Method for calculating temperature difference between inside and outside of groundwater engineering fly ash mixed concrete plate

Abstract

This invention provides a method for calculating the internal and external temperature difference of a fly ash-mixed concrete slab in underground hydraulic engineering, comprising: Step 1. Analyzing and obtaining data; Step 2. Calculating the internal and external temperature difference ΔT of the fly ash-mixed concrete slab in underground hydraulic engineering. nw =1.55t m +13.03α+7.14H+0.46C+0.96T0+0.38T g -0.56T a +0.02H×C-0.10H×T0-0.01H×T g -0.02T0×T g -24.18, where: t m α is the formwork removal time; H is the fly ash content; C is the concrete slab thickness; T0 is the concrete pouring temperature; T g The water temperature effect value during the water circulation period; T w T represents the water temperature. a Step 3: Determine the allowable temperature difference between the inside and outside of the underground hydraulic tunnel during the concrete slab pouring period; Step 4: Analyze and determine the insulation measures for closing the tunnel entrance in winter.

Description

Technical Field

[0001] This invention belongs to the field of concrete temperature crack control technology, specifically involving a method for calculating the internal and external temperature difference of fly ash-mixed concrete slabs in underground hydraulic engineering. Background Technology

[0002] The "Design Code for Temperature Control of Concrete Dams" (NB / T 35092-2017) defines the internal and external temperature difference as the difference between the highest internal temperature of concrete and the surface temperature of concrete. Significant differences in adiabatic temperature rise and hydration processes in concrete with different structures and admixtures such as fly ash can lead to significant differences in the internal and external temperature differences.

[0003] For large-volume concrete structures such as gravity dams and arch dams, cooling water pipes are embedded for water cooling. Initially, chilled water or low-temperature river water is used to lower the maximum temperature of the concrete; in the middle stage, river water can be used for further cooling to control the temperature difference between the inside and outside. Article 8.1.5 of the "Code for Temperature Control Design of Concrete Dams (NB / T 35092-2017)" stipulates that "stress analysis of the surface concrete and surface insulation design should be carried out according to local climatic conditions, and the allowable temperature difference between the inside and outside of the concrete should be proposed." The stress analysis and surface insulation design of large-volume concrete structures such as concrete dams are complex due to the construction process, structural and temperature boundary conditions, and the highly complex temperature evolution process, classifying them as unstable temperature field problems. Therefore, Article 6.4.2 explicitly states that "unstable temperature fields can be calculated using the finite element method or the finite difference method, and can be calculated according to the method in Appendix C of this code." The method in Appendix C is also based on the heat conduction equation, simplifying boundary conditions and using empirical parameters, and employing the finite difference method for calculation. Therefore, all calculation methods are very complex and require experimental research on concrete performance to provide parameters.

[0004] Lining is a widely used structure in underground hydraulic engineering. Figure 1 In underground hydraulic engineering (hydraulic tunnels, underground powerhouses, etc.), there are no regulations regarding the control of temperature differences between the inside and outside of the lining concrete. For the tunnel entrance section (or the section from the sealed insulated door to the entrance), surface insulation design calculations are generally performed as for large-volume concrete structures such as dams. However, for the lining concrete inside underground tunnels, since the temperature variation inside the tunnel is relatively smaller than that of the natural environment, surface covering or wrapping insulation is usually not used. Therefore, there has been no research on the control or design calculation of temperature differences between the inside and outside of the lining concrete inside tunnels. However, as with large-volume concrete, the temperature difference between the inside and outside remains an important factor in the generation of temperature cracks (especially early surface cracks). Moreover, with a thin lining, the surface geometric temperature gradient generated by the temperature difference between the inside and outside is particularly large, which is the main cause of early surface cracks. Water cooling or other measures should be taken to reduce both the maximum internal temperature and the temperature difference between the inside and outside.

[0005] Therefore, it is urgent to conduct research on the control of internal and external temperature differences in concrete linings with fly ash in underground hydraulic engineering, and to propose a simple, accurate, and rapid method for calculating internal and external temperature differences, so that construction personnel can quickly use it on-site for internal and external temperature difference control or for winter insulation design of sealed openings. Summary of the Invention

[0006] The purpose of this invention is to provide a method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash concrete slabs, so as to better control the temperature cracks of underground hydraulic engineering fly ash concrete slabs and quickly control the internal and external temperature difference or design the insulation of sealed openings in winter.

[0007] To achieve the above objectives, the present invention employs the following solution:

[0008] like Figure 2 As shown, this invention provides a method for calculating the internal and external temperature difference of a fly ash-mixed concrete slab in underground hydraulic engineering, characterized by comprising the following steps:

[0009] Step 1. Analyze and obtain relevant data on temperature crack control in groundwater engineering fly ash concrete lining;

[0010] Step 2. Calculate the internal and external temperature difference ΔT of the groundwater hydraulic engineering fly ash-mixed concrete slab based on the data obtained in Step 1. nw (°C):

[0011] △T nw =1.55t m +13.03α+7.14H+0.46C+0.96T0+0.38T g -0.56T a +0.02H×C-0.10H×T0-0.01H×T g -0.02T0×T g -24.18 (Formula 1)

[0012] In the formula: t m Here, α represents the formwork removal time (d); α represents the fly ash content, for example, α = 0.2 for a 20% content; H represents the concrete slab thickness (m); and C represents the 90-day design strength grade (MPa) of the fly ash-added concrete slab, such as C... 90 40, then C = 40; T0 is the concrete pouring temperature (°C); T g T represents the water temperature effect value (°C) during the water circulation period. g =35-T w T w The water temperature (T is taken as the water temperature when water cooling is not performed) w =35℃); T a The indoor temperature value (°C) of the underground hydraulic tunnel during the concrete slab pouring period;

[0013] Step 3. Determine the allowable temperature difference between the inside and outside of the fly ash-mixed concrete lining in underground hydraulic engineering [△T] nw 】;

[0014] Step 4. Based on △T nw and [△T] nw Analysis determined the measures for sealing the cave entrance and maintaining its insulation during winter.

[0015] Preferably, the method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash concrete slabs provided by the present invention may also have the following features: Step 1 analyzes relevant data on temperature crack control of underground hydraulic engineering fly ash concrete lining, including: collecting and analyzing data on the general situation of underground hydraulic engineering lining projects, hydrological and meteorological data, etc.; collecting and analyzing data on concrete temperature control design technical requirements.

[0016] In step 2, it must be noted that when the lining concrete is designed with a 28-day strength grade, it needs to be converted to a 90-day strength grade according to the specifications; if curtain insulation is used during construction, causing the air temperature in the underground cavern to increase, then T a The increased air temperature inside the cavern should be used. Furthermore, the lining thickness is generally small, and the cooling water pipes mentioned above are all arranged in a single row; that is, the formulas apply to the case of a single-row arrangement of cooling water pipes. Since the underground cavern lining concrete is not covered with insulation, and the surface concrete temperature drops rapidly to reach the cavern air temperature, the concrete surface temperature after demolding is approximately taken as the cavern air temperature, i.e., the cavern air temperature T during the concrete pouring period. a The calculated internal and external temperature difference is slightly too large, so using this calculated value for control is on the safe side.

[0017] Preferably, the method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs provided by the present invention may also have the following characteristics: if the data obtained in step 1 specifies the allowable internal and external temperature difference, then in step 3, [△T] is taken. nw The allowable internal and external temperature difference is defined as [ΔT]. If there is no allowable internal and external temperature difference in the design, and the relevant specifications for water conservancy and hydropower projects do not specify an allowable internal and external temperature difference, then [ΔT] shall be used. nw =25℃; For particularly important spillway tunnels, the experience of water conservancy and hydropower projects can be referenced, and for concrete slabs with a thickness much smaller than the planar dimensions (thickness less than 20% of the planar dimensions, belonging to the strongly constrained zone), the allowable internal and external temperature difference [△T] can be taken. nw = 20~22℃.

[0018] Preferably, the method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs provided by the present invention may also have the following characteristics: Step 4 includes the following sub-steps:

[0019] Step 4.1 Compare and analyze the internal and external temperature difference ΔT nw Does it exceed the allowable value? [△T] nw 】;

[0020] Step 4.2 If △T nw ≤

【△T nw If △T nw >

【△T nw If the opening is sealed, it will be kept warm.

[0021] Preferably, the method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs provided by the present invention may also have the following characteristics: In step 4.2, if [△T] nw 】<△T nw ≤【△T nw If the temperature is +2.0℃, a simple curtain should be used to seal the opening for insulation, allowing for ventilation or gaps; if △T nw >【△T nw If the temperature is above +2.0℃, strict measures will be taken to seal the opening and insulate it, and air gaps will be basically not allowed.

[0022] Preferably, the method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs provided by the present invention may also have the following characteristics: Figure 3 As shown, the simple curtain-style insulation measure for sealing openings refers to a method of sealing openings by hanging thin geotextiles, plastic films, etc., to cover the opening. However, the strips / blocks are not tightly bonded, resulting in air leaks or gaps. For example... Figure 4 As shown, strict sealing of the opening and insulation measures refer to the method of sealing the opening by using thick insulation blankets, cotton felts, etc. to strictly fix the entire opening and seal it. The sealed structure forms a whole and there are no gaps for ventilation.

[0023] In addition, step 2 above calculates the temperature difference ΔT between the inside and outside of the groundwater-mixed fly ash concrete slab. nw Formula 1's reliability was verified in the following way: Taking a large-scale hydraulic tunnel in China as an example, the three-dimensional finite element method was used to simulate the temperature and temperature stress of 175 schemes with different thicknesses, strength grades, and fly ash content of the lining concrete of the city gate-shaped cross-section sidewall under different pouring temperatures, different formwork removal times, and different cooling water temperatures. The temperature control and crack prevention effect of the lining concrete and the internal and external temperature differences throughout the process were compiled and analyzed and listed in Table 1. Then, the data were statistically analyzed, which confirmed that the calculation results were basically consistent with the actual measurements.

[0024] Table 1. Simulation results of temperature difference calculation between the inside and outside of the concrete lining of the city gate-shaped cross-section.

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] The role and effect of invention

[0032] The present invention relates to a method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs. It proposes for the first time a high-precision scientific calculation method applicable to the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs. The internal and external temperature difference is calculated based on factors such as formwork removal time, fly ash content, lining structure thickness and strength, pouring temperature, water cooling and its water temperature, and air temperature inside the tunnel during the pouring period. Based on the comparative analysis with the allowable internal and external temperature difference, the sealing and insulation measures required for the tunnel entrance during the low-temperature season can be quickly determined. Attached Figure Description

[0033] Figure 1 The present invention relates to a cross-sectional view of the portal-type lining structure of a hydraulic tunnel (unit: m);

[0034] Figure 2 This invention relates to a flowchart of a method for calculating the internal and external temperature differences of a fly ash-mixed concrete slab in underground hydraulic engineering.

[0035] Figure 3 This invention relates to a simple, sealed opening insulation structure for winter and prevention of drafts.

[0036] Figure 4 This is a schematic diagram of the strictly sealed opening insulation structure involved in the present invention;

[0037] Figure 5 This is a cross-sectional view of the 1.0m thick lining structure of the upper horizontal section of the Baihetan flood discharge tunnel, which is involved in this invention.

[0038] Figure 6 This is a cross-sectional view of the 2.5m thick lining structure of the upper section of the Baihetan flood discharge tunnel, which is involved in this invention. Detailed Implementation

[0039] The following, in conjunction with the accompanying drawings, uses the lining concrete of different parts of the spillway tunnel project of Baihetan Hydropower Station as an example to illustrate the specific implementation plan of the method for calculating the internal and external temperature difference of the underground hydraulic engineering fly ash concrete slab involved in this invention.

[0040] <Temperature Control Data for the Lining Concrete of the Baihetan Hydropower Station Spillway Tunnel Project>

[0041] The Baihetan Hydropower Station, with an installed capacity of 16,000 MW, is the world's second-largest hydropower station (after the Three Gorges Dam). It consists of major structures including a dam, flood discharge and energy dissipation structures, and a water diversion and power generation system. The flood discharge facilities include six surface outlets and seven deep outlets on the dam, and three flood discharge tunnels on the left bank. The three flood discharge tunnels are located on the left bank and are of the unpressurized type. Each tunnel consists of an intake (gate chamber), an unpressurized gentle slope section, a tail section, and an outlet spillway. For tunnels #1 and #2, the tail section connects directly to the spillway. For tunnel #3, due to terrain limitations, the tail section is connected to a lower horizontal section with an 8% slope before connecting to the outlet spillway.

[0042] The spillway tunnel consists of two sections: the unpressurized section and the tail section, both with a gate-shaped cross-section. Based on differences in lining thickness and surrounding rock, it is divided into four basic lining types with thicknesses of 1.0m, 1.2m, 1.5m, and 2.5m. The maximum allowable design temperature for the spillway tunnel lining concrete is shown in Table 2.

[0043] Table 2. Maximum Allowable Temperature During Construction of Concrete Lining for Flood Discharge Tunnel (Unit: °C)

[0044] Engineering parts May to September March, April, October, November December, January, February Upper level section 1.0m 38 36 34 Upper level section 1.5m 40 38 36 Upper level section 2.5m 42 40 38 The dragon's tail fell 1.2 meters. 40 38 36 The dragon's tail fell 1.5 meters. 42 40 38

[0045] Temperature control of concrete is required throughout the entire process of concrete pouring and curing to prevent cracking. The design requires temperature control measures including:

[0046] (1) Optimize the concrete mix proportion and improve the concrete crack resistance.

[0047] (2) Arrange the concrete construction procedure and schedule in a reasonable manner, and strive to improve the level of construction management.

[0048] (3) Control the maximum internal temperature of the concrete. Effective measures include reducing the concrete pouring temperature, reducing the temperature rise of the cementitious material hydration heat, and initial water supply. The water cooling time should be such that the concrete surface temperature reaches the tunnel air temperature, generally requiring 10–20 days. The lining concrete pouring temperature should be controlled at 20℃ from April to September and 18℃ from October to March of the following year. Concrete transport vehicles should have heat insulation and sunshade measures to shorten the concrete exposure time and reduce the temperature rise during concrete transportation and pouring. Concrete pouring should be avoided during high-temperature periods as much as possible; pouring should be fully utilized during low-temperature seasons and during the early morning, evening, and nighttime when temperatures are low.

[0049] <Example 1> Calculation of temperature difference between the inside and outside of the 1.0m thick concrete lining of the upper section of the spillway tunnel during summer pouring.

[0050] The upper section of the spillway is lined with concrete, with a 1.0m thick lining in Class II surrounding rock. It has a gate-shaped cross-section, and circumferential construction joints are set every 12m along the spillway axis. The bottom slab and sidewalls of the lining structure are C... 9040 low-heat concrete, with C-shaped crown. 90 30 Low-heat concrete, mixed with 25% fly ash, such as Figure 5 As shown. The concrete was poured in three stages: first the side walls, then the top arch, and finally the base slab. Basic temperature control data is the same as above. The concrete was cured with tap water at room temperature for 90 days, and the internal temperature was controlled by water cooling.

[0051] Based on the above temperature control data, the construction unit proposes the following temperature control measures for the lining concrete pouring: pouring in summer at T0 = 20℃, T... w =22℃ (Calculate T) g =35-22=13℃) River water cooling for 10 days, demolding time t m =3d. The average annual temperature inside the cave is 14-26℃, based on the monitoring data of the diversion cave's interior temperature, without the cave entrance being sealed and insulated.

[0052] like Figure 2 As shown in this embodiment, the method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete lining includes the following:

[0053] Step 1. Analyze relevant data on temperature crack control in fly ash-mixed concrete linings for underground hydraulic engineering projects. Since the Baihetan Hydropower Station's spillway tunnel is a Class I structure with a maximum water flow velocity reaching nearly 50 m / s, temperature control and crack prevention of the lining concrete are crucial. According to design requirements, effective measures, including water cooling, are necessary for temperature control. Taking the July pouring as an example, the air temperature inside the tunnel is calculated using a cosine function, taking T... a =26℃.

[0054] Step 2. Calculate the temperature difference ΔT between the inside and outside of the fly ash-mixed concrete lining in the groundwater engineering project. nw The summer pouring will be carried out at a height of H=1.0m, a sidewall pressure of C=40MPa, a temperature of T0=20℃, and a temperature of T... g =13℃, t m Substituting 3d and Ta = 26℃ into (Formula 1) yields ΔT. nw =12.32℃.

[0055] Step 3. Determine the allowable temperature difference between the inside and outside of the fly ash-mixed concrete lining in underground hydraulic engineering [△T] nw Since the design did not specify an allowable temperature difference between the inside and outside, and the Baihetan spillway is a particularly important project, the allowable temperature difference between the inside and outside is determined according to step 3 [△T]. nw = 20~22℃.

[0056] Step 4. Analyze and propose the necessary insulation measures. This is because the calculation of ΔT... nw =12.32℃, less than [△T] nw =20~22℃. Therefore, in summer, the sidewall of the spillway should be poured with a thickness of 1.0m. 9040 Concrete lining does not require insulation measures.

[0057] <Example 2> Calculation of temperature difference between the inside and outside of the 2.5m thick concrete lining of the upper section of the spillway tunnel during winter pouring.

[0058] The upper section of the spillway is lined with concrete, with a 2.5m thick lining in Class V surrounding rock. It has a gate-shaped cross-section, and circumferential construction joints are set every 12m along the spillway axis. The bottom slab and sidewalls of the lining structure are C... 90 40 low-heat concrete, with C-shaped crown. 90 30 Low-heat concrete, mixed with 25% fly ash, such as Figure 6 As shown. The concrete was poured in three stages: first the side walls, then the top arch, and finally the base slab. Basic temperature control data is the same as above. The concrete was cured with tap water at room temperature for 90 days, and the internal temperature was controlled by water cooling.

[0059] Based on the above temperature control data, the construction unit proposes the following temperature control measures for the lining concrete pouring: Pouring at T0 = 18℃ in winter, without water cooling, T is calculated... g =0.0℃, demolding time t m =3d. The average annual temperature inside the cave is 14-26℃, based on the monitoring data of the diversion cave's interior temperature, without the cave entrance being sealed and insulated.

[0060] like Figure 2 As shown in this embodiment, the method for calculating the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete lining includes the following:

[0061] Step 1. Analyze relevant data on temperature crack control in fly ash-mixed concrete linings for underground hydraulic engineering. Since the Baihetan Hydropower Station's spillway tunnel is a Class I structure with a maximum water flow velocity reaching nearly 50 m / s, temperature control and crack prevention of the lining concrete are crucial. According to design requirements, effective measures, including water cooling, are necessary for temperature control. Taking the pouring in February as an example, the air temperature inside the tunnel is calculated using a cosine function, taking Ta = 14℃.

[0062] Step 2. Calculate the temperature difference ΔT between the inside and outside of the fly ash-mixed concrete lining in the groundwater engineering project. nw The 2.5m lining will be poured at 18℃ in February during winter, without water cooling. H = 2.5m, sidewall C = 40MPa, T0 = 18℃, T... g =0.0℃, t m =3d,T a Substituting 14℃ into formula (1), we can calculate △T. nw =26.92℃.

[0063] Step 3. Determine the allowable temperature difference between the inside and outside of the fly ash-mixed concrete lining in underground hydraulic engineering [△T] nwSince the design did not specify an allowable temperature difference between the inside and outside, and the Baihetan spillway is a particularly important project, the allowable temperature difference between the inside and outside is determined according to step 3 [△T]. nw = 20~22℃.

[0064] Step 4. Analyze and propose the necessary insulation measures. This is because the calculation of ΔT... nw =26.92℃, greater than [△T] nw The temperature range is 26.92 to 22 = 4.92℃, which falls under the category of ΔT. nw >【△T nw If the temperature is +2.0℃, then during the cold season, measures should be taken. Figure 4 Strictly seal the entrance and insulate it.

[0065] Based on the above calculations and analysis, pouring thinner lining sidewall concrete in summer results in higher internal temperatures and a smaller temperature difference between the inside and outside of the tunnel; while pouring thicker lining concrete in winter results in lower internal temperatures and a larger temperature difference between the inside and outside of the tunnel, necessitating insulation measures such as sealing the tunnel entrance during the cold season. For the upper horizontal section of the spillway tunnel, measures are required... Figure 4 Strict measures were taken to seal and insulate the opening.

[0066] In actual engineering, the concrete lining of the upper section (i.e., the entrance) of the Baihetan flood discharge tunnel is poured at 18℃ in summer and 15℃ in winter, and measures are taken to ensure its integrity. Figure 4 Strict sealing and insulation of the tunnel entrance resulted in a significant reduction in both the highest internal temperature and the maximum internal surface temperature difference of the concrete, and a marked increase in the temperature inside the tunnel during winter. The measured lowest temperature inside the tunnel during winter was 18℃, achieving the effect of no temperature cracks in the lining concrete (for details on temperature and temperature crack control effects, see Fan Qixiang, Duan Yahui, Wang Yezhen, Wang Xiaohai, Yang Simeng, Kang Xusheng. Research on Intelligent Closed-Loop Control of Concrete Moisture Curing [J]. Journal of Tsinghua University (Natural Science Edition), 2021, 61(07):671-680.). This indicates that the above calculation and analysis results are consistent with the actual engineering situation.

[0067] The above embodiments are merely illustrative examples of the technical solution of the present invention. The method for calculating the internal and external temperature difference of fly ash-mixed concrete slabs in underground hydraulic engineering involved in this invention is not limited to the content described in the above embodiments, but is subject to the scope defined by the claims. Any modifications, additions, or equivalent substitutions made by those skilled in the art based on these embodiments are within the scope of protection claimed by the claims of this invention.

Claims

1. A method for controlling the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs, characterized in that, Includes the following steps: Step 1. Analyze and obtain relevant data on temperature crack control in groundwater engineering fly ash concrete lining; Step 2. Calculate the internal and external temperature difference ΔT of the fly ash-mixed concrete slab in the groundwater engineering project based on the data obtained in Step 1. nw : △T nw = 1.55t m +13.03α+7.14H+0.46C+0.96T0+0.38T g -0.56T a +0.02H×C-0.10H×T0-0.01H×T g -0.02T0×T g -24.18 (Official 1) In the formula: t m α is the formwork removal time; H is the fly ash content; C is the 90-day design strength grade of the fly ash-mixed concrete slab; T0 is the concrete pouring temperature; T g The water temperature effect value during the water circulation period; T a The indoor temperature value of the underground hydraulic tunnel during the concrete slab pouring period; Step 3. Determine the allowable temperature difference between the inside and outside of the fly ash-mixed concrete lining in underground hydraulic engineering [△T] nw 】; Step 4. Based on △T nw and [△T] nw Analysis determined the measures for sealing the cave entrance and maintaining its insulation during winter.

2. The method for controlling the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs according to claim 1. Its features are: in, If the data obtained in step 1 specifies the allowable internal and external temperature difference, then in step 3, [△T] should be taken. nw The design allows for temperature differences between the inside and outside. If the design does not allow for an internal-external temperature difference, and the relevant specifications for water conservancy and hydropower projects do not specify an allowable internal-external temperature difference, then take [△T]. nw =25℃; For concrete slabs with a thickness less than 20% of the planar dimension, take the allowable internal and external temperature difference [△T]. nw =20~22℃.

3. The method for controlling the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs according to claim 1, characterized in that: in, Step 4 includes the following sub-steps: Step 4.1 Compare and analyze the internal and external temperature difference ΔT nw Does it exceed the allowable value? [△T] nw 】; Step 4.2 If △T nw ≤【△T nw If △T nw >【△T nw If the opening is sealed, it will be kept warm.

4. The method for controlling the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs according to claim 1, characterized in that: in, In step 4.2, if [△T] nw 】<△T nw ≤【△T nw If the temperature is +2.0℃, a simple curtain should be used to seal the opening for insulation, allowing for ventilation or gaps; if △T nw >【△T nw If the temperature is above +2.0℃, strict measures will be taken to seal the opening and insulate it, and air gaps will be basically not allowed.

5. The method for controlling the internal and external temperature difference of underground hydraulic engineering fly ash-mixed concrete slabs according to claim 4, characterized in that: in, Simple curtain-sealing insulation measures refer to sealing the opening by hanging thin geotextile or plastic film to cover the opening. However, the strips / blocks are not tightly connected, resulting in air leakage or gaps. Strictly sealed opening insulation measures refer to the method of sealing the opening by using thick insulation blankets and cotton felts to strictly fix the entire opening. The sealed structure forms a whole, with no gaps for ventilation.

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