Mass concrete temperature evolution analysis model based on multi-field coupling model

Abstract

The invention discloses a mass concrete temperature evolution analysis model based on a multi-field coupling model. The mass concrete temperature evolution analysis model comprises the following steps: S1, establishing a concrete hydration field model containing temperature and relative humidity correction; s2, establishing a temperature field model containing common characterization of concrete matching, hydration degree and relative humidity; s3, establishing a humidity field model for correcting an early concrete water storage function and a humidity transmission coefficient based on the hydration degree; s4, establishing a water cooling model coupled with the concrete temperature field based on the non-isothermal pipeline flow; and S5, establishing an early concrete temperature rise analysis model based on hydration-heat-wet-water cooling coupling based on a finite element method. According to the method, environmental factors, material factors, construction factors and maintenance factors in the concrete hydration process are fully combined, the application scene is more comprehensive, and the accuracy is higher.

Description

Technical Field

[0001] The invention belongs to the technical field of mass concrete temperature control, and in particular relates to a mass concrete temperature evolution analysis model based on a multi-field coupling model. Background Art

[0002] During the hydration process of mass concrete, due to the effect of hydration heat, its internal temperature is high, forming a large temperature difference with the surface concrete. Due to the self-restraint effect, its internal temperature changes but cannot deform freely, thus generating temperature restraint stress. When the temperature stress exceeds the early tensile strength of concrete, cracks will form.

[0003] Therefore, reducing temperature gradient and controlling temperature stress are the core issues in controlling early cracking of mass concrete;

[0004] At present, most methods use finite element software to simulate the mass concrete pouring process, and the results obtained are used to guide the actual construction. However, environmental factors, material factors, construction factors, and maintenance factors in the hydration process will affect the evolution of the early temperature of mass concrete, resulting in low simulation accuracy and difficulty in adapting to various construction scenarios. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a temperature evolution analysis model for large-volume concrete based on a multi-field coupling model, which fully combines environmental factors, material factors, construction factors and maintenance factors in the hydration process, has more comprehensive applicable scenarios and higher accuracy.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A temperature evolution analysis model for large-volume concrete based on a multi-field coupling model, step S1, establishing a concrete hydration field model including temperature and relative humidity corrections;

[0008] Step S2, establishing a temperature field model including the common characterization of concrete mix, hydration degree and relative humidity;

[0009] Step S3, establishing a humidity field model based on the hydration degree to correct the early concrete water storage function and the humidity transmission coefficient;

[0010] Step S4, establishing a water cooling model coupled with the concrete temperature field based on non-isothermal pipe flow;

[0011] Step S5, establishing an early concrete temperature rise analysis model based on hydration-heat-humidity-water cooling coupling based on the finite element method;

[0012] Step S6, back-calculating the concrete hydration affinity parameters through the temperature evolution curve of the concrete sealing insulation temperature rise test and the numerical values ​​of steps S1 to S3;

[0013] Step S7, establishing a concrete layered geometric structure, setting a hydration affinity coefficient that changes with time for the concrete hydration fields of different layers, thereby establishing a concrete hydration field that is activated layer by layer along the pouring time course;

[0014] Step S8, establishing a large volume concrete pouring temperature evolution analysis model based on the early concrete temperature rise analysis model of step S5, the concrete hydration affinity parameters back-calculated in step S6, and the concrete hydration field activated layer by layer along the pouring time established in step S7.

[0015] In one embodiment, the hydration field model of step S1 is composed of the following equations:

[0016]

[0017] Where α is the degree of hydration; A 25 is the chemical affinity of concrete at the reference temperature of 25°C; is the influence coefficient of relative humidity on hydration rate; β T is the influence coefficient of temperature on hydration rate; α u is the final hydration degree, which can be calculated according to the final hydration degree model of Mills, Schindler or Luzio; B1, B2 and η are the hydration affinity coefficients. For ordinary concrete, the values ​​of B1, B2 and η are approximately 0.4 [1 / h] ~ 1.5 [1 / h], 1×10 -4 ~10×10 -4 and 4.0~10.0. For a specific concrete, its value needs to be calculated by back-calculating the results of adiabatic temperature rise test; e is the material constant, which characterizes the sensitivity of hydration rate to the influence of relative humidity φ, and its value is 5.5~12.5; R is the molar gas constant, and its value is 8.314 J / (mol·K); T is the Kelvin temperature at the current moment, K; T 25 is the Kelvin temperature corresponding to 25℃, K; E a It is the activation energy of concrete, J / mol, which characterizes the sensitivity of hydration rate to changes in temperature T and is calculated based on cement fineness, cement components and admixture fineness.

[0018] In one embodiment, the temperature field model of step S2 is composed of the following equations:

[0019]

[0020] Among them, (ρC) e is the volume heat capacity, J / (m 3·K); λ is thermal conductivity, W / (m·K); Q h is the hydration heat release, J / m 3 ;

[0021] The early concrete volume heat capacity can be expressed as a function of the degree of hydration and free water content:

[0022] (ρC) eff =m c (1+0.25)αC cp +m a C a +m c (1-α)C c +w e C w ;

[0023] The evolution of thermal conductivity of early concrete is expressed as the change of internal free water content:

[0024]

[0025] λ0=(m c λ c +m a λ a +m w λ w ) / (m c +m a +m w );

[0026] The heat release rate of concrete hydration is proportional to the hydration rate:

[0027]

[0028] Among them, m c is the mass of cement per unit volume of concrete, kg / m 3 ;m a is the mass of aggregate per unit volume of concrete, kg / m 3 ; C a is the specific heat capacity of aggregate, kJ / (kg·K); C c is the specific heat capacity of unhydrated cement, which is 0.85 kJ / (kg·K); C cp is the specific heat capacity of mature cement skeleton, which is 0.72 kJ / (kg·K); C w is the specific heat capacity of water, which is 4.187 / (kg·K); w e is the mass of free water in the concrete at the current moment during the hydration process, kg / m 3 ; Δw e The mass reduction of free water in concrete compared to the initial mixing, kg / m 3;f w is the coefficient of influence of free water content on thermal conductivity, which is 6.0-8.0 for ordinary concrete; λ0 is the thermal conductivity of concrete at the initial mixing stage, which is calculated by weighting the mass fraction of each component in the concrete mix ratio; λ c is the thermal conductivity of cement, which is 1.3W / (m·K); w is the thermal conductivity of water, which is 0.6W / (m·K); a is the thermal conductivity of aggregate, W / (m·K); m w is the mass of water in the initial concrete mix, kg / m 3 ;Q h ∞ It is the heat released when unit mass of cement is completely hydrated, in kJ / kg.

[0029] In one embodiment, the temperature field model of step S3 is composed of the following equations:

[0030]

[0031]

[0032]

[0033] Among them, w n is the water consumption for hydration, kg / m 3 ; is the water storage function, which characterizes the relationship between relative humidity and free water content; D w is the relative humidity diffusion coefficient of concrete, m / s 2 ; δ p is the vapor diffusion coefficient in concrete, kg / (m·s·Pa); P sat is the saturated vapor pressure at temperature T, Pa;

[0034] Hydration water consumption refers to the mass of free water consumed by the hydration reaction to become bound water:

[0035]

[0036] in, is the water consumption per unit mass of cement, and its value is 0.25;

[0037] The water storage function is expressed as the relationship between relative humidity and volumetric water content:

[0038]

[0039]

[0040] b=b0+n b exp(mb α);

[0041] Among them, w f is the moisture content of concrete in a saturated relative humidity state, kg / m 3 , w f0 is the free water content of the initial mix of roadbed concrete, taking the mass of the mix water, kg / m 3 ;w fu The ballast bed reaches the final hydration degree α u Saturated free water content at , kg / m 3 ; b is the early concrete infinite factor, b0, n b and m b is the correction coefficient of b, which can be obtained by back-calculating the parameters through the relative humidity evolution curve of concrete during hydration under sealed conditions;

[0042] Relative humidity diffusion coefficient D w Expressed as a function of relative humidity and degree of hydration:

[0043]

[0044] in, It indicates the relative humidity when the relative humidity diffusion coefficient is 0.5D1; is the relative humidity diffusion coefficient curve fitting index; is the permeability coefficient of mature roadbed concrete under moisture saturation state, m 2 / h;n D is the material coefficient, ranging from 6.0 to 10.0;

[0045] The vapor diffusion coefficient of the early concrete humidity field is expressed as:

[0046]

[0047] Among them, P A is the standard atmospheric pressure, Pa; μ is the water vapor diffusion resistance factor of concrete; μ0 is the initial water vapor diffusion resistance factor, which is 30-50; n μ It is the hydration degree correction coefficient of water vapor diffusion resistance factor, and takes the value of 4.0 to 6.0.

[0048] In one embodiment, when the cooling water pressure and flow rate are constant, the water cooling model in step S4 can be expressed by the energy conservation control equation as follows:

[0049]

[0050] Where u is the average fluid velocity in the cross section in the tangent direction of the pipeline centerline, m / s; A is the cross-sectional area of ​​the pipeline, m 2; ρ is the density of water, kg / m 3 ; p is the fluid pressure in the pipeline, N / m 2 ;f d is the pipe wall friction factor; C p is the constant pressure heat capacity of cooling water, J / (kg·K); T2 is the cooling water temperature, K; k is the thermal conductivity of cooling water, W / (m·K); d h is the hydraulic diameter of the cooling pipe, m; Z is the circumference of the cooling pipe, m; Te is the average external temperature of the cooling pipe, Nu is the Nusselt number of the cooling water, and for laminar flow, the Nusselt number of the circular pipe is 3.66.

[0051] In one embodiment, in step S2, the temperature field boundary conditions are convection heat transfer, solar radiation, radiation heat transfer, consistent contact, and water evaporation heat dissipation;

[0052] Convective heat transfer surface heat flux density qv(W / m 2 )for:

[0053] q v =α v (T a -T surf );

[0054] Among them, T a is the ambient temperature, °C; T surf is the surface temperature, °C; a v is the surface convection heat transfer coefficient, W / m 2 K;

[0055] The convective heat transfer capacity of the exposed concrete surface is expressed by wind speed as:

[0056]

[0057] The concrete surface absorbs solar radiation, and its heat flux density is:

[0058] q s =a s Q s ;

[0059] Among them, a s is the solar radiation absorption coefficient of the surface, ranging from 0.5 to 0.6; Q s is the solar radiation intensity per unit area, W / m 2 ;

[0060] The heat flux density q of heat exchange between the concrete surface and the atmosphere r (W / m 2 )for:

[0061] q r=ε r σ r (T a 4 -T surf 4 );

[0062] Among them, σ r is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 ·K 4 ); r is the blackness coefficient, and the blackness coefficient of the exposed concrete surface is 0.6 to 0.8;

[0063] The boundary conditions of concrete poured at different times are:

[0064] T a =T b ;

[0065]

[0066] Among them, T a and T b are the temperatures of the contact surfaces of different casting layers, λ a and λ b are the thermal conductivity of concrete in different pouring layers;

[0067] The heat removed by evaporation of water from the concrete surface is qv (W / m 2 )for:

[0068] q v =h v g a ;

[0069] Where hv is the latent heat of evaporation of water per unit mass, J / kg; g a is the evaporation flux of water on the concrete surface, kg / (m2·s).

[0070] In one embodiment, in step S3, the humidity field boundary conditions include water evaporation and consistent contact humidity exchange;

[0071] After early concrete pouring, there is moisture exchange between the surface and the flowing air, causing the moisture evaporation flux g w for:

[0072]

[0073] in, are ambient and surface relative humidity, % respectively; are the external and surface saturated vapor pressures, Pa, respectively, which are functions of temperature; β is the water vapor transmission coefficient, s / m, which is:

[0074] β=8.7×10 -8 (0.253+0.216v f );

[0075] When the concrete poured at different times is in good contact, the relative humidity and humidity flow on the contact surface, the boundary conditions are:

[0076]

[0077] in, and are the relative humidity of the contact surfaces of different casting layers.

[0078] The beneficial effects of the present invention are:

[0079] Based on the hydration-heat-humidity-non-isothermal pipe flow coupling theory, a temperature evolution analysis model for mass concrete is built. By establishing models, finite element programs and parameter backcalculations, early mass concrete temperature prediction is achieved in almost all scenarios. This method can predict the influence of mix proportion, external environment, pouring method or maintenance measures on the temperature development law, estimate the temperature rise process of mass concrete and guide the pouring and maintenance of early concrete to a certain extent, providing guidance for the prevention of early concrete cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, wherein:

[0081] Figure 1 A flow chart showing the solution of the analytical model of the present invention is shown;

[0082] Figure 2 A schematic diagram of the hydration development verification of the present invention is shown;

[0083] Figure 3 A schematic diagram of the evolution verification of the temperature field model of the present invention is shown;

[0084] Figure 4 The figure shows the verification result of the humidity field model of the present invention under the condition of sealing and curing;

[0085] Figure 5 A diagram showing the verification results of the humidity field model of the present invention under dry conditions;

[0086] Figure 6 The figure shows the verification result of the temperature field model of the present invention under water cooling conditions;

[0087] In the drawings, like reference numerals are used for like parts. The drawings are not necessarily to scale. DETAILED DESCRIPTION

[0088] The present invention will be further described below in conjunction with the accompanying drawings.

[0089] The present invention provides a temperature evolution analysis model for mass concrete based on a multi-field coupling model, wherein step S1 is to establish a concrete hydration field model including temperature and relative humidity corrections;

[0090] Step S2, establishing a temperature field model including the common characterization of concrete mix, hydration degree and relative humidity;

[0091] Step S3, establishing a humidity field model based on the hydration degree to correct the early concrete water storage function and the humidity transmission coefficient;

[0092] Step S4, establishing a water cooling model coupled with the concrete temperature field based on non-isothermal pipe flow;

[0093] Step S5, establishing an early concrete temperature rise analysis model based on hydration-heat-humidity-water cooling coupling based on the finite element method;

[0094] Step S6, back-calculating the concrete hydration affinity parameters through the temperature evolution curve of the concrete sealing insulation temperature rise test and the numerical values ​​of steps S1 to S3;

[0095] Step S7, establishing a concrete layered geometric structure, setting a hydration affinity coefficient that changes with time for the concrete hydration fields of different layers, thereby establishing a concrete hydration field that is activated layer by layer along the pouring time course;

[0096] Step S8, establishing a mass concrete pouring temperature evolution analysis model based on the early concrete temperature rise analysis model of step S5, the concrete hydration affinity parameters back-calculated in step S6, and the concrete hydration field activated layer by layer along the pouring time established in step S7;

[0097] Specifically: the hydration field model of step S1 is composed of the following equations:

[0098]

[0099]

[0100]

[0101]

[0102] Where α is the degree of hydration; A 25 is the chemical affinity of concrete at the reference temperature of 25°C; is the influence coefficient of relative humidity on hydration rate; β T is the influence coefficient of temperature on hydration rate; α u is the final hydration degree, which can be calculated according to the final hydration degree model of Mills, Schindler or Luzio; B1, B2 and η are the hydration affinity coefficients. For ordinary concrete, the values ​​of B1, B2 and η are approximately 0.4 [1 / h] ~ 1.5 [1 / h], 1×10 -4 ~10×10 -4 and 4.0~10.0. For a specific concrete, its value needs to be calculated by back-calculating the results of adiabatic temperature rise test; e is the material constant, which characterizes the sensitivity of hydration rate to the influence of relative humidity φ, and its value is 5.5~12.5; R is the molar gas constant, and its value is 8.314 J / (mol·K); T is the Kelvin temperature at the current moment, K; T 25 is the Kelvin temperature corresponding to 25℃, K; E a is the activation energy of concrete, J / mol, which characterizes the sensitivity of hydration rate to changes in temperature T and is calculated based on cement fineness, cement components and admixture fineness;

[0103] Furthermore, the temperature field model of step S2 is composed of the following equations:

[0104]

[0105] Among them, (ρC) e is the volume heat capacity, J / (m 3 ·K); λ is thermal conductivity, W / (m·K); Q h is the hydration heat release, J / m 3 ;

[0106] The early concrete volume heat capacity can be expressed as a function of the degree of hydration and free water content:

[0107] (ρC) eff =m c (1+0.25)αC cp +m a C a +m c (1-α)C c +w e C w ;

[0108] The evolution of thermal conductivity of early concrete is expressed as the change of internal free water content:

[0109]

[0110] λ0=(m c λ c +ma λ a +m w λ w ) / (m c +m a +m w );

[0111] The heat release rate of concrete hydration is proportional to the hydration rate:

[0112]

[0113] Among them, m c is the mass of cement per unit volume of concrete, kg / m 3 ;m a is the mass of aggregate per unit volume of concrete, kg / m 3 ; C a is the specific heat capacity of aggregate, kJ / (kg·K); C c is the specific heat capacity of unhydrated cement, which is 0.85 kJ / (kg·K); C cp is the specific heat capacity of mature cement skeleton, which is 0.72 kJ / (kg·K); C w is the specific heat capacity of water, which is 4.187 / (kg·K); w e is the mass of free water in the concrete at the current moment during the hydration process, kg / m 3 ; Δw e The mass reduction of free water in concrete compared to the initial mixing, kg / m 3 ;f w is the coefficient of influence of free water content on thermal conductivity, which is 6.0-8.0 for ordinary concrete; λ0 is the thermal conductivity of concrete at the initial mixing stage, which is calculated by weighting the mass fraction of each component in the concrete mix ratio; λ c is the thermal conductivity of cement, which is 1.3W / (m·K); w is the thermal conductivity of water, which is 0.6W / (m·K); a is the thermal conductivity of aggregate, W / (m·K); m w is the mass of water in the initial concrete mix, kg / m 3 ; The heat released by complete hydration of unit mass of cement, in kJ / kg;

[0114] Furthermore, the temperature field model of step S3 is composed of the following equations:

[0115]

[0116]

[0117] Among them, w nis the water consumption for hydration, kg / m 3 ; is the water storage function, which characterizes the relationship between relative humidity and free water content; D w is the relative humidity diffusion coefficient of concrete, m / s 2 ; δ p is the vapor diffusion coefficient in concrete, kg / (m·s·Pa); P sat is the saturated vapor pressure at temperature T, Pa;

[0118] Hydration water consumption refers to the mass of free water consumed by the hydration reaction to become bound water:

[0119]

[0120] in, is the water consumption per unit mass of cement, and its value is 0.25;

[0121] The water storage function is expressed as the relationship between relative humidity and volumetric water content:

[0122]

[0123]

[0124] b=b0+n b exp(m b α);

[0125] Among them, w f is the moisture content of concrete in a saturated relative humidity state, kg / m 3 , w f0 is the free water content of the initial mix of roadbed concrete, taking the mass of the mix water, kg / m 3 ;w fu The ballast bed reaches the final hydration degree α u Saturated free water content at , kg / m 3 ; b is the early concrete infinite factor, b0, n b and m b is the correction coefficient of b, which can be obtained by back-calculating the parameters through the relative humidity evolution curve of concrete during hydration under sealed conditions;

[0126] Relative humidity diffusion coefficient D w Expressed as a function of relative humidity and degree of hydration:

[0127]

[0128] in, It indicates the relative humidity when the relative humidity diffusion coefficient is 0.5D1; is the relative humidity diffusion coefficient curve fitting index; is the permeability coefficient of mature roadbed concrete under moisture saturation state, m 2 / h;n D is the material coefficient, ranging from 6.0 to 10.0;

[0129] The vapor diffusion coefficient of the early concrete humidity field is expressed as:

[0130]

[0131] Among them, P A is the standard atmospheric pressure, Pa; μ is the water vapor diffusion resistance factor of concrete; μ0 is the initial water vapor diffusion resistance factor, which is 30-50; n μ The hydration degree correction coefficient of the water vapor diffusion resistance factor is 4.0 to 6.0;

[0132] In one embodiment, since the control equations of the hydration field, temperature field and humidity field are partial differential / ordinary differential equations in the domain, and the water cooling field is a partial differential equation on the edge, this model adopts a model solution scheme that is shared by full coupling and separate coupling, in which the hydration field, temperature field and humidity field adopt a full coupling solution scheme, and the hydration-heat-humidity full coupling calculation results and the water cooling field adopt a separate coupling solution scheme;

[0133] The fully coupled hydration-heat-humidity solution is established using the general form partial differential equation as follows:

[0134] For multi-field coupling problems, assume that the system of equations has n independent variables uF 1, uF 2…uF n, and its general form of partial differential equation and boundary conditions are defined as:

[0135]

[0136] Among them, the first equation in the equation group is a differential equation, which represents the change process of each field variable in the calculation domain; the second equation represents the Neuman natural boundary condition and the Dirichlet boundary, where n is the external normal tensor on the boundary. Taking the temperature field as an example, that is, the fixed heat flux G set on the boundary F and temperature value r, the coefficient matrices of the n independent variables are defined as follows:

[0137]

[0138]

[0139]

[0140]

[0141] is the attenuation coefficient, is the diffusion coefficient, is the conserved flux convection coefficient, γ ij is the conserved flux source, is the convection coefficient, is the absorption coefficient, f Fk is the source term, is the boundary flux / source, is the boundary absorption term;

[0142] According to the expression of the general differential equation group, the independent variables and attenuation matrix of the early roadbed concrete hydration-heat-moisture coupling equation group can be expressed as:

[0143]

[0144] The diffusion coefficient is expressed as:

[0145]

[0146] For a three-dimensional isotropic problem, the diffusion coefficient term can be expressed as:

[0147]

[0148] Where I is the third-order unit matrix, the conserved flux convection coefficient Conserved Flux Source γ ij , convection coefficient And the absorption coefficient are all 0, and the source term of the partial differential equation system It can be expressed as:

[0149]

[0150] When the temperature field / humidity field exchanges heat / moisture with the environment, the boundary absorption term Boundary flux / source g f It is expressed as:

[0151]

[0152] For heat / moisture exchange between layers or sections of concrete, the boundary flux / source g f for:

[0153]

[0154] Since the cooling field is the governing equation of the edge, it needs to be created using the partial differential equation of the edge alone;

[0155]

[0156] Among them, U F =T2,

[0157]

[0158] For the heat flow problem in the tube, the diffusion coefficient term can be expressed as:

[0159]

[0160] The convection coefficient term can be expressed as:

[0161]

[0162] Where I is the second-order identity matrix, e t is the cooling tube tangential vector, the conservative flux convection coefficient Conserved Flux Source γ ij And the absorption coefficient are all 0, and the source term of the partial differential equation system for:

[0163]

[0164] Since the control equations of multi-field coupling problems have different forms, it is generally necessary to consider using a hybrid finite element grid, that is, using different unit order grids for different physical fields. The partial differential equations in the multi-field coupling model of this embodiment can be roughly classified into two categories, one is a Poisson type partial differential equation, and the other is a transfer type partial differential equation;

[0165] Poisson's partial differential equation is used to describe heat and moisture transfer processes and generally takes the following form:

[0166]

[0167] The temperature field and humidity field are described by the above second-order partial differential equation, where K is the thermal conductivity or humidity diffusion coefficient, Ψ is the temperature field variable T or the humidity field variable Generally, it is appropriate to use second-order units to solve such problems. In addition, since the hydration-heat-humidity coupling control equation of this patent adopts a fully coupled solution scheme of general partial differential equations, the hydration degree field α should also be used in conjunction with the temperature field variable T or the humidity field Consistent second-order unit solution. For the water cooling field, its energy conservation control equation is described by the second-order partial differential equation of water temperature T2, so the water temperature T2 uses a second-order unit;

[0168] Since each field variable presents different distribution characteristics, each field variable requires a different finite element mesh division form. For the hydration-heat-moisture-force coupling subsystem, if the mesh division cannot meet the spatial nonlinear changes of each field variable, the solution needs to use a very small time step to reduce the error, and even cause the numerical calculation to fail to converge.

[0169] For the hydration field, there is no diffusion process in the hydration reaction, and only temperature and relative humidity affect the hydration reaction rate. Therefore, the grid division that meets the calculation accuracy of the temperature field and humidity field can be adapted to the calculation of the hydration field. For the humidity field and temperature field involving diffusion and convection, the diffusion coefficients of the two are quite different in magnitude (the humidity diffusion coefficient of concrete is 3 orders of magnitude smaller than the thermal conductivity), and there are completely different requirements for the grid division density. Except for the case where the temperature boundary conditions change drastically, the temperature gradient in the concrete is relatively small, and the grid density requirement is relatively low. The grid size of 10 cm at the heat exchange boundary between the temperature field and the environment can meet the calculation accuracy requirements, and the remaining areas can be coarsened by 2 to 5 times (but the maximum grid should not be greater than 0.5 m). The humidity diffusion of early concrete is very slow. In the short term, the relative humidity only changes significantly in the shallow area (within 5 cm from the surface), and there is a large relative humidity change gradient. The grid size required in the internal area of ​​the humidity field is relatively low, but it is necessary to finely divide the grid in the surface area affected by the exchange with the environment or the humidity exchange of the old concrete joint surface. The grid thickness of the humidity exchange boundary needs to be about 5 mm.

[0170] Therefore, if the humidity exchange between concrete and the environment or old concrete is not considered, the mesh size of the hydration-heat-humidity field coupling is mainly controlled by the temperature field, that is, the mesh size at the heat exchange boundary is about 10 cm, and the remaining areas can be coarsened by 2 to 5 times (but the maximum mesh should not be greater than 50 cm). If the humidity exchange between concrete and the environment or old concrete is considered, the surface mesh is controlled by the humidity field, the mesh thickness of the humidity exchange boundary needs to be about 5 mm, and the mesh is coarsened by 5 to 10 times within 5 cm from the surface, and the mesh in the remaining areas is controlled by the temperature field mesh density.

[0171] For the water cooling field, considering that the difference between the cooling water temperature and the concrete temperature will not be too large, the grid size of the water cooling field should be controlled between 10cm and 50cm;

[0172] Controlling the error growth of each variable during the calculation process and ensuring the stability of the calculation process are the primary goals of numerical calculation. Since there are many variables and their coupling relationships in this model, and the time-space nonlinearity is strong, the model is difficult to solve, which can easily lead to distortion of the calculation results. The relative tolerance of the model needs to be controlled within 1% to avoid obvious error accumulation. The model solution process is as follows: Figure 1 As shown;

[0173] Verification process:

[0174] (1) Hydration process verification

[0175] Accurate simulation of the hydration process is the basis for evaluating the early concrete behavior. The applicability of the model to calculate the hydration field is verified by using the Hason test. The applicability of the model to the effect of temperature on the hydration process is verified by simulating the hydration development test of cement paste with a water-cement ratio of 0.4 at different mold entry temperatures; the applicability of the model to the effect of humidity on the hydration process is verified by simulating the hydration degree development test of cement paste with different water-cement ratios at the same mold entry temperature.

[0176] The calculation parameters of the temperature field affecting the hydration development are shown in Table 1. Different mold entry temperatures affect the hydration development conditions. Except for the different initial temperature settings, the other parameter settings are the same. The hydration parameters and temperature field parameters of the humidity field affecting the hydration development are also shown in Table 1. However, the humidity field parameters of cement slurry with different water-cement ratios are shown in Table 2.

[0177] Table 1 Main parameters of temperature effect model verification

[0178]

[0179]

[0180] Table 2 Main parameters of Hason water-cement ratio affecting test model verification

[0181]

[0182] The comparison between the test values ​​of cement paste hydration development at different mold entry temperatures and different water-cement ratios and the model calculation results is shown in the figure below. Figure 2 (a) and Figure 2 (b) shows that the proposed model can reflect the influence of temperature and humidity on hydration degree and can effectively predict the hydration development process;

[0183] (2) Temperature field verification

[0184] The applicability of the model to calculate the temperature field is verified by the Hason test. Temperature sensors are set at the depths of the center of the specimen section at 0.25m (TC1), 0.5m (TC2) and 0.7m (TC3) to detect the temperature evolution. The calculation model is as follows Figure 3 As shown in (a), the red arrows represent heat exchange, and the green arrows represent water evaporation. The initial temperature of the concrete is 25.5℃, the ambient temperature is 24℃, and the main calculation parameters are shown in Table 3. The calculation results of this model are compared with the experimental results of the literature. Figure 3As shown in (b), the calculation results of the model in this paper are in good agreement with the experimental results of the heat conduction process of early concrete, with the maximum error less than 0.5°C, indicating that the model can accurately predict the temperature development law of early concrete under the combined effect of hydration and environmental heat exchange;

[0185] Table 3 Main parameters verified by early concrete heat conduction test

[0186]

[0187] (3) Humidity field verification

[0188] The decrease in relative humidity of concrete under sealed conditions is an important basis for evaluating the self-drying performance and shrinkage cracking of early concrete, and is also the core issue of humidity field theory research. The applicability of the model humidity field was verified using Su Shuangan’s relative humidity test under sealed conditions for early concrete. Since the spatial distribution of relative humidity inside concrete under sealed conditions is uniform, humidity field simulation does not need to provide humidity transmission related parameters. The required calculation parameters are shown in Table 4. Since the original text does not give the temperature results of the test concrete, the hydration and thermal parameters of the test concrete cannot be obtained. However, the humidity field test uses PO 42.5 type ordinary Portland cement, so the activation energy, hydration heat, and hydration coefficient in Table 1 are used. A comparison between the calculation model in this paper and the test results of the reference paper is shown in Table 4. Figure 4 As shown. Figure 4 It can be seen that the relative humidity variances between the calculated values ​​of the model in this paper and the test results in the reference paper are 0.5%, 0.4% and 0.9% respectively. The calculation accuracy of the model in this paper is sufficient and can be used to predict the moisture consumption caused by self-drying of early concrete under sealed curing conditions.

[0189] Table 4 Main parameters for humidity field solution

[0190]

[0191] In addition, it is difficult to carry out moisture sealing treatment in time after concrete pouring. External drying will reduce the relative humidity of the surface and quickly reduce the surface concrete temperature. At present, most models do not consider the influence of hydration degree on humidity transmission rate, or do not consider the relationship between relative humidity and free water content. The prediction ability of concrete drying loss under early external drying environment is limited. The humidity evolution test of Su Shuangan's early concrete under single-sided drying conditions is used to verify the humidity transmission reliability of the humidity field. The main parameters of the relationship between moisture transmission and hydration degree, humidity and temperature are shown in Table 5. Figure 5It can be seen that considering the influence of hydration degree on humidity transmission, the evolution law of relative humidity and water loss rate under early concrete drying conditions can be calculated more reasonably. The relative humidity evolution law and drying water loss rate predicted by the model of this embodiment are in good agreement with the test values ​​of the reference, indicating that the prediction method of the early concrete humidity transmission process in the model of this embodiment is more effective and feasible.

[0192] Table 5 Main parameters of humidity diffusion in humidity field

[0193]

[0194] To verify the rationality of the cooling field, the test specimen (0.5m×0.5m×1.0m) was placed in a constant temperature environment of 20℃, and XPS extruded board was used for insulation treatment on all sides. A cooling pipe (inner diameter 4.6cm) was buried in the longitudinal direction, the cooling water flow rate was 0.1m / s, and the cooling water temperature was 20℃. Temperature sensors were set at about 6cm (point A), 12.5cm (point B) and 20cm (point C) from the center of the insulation pipe to detect the temperature evolution. According to Zhu Bofang's empirical formula for convective heat transfer under the conditions of insulation covering materials, the boundary convective heat transfer coefficient α of the test specimen is v =20W / m 2 K, the main calculation parameters of the model are shown in Table 6, and the calculation results of the model in this embodiment are compared with the experimental results in the literature. Figure 6 As shown in (b), it can be seen from the figure that the calculation results of the model in this paper are in good agreement with the test results of the early concrete heat conduction process. However, due to the unknown hydration affinity coefficient of the test concrete, the calculation results still have a difference of about 3°C ​​at about 50h, but it is less than 10% of the maximum temperature rise value, which shows that this model can accurately predict the temperature development law of early concrete under water cooling. Here, the temperature spatial distribution when the maximum temperature rise value appears (15h) is also given;

[0195] Table 6 Main parameters of temperature effect model verification

[0196]

[0197] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "bottom", "top", "front", "back", "inside", "outside", "left", "right", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0198] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A temperature evolution analysis model for mass concrete based on a multi-field coupling model, characterized in that: The steps include: Step S1, establishing a concrete hydration field model including temperature and relative humidity corrections; Step S2, establishing a temperature field model including the common characterization of concrete mix, hydration degree and relative humidity; Step S3, establishing a humidity field model based on the hydration degree to correct the early concrete water storage function and the humidity transmission coefficient; Step S4, establishing a water cooling model coupled with the concrete temperature field based on non-isothermal pipe flow; Step S5, establishing an early concrete temperature rise analysis model based on hydration-heat-humidity-water cooling coupling based on the finite element method; Step S6, back-calculating the concrete hydration affinity parameters through the temperature evolution curve of the concrete sealing insulation temperature rise test and the numerical values ​​of steps S1 to S3; Step S7, establishing a concrete layered geometric structure, setting a hydration affinity coefficient that changes with time for the concrete hydration fields of different layers, thereby establishing a concrete hydration field that is activated layer by layer along the pouring time course; Step S8, establishing a large volume concrete pouring temperature evolution analysis model based on the early concrete temperature rise analysis model of step S5, the concrete hydration affinity parameters back-calculated in step S6, and the concrete hydration field activated layer by layer along the pouring time established in step S7.

2. The temperature evolution analysis model of mass concrete based on multi-field coupling model according to claim 1 is characterized in that: The hydration field model of step S1 is composed of the following equations: Where α is the degree of hydration; A 25 is the chemical affinity of concrete at the reference temperature of 25°C; is the influence coefficient of relative humidity on hydration rate; β T is the influence coefficient of temperature on hydration rate; α u is the final hydration degree; B1, B2 and η are the hydration affinity coefficients. For ordinary concrete, the values ​​of B1, B2 and η are 0.4 [1 / h] ~ 1.5 [1 / h], 1×10 -4 ~10×10 -4 and 4.0~10.

0. For a specific concrete, its value is calculated by back-calculating the results of adiabatic temperature rise test; e is the material constant, which characterizes the sensitivity of hydration rate to the influence of relative humidity φ, and its value is 5.5~12.5; R is the molar gas constant, and its value is 8.314 J / (mol·K); T is the Kelvin temperature at the current moment, K; T 25 is the Kelvin temperature corresponding to 25℃, K; E a It is the activation energy of concrete, J / mol, which characterizes the sensitivity of hydration rate to changes in temperature T and is calculated based on cement fineness, cement components and admixture fineness.

3. The temperature evolution analysis model of mass concrete based on multi-field coupling model according to claim 2 is characterized in that: The temperature field model of step S2 is composed of the following equations: Among them, (ρC) e is the volume heat capacity, J / (m 3 ·K); λ is thermal conductivity, W / (m·K); Q h is the hydration heat release, J / m 3 ; The early concrete volume heat capacity can be expressed as a function of the degree of hydration and free water content: (ρC) eff =m c (1+0.25)αC cp +m a C a +m c (1-α)C c +w e C w ; The evolution of thermal conductivity of early concrete is expressed as the change of internal free water content: λ0=(m c λ c +m a λ a +m w λ w ) / (m c +m a +m w ); The heat release rate of concrete hydration is proportional to the hydration rate: Among them, m c is the mass of cement per unit volume of concrete, kg / m 3 ;m a is the mass of aggregate per unit volume of concrete, kg / m 3 ; C a is the specific heat capacity of aggregate, kJ / (kg·K); C c is the specific heat capacity of unhydrated cement, which is 0.85 kJ / (kg·K); C cp is the specific heat capacity of mature cement skeleton, which is 0.72 kJ / (kg·K); C w is the specific heat capacity of water, which is 4.187 / (kg·K); w e is the mass of free water in the concrete at the current moment during the hydration process, kg / m 3 ; Δw e The mass reduction of free water in concrete compared to the initial mixing, kg / m 3 ;f w is the coefficient of influence of free water content on thermal conductivity, which is 6.0-8.0 for ordinary concrete; λ0 is the thermal conductivity of concrete at the initial mixing stage, which is calculated by weighting the mass fraction of each component in the concrete mix ratio; λ c is the thermal conductivity of cement, which is 1.3W / (m·K); w is the thermal conductivity of water, which is 0.6W / (m·K); a is the thermal conductivity of aggregate, W / (m·K); m w is the mass of water in the initial concrete mix, kg / m 3 ;Q h ∞ It is the heat released when unit mass of cement is completely hydrated, in kJ / kg.

4. The temperature evolution analysis model of mass concrete based on multi-field coupling model according to claim 3 is characterized in that: The temperature field model of step S3 is composed of the following equations: Among them, w n is the water consumption for hydration, kg / m 3 ; is the water storage function, which characterizes the relationship between relative humidity and free water content; D w is the relative humidity diffusion coefficient of concrete, m / s 2 ; δ p is the vapor diffusion coefficient in concrete, kg / (m·s·Pa); P sat is the saturated vapor pressure at temperature T, Pa; Hydration water consumption refers to the mass of free water consumed by the hydration reaction to become bound water: in, is the water consumption per unit mass of cement, and its value is 0.25; The water storage function is expressed as the relationship between relative humidity and volumetric water content: b=b0+n b exp(m b α); Among them, w f is the moisture content of concrete in a saturated relative humidity state, kg / m 3 , w f0 is the free water content of the initial mix of roadbed concrete, taking the mass of the mix water, kg / m 3 ;w fu The ballast bed reaches the final hydration degree α u Saturated free water content at , kg / m 3 ; b is the early concrete infinite factor, b0, n b and m b is the correction coefficient of b, which can be obtained by back-calculating the parameters through the relative humidity evolution curve of concrete during hydration under sealed conditions; Relative humidity diffusion coefficient D w Expressed as a function of relative humidity and degree of hydration: in, It indicates the relative humidity when the relative humidity diffusion coefficient is 0.5D1; is the relative humidity diffusion coefficient curve fitting index; is the permeability coefficient of mature roadbed concrete under moisture saturation state, m 2 / h;n D is the material coefficient, ranging from 6.0 to 10.0; The vapor diffusion coefficient of the early concrete humidity field is expressed as: Among them, P A is the standard atmospheric pressure, Pa; μ is the water vapor diffusion resistance factor of concrete; μ0 is the initial water vapor diffusion resistance factor, which is 30-50; n μ It is the hydration degree correction coefficient of water vapor diffusion resistance factor, and takes the value of 4.0 to 6.

0.

5. The temperature evolution analysis model of mass concrete based on multi-field coupling model according to claim 4 is characterized in that: When the cooling water pressure and flow rate are constant, the water cooling model in step S4 can be expressed by the energy conservation control equation as follows: Where u is the average fluid velocity in the cross section in the tangent direction of the pipeline centerline, m / s; A is the cross-sectional area of ​​the pipeline, m 2 ; ρ is the density of water, kg / m 3 ; p is the fluid pressure in the pipeline, N / m 2 ;f d is the pipe wall friction factor; C p is the constant pressure heat capacity of cooling water, J / (kg·K); T2 is the cooling water temperature, K; k is the thermal conductivity of cooling water, W / (m·K); d h is the hydraulic diameter of the cooling pipe, m; Z is the circumference of the cooling pipe, m; Te is the average external temperature of the cooling pipe, Nu is the Nusselt number of the cooling water, and for laminar flow, the Nusselt number of the circular pipe is 3.

66.

6. The temperature evolution analysis model of mass concrete based on multi-field coupling model according to claim 5 is characterized in that: In step S2, the temperature field boundary conditions are convection heat transfer, solar radiation, radiation heat transfer, uniform contact, and water evaporation heat dissipation; Convective heat transfer surface heat flux density q v (W / m 2 )for: q v =α v (T a -T surf ); Among them, T a is the ambient temperature, °C; T surf is the surface temperature, °C; a v is the surface convection heat transfer coefficient, W / m 2 K; The convective heat transfer capacity of the exposed concrete surface is expressed by wind speed as: The concrete surface absorbs solar radiation, and its heat flux density is: q s =a s Q s ; Among them, a s is the solar radiation absorption coefficient of the surface, ranging from 0.5 to 0.6; Q s is the solar radiation intensity per unit area, W / m 2 ; The heat flux density q of heat exchange between the concrete surface and the atmosphere r (W / m 2 )for: q r =e r s r (T a 4 -T surf 4 ); Among them, σ r is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 ·K 4 ); r is the blackness coefficient, and the blackness coefficient of the exposed concrete surface is 0.6 to 0.8; The boundary conditions of concrete poured at different times are: T a =T b ; Among them, T a and T b are the temperatures of the contact surfaces of different casting layers, λ a and λ b are the thermal conductivity of concrete in different pouring layers; The heat removed by evaporation of water from the concrete surface v (W / m 2 )for: q v =h v g a ; Where hv is the latent heat of evaporation of water per unit mass, J / kg; g a is the evaporation flux of water on the concrete surface, kg / (m2·s).

7. The temperature evolution analysis model of mass concrete based on multi-field coupling model according to claim 6 is characterized in that: In step S3, the humidity field boundary conditions include water evaporation and consistent contact humidity exchange; After early concrete pouring, there is moisture exchange between the surface and the flowing air, causing the moisture evaporation flux g w for: in, are ambient and surface relative humidity, % respectively; are the external and surface saturated vapor pressures, Pa, respectively, which are functions of temperature; β is the water vapor transmission coefficient, s / m, which is: β＝8.7×10 -8 (0.253+0.216v f )； When the concrete poured at different times is in good contact, the relative humidity and humidity flow on the contact surface, the boundary conditions are: in, and are the relative humidity of the contact surfaces of different casting layers.

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