Mass concrete hydration gradient control method based on hydration heat inhibitor

Abstract

The invention relates to a mass concrete hydration gradient control method based on a hydration heat inhibitor. The mass concrete hydration gradient control method comprises the following steps: S1, establishing an adiabatic temperature rise equation and a heat transfer model; s2, adjusting the delayed heat release time; s3, establishing a fine temperature field numerical calculation model based on different hydration gradients; s4, adjusting an adiabatic temperature rise equation; s5, re-calculating the numerical value of the temperature field, and testing thermal parameters of the mass concrete; and S6, judging whether the thermal parameters meet the requirements or not until the design requirements are met. According to the method, the problem that a large temperature gradient is easily formed due to pouring time difference of mass concrete is solved, hydration heat gradient regulation and control decisions which can be applied to different engineering scenes are confirmed, arrangement of cooling water pipes is reduced, and the technology and construction cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering concrete construction, and in particular relates to a method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor. Background Art

[0002] Mass concrete is widely used in engineering fields such as bridges and water conservancy projects. During the hydration process, the exothermic hydration reaction can easily cause the internal temperature of the concrete to rise, leading to problems such as cracking, deformation, and quality degradation. To address this issue, researchers have proposed a concrete hydration heat control method based on the application of inhibitors. This method reduces the maximum internal temperature and the temperature difference between the surface and interior of the concrete, while also reducing the need for cooling water pipes. This reduces technical and construction costs, ensuring energy conservation and environmental protection for the project.

[0003] During construction, large temperature gradients can easily form due to the varying hydration start times of the concrete layers. After pouring, concrete has poor thermal conductivity and slow internal heat transfer, especially in large volumes, making it slow to respond to various external measures. Extensive construction monitoring data indicates that as the volume of concrete poured increases, the temperature gradient stress increases and the heat release time increases. The bottom layer of concrete, poured first, is affected by the heat released by the already poured layers, while the surface layer, poured last, cools due to environmental conditions. Given the different external temperature environments, the bottom layer of concrete heats up first as the cement hydration reaction releases heat, while the middle layer accumulates heat and heats up, while the surface layer heats up on one side and dissipates heat through contact with the outside world. A temperature gradient is already established at the beginning of pouring.

[0004] Therefore, in order to reduce the temperature gradient, the present invention proposes a method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a large-volume concrete hydration gradient control method based on a hydration heat inhibitor. The method controls the hydration rate of different concrete layers according to the casting layer, achieves the purpose of temperature homogenization of the entire structure, and reduces the temperature stress caused by the temperature difference of concrete in each layer. Combined with an intelligent temperature control system, the concrete temperature can be precisely controlled, thereby ensuring the safety and durability of the concrete, while avoiding the layout of cooling water pipes. The method has significant application prospects and economic benefits.

[0006] The present invention solves the technical problem by the following technical solutions:

[0007] A method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor, the method comprising the following steps:

[0008] S1. Test the hydration heat release and concrete thermal parameters of cement-based binders with and without hydration heat inhibitors, and establish an adiabatic temperature rise equation and heat transfer model.

[0009] S2. According to the adiabatic temperature rise equation of S1, the delayed heat release time is adjusted to correspond to the gradient dosage of inhibitors in different concrete pouring layers;

[0010] S3. According to the construction process, the pouring layer is divided into the lower, middle and top parts, and a fine temperature field numerical calculation model based on different hydration gradients is established;

[0011] S4. The time from the time node after pouring is completed to the time node when the equivalent age of the upper center measuring point of the model without inhibitor is consistent with the actual pouring time is used as the extraction interval of equivalent age data for different pouring layers. The average value of the equivalent age data extracted from the upper center measuring point is taken as the benchmark value. The average value of the equivalent age data extracted from the middle and bottom center measuring points is subtracted from the benchmark value. The obtained difference is directly added to the delayed heat release time in the adiabatic temperature rise model of the corresponding pouring layer as the hydration gradient control index to adjust the adiabatic temperature rise equation.

[0012] S5. After the adjustment in S4, recalculate the temperature field numerically, extract the data of the maximum temperature inside the model, the maximum temperature difference between the inside and outside, and the maximum temperature difference between the ring and the surface, and carry out the pouring construction of large-volume concrete with gradient inhibitor dosage according to the previously determined hydration gradient control index. Test the thermal parameters of large-volume concrete, including the temperature rise history of the structure, the maximum temperature inside, and the maximum temperature difference between the inside and outside, to verify the accuracy of the temperature field numerical calculation;

[0013] S6. Compare the thermal parameters obtained in S5 with the specifications and design requirements. If the requirements are met, the hydration heat inhibitor gradient dosage pouring index at this time can be used as the hydration gradient control technology output; if the requirements are not met, it is necessary to recalculate the delayed heat release time gradient of the mass concrete pouring at different layers according to the hydration gradient setting steps in S4;

[0014] S7. After adjustment, perform numerical calculation again and iterate step by step until the design requirements are met.

[0015] Furthermore, the hydration heat released by the cement-based gelling material in step S1 is used to calculate and measure the degree of hydration, and the formula is:

[0016] α(t)=Q(t) / Q ∞

[0017] Where: Q ∞ Heat accumulated for complete hydration;

[0018] Q(t) is the heat released at time t;

[0019] The experimentally based hydration degree α(t) is expressed by a double exponential fitting formula, which is:

[0020]

[0021] According to the mass concrete construction standard, the adiabatic temperature rise equation is:

[0022] F(t)=WQ ∞ α(t e ) / cρ

[0023] The adiabatic temperature rise equation is determined by the thermal conductivity k, specific heat c, gel material mass W and concrete density ρ. The thermal parameters and hydration degree α(t) are jointly determined. At the same time, the thermal conductivity k and specific heat c also change dynamically with the hydration degree α(t);

[0024] The formula for thermal conductivity k based on hydration degree is:

[0025] k(α)=k ∞ (1.33-0.33α)

[0026] Where: k ∞ is the final thermal conductivity of concrete after hardening;

[0027] α is the current degree of hydration;

[0028] The formula for specific heat c based on hydration degree is:

[0029] c=(W c αc cef +W c (1-α)c c +W a c a +W w c w ) / ρ

[0030] c cef =8.4T+339

[0031] Where: W c ,W a ,W w are the masses of cement, aggregate and water per cubic meter respectively;

[0032] c c , c α , c w are the specific heats of cement, aggregate and water respectively;

[0033] c cef is the assumed specific heat of concrete cement;

[0034] T is the current temperature;

[0035] After concrete hydration generates heat, the effect of temperature on the cement hydration chemical reaction rate is calculated using the equivalent age (maturity function) to homogenize the overall maturity of concrete. The formula is:

[0036]

[0037] Where: E a is the reaction activation energy; R is the ideal gas constant; T r is the reference temperature at equivalent age, T is the average concrete temperature during the time interval; Δt is the calculation time increment; t e is the equivalent age.

[0038] Moreover, the thicknesses of the lower, middle and top parts of the fine temperature field numerical calculation model in step S3 are 50 cm to 150 cm respectively.

[0039] Moreover, the adiabatic temperature rise equation of each layer in S4 sets the delayed heat release time t de as follows:

[0040]

[0041]

[0042] t de_顶部 =0

[0043] in: The time point when the equivalent age of ordinary concrete at the top is consistent with the actual pouring time;

[0044] t po The time point when mass concrete pouring is completed;

[0045] N is the value of FEM software from t po Iterate to Number of steps required;

[0046] t e_底部 , t e_中部 , t e_顶部 are the equivalent ages obtained by iterative calculation at the bottom, middle and top of the model respectively.

[0047] Furthermore, the arrangement principle of temperature measurement points during the numerical calculation of the temperature field in S5 is as follows:

[0048] (1) Taking full account of the temperature field distribution law of early-age mass concrete, the temperature measurement points include surface temperature measurement points and internal temperature measurement points. The surface temperature measurement is divided into top surface temperature measurement and side surface temperature measurement. The top surface temperature measurement point is arranged 30 cm below the surface of the center of the component, the side surface temperature measurement point is arranged 5 cm below the surface of the center of the component, and the internal temperature measurement point is arranged at the center of the component;

[0049] (2) According to the casting layer position in the construction plan, set the center measuring point of each casting layer in the vertical direction of the center of the component;

[0050] (3) According to the symmetry of the component, 1 / 4 of the component is selected to arrange the measuring points. In order to prove the validity of the collected data, a check point is arranged at a horizontal position of 10 cm from the center measuring point.

[0051] Moreover, the concrete temperature control target that meets the requirements in S6 is:

[0052] (1) The peak temperature inside the concrete dropped to 55°C;

[0053] (2) The maximum temperature difference between the inner and outer surfaces of concrete shall not exceed 22°C.

[0054] Moreover, the total delayed heat release time of each pouring layer output in S7 is as follows:

[0055]

[0056] Where: n is the number of hydration gradient iterations when the mass concrete is poured to meet the temperature control target.

[0057] The advantages and beneficial effects of the present invention are:

[0058] 1. The present invention is dedicated to controlling the adiabatic temperature rise equation based on an inhibitor to obtain a normalized hydration temperature rise, while applying the most appropriate hydration gradient control scheme. This method solves the problem of large temperature gradients easily formed during the time difference of large-volume concrete pouring, confirms that the hydration heat gradient control decision can be applied to different engineering scenarios, reduces the layout of cooling water pipes, and reduces technical and construction costs.

[0059] 2. Through numerical calculation results of several temperature fields in a certain background project, the present invention found that compared with the benchmark concrete, the hydration heat temperature peaks at the bottom and middle parts of the concrete with the gradient addition of inhibitors were synchronously delayed, the overall temperature rose evenly, and the temperature difference between the inside and the outside was low; as the hydration gradient was set, the temperature difference peaks between the center and the top, side, and bottom surfaces of the large volume of concrete were continuously reduced and delayed.

[0060] 3. The present invention combines the adiabatic temperature rise equation with concrete inhibitor gradient dosage pouring engineering examples to discover the correlation between the delayed heat release time and gradient and the maximum temperature and maximum temperature difference between the inside and outside of concrete, and determines the optimal delayed heat release time gradient. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a flow chart of the hydration gradient control of the present invention;

[0062] Figure 2 FIG. 1 is a diagram of the test device of the present invention;

[0063] Figure 3 This is a graph showing the adiabatic temperature rise of the test block of the present invention;

[0064] Figure 4 This is a temperature history diagram of the test measuring points of the present invention;

[0065] Figure 5 This is a conceptual diagram of cement hydration heat release based on inhibitors of the present invention;

[0066] Figure 6 This is a comparison chart of the measured and simulated temperature history of the test block of the present invention;

[0067] Figure 7 This is a diagram of a large-volume concrete construction pouring model of the present invention;

[0068] Figure 8 This is a graph showing the equivalent age development curve and hydration gradient extraction results of mass concrete under five calculation conditions of the present invention;

[0069] Figure 9 It is the maximum temperature envelope diagram inside the mass concrete of the present invention;

[0070] Figure 10 The temperature variation of mass concrete under five calculation conditions includes the comparison diagram between actual measurement and simulation;

[0071] Figure 11 The graph shows the changing pattern of heat release during gradient pouring of concrete with different delayed heat release times. DETAILED DESCRIPTION

[0072] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0073] like Figure 1 As shown, a method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor is innovative in that the method comprises the following steps:

[0074] Step S1, testing the hydration heat release and concrete thermal parameters of cement-based cementitious materials with and without the addition of a hydration heat inhibitor, and establishing an adiabatic temperature rise equation and a heat transfer model based on the test results;

[0075] Step S2: Based on the adiabatic temperature rise equation, the delayed heat release time is adjusted to correspond to the gradient dosage of the inhibitor at different concrete pouring layers;

[0076] Step S3: Divide the pouring layer into the lower part, the middle part, and the top part according to the construction process, and establish a fine temperature field numerical calculation model based on different hydration gradients;

[0077] Step S4: The time from the completion of pouring to the equivalent age of the upper center measuring point of the model without inhibitors, which coincides with the actual pouring time, is used as the interval for extracting equivalent age data for different pouring layers, and an initial hydration gradient is set. The average of the equivalent age data extracted from the upper center measuring point is taken as the baseline value. The baseline value is subtracted from the average of the equivalent age data extracted from the middle and bottom center measuring points. The resulting difference is directly added to the delayed heat release time in the adiabatic temperature rise model of the corresponding pouring layer as the hydration gradient control index to adjust the adiabatic temperature rise curve.

[0078] Step S5: After the adjustment, the temperature field is recalculated to extract the data of the maximum temperature inside the model, the maximum temperature difference between the inside and outside, and the maximum temperature difference between the ring and the surface. The mass concrete pouring construction with the gradient dosage of the inhibitor is carried out according to the previously determined hydration gradient control index. The thermal parameters of the mass concrete are tested, including the temperature rise history of the structure, the maximum temperature inside, and the maximum temperature difference between the inside and outside, to verify the accuracy of the temperature field numerical calculation;

[0079] Step S6: Compare the thermal parameters obtained in step S5 with the specifications and design requirements. If they meet the requirements, the hydration heat inhibitor gradient dosage pouring index can be used as the output of the hydration gradient control technology. If they do not meet the requirements, the delayed heat release time gradient for pouring different layers of mass concrete needs to be recalculated according to the hydration gradient setting steps in step S4.

[0080] Step S7: After adjustment, numerical calculation is performed again and iterated step by step until the requirements are met and the result can be output as the hydration gradient control technology.

[0081] Example 1

[0082] 1. Establish cement hydration and concrete heat transfer model

[0083] Based on the first construction experiment, the project team tested the mix design of low-heat mass concrete and the effectiveness of hydration heat inhibitors. The experimental equipment is as follows: Figure 2 As shown, Figure 2 a) is the vertical cross-section of the inhibitor temperature measuring component, Figure 2 b) is a vertical cross-section of a blank temperature measuring component.

[0084] The boundary conditions for pouring and layout are shown in Table 1. First, low-heat mass concrete is configured, and a high amount of fly ash (40% by gel mass) and a hydration heat inhibitor are introduced to achieve the temperature control effect of reducing the temperature peak and simultaneously delaying the overall temperature rise process, thereby replacing the traditional cooling water control temperature control solution.

[0085] Table 1 Design boundary conditions for pouring concrete

[0086]

[0087] (1) Obtaining the adiabatic temperature rise equation

[0088] The 120-hour hydration heat curve of specimens with the same mix ratio as the experimental blocks was measured using an I-Cal Flex Calorimeter JO325066. The adiabatic temperature rise of concrete was then calculated according to Appendix B of the "Standard for Construction of Mass Concrete" (GB 50496-2018) using the following formula:

[0089] F(t)=WQ ∞ α(t) / cρ

[0090] Where: W is the mass of the gel material; α(t) is the fitting function of the previously measured 120h hydration heat curve, which is implemented by calling a custom exponential fitting function in the Origin software. The fitting formula is as follows:

[0091]

[0092] Combined with the 120h hydration heat curve, the adiabatic temperature rise equations and corresponding curves of the blank group concrete and the inhibitor group concrete are obtained as follows: Figure 3 shown.

[0093] (2) Obtaining concrete thermal parameters

[0094] The mix proportion of C30 concrete is shown in Table 2. The thermal parameters of concrete obtained by calculation are shown in Table 3. The comparison of the temperature change curves of each test point shows that the temperature difference between the inside and outside of the blank group concrete is larger than that of the inhibitor group, and the temperature peak is reached faster. The inhibitor concrete delays the temperature peak by 38 hours compared with the blank group, and reduces the temperature peak by 6°C. Figure 4 shown.

[0095] Table 2 Design mix ratio of C30 concrete (kg / m 3 )

[0096]

[0097] Table 3 Concrete thermal parameters (when hydration degree a is 1)

[0098] type Linear expansion coefficient 1 / T Specific heat capacity (kJ / (kg·k)) Thermal conductivity (W / (m·k)) C30 concrete <![CDATA[1×10 -5 ]]> 1.000 2.595 C25 foundation <![CDATA[1×10 -5 ]]> 0.837 1.9766

[0099] The formula for thermal conductivity as the degree of hydration changes is as follows:

[0100] k(α)=k ∞ (1.33-0.33α)

[0101] Where: k ∞ is the final thermal conductivity of concrete after hardening; α is the current degree of hydration.

[0102] The formula for specific heat capacity as the degree of hydration changes is as follows:

[0103] c=(W c αc cef +W c (1-α)c c +W a c a +W w c w ) / ρ

[0104] Where: W c ,W a ,W w are the mass of cement, aggregate (admixture, sand and crushed stone) and water per cubic meter respectively;

[0105] c c , c α , c w are the specific heats of cement, aggregate and water respectively;

[0106] c cef is the assumed specific heat of concrete cement, which is 8.4T+339; T is the current temperature.

[0107] 2. Reconstruction and verification of the adiabatic temperature rise equation

[0108] The piecewise function representation of the adiabatic temperature rise equation is as follows Figure 5 As shown. Based on the specification "Concrete Hydration Temperature Rise Inhibitor" and the hydration temperature rise theory, the controllable adiabatic temperature rise equation f(x) is derived and optimized, and the formula is as follows:

[0109]

[0110] Where: t de It is the rapid temperature rise inflection point time of concrete with different inhibitor dosages, that is, the time point when the heat release reaches 30.0 J / g. It can be set according to the hydration gradient control requirements during temperature rise control design;

[0111] T ra For the duration of rapid reaction, the same material may extend the rapid reaction period according to the increase of inhibitor dosage, but the change is not significant;

[0112] Based on the most unfavorable safety design requirements, the rapid reaction duration with the number of days of heat release suppression of 0 days can be taken into account in the calculation of the longer suppression time. Figure 3 , the quick response time is 50h; f T (t de ) is affected by the thermal diffusion coefficient of the material, so even if the delay time t is set de Between materials with the same or different mix ratios T (t de) are also different, because f T (t de ) exists in the early stage of hydration heat release, so the influence of hydration degree can be ignored. Its value can be taken as 30W / cρ, which is generally 3-5℃ and 4.4℃ in this project; Q is the peak adiabatic temperature rise of concrete hydration.

[0113] Taking into account the previously obtained concrete thermal parameters, a segmented adiabatic temperature rise equation with delayed heat release for 48 hours applicable to this project is constructed. The formula is as follows:

[0114]

[0115] The reconstructed adiabatic temperature rise equation is loaded into the Abaqus main program for trial calculation, and the trial calculation results are compared with the test results. Figure 6 As shown, Figure 6 a) is a comparison chart of the actual and simulated temperature continuity curves at the center of the temperature measuring element. Figure 6 b) is a comparison chart of the actual and simulated temperature continuity curves at the measuring points on the surface of the temperature measuring piece. Figure 6 Comparison of the calculated results with the experimental values shows that the two values are relatively close, which verifies the rationality of the adiabatic temperature rise equation using piecewise functions considering the characteristics of the inhibitor in the context of this project.

[0116] 3. Establish a numerical calculation model of the fine temperature field based on different hydration gradients

[0117] (1) Temperature field numerical calculation parameters

[0118] The simulation was performed on a typical bridge, using the pouring of large-volume concrete and temporary anchors for the second layer. The model was pre-processed based on engineering geometry, boundary heat transfer conditions (ambient wind speed and temperature, internal cooling water pipes in the structure, and heat transfer between pouring layers), and construction and maintenance measures (pouring intervals and thermal insulation).

[0119] ①Pour large volume concrete on the second layer

[0120] Component dimensions: bottom 34.4×34.4m, top 35.4×35.4m, height 2m.

[0121] Constraints: The simulation calculation is based on 2m thick poured C30 concrete.

[0122] Pouring steps: The bottom concrete is poured in layers with a thickness of 25 cm, twice, with an interval of 3.5 hours between each time; the middle concrete is poured in layers with a thickness of 30 cm, three times, with an interval of 4.2 hours between each time; the top concrete is poured in layers with a thickness of 30 cm, twice, with an interval of 4.2 hours between each time.

[0123] ② Temporary casting buckle seat

[0124] Component dimensions: The first concrete layer is 23.0×18.0m and 3m high; the second concrete layer is 23.0×12.1m at the bottom and 23.0×10.6m at the top, with a height of 3m.

[0125] Constraints: The simulation calculation is based on 3m thick poured C30 concrete.

[0126] Pouring steps: The first layer of concrete was poured in layers of 30 cm thick at the bottom, three times, with an interval of 3.5 hours between each pour; the middle layer of concrete was poured in layers of 55 cm thick, twice, with an interval of 9.2 hours between each pour; the top layer of concrete was poured in layers of 25 cm thick, four times, with an interval of 2.9 hours between each pour. The second layer of concrete was poured in layers of 30 cm thick at the bottom, three times, with an interval of 2.3 hours between each pour; the middle layer of concrete was poured in layers of 55 cm thick, twice, with an interval of 6.3 hours between each pour; the top layer of concrete was poured in layers of 25 cm thick, four times, with an interval of 1.0 hour between each pour.

[0127] The concrete pouring interval is achieved through the main program time step setting and life and death units.

[0128] Low heat mass concrete mix ratio: gel material 350kg / m 3 , fly ash content 40%, hydration heat inhibitor (set according to the number of days of delayed heat release), see Table 4.

[0129] Table 4 Mix proportion of low heat mass concrete (kg / m 3 )

[0130]

[0131] Simulation location and measurement point arrangement: Take a large volume of concrete for temperature field calculation. The calculation model and measurement points are shown in Figure 7 .

[0132] The boundary conditions for mass concrete pouring are shown in Table 5.

[0133] Table 5 Boundary conditions of mass concrete

[0134]

[0135] The boundary equivalent heat dissipation coefficient is calculated according to Section 3.3 “Approximate Treatment of Boundary Conditions” of Temperature Stress and Temperature Control of Mass Concrete (2nd Edition) (written by Zhu Bofang, China Electric Power Industry Press, 2012).

[0136] The construction wind speed is 4m / s, and the equivalent heat dissipation coefficient of the structure side is 35.49kJ / (m 2 ·h·℃), the equivalent heat dissipation coefficient of the top surface of the structure is 15.79kJ / (m 2 ·h·℃).

[0137] (2) Concrete heat generation and heat exchange realization

[0138] The UMATHT subroutine converts incremental time into equivalent age to calculate the degree of hydration, thereby enabling the continuous change of concrete thermal parameters (specific heat and thermal conductivity) as the hydration progresses. The hydration temperature and equivalent age are independently extracted as field output conditions. Various boundary heat transfer and thermal insulation curing measures are implemented through the membrane heat exchange settings embedded in the main program and the call of the FILM subroutine.

[0139] 4. Research on hydration gradient control method for large volume concrete pouring

[0140] (1) Working condition setting

[0141] Relying on the background engineering application of hydration gradient control technology, representative concrete pouring conditions were selected, and different hydration control gradients were considered to establish a numerical calculation model of the temperature field of concrete in the early stage of mass concrete construction.

[0142] Condition 1: No hydration control measures are considered.

[0143] Case 2: Consider hydration control measures based on the initial hydration gradient.

[0144] Working condition 3: The temperature control design requirements are still not met based on the hydration gradient control. Consider adjusting and iterating the hydration gradient control measures.

[0145] Working condition 4: Temporary base casting does not consider any hydration control measures.

[0146] Working condition 5: Temporary base casting takes into account hydration control measures based on the initial hydration gradient.

[0147] Working condition 2 involves pouring construction with a gradient dosage of inhibitor. This method was used to monitor the actual construction of the second layer of mass concrete on a bridge to verify the accuracy of the hydration gradient control method. Working conditions 1 and 4 are numerical simulation calculations of a benchmark group of concrete for setting the initial hydration gradient. Working conditions 4 to 5 all use the pouring of the first layer of concrete as an example to calculate and set the hydration gradient.

[0148] (2) Hydration gradient calculation and setting

[0149] The equivalent age segments extracted from the interior of the mass concrete and the hydration gradient settings for each working condition are shown in Table 6.

[0150] Table 6 Hydration gradient setting results

[0151]

[0152]

[0153] The concrete equivalent age curves extracted from each working condition are shown in Figure 8 , Figure 8 a) to 8e) are the equivalent age curves and calculated hydration gradients for conditions 1, 2, 3, 4 and 5 respectively.

[0154] Considering the set concrete hydration gradient, the piecewise adiabatic temperature rise equations for working conditions 1, 2, 3, 4, and 5 are constructed as follows:

[0155] Delayed heat release 0h,

[0156] Delay heat release for 48 hours,

[0157] Delayed heat release for 54 hours,

[0158] Delayed heat release for 78h,

[0159] Delayed heat release for 58 hours,

[0160] Delayed heat release 84h,

[0161] (3) Numerical calculation results of temperature field

[0162] Under the above conditions, the calculation results of the maximum temperature and maximum temperature difference at each pouring layer of the second layer of mass concrete and the first layer of temporary buckle base are shown in Table 7.

[0163] Table 7 Calculation results

[0164]

[0165] In the specifications and design requirements, the design value of the temperature difference between the inside and outside surfaces of concrete is 22°C, and the limit is 25°C. Obviously, the hydration gradient control in working condition 2 can significantly reduce the temperature difference between the inside and outside, but the ability to control the internal temperature peak is limited. For working condition 3, as the delayed heat release time is set according to the gradient of the pouring layer, the internal temperature peak is reduced by 5.3°C compared with working condition 2, and the control effect of the temperature difference between the inside and outside is improved by 10% compared with working condition 2. As for the temperature difference between the center and bottom surface concrete, it even increased after setting the hydration gradient, but the overall temperature difference was reduced and the temperature peak was delayed. Compared with working condition 4, the overall temperature indicators of working condition 5 met the requirements of the specification.

[0166] The maximum temperature envelope diagram inside the concrete structure is shown in Figure 9 , Figure 9 a) is the concrete temperature envelope diagram of working condition 1 (27h), Figure 9 b) is the concrete temperature envelope diagram of working condition 2 (75h), Figure 9c) is the concrete temperature envelope diagram of working condition 3 (90h), Figure 9 d)~ Figure 9 e) is the temperature envelope diagram of the temporary buckle concrete under working condition 4 (32h for the first layer, 255h for the second layer), Figure 9 f)~ Figure 9 g) is the temperature envelope diagram of the temporary anchor concrete in working condition five (137h for the first layer, 320h for the second layer).

[0167] Figure 10 a), 10c), 10e), 10g), and 10i) are respectively the internal and external temperature history of concrete under working conditions 1, 2, 3, 4, and 5. Figure 10 b), 10d), 10f), 10h), and 10j) are the temperature differences between the inside and outside of concrete in working conditions 1, 2, 3, 4, and 5, respectively. 10c) and 10d) compared and verified the measured data of the project. It can be seen that the prediction error was less than 1° at the end of the measured data. Under the five working conditions, the highest temperature of the concrete appeared at different positions and times. In working condition 1, due to the large volume of concrete and the lack of temperature control measures, the temperature difference between the inside and outside reached 34.4°C. In working condition 2, due to the setting of the initial hydration gradient, the peak temperatures of the top and bottom concrete were reduced by 17.8°C and 1.4°C, respectively. At the same time, from the comparison of the trial calculation results with the experimental values, it can be seen that the two values are relatively close, which verifies the accuracy of the numerical calculation model. From Condition 1 to Condition 3, with further optimization and resetting of the hydration gradient, the peak temperature of the bottom concrete first decreased and then increased, while the peak temperature of the middle concrete first increased and then decreased compared to the baseline group. The former was due to the inhibitor reducing the temperature peak, but then the heat accumulation raised the temperature; the latter was due to the heat accumulation raising the temperature, but then the setting of the hydration gradient allowed the heat to be released in an orderly manner. Similarly, from Condition 4 to Condition 5, the peak temperatures of the top and middle concrete decreased by 11.9°C and 4.7°C, respectively.

[0168] The changing rules of concrete heat release under different hydration gradient control are as follows: Figure 11 In general, the maximum temperature of concrete and the temperature difference between the inside and outside of concrete decrease with the increase of hydration gradient. Figure 11In (a), after setting the hydration gradient (delayed heat release for 78h), the maximum temperature of the bottom concrete began to rise, but the amplitude was small, rising to 54.7℃. This is because the bottom concrete is not easy to dissipate heat and is less affected by the hydration gradient setting. If the hydration gradient is further increased, it may exceed the temperature control design standard. In fact, the maximum temperature of the middle concrete and the temperature difference between the inside and outside are most affected by the hydration gradient setting. After setting the hydration gradient (delayed heat release for 54h), they all dropped significantly. Therefore, considering the temperature control measures and design requirements, it is the best choice to delay the heat release of the bottom concrete for 78h, delay the heat release of the middle concrete for 54h, and not set the inhibitor and the hydration gradient formed on the top concrete. Based on this, the hydration gradient control of the temporary buckle casting is carried out, such as Figure 11 (b) Therefore, considering the temperature control measures and the requirements of the specification, the best option for the temporary buckle is to delay the heat release of the bottom concrete for 84 hours, the middle concrete for 58 hours, and the top concrete without an inhibitor to form a hydration gradient.

[0169] The present invention adopts a gradient dosage design method of a hydration heat inhibitor to gradiently control the hydration speed of different concrete layers and reduce the overall temperature gradient of the concrete.

[0170] Through numerical calculation results of the temperature field of two structural forms in a certain background project, the present invention found that: compared with the benchmark concrete, the hydration heat temperature peaks at the bottom and middle parts of the concrete with gradient-added inhibitors were synchronously delayed, the overall temperature rose evenly, and the temperature difference between the inside and outside was low; as the hydration gradient was set, the temperature difference peaks between the center of the structure and the top, side, and bottom surfaces were continuously reduced and delayed.

[0171] The present invention combines the adiabatic temperature rise equation with concrete inhibitor gradient dosage pouring engineering examples to discover the correlation between the delayed heat release time and gradient and the maximum temperature and maximum temperature difference between the inside and outside of concrete, and determines the optimal delayed heat release time gradient.

[0172] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor, characterized by: The steps of the method are: S1. Test the hydration heat release and concrete thermal parameters of cement-based binders with and without hydration heat inhibitors, and establish an adiabatic temperature rise equation and heat transfer model. S2. According to the adiabatic temperature rise equation of S1, the delayed heat release time is adjusted to correspond to the gradient dosage of inhibitors in different concrete pouring layers; S3. According to the construction process, the pouring layer is divided into the lower, middle and top parts, and a fine temperature field numerical calculation model based on different hydration gradients is established; S4. The time from the time node after pouring is completed to the time node when the equivalent age of the upper center measuring point of the model without inhibitor is consistent with the actual pouring time is used as the extraction interval of equivalent age data for different pouring layers. The average value of the equivalent age data extracted from the upper center measuring point is taken as the benchmark value. The average value of the equivalent age data extracted from the middle and bottom center measuring points is subtracted from the benchmark value. The obtained difference is directly added to the delayed heat release time in the adiabatic temperature rise model of the corresponding pouring layer as the hydration gradient control index to adjust the adiabatic temperature rise equation. S5. After the adjustment in S4, recalculate the temperature field numerically, extract the data of the maximum temperature inside the model, the maximum temperature difference between the inside and outside, and the maximum temperature difference between the ring and the surface, and carry out the pouring construction of large-volume concrete with gradient inhibitor dosage according to the previously determined hydration gradient control index. Test the thermal parameters of large-volume concrete, including the temperature rise history of the structure, the maximum temperature inside, and the maximum temperature difference between the inside and outside, to verify the accuracy of the temperature field numerical calculation; S6. Compare the thermal parameters obtained in S5 with the specifications and design requirements. If the requirements are met, the hydration heat inhibitor gradient dosage pouring index at this time can be used as the hydration gradient control technology output; if the requirements are not met, it is necessary to recalculate the delayed heat release time gradient of the mass concrete pouring at different layers according to the hydration gradient setting steps in S4; S7. After adjustment, perform numerical calculation again and iterate step by step until the design requirements are met.

2. The method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor according to claim 1, characterized in that: The hydration heat released by the cement-based gelling material in step S1 is used to calculate and measure the hydration degree, and the formula is: α(t)=Q(t) / Q ∞ Where: Q ∞ Heat accumulated for complete hydration; Q(t) is the heat released at time t; The experimentally based hydration degree α(t) is expressed by a double exponential fitting formula, which is: According to the mass concrete construction standard, the adiabatic temperature rise equation is: F(t)=WQ ∞ α(t e ) / cρ The adiabatic temperature rise equation is determined by the thermal conductivity k, specific heat c, gel material mass W and concrete density ρ. The thermal parameters and hydration degree α(t) are jointly determined. At the same time, the thermal conductivity k and specific heat c also change dynamically with the hydration degree α(t); The formula for thermal conductivity k based on hydration degree is: k(a)=k ∞ (1.33-0.33a) Where: k ∞ is the final thermal conductivity of concrete after hardening; α is the current degree of hydration; The formula for specific heat c based on hydration degree is: c=(W c a c cef +W c (1-a)c c +W a c a +W w c w ) / p c cef =8.4T+339 Where: W c ,W a ,W w are the masses of cement, aggregate and water per cubic meter respectively; c c , c α , c w are the specific heats of cement, aggregate and water respectively; c cef is the assumed specific heat of concrete cement; T is the current temperature; After concrete hydration generates heat, the effect of temperature on the cement hydration chemical reaction rate is calculated using the equivalent age (maturity function) to homogenize the overall maturity of concrete. The formula is: Where: E a is the reaction activation energy; R is the ideal gas constant; T r is the reference temperature at equivalent age, T is the average concrete temperature during the time interval; Δt is the calculation time increment; t e is the equivalent age.

3. The method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor according to claim 1, characterized in that: The thicknesses of the lower, middle and top parts of the fine temperature field numerical calculation model in step S3 are 50 cm to 150 cm respectively.

4. The method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor according to claim 1, characterized in that: The adiabatic temperature rise equation of each layer in S4 is set to delay the heat release time t de as follows: in: The time point when the equivalent age of ordinary concrete at the top is consistent with the actual pouring time; t po The time point when mass concrete pouring is completed; N is the value of FEM software from t po Iterate to Number of steps required; t e_底部 , t e_中部 , t e_顶部 are the equivalent ages obtained by iterative calculation at the bottom, middle and top of the model respectively.

5. The method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor according to claim 1, characterized in that: The principle of arranging temperature measurement points during the numerical calculation of the temperature field in S5 is as follows: (1) Taking full account of the temperature field distribution law of early-age mass concrete, the temperature measurement points include surface temperature measurement points and internal temperature measurement points. The surface temperature measurement is divided into top surface temperature measurement and side surface temperature measurement. The top surface temperature measurement point is arranged 30 cm below the surface of the center of the component, the side surface temperature measurement point is arranged 5 cm below the surface of the center of the component, and the internal temperature measurement point is arranged at the center of the component; (2) According to the casting layer position in the construction plan, set the center measuring point of each casting layer in the vertical direction of the center of the component; (3) According to the symmetry of the component, 1 / 4 of the component is selected to arrange the measuring points. In order to prove the validity of the collected data, a check point is arranged at a horizontal position of 10 cm from the center measuring point.

6. The method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor according to claim 1, characterized in that: The concrete temperature control target that meets the requirements in S6 is: (1) The peak temperature inside the concrete dropped to 55°C; (2) The maximum temperature difference between the inner and outer surfaces of concrete shall not exceed 22°C.

7. The method for controlling the hydration gradient of large-volume concrete based on a hydration heat inhibitor according to claim 1, characterized in that: The total delayed heat release time of each pouring layer output in S7 is as follows: Where: n is the number of hydration gradient iterations when the mass concrete is poured to meet the temperature control target.

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