate the total hydration heat Q of the cementitious material according to the standard calculation methods in Clauses B.1.1, B.1.2, and B.1.3 of Appendix B.1 - Adiabatic Temperature Rise of Concrete in the "Standard for Mass Concrete Construction" (GB 50496-2018); the concrete age is 60 days;

[0133] 2. Calculation method: According to the standard calculation methods in Clauses B.1.1, B.1.2, B.1.3, B.1.4, and B.1.5 of Appendix B.1 - Adiabatic Temperature Rise of Concrete in the "Standard for Mass Concrete Construction" (GB 50496-2018), calculate the adiabatic temperature rise T(t) at the age of 60 days of the concrete, and calculate according to formula (1):

[0134]

[0135] In the formula: T(t) - Adiabatic temperature rise (°C) at the age of t of the concrete;

[0136] W - Cementitious material dosage per cubic meter of concrete (kg / m 3 );

[0137] C - Specific heat capacity of concrete [kJ / (kg·°C)];

[0138] ρ - Mass density of concrete (kg / m 3 );

[0139] Q - Total hydration heat of cementitious material (kJ / kg);

[0140] t - Concrete age (d);

[0141] m - Unit mass coefficient of cementitious material related to cement variety, dosage, and pouring temperature, etc.

[0142] 3. Calculation results: After calculation, the adiabatic temperature rises at the age of 60 days of the 5 groups of optimized mix proportions of C40 concrete with different water-binder ratios are 55.3°C, 52.2°C, 49.5°C, 47.0°C, and 44.8°C respectively, as shown in Table 3.

[0143] 4. In summary, the adiabatic temperature rises of the optimized mix proportions of C40 concrete at water-binder ratios of 0.38, 0.40, and 0.42 at the age of 60 days are 49.5°C, 47.0°C, and 44.8°C respectively, all meeting the requirement in the "Code for Design of Ordinary Concrete Mix Proportions" (JGJ55-2011) and the "Standard for Mass Concrete Construction" (GB 50496-2018) that the adiabatic temperature rise of concrete should not be greater than 50°C.

[0144] S2052: Determine the best mix proportion of concrete according to the requirements of current standards and specifications and the actual working requirements of concrete. That is, according to Tables 1 - 3 and the requirement in Clause 6.15.9 of the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T 3650-2020) that "for the concrete of general components exposed to the air, the dosage of fly ash should preferably not be greater than 20%, and the dosage of Portland cement in the cementitious materials per cubic meter of concrete should preferably not be less than 240 kg", and considering the workability, strength, durability, and economy of concrete comprehensively, the best mix proportion of C40 high-performance mass concrete is determined as: cement: fly ash: slag powder: manufactured sand: crushed stone: retarder-type high-performance water reducer: mixing water = 260:60:80:745:1073:12.00:160 (unit: kg / m 3 ).

[0145] Optionally, the step "S3: Control of the temperature difference between the inside and the surface of the concrete" specifically includes the following steps:

[0146] S301: Temperature detection and calculation at each stage of the concrete;

[0147] S302: Layout of cooling water pipes and setting of the cooling system;

[0148] S303: Layout of the temperature control monitoring network.

[0149] In this optional solution, the step "S301: Temperature detection and calculation at each stage of the concrete" specifically includes the following steps:

[0150] S3011: Detection of the temperature of concrete raw materials and the temperature of the concrete mixing environment; Specifically, according to the plan in the construction plan of the No. 7 main pier cap, the cap concrete is constructed during October - November 2024. The concrete is commercial concrete, and the target control of the concrete pouring temperature is ≤28°C. The transportation time t1 of the concrete from the mixing plant to the construction site and the waiting time is 1.0 h, the conveying time t2 of the concrete in the pump pipe is 0.1 h, the number of rotations n of the concrete mixture is 2 times, the specific heat capacity C C of the concrete is 0.94 kJ / (kg·K), and the measured mass density ρ C of the concrete is 2390 kg / m 3 . During the actual construction process, the outdoor ambient temperature Ta is 29°C (see the ambient temperature of 25±4°C for the first concrete pouring of the pile cap in October 2024 in Table 4 below), and the temperature T in the mixer shed P is 25°C; the measured temperature of cement and slag powder is 45°C, the measured temperature of fly ash is 40°C, the measured temperatures of manufactured sand, crushed stone, and retarder are 25°C, the temperature of mixing water is 8°C, and the temperature of flake ice is -4°C; the moisture content of manufactured sand is 2.2%, and the moisture content of crushed stone is 1.5%.

[0151] S3012: The calculation of the temperature T0 of the concrete mixture, the discharge temperature T1, the temperature T2 at the pouring site after transportation, and the temperature T3 at the completion of pouring is as follows:

[0152] (1) Temperature of the concrete mixture

[0153] 1) Calculation formula. Calculate the temperature T0 of the concrete mixture according to Appendix A of the "Code for Winter Construction of Building Engineering" (JGJ / T 104 - 2011) standard. The calculation formula is as follows:

[0154]

[0155] In the formula:

[0156] T0 - Temperature of the concrete mixture (°C);

[0157] T ce - Temperature of cement (°C);

[0158] T s - Temperature of admixture (°C);

[0159] T sa - Temperature of sand (°C);

[0160] T g - Temperature of gravel (°C);

[0161] T w - Temperature of water (°C);

[0162] m ce - Cement dosage (kg);

[0163] m s - Admixture dosage (kg);

[0164] m sa - Sand dosage (kg);

[0165] m g - Gravel dosage (kg);

[0166] m w - Mixing water dosage (kg);

[0167] ω sa - Water content rate of sand (%);

[0168] ω g - Water content rate of gravel (%);

[0169] C w - Specific heat capacity of water [kJ / (kg·K)];

[0170] C i - Heat of fusion of ice (kJ / kg); When the aggregate temperature is greater than 0°C: C w = 4.2, C i = 0; When the aggregate temperature is less than or

[0171] equal to 0°C: C w = 2.1, C i = 335.

[0172] 2) Calculation result. Substitute the raw material dosage and raw material temperature parameters in the optimal mix proportion of C40 high-performance mass concrete into formula (2) for calculation, and the temperature T0 of the concrete mixture is obtained as 24.3°C.

[0173] (2) Temperature of the concrete mixture out of the mixer

[0174] 1) Calculation formula. Calculate the temperature T1 of the concrete mixture out of the mixer according to Appendix A of the "Code for Winter Construction of Building Engineering" (JGJ / T 104 - 2011) standard. The calculation formula is as follows:

[0175] T1 = T0 - 0.16(T0 - T P ) (3)

[0176] In the formula:

[0177] T1 - Temperature of the concrete mixture out of the mixer (°C);

[0178] T P - Temperature in the mixer shed (°C).

[0179] 2) Calculation result. Substitute the temperature T0 of the concrete mixture and the temperature T P parameter in the mixer shed into formula (3) for calculation. The temperature T1 of the concrete mixture out of the mixer is 24.4°C, and the difference from the temperature T0 of the concrete mixture is not significant. It can be considered that T1≈T0.

[0180] (3) Temperature of the concrete mixture during transportation and delivery to the pouring site

[0181] 1) Calculation formula. The concrete mixture is transported by a concrete mixer truck and the concrete is conveyed by a pump pipe. The temperature of the concrete in the pump pipe is 25.6°C, where: D lThe inner diameter of the pump pipe is 0.15 m, and the outer diameter of the pump pipe (including the outer insulation material) D W is 0.17 m, and the thickness d of the outer insulation layer of the pump pipe b is 0.01 m. The outer insulation material of the pump pipe is extruded polystyrene board, and its thermal conductivity λ b is 0.04 W / (m·K) 。 According to Appendix A of the "Code for Winter Construction of Building Engineering" (JGJ / T 104-2011) standard, calculate the temperature T2 of the concrete mixture during transportation and delivery to the pouring site. The calculation formula is as follows:

[0182] T2 = T1 - ΔT y -ΔT b (4)

[0183] ΔT y =(α×t1 + 0.032n)×(T1 - T a ) (5)

[0184]

[0185] In the formula:

[0186] T2 - The temperature of the concrete mixture when transported to the pouring site (°C);

[0187] ΔT y - The temperature drop (°C) when transporting concrete using a detachable transportation tool;

[0188] ΔT b - The temperature drop (°C) when transporting concrete using a pump pipe;

[0189] ΔT1 - The temperature difference between the concrete in the pump pipe and the ambient air temperature (°C);

[0190] T a - The outdoor ambient air temperature (°C);

[0191] t1 - The transportation time of the concrete mixture (h);

[0192] t2 - The transportation time of the concrete in the pump pipe (h);

[0193] n - The number of revolutions of the concrete mixture;

[0194] C C - The specific heat capacity of the concrete [kJ / (kg·K)];

[0195] ρ C - The mass density of the concrete (kg / m 3 );

[0196] λ b- Thermal conductivity of the thermal insulation material outside the pump pipe [W / (m·K)];

[0197] d b - Thickness of the thermal insulation layer outside the pump pipe (m);

[0198] D l - Inner diameter of the concrete pump pipe (m);

[0199] D W - Outer diameter of the concrete pump pipe (including the outer thermal insulation material) (m);

[0200] ω - Ventilation coefficient, which is taken according to Table A.2.2 - 2 of the "Code for Winter Construction of Building Engineering" (JGJ / T 104 - 2011), and the value of ω is 1.5;

[0201] α - Temperature loss coefficient (h -1 )), when using a concrete mixer truck: the value of α is 0.25.

[0202] 2) Calculation results. Substitute the above - related parameters into Formulas (4) to (6) for calculation. The temperature T2 of the concrete mixture during transportation and delivery to the pouring site is 25.9 °C, which is less than the target control value of the concrete pouring temperature of 28 °C, meeting the requirements.

[0203] (4) Temperature at the completion of concrete pouring

[0204] 1) Calculation formula. The outdoor ambient temperature T a during concrete pouring is 29 °C, the specific heat capacity C C of the concrete is 0.94 kJ / (kg·K), the formwork uses bamboo plywood formwork, and its specific heat capacity C f is 0.16 kJ / (kg·K), the specific heat capacity C δ of the steel bars is 0.46 kJ / (kg·K), the weight m C of per cubic meter of concrete is 2390 kg, the weight m f of the formwork in contact with per cubic meter of concrete is 2.09 kg, and the weight m δ of the steel bars in contact with per cubic meter of concrete is 130 kg. Considering the heat absorption effect of the bamboo plywood formwork and the steel bars, calculate the temperature T3 at the completion of concrete pouring according to Appendix A of the "Code for Winter Construction of Building Engineering" (JGJ / T 104 - 2011). The calculation formula is as follows:

[0205]

[0206] In the formula:

[0207] T3 - Temperature at the completion of concrete pouring (°C);

[0208] C C- Specific heat capacity of concrete [kJ / (kg·K)];

[0209] C f - Specific heat capacity of formwork [kJ / (kg·K)];

[0210] C δ - Specific heat capacity of steel bars [kJ / (kg·K)];

[0211] m C - Weight of concrete per cubic meter (kg);

[0212] m f - Weight of formwork in contact with concrete per cubic meter (kg);

[0213] m δ - Weight of steel bars in contact with concrete per cubic meter (kg);

[0214] T f - Temperature of formwork (°C), when not preheated, the ambient temperature at that time can be adopted, take 29°C;

[0215] T δ - Temperature of steel bars (°C), when not preheated, the ambient temperature at that time can be adopted, take 29°C.

[0216] 2) Calculation results. Substitute the above relevant parameters into formula (7) for calculation. The temperature T3 at the completion of concrete pouring is 26.0°C, which is less than the target control value of the concrete pouring temperature of 28°C, meeting the requirements.

[0217] In this alternative solution, through the control of 7 aspects including the temperature of concrete raw materials, the ambient temperature of concrete mixing, the temperature of concrete mixture, the temperature of concrete mixture leaving the mixer, the temperature of concrete mixture during transportation and delivery to the pouring site, the temperature at the completion of concrete pouring, and the temperature of pile cap concrete, the effective control of the temperature difference between the inside and the surface of high-performance mass concrete for ultra-thick and extra-large pile caps is realized, so that the temperature reduction rate of pile cap concrete ≤ 2.0°C / d and the difference between the highest temperature inside the pile cap concrete and the surface temperature ≤ 20°C, thereby effectively reducing the generation of temperature cracks on the top and side surfaces of pile cap concrete.

[0218] Step "S302: Layout of cooling water pipes and setting of cooling system" specifically includes the following steps:

[0219] S3021: Layout of cooling water pipes; The specific operation is as follows:

[0220] (1) Layout of cooling water pipes in the construction design drawings: According to the construction design drawings of the bearing platform of the 7# main pier of the bridge, five layers of horizontal cooling water pipes 3 are arranged in the bearing platform 2 in a "longitudinal and transverse staggered" manner. Among them, the first layer of cooling water pipes 301, the third layer of cooling water pipes 303, and the fifth layer of cooling water pipes 305 are arranged in the cross-bridge direction, and the second layer of cooling water pipes 302 and the fourth layer of cooling water pipes 304 are arranged in the longitudinal-bridge direction. After installation, the first layer of cooling water pipes 301 is 0.5 m away from the bottom surface of the bearing platform 2 (i.e., the top surface of the bottom-sealing concrete 1), the fifth layer of cooling water pipes 305 is 0.5 m away from the top surface of the bearing platform 2, the vertical distance between each layer of cooling water pipes 3 is 1.0 m, and the horizontal distance is 1.0 m, as Figures 10 to 13 shown.

[0221] (2) Layout of cooling water pipes in the construction plan by grading, layering, and longitudinal and transverse staggering: According to the construction plan of the bearing platform of the 7# main pier of the bridge, the concrete of the bearing platform 2 is poured in two times, 3.0 m + 2.0 m. In the first concrete of the bearing platform 2, three layers of horizontal cooling water pipes 3 are arranged in the bearing platform 2 in a "longitudinal and transverse staggered" manner. The first layer of cooling water pipes 301 and the third layer of cooling water pipes 303 are arranged in the cross-bridge direction, and the second layer of cooling water pipes 302 is arranged in the longitudinal-bridge direction. Among them, the first layer of cooling water pipes 301 is 0.5 m away from the bottom surface of the first concrete of the bearing platform 2 (i.e., the top surface of the bottom-sealing concrete 1), the third layer of cooling water pipes 303 is 0.5 m away from the top surface of the first concrete of the bearing platform 2 (i.e., the layer-casting boundary 202 of the bearing platform), the vertical distance between each layer of cooling water pipes 3 is 1.0 m, and the horizontal distance is 1.0 m; in the second concrete of the bearing platform 2, two layers of horizontal cooling water pipes 3 are arranged in the bearing platform 2 in a "longitudinal and transverse staggered" manner. The fourth layer of cooling water pipes 304 is arranged in the longitudinal-bridge direction, and the fifth layer of cooling water pipes 305 is arranged in the cross-bridge direction. Among them, the fourth layer of cooling water pipes 304 is 0.5 m away from the top surface of the first concrete of the bearing platform 2 (i.e., the layer-casting boundary 202 of the bearing platform), the fifth layer of cooling water pipes 305 is 0.5 m away from the top surface of the second concrete of the bearing platform 2 (i.e., the top surface of the bearing platform 2), the vertical distance between each layer of cooling water pipes 3 is 1.0 m, and the horizontal distance is 1.0 m. It realizes the uniform temperature reduction of the concrete inside the ultra-thick and large bearing platform, and reduces the temperature cracks generated by the local excessive temperature difference between the inside and the surface of the bearing platform concrete.

[0222] S3022: Cooling system setup; specifically, the cooling water pipe 3 is made of a steel pipe with a diameter of Φ42.25mm × 3.25mm. Each set of cooling water pipes 3 on each floor is centrally branched out by a water distributor. The water distributor is provided with a corresponding number of independent water valves to control the cooling water flow rate of each set of cooling water pipes 3, and a certain number of pressure reducing valves are provided upstream of the water distributor to control the water passing rate of the water distributor in the later stage. Each water distributor corresponds to a water pump. The connection between the cooling water pipes 3 is made by means of threaded screw + raw tape connection. The suspended part of the cooling water pipe 3 must be welded with vertical steel bars for fixation. Before concrete pouring, the cooling water pipe 3 must be subjected to a pressurized water passing test for no less than 30 minutes to check whether the water flow rate is appropriate. If it is found that the cooling water pipe 3 is cracked or the joint leaks or blocks water, it must be repaired in time until it can work normally.

[0223] S3023: Temperature control of the bearing platform concrete, specifically set as follows:

[0224] 1. Inlet water temperature and flow control

[0225] The cooling water uses recycled fresh water: In the initial stage of the temperature rise of the bearing platform 2 concrete, external circulation is adopted, that is, the cooling water outlet is directly discharged and fresh water is continuously supplemented to cool the bearing platform 2 concrete to the greatest extent; after the temperature difference between the internal temperature of the bearing platform 2 concrete and the inlet water temperature reaches 20°C, it is changed to internal circulation, that is, the cooling water outlet returns to the circulation water tank. Fresh water is supplemented as needed, and on the premise of fully cooling the bearing platform 2 concrete, the inlet water temperature is avoided from being too low to cause cold shock to the bearing platform 2 concrete; after the temperature peak of the bearing platform 2 concrete, according to the temperature monitoring results, control the temperature difference between the cooling water inlet temperature and the highest internal temperature of the bearing platform 2 concrete to be less than 20°C, and adjust the cooling water flow rate through an independent water valve to control the cooling rate of the bearing platform 2 concrete: ≤4.0°C / d within 7 days (168 hours) of age, and ≤3.0°C / d after 7 days (168 hours) of age (concrete temperature control plan).

[0226] 2. Requirements for water passing and stopping of the cooling water pipe

[0227] (1) Starting water passing time and temperature rise period requirements: After the bearing platform 2 concrete covers each layer of the cooling water pipe 3, the cooling water pipe 3 starts to pass water immediately. The cooling water temperature is 15°C, the water flow rate ≥ 3m 3 / h, the water flow velocity ≥ 0.6m / s, the water passing time is 15 days, and the temperature difference between the outlet water and the inlet water ≤ 10°C; during the temperature rise stage of the bearing platform 2 concrete, the cooling water uses seasonal normal temperature water or deep river water.

[0228] (2) Water passing time and requirements during the temperature drop period: According to the temperature monitoring results, reduce the water flow rate to ensure that the cooling rate of the bearing platform 2 concrete is within the temperature control standard of 3.0°C / d, and the temperature difference between the inlet and outlet ≤ 10°C; after the temperature peak of the bearing platform 2 concrete, the cooling water should preferably use recycled cooling water.

[0229] (3) Water cut-off time requirement: It is necessary to ensure simultaneously that the temperature drop rate of the concrete in Cap 2 ≤ 2.0 °C / d and the difference between the maximum internal temperature and the surface temperature of the concrete in Cap 2 ≤ 20 °C, then the water supply can be stopped.

[0230] 3. Plugging of the cooling water pipe orifices

[0231] After the cooling water in the cooling water pipe 3 stops circulating and the curing of the concrete in Cap 2 is completed, the orifices of the cooling water pipe 3 shall be grouted and plugged in a timely manner. First, use an air compressor to pump out and dry the residual water pressure in the cooling water pipe 3, and then use a grouting machine to inject micro-expansion cement slurry with the same strength as the concrete in Cap 2 into the cooling water pipe 3 to seal the pipeline of the cooling water pipe 3.

[0232] S303: Layout of the temperature control monitoring network, the specific operation is as follows:

[0233] 1. Selection of instruments and equipment

[0234] The temperature control monitoring system for the mass concrete of the 7# main pier Cap 2 consists of a collection system and temperature sensors. The collection system is mainly responsible for real-time online transmission, and the temperature sensors are buried in the mass concrete of Cap 2 to collect the internal temperature of the concrete; the temperature monitoring equipment adopts a multi-channel temperature collection system (SZDQ-WT16) with a resolution of 0.1 °C; the temperature sensors are thermistor sensors (SZWT-18G) with a resolution of 0.25 °C; the large concrete temperature measurement sensors have a resolution of 0.1 °C. The temperature sensors are fixed to the steel bars by tying and buried in the mass concrete.

[0235] 2. Layout of the temperature control monitoring points

[0236] The layout of the temperature control monitoring points in a T-shape in sub-layers and sub-levels of 1 / 4 of the cap can not only scientifically reflect the hydration heat process of the ultra-thick and large-cap concrete, can be compared and analyzed with the theoretical calculation at any time, adjust the parameter values and correct the calculation model in a timely manner, and take corresponding temperature control measures to ensure that the temperature stress of the cap concrete does not exceed the tensile strength of the concrete and avoid the occurrence of temperature cracks, but also reduce the waste of temperature monitoring elements and lower the construction monitoring cost.

[0237] The temperature control monitoring points 4 are operated by professional technical personnel according to the characteristics of the mass concrete of Cap 2. To protect the wires and measuring points from the influence of concrete vibration, equal-angle steel 35×3mm is used for protection. The temperature control monitoring points 4 are arranged on the left or right half of the cross-bridge direction of Cap 2. Five layers of horizontal temperature control monitoring points 4 are arranged in the height direction of Cap 2, with 14 temperature control monitoring points 4 arranged in each layer, totaling 70 temperature control monitoring points 4. Also according to the construction plan of Cap 2, Cap 2 is divided into two pouring constructions of 3.0m + 2.0m, and the temperature control monitoring points 4 of Cap 2 are also divided into two layouts. Taking the layout of the temperature control monitoring points 4 on the right half of Cap 2 as an example, as Figure 21, Figure 22 as shown below:

[0238] (1) Layout of the first temperature control monitoring points 4 for the 7# main pier cap 2. Three layers of horizontal temperature control monitoring points 4 are arranged in the first concrete of the 7# main pier cap 2, with 14 temperature control monitoring points 4 arranged in each layer, for a total of 42 temperature control monitoring points 4. Among them: in the height direction of the pier cap 2, the first layer of temperature control monitoring points 4 is 0.05 m away from the bottom surface of the first concrete of the pier cap 2 (i.e., the top surface of the bottom seal concrete 1), the second layer of temperature control monitoring points 4 is 1.5 m away from the bottom surface of the first concrete of the pier cap 2 (i.e., the top surface of the bottom seal concrete 1), and the third layer of temperature control monitoring points 4 is 2.95 m away from the bottom surface of the first concrete of the pier cap 2 (i.e., the top surface of the bottom seal concrete 1); in the cross-bridge direction plane of the 7# main pier cap 2, 14 temperature control monitoring points 4 are arranged in each layer.

[0239] (2) Layout of the second temperature control monitoring points 4 for the 7# main pier cap 2. Two layers of horizontal temperature control monitoring points 4 are arranged in the second concrete of the 7# main pier cap 2, with 14 temperature control monitoring points 4 arranged in each layer, for a total of 28 temperature control monitoring points 4. Among them: in the height direction of the pier cap 2, the fourth layer of temperature control monitoring points 4 is 4.00 m away from the bottom surface of the first concrete of the pier cap 2 (i.e., the top surface of the bottom seal concrete 1), and the fifth layer of temperature control monitoring points 4 is 4.95 m away from the bottom surface of the first concrete of the pier cap 2 (i.e., the fifth layer of temperature control monitoring points is 0.05 m away from the top surface of the pier cap 2); in the cross-bridge direction plane of the 7# main pier cap 2, 14 temperature control monitoring points 4 are arranged in each layer.

[0240] (3) Layout of each layer of temperature control monitoring points 4. In the cross-bridge direction plane of the 7# main pier cap 2, 14 temperature control monitoring points 4 are arranged in each layer, as Figure 22 shown below:

[0241] 1) Cross-bridge direction temperature control monitoring line. Starting from the center point of the 7# main pier cap 2 plane and extending along the cross-bridge direction of the pier cap 2 to the right edge range of the pier cap 2, 9 temperature control monitoring points 4 are arranged to form a cross-bridge direction temperature control monitoring line, and they are numbered in sequence as: WKJCD1, WKJCD2, WKJCD3, WKJCD4, WKJCD5, WKJCD6, WKJCD7, WKJCD8, WKJCD9. Among them: the horizontal distance between WKJCD1 and WKJCD2 is 7 m, the horizontal distance between WKJCD2 and WKJCD3 is 6 m, the horizontal distance between WKJCD3 and WKJCD4 is 6 m, the horizontal distance between WKJCD4 and WKJCD5 is 5 m, the horizontal distance between WKJCD5 and WKJCD6 is 4 m, the horizontal distance between WKJCD6 and WKJCD7 is 2 m, the horizontal distance between WKJCD7 and WKJCD8 is 1 m, the horizontal distance between WKJCD8 and WKJCD9 is 0.45 m, and the horizontal distance between WKJCD9 and the right edge of the pier cap 2 is 0.05 m.

[0242] 2) Temperature control monitoring line along the bridge axis. Starting from the point numbered WKJCD4 on the plane of the 7# main pier cap 2 and extending along the bridge axis direction of the cap 2 to the rear edge range of the cap 2, 5 temperature control monitoring points 4 are arranged to form a temperature control monitoring line along the bridge axis, and they are numbered in sequence as: WKJCD10, WKJCD11, WKJCD12, WKJCD13, WKJCD14. Among them: the horizontal distance between WKJCD4 and WKJCD10 is 3.75m, the horizontal distance between WKJCD10 and WKJCD11 is 3m, the horizontal distance between WKJCD11 and WKJCD12 is 2m, the horizontal distance between WKJCD12 and WKJCD13 is 1m, the horizontal distance between WKJCD13 and WKJCD14 is 0.45m, and the horizontal distance between WKJCD14 and the rear edge of the cap 2 is 0.05m.

[0243] 3) Angle between the transverse and longitudinal bridge axis temperature control monitoring lines. The transverse bridge axis temperature control monitoring line and the longitudinal bridge axis temperature control monitoring line are arranged, forming a 90° angle on the plane of the cap 2, presenting a T-shaped configuration.

[0244] Optionally, step "S4: Use analysis software to calculate the temperature and stress of the concrete hydration heat" specifically includes the following steps:

[0245] S401: Establish a finite element calculation model for the cap; the specific operation is as follows:

[0246] Using finite element analysis software, with the component dimensions, boundary conditions, and layered pouring conditions as model parameters, and then according to the symmetry of the cap 2, take 1 / 4 of the cap 2 (i.e., 1 / 2 of the symmetry axis) for theoretical calculation, establish a 1 / 4 model of the cap 2 and a 1 / 4 model of the cooling water pipe 3 layout, as Figures 14 to 16 shown, calculate the temperature and stress of the C40 high-performance mass concrete hydration heat of the cap 2. The model parameters of the cap 2 are as follows:

[0247] 1) Component dimensions: The plane of the cap 2 is composed of two rectangular round-ended caps + connected by a crossbeam. The plane contour dimensions of the cap 2 are 20.5m (transverse bridge axis) × 20.5m (longitudinal bridge axis), the thickness of the cap 2 is 5m, the width of the crossbeam of the cap 2 is 12m and the thickness is 5m, and the overall plane contour dimensions of the cap 2 and the crossbeam are 63m (transverse bridge axis) × 20.5m (longitudinal bridge axis).

[0248] 2) Boundary conditions: Constrained by the C25 bottom-sealing concrete 1 with a thickness of 0.8m.

[0249] 3) Layered pouring conditions: The concrete of the cap 2 is poured in two layers of 3.0m + 2.0m.

[0250] S402: Set boundary conditions, specifically as follows:

[0251] According to the average high and low temperature data in the same period in Shantou City, Guangdong Province, combined with the construction plan in the construction plan of the main pier cap of Bridge No. 7, the pouring temperature, ambient temperature and boundary conditions of the concrete of Pier Cap 2 are shown in Table 4.

[0252] Table 4 Predicted pouring time and pouring temperature of mass concrete of pier cap

[0253] Component Formwork material Curing condition Expected pouring time Ambient temperature Temperature at the time of placing into the form First concrete for the pile cap Bamboo plywood formwork Water storage on the upper surface, formwork on the sides October 25±4℃ 28℃ Second concrete for the pile cap Bamboo plywood formwork Water storage on the upper surface, formwork on the sides November 25±2℃ 28℃

[0254] Among them:

[0255] 1) Pouring temperature: The construction date of the first layer of concrete of Pier Cap 2 is in October 2024, and the construction date of the second layer of concrete of the pier cap is in November 2024. The pouring temperature of the concrete of Pier Cap 2 is considered to be 28°C.

[0256] 2) Ambient temperature: The air temperature value when the first layer of concrete of Pier Cap 2 is constructed in October 2024 is 25±4°C, and the air temperature value when the second layer of concrete of the pier cap is constructed in November 2024 is 25±2°C.

[0257] 3) Formwork material: According to the calculation of the surface insulation layer thickness of the mass concrete pouring body in Appendix C of the "Standard for Mass Concrete Construction" (GB 50496-2018):

[0258] During construction, the wind speed is taken as 0.5 m / s, the heat transfer coefficient of the smooth surface in the air is 28.646 W / (m 2 ·K); the heat transfer coefficient of the rough surface in the air is 31.322 W / (m 2 ·K).

[0259] For the side of Pier Cap 2: Bamboo plywood formwork with a thickness of 0.015 m is used, which has lower thermal conductivity and better heat insulation performance. The thermal conductivity of the bamboo plywood formwork is 0.09 W / (m·K), and the heat transfer coefficient is 6.00 kW / (m 2 ·K).

[0260] Water storage on the rough surface during layered pouring: The water storage depth is 0.10 m, the thermal conductivity of water is 0.58 W / (m·K), and the heat transfer coefficient is 5.80 kW / (m 2 ·K).

[0261] Water storage on the smooth surface during layered pouring: The water storage depth is 0.10 m, the thermal conductivity of water is 0.58 W / (m·K), and the heat transfer coefficient is 10.26 kW / (m 2 ·K).

[0262] 4) Cooling water pipes: According to the construction design drawing of the 7# main pier cap of the bridge, five layers of horizontal cooling water pipes 3 are arranged in the form of "longitudinal and transverse intersection" in the pier cap 2, where: the first layer of cooling water pipes 301, the third layer of cooling water pipes 303, and the fifth layer of cooling water pipes 305 are arranged in the cross-bridge direction, and the second layer of cooling water pipes 302 and the fourth layer of cooling water pipes 304 are arranged in the longitudinal-bridge direction. After installation, the first layer of cooling water pipes 301 is 0.5 m away from the bottom surface of the pier cap 2 (i.e., the top surface of the bottom-sealing concrete 1), the fifth layer of cooling water pipes 305 is 0.5 m away from the top surface of the pier cap 2, the vertical spacing between each layer of cooling water pipes 3 is 1.0 m, and the horizontal spacing is 1.0 m, as Figures 10 to 13 shown.

[0263] 5) Cooling water: The specific heat of the cooling water is 4.186 kJ / (kg·°C), and the density is 10 kN / m 3 . The cooling water pipes 3 are made of Φ42.25 mm × 3.25 mm steel pipes. The temperature of the cooling water is 15 °C, the water flow velocity ≥ 0.6 m / s, the water flow rate ≥ 3 m 3 / h, the convection coefficient is 1372 kJ / (m 2 ·h·°C), and the water passing time is 15 d.

[0264] S403: Temperature calculation; specifically as follows:

[0265] 1) Establish the temperature nephograms at 24 h, 48 h, 72 h, and 168 h after the first concrete pouring of the pier cap 2 for temperature calculation, as Figure 17 shown.

[0266] 2) Establish the temperature nephograms at 24 h, 48 h, 72 h, and 168 h after the second concrete pouring of the pier cap 2 for temperature calculation, as Figure 18 shown.

[0267] 3) The calculation results of the concrete temperature of the pier cap 2 are shown in Table 5.

[0268] Table 5 Calculation Results of Pier Cap Concrete Temperature

[0269]

[0270] 4) It can be concluded from the calculation results in Table 5 that the temperature rise (°C) and the maximum internal and surface temperature difference (°C) of the C40 high-performance mass concrete both meet the requirements specified in the "Standard for Mass Concrete Construction" (GB50496-2018).

[0271] S404: Stress calculation, the specific operation is as follows:

[0272] 1) Establish the stress nephograms at 72 h and 168 h after the first concrete pouring of the pier cap 2 for stress calculation, as Figure 19as shown

[0273] 2) After the second concrete pouring of the bearing platform 2 is completed, stress nephograms at 72h and 168h are established for stress calculation, as Figure 20 shown

[0274] 3) The calculation results of the concrete stress of the bearing platform 2 are shown in Table 6 as follows.

[0275] Table 6 Calculation Results of the Concrete Stress of the Bearing Platform

[0276]

[0277] 4) It can be obtained from the calculation results in Table 6 that the anti-cracking safety factors of C40 high-performance mass concrete at 3d and 7d are both greater than 1.15, meeting the requirements specified in Appendix B of the "Construction Standard for Mass Concrete" (GB 50496-2018).

[0278] In this alternative solution, by using finite element analysis software and taking the component size, restraint conditions, and layered pouring conditions as model parameters, a 1 / 4 model of the bearing platform 1 and a 1 / 4 model of the cooling water pipe layout are established to calculate the temperature stress of the hydration heat of C40 high-performance mass concrete, theoretically master the development and change of the internal temperature and temperature stress of the concrete, and evaluate the anti-cracking safety of the high-performance mass concrete, so as to timely discover and handle potential crack problems, ensure the safety of the bearing platform concrete structure during use; extend the service life of the bearing platform concrete structure; help ensure the flatness and beauty of the bearing platform concrete surface and improve the overall quality of the bridge; monitor and control the errors in the production process of the bearing platform concrete, eliminate the quality problems caused by non-standard production of the bearing platform concrete, improve the production level and ensure the stable and reliable quality of the bearing platform concrete products; the evaluation results of the anti-cracking safety of the high-performance mass concrete, as an important basis for engineering quality control, help the construction unit and the supervision unit to timely discover and solve quality problems and ensure that the overall quality of the bridge project meets the standards.

[0279] Optionally, step "S5: Concrete Pouring, Curing and Form Removal Construction" specifically includes the following steps:

[0280] S501: Concrete Pouring Construction

[0281] 1. Preparation before pouring: After the installation quality of the steel bars of the 7# main pier bearing platform, the steel bars and embedded parts of the tower base and tower column, and the formwork have been inspected and accepted as qualified, the C40 high-performance mass concrete of the 7# main pier bearing platform can be poured.

[0282] 2. The concrete is poured in batches and sections.

[0283] The batch pouring is as follows: In the height direction of the bearing platform 2, the mass concrete is divided into two pouring constructions of 3.0m + 2.0m, specifically as follows:

[0284] (1) Pouring the first layer of concrete with a height of 3.0 m for the 7# main pier cap. When pouring the first layer of concrete with a height of 3.0 m for the cap on the top surface of the bottom-sealing concrete, the mass concrete is divided into 10 layers for continuous pouring, with a layer thickness of 0.3 m. Before pouring, thoroughly clean the sundries within the scope of the cap, and sprinkle water to moisten the top surface of the bottom-sealing concrete, the steel bars of the cap, the steel bars and embedded parts of the tower base and tower column, and the formwork, to prevent the first layer of concrete of the cap from absorbing the water in the first layer of concrete due to the excessive dryness of the formwork and the bottom-sealing concrete during the pouring process, reduce the water loss of the first layer of concrete, and avoid the appearance of dry shrinkage cracks on the concrete surface. During pouring, the measured concrete slump is 165 - 180 mm, the spread is 455 - 530 mm, the pouring temperature into the formwork is 24.9 - 27.8 °C, and the free fall height is 1.8 m. Complete the pouring of the upper layer of concrete before the initial setting of the lower layer of concrete, and so on. Before the initial setting of the 10th layer of concrete, chisel the top surface to make it rough and uneven, increasing the surface roughness of the concrete, which is beneficial to the bonding between the second layer of concrete of the cap and the first layer of concrete of the cap, and increasing the bonding strength between the first and second layers of concrete of the cap.

[0285] (2) Pouring the second layer of concrete with a height of 2.0 m for the 7# main pier cap. When pouring the second layer of concrete with a height of 2.0 m for the cap on the top surface of the first layer of concrete of the cap, the mass concrete is divided into 7 layers for continuous pouring, with a layer thickness of 0.3 m. Before pouring, thoroughly clean the sundries within the scope of the cap, and sprinkle water to moisten the top surface of the first layer of concrete of the cap, the steel bars of the cap, the steel bars and embedded parts of the tower base and tower column, and the formwork, to prevent the second layer of concrete of the cap from absorbing the water in the second layer of concrete due to the excessive dryness of the formwork and the first layer of concrete of the cap during the pouring process, reduce the water loss of the second layer of concrete, and avoid the appearance of dry shrinkage cracks on the concrete surface. During pouring, the measured concrete slump is 160 - 175 mm, the spread is 450 - 505 mm, the pouring temperature into the formwork is 20.8 - 27.9 °C, and the free fall height is 1.6 m. Complete the pouring of the upper layer of concrete before the initial setting of the lower layer of concrete, and so on. Before the initial setting of the 7th layer of concrete, trowel and finish the top surface, and chisel the top surface of the concrete at the tower base and tower column to make it rough and uneven, increasing the surface roughness of the concrete, which is beneficial to the bonding between the tower base concrete and the cap concrete, and increasing the bonding strength between the tower base concrete and the cap concrete.

[0286] (3) The interval period between the two pourings of the 7# main pier cap. The interval time between the first and second pourings of the 7# main pier cap does not exceed 7 days.

[0287] The segmented pouring is as follows: on the plane of the 2nd cross-bridge direction of the 7# main pier cap, the mass concrete is divided into 3 sections for pouring. At the construction site, 3 concrete pump trucks are used to pump concrete to the pouring location in sections. The pouring sequence of the concrete of the 2nd pier cap is from the middle to both sides and from the upstream to the downstream, and the layered thickness is strictly controlled, with the layered thickness being 0.3m.

[0288] 3. Concrete vibration: For each layer of concrete placement in the front, a vibrating rod is used to follow up and vibrate in the back. The vibration spacing is controlled at 60 - 70cm. When vibrating, the vibrating rod should be inserted into the concrete. When vibrating the upper and lower layers of concrete, the vibrating rod should be inserted 5 - 10cm into the lower layer of concrete. Each vibration must be fast inserted and slowly pulled out until the concrete at that place no longer subsides, the bubbles no longer emerge, and the surface shows bleeding. In particular, strengthen the vibration of the concrete in the areas where the steel bars of the tower base and tower column are dense to prevent the concrete from being under-vibrated, resulting in loose and non-compact concrete and low strength at the tower base and tower column.

[0289] 4. Concrete inspection and specimen making: When the first and second concrete pourings of the 2nd pier cap of the 7# main pier are carried out, a certain amount of concrete mixture is respectively sampled at the on-site pouring location for slump, spread, and setting time detection, and compressive strength, early anti-cracking, electric flux, and carbonation depth specimens of the concrete are made according to the specified frequencies in the "Concrete Quality Control Standard" (GB50164), "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650), and "Standard for Mass Concrete Construction" (GB50496), and are cured under standard conditions until the specified age.

[0290] In this optional plan, through the two-time pouring construction of 3.0m + 2.0m for the mass concrete of the 2nd pier cap, the effective control of the temperature difference between the inside and the surface of the mass concrete of the 2nd pier cap ≤ 25°C, the temperature difference between the concrete surface and the air temperature ≤ 20°C, and the peak temperature is realized; through the curing with water stored in the formwork, both the temperature and humidity of the layered pouring surface and the top surface of the concrete of the 2nd pier cap are guaranteed, and the temperature of the side surface of the concrete of the 2nd pier cap is also guaranteed, effectively reducing the generation of temperature cracks on the top and side surfaces of the concrete of the 2nd pier cap.

[0291] S502: Concrete curing and form removal

[0292] 1. Concrete curing, the specific operation is as follows:

[0293] (1) The first concrete curing of the 2nd pier cap of the 7# main pier. After the strength of the 10th layer of concrete reaches 2.5MPa, cure with water stored in the formwork, using the hot water circulated from the cooling water pipes, and the water storage depth is not less than 0.1m. The curing period with water stored in the formwork is not less than 5 days.

[0294] (2) Curing of the second batch of concrete for the main pier cap 2 of Pier 7. Before the initial setting of the 7th layer of concrete, finish troweling and covering with plastic film simultaneously. After the strength reaches 2.5 MPa, cure with water stored in the formwork, using the hot water circulated by the cooling water pipes. The water storage depth shall not be less than 0.1 m. The curing period with water stored in the formwork shall not be less than 5 days.

[0295] (3) Curing after form removal. After the first form removal of the pier cap 2, backfill the cavity between the concrete of the pier cap 2 and the steel sheet piles of the foundation pit with cohesive soil in layers, with each layer having a thickness of 300 mm and a compactness of ≥ 90%, which is beneficial to the side insulation of the first batch of concrete of the pier cap 2. After the second form removal of the pier cap 2, cover the top surface of the concrete of the pier cap 2 with geotextile for heat and moisture preservation curing for not less than 7 days. Backfill the cavity between the concrete of the pier cap 2 and the steel sheet piles of the foundation pit with cohesive soil in layers, with each layer having a thickness of 300 mm and a compactness of ≥ 90%, which is beneficial to the side insulation of the second batch of concrete of the pier cap 2.

[0296] Through the heat preservation curing of the concrete of the pier cap 2, the temperature difference between the inside and surface of the concrete is reduced; through the moisture preservation curing of the concrete of the pier cap 2, the surface stress caused by concrete shrinkage is reduced. Curing with water stored in the formwork can not only ensure the temperature and humidity of the layered pouring surface and the top surface of the concrete of the pier cap 2, but also ensure the temperature of the side surface of the concrete of the pier cap 2. During the curing process of the concrete of the pier cap 2, according to the monitoring results of the internal temperature, surface temperature and air temperature of the concrete and the environmental changes, adjust the curing method in a timely manner to control the temperature difference between the inside and surface of the concrete ≤ 25 °C, the temperature difference between the concrete surface and the air temperature ≤ 20 °C, and the temperature difference between the curing water temperature and the concrete surface temperature ≤ 15 °C. At the same time, during the entire curing period and the cooling process of the concrete of the pier cap 2, take measures to protect the concrete from moisture loss.

[0297] 2. Form removal time. The form removal time of the concrete of the main pier cap 2 of Pier 7 is controlled by both concrete age and measured temperature:

[0298] (1) The form can be removed 5 days after the concrete pouring of the pier cap 2 is completed. Do not loosen or remove the form within 5 days.

[0299] (2) When the temperature difference between the inside and surface of the concrete of the pier cap 2 < 20 °C and the temperature difference between the concrete surface and the air temperature < 20 °C, the form can be removed. The form removal time is selected during a period of relatively high air temperature in a day, avoiding form removal at night or during a sudden drop in air temperature. Take measures such as removing the form, covering and backfilling simultaneously for heat and moisture preservation curing.

[0300] Optionally, when performing step "S5: Concrete pouring, curing and form removal construction", step S6: Temperature monitoring during the pier cap pouring can also be carried out, which specifically includes: monitoring content setting, monitoring frequency setting, monitoring result feedback and monitoring data analysis, as follows:

[0301] 1. Monitoring content setting:

[0302] The main contents of temperature monitoring include: ① Measurement of the concrete temperature field; ② Measurement of the environmental system temperature. Among them: The temperature field of concrete refers to the actual temperature and temperature distribution of the cast concrete at each part under the influence of various on-site environmental factors. Measuring the environmental system temperature means monitoring the air temperature. While monitoring the temperature change of concrete, the air temperature, the concrete pouring temperature, the inlet and outlet temperatures of the cooling pipes, etc. should also be monitored.

[0303] 2. Monitoring frequency setting, the requirements during the temperature monitoring are as follows:

[0304] (1) Measurement of the concrete temperature field: During the concrete pouring process, the temperature is measured once every 2 hours; after the concrete is poured until the hydration heat temperature rise stage, it is measured once every 2 hours; in the first week of the hydration heat temperature drop stage, it is measured once every 4 hours, and after one week, the typical temperature change periods of the air temperature are selected for measurement every day, and the measurement is carried out 2 - 4 times a day.

[0305] (2) Measurement of the environmental system temperature: Synchronously observed with the concrete temperature.

[0306] (3) In special cases, such as during cold snaps, the measurement frequency is appropriately increased.

[0307] (4) After all the concrete is poured, according to the predicted calculation results of the temperature field and stress field, combined with the comparative analysis of the monitoring results, the termination time of measurement is determined.

[0308] 3. Feedback of monitoring results

[0309] (1) The monitoring data of the temperature characteristic values of the first - time concrete of the No. 7 main pier cap 2 are shown in Table 7.

[0310] Table 7 Monitoring data of the temperature characteristic values of the first - time concrete of the No. 7 main pier cap

[0311]

[0312] From Table 7 and Figures 23 to 25 Analysis shows that: After the first - time concrete pouring of the No. 7 main pier cap 2:

[0313] 1) The highest internal temperatures of the concrete in the first, second, and third layers are 54.75 °C, 65.75 °C, and 58.25 °C respectively, meeting the control standard in the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T 3650 - 2020) that the highest internal temperature of concrete does not exceed 75 °C;

[0314] 2) The maximum temperature differences between the inside and the surface of the concrete in the first, second, and third layers are 15.50 °C, 23.75 °C, and 19.75 °C respectively, meeting the temperature control standard in the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T 3650 - 2020) that the temperature difference between the inside and the surface of concrete does not exceed 25 °C;

[0315] 3) The maximum temperature differences between the surfaces of the first, second, and third layers of concrete and the air temperature are 19.40°C, 19.75°C, and 16.00°C respectively, meeting the temperature control standard in the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T 3650 - 2020) that the temperature difference between the inside and the surface of the concrete should not be greater than 20°C.

[0316] 4) After the temperature peak, the cooling rates of the center point of the first layer of concrete are 1.25 - 1.75°C / d during 27 - 168 h and 0.50 - 1.25°C / d during 168 - 205 h; the cooling rates of the center point of the second layer of concrete are 2.25 - 3.75°C / d during 29 - 168 h and 1.00 - 2.25°C / d during 168 - 205 h; the cooling rates of the center point of the third layer of concrete are 2.25 - 3.75°C / d during 28 - 168 h and 0.50 - 2.25°C / d during 168 - 205 h, all meeting the control standard in the concrete temperature control plan that the cooling rate of the concrete should be ≤ 4.0°C / d within 7 days (168 h) of age and ≤ 3.0°C / d after 7 days (168 h) of age.

[0317] (2) The monitoring data of the temperature characteristic values of the second - time concrete of the 7# main pier cap 2 are shown in Table 8.

[0318] Table 8 Monitoring data of the temperature characteristic values of the second - time concrete of the 7# main pier cap

[0319]

[0320] From Table 8 and Figures 26 to 27 Analysis shows that after the second - time concrete pouring of the 7# main pier cap 2:

[0321] 1) The maximum internal temperatures of the fourth and fifth layers of concrete are 60.25°C and 56.00°C respectively, meeting the control standard in the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T 3650 - 2020) that the maximum internal temperature of the concrete should not be higher than 75°C.

[0322] 2) The maximum temperature differences between the inside and the surface of the concrete are 24.75°C and 19.25°C respectively, meeting the temperature control standard in the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T 3650 - 2020) that the temperature difference between the inside and the surface of the concrete should not be greater than 25°C.

[0323] 3) The maximum temperature differences between the surface of the concrete and the air temperature are 19.75°C and 19.75°C respectively, meeting the temperature control standard in the "Technical Specification for Highway Bridge and Culvert Construction" (JTG / T 3650 - 2020) that the temperature difference between the inside and the surface of the concrete should not be greater than 20°C.

[0324] 4) After the temperature peak, the temperature drop rate of the center point of the 4th layer of concrete is 2.75 - 3.75 °C / d during 35 - 168 h and 1.75 - 2.75 °C / d during 168 - 226 h; the temperature drop rate of the center point of the 5th layer of concrete is 2.75 -

[0325] 3.75 °C / d during 38 - 168 h and 1.00 - 2.75 °C / d during 168 - 226 h, both meeting the control standard of the concrete temperature drop rate in the concrete temperature control plan, which is ≤ 4.0 °C / d within 7 days (168 h) of age and ≤ 3.0 °C / d after 7 days (168 h) of age.

[0326] 4. Monitoring data analysis

[0327] (1) Concrete temperature time - history curve

[0328] 1) The development of the time - history curve of the temperature characteristic values of the first concrete monitoring layer of the 7# main pier cap 2 can be divided into two stages. The first stage: After the concrete in the measuring point monitoring area covers the measuring point, it starts to hydrate and heat up until it reaches the temperature peak. The second stage: After the internal temperature of the cap 2 concrete reaches the temperature peak, under the action of forced cooling by water circulation, the internal temperature of the concrete begins to drop.

[0329] 2) The development of the time - history curve of the temperature characteristic values of the second concrete monitoring layer of the 7# main pier cap 2 can be divided into two stages. The first stage: After the concrete in the measuring point monitoring area covers the measuring point, it starts to hydrate and heat up until it reaches the temperature peak. The second stage: After the internal temperature of the cap 2 concrete reaches the temperature peak, under the action of forced cooling by water circulation, the internal temperature of the concrete begins to drop.

[0330] (2) Temperature control measures for concrete production and pouring

[0331] 1) By controlling the temperature of the mixing water, cleaning the aggregate in advance to reduce the mud content, and spraying in the bunker in advance to reduce the aggregate temperature.

[0332] 2) The in - mold temperature is detected before the concrete enters the mold. The in - mold temperature during the first concrete pouring of the cap 2 is 24.9 - 27.8 °C, and the in - mold temperature during the second concrete pouring of the cap 2 is 20.8 - 27.9 °C;

[0333] 3) Select a period with a lower temperature for pouring, use 3 concrete pumping trucks to transport the concrete, and shorten the pouring time (the completion time of the first concrete pouring of the cap 2 is about 30 h, and the completion time of the second concrete pouring of the cap 2 is about 18 h).

[0334] 4) In the early stage of the temperature rise of the concrete of the bearing platform 2: Groundwater is used as the cooling water. Adjust the inlet flow rate (velocity) to control the inlet temperature and outlet temperature of the cooling water ≤ 10°C; in the temperature drop stage: Prevent the temperature drop rate of the concrete from being too fast. Adjust the cooling water flow rate, use circulating water for curing, and control the temperature difference between the inlet temperature of the circulating water and the highest internal temperature ≤ 20°C, and reduce the inlet flow rate (velocity).

[0335] 5) After the concrete of the bearing platform 2 is poured, it is cured with the formwork. On the top surface of the concrete, circulating water is used for water storage and heat preservation curing, and the temperature difference between the curing water temperature and the concrete surface temperature ≤ 15°C.

[0336] (3) When the on-site monitored temperature exceeds the temperature control standard, the following countermeasures shall be taken:

[0337] 1) The concrete pouring temperature is too high: Select a time with a lower temperature for pouring, optimize the transportation route, optimize the temperature of the concrete raw materials and mixing environment, reduce the temperature of the concrete mixture when it leaves the mixer, and ensure that the concrete temperature when it enters the formwork ≤ 28°C.

[0338] 2) The inlet temperature of the cooling water is too high: Measure the inlet temperature of the cooling water once every hour during the water cooling process to ensure that the temperature difference between the inlet temperature and the highest internal temperature ≤ 20°C. If the inlet temperature is too high, cool the cooling water by changing the water or adding ice cubes to achieve the effect of cooling the interior of the concrete. Since the temperature drop of the ice cubes is relatively large, first replace a part of the fresh water and then add ice for cooling to minimize the impact of the temperature gradient on the quality of the concrete.

[0339] 3) The highest internal temperature of the concrete is on the high side: Take measures to increase the water flow rate of the cooling water and reduce the temperature of the cooling water, so that the temperature of the cooling water is controlled to be 15 - 20°C lower than the center temperature of the concrete.

[0340] 4) The temperature difference between the interior and the surface of the concrete is on the high side: Increase the water flow rate and reduce the inlet temperature to strengthen the internal cooling, and use the cooling water outlet for water storage curing to reduce the heat dissipation on the surface of the concrete, so as to achieve external protection and internal dissipation.

[0341] 5) The concrete temperature drop rate > 2.0°C / d: Reduce the cooling water flow rate or increase the water temperature until the temperature drop rate ≤ 2.0°C / d.

[0342] Optionally, after completing step "S6: Concrete pouring, curing and form removal construction", it further includes step S7: Concrete quality inspection, which specifically includes: Testing and detecting various performance indicators of the concrete, and detecting the on-site entity cracks of the bearing platform, specifically as follows:

[0343] 1. Testing and detecting various performance indicators of the concrete

[0344] For the concrete compressive strength, early anti-cracking, electric flux, and carbonation depth specimens cured under standard conditions to the specified age, conduct relevant project tests and inspections according to the determination methods in the "Standard Test Methods for Properties of Ordinary Concrete Mixtures" (GB / T 50080), "Standard Test Methods for Physical and Mechanical Properties of Concrete" (GB / T 50081), and "Standard Test Methods for Long-Term and Durability Properties of Ordinary Concrete" (GB / T 50082). The test and inspection results of various performance indicators of C40 high-performance mass concrete are shown in Table 9 as follows.

[0345] Table 9 Test and Inspection Results of Various Performance Indicators of C40 High-Performance Mass Concrete

[0346]

[0347]

[0348] The comparison between the test and inspection results in Table 2 and those in Table 9 shows that the test and inspection results of various performance indicators of the C40 trial-mixed concrete during the concrete mix design are not much different from those of the C40 high-performance mass concrete during the concrete pouring construction of Cap 2, verifying the scientificity and reliability of the mix design of C40 high-performance mass concrete.

[0349] 2. On-site Substantive Crack Detection of the Cap

[0350] After the first and second formwork removals of Cap 2 of the 7# main pier, conduct on-site substantive inspections on the top and side surfaces of Cap 2 respectively, and no temperature crack quality defects are found.

[0351] 3. By adopting the above construction control measures, the temperature of the mass concrete is effectively guaranteed to meet the requirements specified in the "Technical Specifications for Construction of Highway Bridges and Culverts" (JTG / T 3650 - 2020), reducing the generation of concrete cracks and no crack quality defects occur, thus verifying the feasibility of the temperature crack control method for high-performance mass concrete of ultra-thick and extra-large caps.

[0352] The method for controlling cracks in high-performance mass concrete of ultra-thick and extra-large caps of the present invention can be applied not only to the construction field of Cap 2 of the main pier of the cable-stayed bridge in the above-mentioned embodiment, but also to the construction of Cap 2 of highway bridges, foundations of industrial and civil buildings, floor slabs of underground stations of urban rail transit, and dams in ocean and water conservancy projects, etc.

[0353] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete, characterized in that: The following steps are involved: Preparation before construction; The concrete mix ratio is optimized by using the concrete mix ratio set intersection design method; Control of temperature difference between concrete interior and surface; Use analytical software to calculate temperature and stress of concrete hydration heat; Concrete pouring, curing and formwork removal construction.

2. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 1 is characterized in that: The step of "optimizing the concrete mix ratio by using the concrete mix ratio set intersection design method" specifically includes the following steps: Raw materials preparation and quality inspection; Test mix and test multiple groups of trial concrete with different water-binder ratios; According to the test results, conventional software is used to draw the relationship curve between various performance indicators of the trial-mixed concrete and the water-cement ratio, and a polynomial fitting curve model is established and evaluated; According to the current standard specifications of various concrete performance indicators and the corresponding polynomial fitting curve model, multiple groups of optimized concrete mix ratios are obtained; The adiabatic temperature rise of concrete for each group of optimized concrete mix ratio is calculated to determine the best concrete mix ratio.

3. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 2 is characterized in that: The step of "trial mixing multiple groups of trial concrete with different water-cement ratios and testing" specifically includes the following steps: It is planned to give multiple groups of initial concrete mix proportions with different water-binder ratios; Use raw materials to test mix the trial concrete corresponding to the initial mix ratio of each group of concrete; The performance indicators of each group of trial-mixed concrete were tested and inspected.

4. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 2 is characterized in that: The step "using conventional software to draw the relationship curve between various performance indicators of the trial-mixed concrete and the water-cement ratio and establish a polynomial fitting curve model and evaluate it according to the test results" specifically includes the following steps: Draw the relationship curve between various performance indicators of trial mix concrete and water-cement ratio; Establish a polynomial fitting curve model between various performance indicators of trial mix concrete and water-binder ratio to obtain the goodness of fit R 2 ; The obtained goodness of fit R 2 Conduct an assessment.

5. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 2 is characterized in that: The step "obtaining multiple groups of optimized concrete mix ratios based on the current standard specifications of various performance indicators of concrete and the corresponding polynomial fitting curve model" specifically includes the following steps: According to the current standard specifications of various performance indicators of concrete and the corresponding polynomial fitting curve model, a water-cement ratio set for each performance indicator is established; Fit the water-binder ratio set of all performance indicators to obtain multiple groups of optimized water-binder ratios of concrete; According to the optimized water-cement ratio of each group of concrete, the corresponding optimized concrete mix ratio is calculated.

6. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 1 is characterized in that: The step "controlling the temperature difference between the interior and the surface of concrete" specifically includes the following steps: Temperature detection and calculation of concrete at each stage; Cooling water pipe layout and cooling system setting; Temperature control monitoring network deployment.

7. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 6 is characterized in that: The step "temperature detection and calculation of concrete at each stage" specifically includes the following steps: Detection of concrete raw material temperature and concrete mixing environment temperature; Calculation of concrete mixture temperature, temperature out of machine, temperature during transportation to pouring site, and temperature when pouring is completed.

8. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 6 is characterized in that: Step "Cooling water pipe layout and cooling system settings" The following steps are involved: Cooling water pipe layout; Cooling system settings; Temperature control of foundation concrete.

9. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 1 is characterized in that: The step "using analysis software to calculate the temperature and stress of concrete hydration heat" specifically includes the following steps: Establish the finite element calculation model of the foundation; Boundary condition setting; Temperature calculation; Stress calculation.

10. The method for controlling cracks in ultra-thick and ultra-large capping high-performance mass concrete according to claim 1, characterized in that: When performing the step "concrete pouring, curing and demoulding construction", you can also perform the step: temperature monitoring during the pouring of the cap, which specifically includes: monitoring content setting, monitoring frequency setting, monitoring result feedback and monitoring data analysis; After completing the step of "concrete pouring, curing and demolding construction", it also includes the step of: concrete quality inspection, which specifically includes: testing and detecting various performance indicators of concrete and detection of actual cracks on the foundation on site.

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