Concrete structure anti-permeability performance analysis method considering multi-physics coupling effect

Abstract

The invention relates to a structure anti-seepage waterproof technology, in particular to a concrete structure anti-seepage performance analysis method considering a multi-physics field coupling effect, which comprises the following steps of: establishing a chemical-thermal-mechanical multi-field coupling model in a concrete hydration process by comprehensively considering various influence factors such as hydration heat, temperature, humidity and structure constraint and combining a phase field theory; solving is carried out through refined numerical simulation, and the concrete crack development and evolution process is obtained. The method has the advantages that multiple influence factors such as hydration heat, temperature, humidity and structural constraint are comprehensively considered by constructing the multi-factor coupled phase field model, the cracking risk of the concrete can be accurately estimated, and comprehensiveness and accuracy of impermeability performance evaluation are improved. By combining finite element simulation and based on a high-precision numerical simulation technology, the anti-permeability performance of the concrete structure under different working conditions can be predicted, and a scientific basis is provided for engineering design.

Description

Technical Field

[0001] The invention relates to the technical field of structural anti-seepage and waterproofing, and in particular to a method for analyzing the anti-seepage performance of a concrete structure taking into account multi-physical field coupling effects. Background Art

[0002] As an important part of modern architecture, the impermeability of concrete structures is directly related to the durability and safety of buildings. However, the impermeability of concrete is affected by a variety of factors, including temperature changes caused by the heat generated during the hydration process, fluctuations in ambient humidity, and the constraints of the structure itself. These factors interact with each other, causing micro-micro damage inside the concrete, which in turn affects its impermeability. Traditional evaluation methods often find it difficult to fully consider these influencing factors, resulting in inaccurate evaluation results of structural impermeability performance, which leads to waterproofing failure. Summary of the invention

[0003] The purpose of the present invention is to provide a method for analyzing the anti-seepage performance of concrete structures taking into account the coupling effect of multiple physical fields based on the above-mentioned deficiencies in the prior art, and a method for analyzing the anti-seepage performance of concrete structures taking into account multiple influencing factors such as hydration heat, temperature, humidity and structural constraints, so as to achieve a more accurate and comprehensive evaluation of the anti-seepage performance of materials and the waterproof performance of structures.

[0004] The purpose of the present invention is achieved by the following technical solutions:

[0005] A method for analyzing the anti-permeability performance of concrete structures considering multi-physical field coupling effects comprises the following steps:

[0006] S1. Fully consider the mutual coupling between hydration reaction, heat transfer and crack evolution, and establish a chemical-thermal-mechanical multi-field coupling model in the concrete hydration process;

[0007] S2. Combining phase field theory and multi-field coupling, a constitutive model that can consider the coupling of concrete age effect and damage effect is established;

[0008] S3. Set boundary conditions and loading methods that simulate actual working conditions, such as temperature gradient, humidity change, external water pressure, etc., and use numerical simulation to solve the constructed multi-factor coupled phase field model to simulate the internal damage and material degradation process of concrete in complex environments;

[0009] S4. Based on the numerical simulation results, key parameters such as crack width and penetration path are extracted to evaluate the anti-permeability performance of concrete structures. Combined with actual working conditions, materials or construction processes are optimized to improve the anti-cracking and anti-permeability performance of the project.

[0010] Furthermore, in step S1, in order to consider the shrinkage deformation effect during the hydration process of concrete, the total strain tensor ε is decomposed into three parts, namely, the mechanical strain ε m , thermal expansion strain ε t and the autogenous contraction strain ε a :

[0011] ε=ε m +ε t +ε a

[0012] Where thermal expansion strain ε t and the autogenous contraction strain ε a are all second-order isotropic tensors, where the self-shrinkage deformation ε a It has a strong nonlinear relationship with the degree of hydration and can be expressed as:

[0013] ε a =-α a ξ(χ)I

[0014]

[0015] Where I is the second-order unit tensor; α a is a constant coefficient; 0 is the initial hydration degree; ∞ is the final hydration degree; ξ(χ) is the truncated linear function, <x>: =max(x,0).

[0016] Thermal expansion strain ε t It is mainly related to the degree of change between the early hydration temperature rise and the later temperature drop, which can be expressed as:

[0017] ε t =α t (θ-θ 0 )I

[0018] In the formula, α t is the thermal expansion coefficient, which generally changes with age and temperature. For the convenience of calculation, it can be taken as a constant. Since early-age concrete cracks are generally in a tensile state, the isotropic damage constitutive model can be used.

[0019] Further, in step S1, the cement hydration reaction rate is determined for:

[0020]

[0021] Where ω(d) is the energy degradation function, which reflects the effect of damage (cracks) on the hydration reaction of concrete; A(χ) is the standardized chemical affinity; E a is the hydration activation energy; R is the universal gas constant; θ is the temperature.

[0022] In step S1, the heat conduction equation of the cement hydration reaction is determined as:

[0023]

[0024] Where ρ is the mass density of concrete; c is the specific heat capacity of concrete; J is the heat flow; γ is the heat released by cement hydration reaction; p ∞ is the latent heat of hydration reaction.

[0025] As the hydration reaction proceeds, the mechanical properties of concrete show obvious age effects, which are reflected in the elastic modulus E 0 , tensile strength f t and fracture energy G c As the degree of hydration changes, Poisson's ratio υ 0 It is assumed that the hydration threshold of concrete at early age begins to form mechanical properties and the hydration threshold of autogenous shrinkage strain χ 0 Taking the same value, the evolution of mechanical properties of early-age concrete is calculated using the following formula:

[0026]

[0027] Where f M (χ)——mechanical properties of concrete when the degree of hydration is χ (such as elastic modulus, tensile strength, fracture energy); ——Elastic modulus, tensile strength or breaking energy when the maximum degree of hydration is reached.

[0028] In step S2, the cracking behavior of concrete is governed by the following governing equations of the displacement subproblem describing the force balance and the phase field subproblem describing the phase field evolution:

[0029]

[0030] In the formula is the Laplace operator; σ is the stress; b is the volume uniform force; the volume where the material is located is Ω, and its external boundary is n is the normal vector of the boundary of the structure under consideration; t * is the value of stress on the corresponding structural boundary; Indicates the crack zone inside the material. and n B is the outer boundary of the crack zone and its normal vector. q is the crack phase field flux, Q is the crack phase field source, both of which are functions related to the phase field d (d = 0 means the material is intact, d = 1 means the material is cracked):

[0031]

[0032]

[0033] Where l is the crack width characteristic parameter; c 0 is the scale parameter; represents the derivative of the energy degradation function; represents the effective free energy release rate.

[0034] In step S3, the control equations of the early-age concrete hydration model are given by comprehensive phase field theory, as shown in Table 1 below:

[0035] Table 1 Control equations

[0036]

[0037] Table is the Laplace operator; n is the normal vector of the boundary of the structure under consideration; b is the volume uniform force; q is the crack phase field flux; Q is the crack phase field source; u * ,t * ,θ * , J * are the values ​​of displacement, stress, temperature and heat flux on the corresponding structural boundaries; θ a is the air temperature, and g is the convection / radiation coefficient related to the air temperature.

[0038] In order to facilitate numerical implementation, the control equations in Table 1 are transformed into the following weak form:

[0039]

[0040]

[0041] Where δθ, δχ, δu, and δd are any allowed nodal temperature, hydration degree, displacement, and crack phase field (variation), and g is the convection / radiation coefficient, which can be determined by the wind speed and roughness of the solid surface.

[0042] In step S2, the entire solution domain Ω is discretized by grid, and the characteristic grid size is h. When performing spatial discretization, the entire solution domain can be simultaneously assigned temperature, hydration degree, displacement, and phase field degrees of freedom, or the entire solution domain can be divided into two parts to improve the calculation efficiency: one part is the phase field area where cracks may occur All nodes in this region are assigned temperature, hydration degree, displacement and phase field degrees of freedom at the same time, and the other part is the remaining part The nodes in this region are only assigned temperature, hydration and displacement degrees of freedom.

[0043] After the finite element space is discretized, the standard finite element shape function is used to approximate the displacement field, phase field, temperature field and hydration field:

[0044]

[0045] Where: u e ,d e ,θ e , χ e is the displacement, phase field, temperature and hydration degree of unit e; are the displacement, phase field, temperature and hydration degree variables of node I in unit e; n is the number of nodes in the unit; is the standard finite element shape function.

[0046] Further, the corresponding gradient is expressed as:

[0047]

[0048] Where: ε e , χ e is the strain, fracture phase field gradient, temperature gradient and hydration degree gradient of unit e; are the strain coordination matrix, phase field gradient operator, temperature gradient operator and hydration degree gradient operator.

[0049] Correspondingly, the following equilibrium equation can be obtained from the weak form:

[0050]

[0051] In the formula, the column vector and It is expressed as:

[0052]

[0053] In order to perform time integration, the time step [0, T] is discretized into N time intervals, 0 = t 0 <t 1 <…<t N =T, for the nth step the time increment is Δt: =t n+1 -t n , it is known that n All state variables at time t are solved by incremental iteration method n+1 All state variables at time.

[0054] The advantages of the present invention are: by constructing a multi-factor coupled phase field model, multiple influencing factors such as hydration heat, temperature, humidity and structural constraints are fully considered, the cracking risk of concrete can be accurately estimated, and the comprehensiveness and accuracy of the anti-permeability performance evaluation are improved. Combined with finite element simulation, based on high-precision numerical simulation technology, the anti-permeability performance of concrete structures under different working conditions can be predicted, providing a scientific basis for engineering design. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a flow chart of the present invention;

[0056] Figure 2 The hydration field effect diagram of the bottom plate calculated at different times after pouring in the embodiment provided by the present invention;

[0057] Figure 3 The temperature field effect diagram calculated at different times after the bottom plate is poured in the embodiment provided by the present invention;

[0058] Figure 4 The phase field effect diagram calculated at different times after the bottom plate is poured in the embodiment provided by the present invention;

[0059] Figure 5 This is a diagram showing the crack control effect in the embodiment provided by the present invention. DETAILED DESCRIPTION

[0060] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art:

[0061] Example: Figures 1 to 5 As shown, the concrete structure anti-permeability analysis method considering the multi-physical field coupling effect in this embodiment evaluates the cracking risk of cast-in-place concrete structures and provides a theoretical and methodological basis for scientifically dealing with the leakage problem that has been difficult to solve in underground engineering.

[0062] In the scheme of the present invention, by establishing the coupled control equations of the hydration degree field, temperature field, phase field and displacement field of the concrete hydration process and solving them based on the general finite element method, the mutual influence between the hydration reaction, heat transfer and crack evolution is taken into account, and the hydration reaction and crack evolution of the concrete can be accurately simulated, and then the structural impermeability performance can be evaluated according to the degree of damage and crack evolution.

[0063] Implementation examples:

[0064] The process of the fatigue damage evolution analysis method based on time dual-scale decomposition provided in this embodiment is shown in Figure 1 , which includes the following implementation process:

[0065] The lakebed tunnel section of a city's main road was constructed using the open-cut method, with the process of first pouring the bottom plate, then pouring the side wall, and finally pouring the top plate. The bottom plate of the main structure is about 1.3m thick, and a 20cm thick C20 concrete cushion and a 5cm thick fine stone concrete protective layer are laid on the foundation. The side wall is about 5.45m high and 1.2m thick. A typical construction section was selected to monitor the concrete section that is most prone to cracking and conduct anti-seepage simulation analysis.

[0066] The relevant parameters used in the calculation are as follows: the final elastic modulus of the main structure concrete is 31500MPa, the final destructive strength is 2.01MPa, the final fracture energy is 98.43N / m, the Poisson's ratio is 0.167, and the density is 2400kg / m 3 , specific heat 1kJ / (kg·K), thermal conductivity 10.08kJ / (m·K·h). The ambient temperature is expressed by the cosine function, taking T am =12℃, T a =7℃, the heat transfer coefficient of the corresponding rough surface is 53kJ / (m 2 ·h·℃), the template uses 1.8cm wooden template, and the corresponding equivalent heat transfer coefficient is 24.77kJ / (m 2 ·h·℃).

[0067] For the bottom surface of the base plate, when the concrete contacts other objects (such as the formwork on the concrete surface or the geotextile for thermal insulation and curing), the temperature and heat flow are continuous on the contact surface, and it is assumed that the foundation temperature is constant at 20°C. Solving the hydration field control equation to obtain the simulation results of the hydration field changing with time is as follows: Figure 2 shown.

[0068] Depend on Figure 2 From the hydration field cloud diagram shown, it can be found that the hydration degree reaches a higher degree in a shorter time after pouring. In the initial stage, the heat released by cement hydration increases the temperature inside the structure, and the increase in internal temperature in turn accelerates the rate of hydration reaction. Therefore, cement hydration can reach a higher degree in a shorter time. In addition, it is noted that the hydration degree of some parts inside the structure is inconsistent with the overall. This is because as the hydration reaction proceeds, the cracks generated inside the structure affect the hydration reaction. The model takes into account the interaction between hydration and cracks, which is more in line with the actual situation.

[0069] Solve the temperature field control equation to obtain the simulation results of the temperature field changing with time. Figure 3 shown.

[0070] From the temperature field cloud map, it can be found that the entire base plate has an obvious temperature rise and fall process after pouring. In the initial stage, the heat released by the hydration reaction is greater than the heat lost by convection and heat conduction between the base plate and the surrounding environment, so the temperature inside the structure continues to rise and reaches the temperature peak at around 40h. From the hydration degree field cloud map, it can be seen that the hydration degree of cement has reached a high state at this time, so the rate of hydration heat release begins to decrease. As the heat released by the hydration reaction is less than the heat lost by convection and heat conduction between the base plate and the surrounding environment, the overall temperature of the structure begins to decrease.

[0071] Then, the fracture phase field-displacement coupling equation is solved to obtain the evolution of the phase field distribution over time that reflects the development of the fracture, such as Figure 4 shown.

[0072] From the simulation results, it can be found that through-cracks occurred in the bottom plate area during the accelerated period of hydration reaction, which posed a great threat to the safety and durability of the project and did not meet the project requirements. Therefore, corresponding anti-cracking research is needed to prevent the occurrence of through-cracks.

[0073] First, the causes of cracks are analyzed. During the accelerated hydration reaction period, the heat release rate of concrete hydration continues to accelerate until it reaches a peak value, the temperature inside the concrete continues to rise, and the highest temperature in the center of the bottom plate area can reach about 53°C, while the temperature of the surface in direct contact with the atmosphere is lower, and a large temperature gradient is generated between the inside and the surface of the bottom plate, resulting in uncoordinated deformation, which is constrained and generates self-stress. In addition, the destructive strength of the concrete is at a low level at this time, which leads to the generation of cracks.

[0074] Based on the analysis of the cracking characteristics of the bottom plate, prevention and control measures are proposed. First, from the perspective of cement mineral composition, on the basis of ensuring the strength grade, durability and workability of concrete, medium and low heat cement is selected, and the mix ratio is optimized to reduce the use of cement. For every 10kg reduction in cement, the temperature is reduced by about 1°C. In addition to material measures, it is necessary to further control the mold temperature to be less than or equal to 20°C, and use 1.8cm thick cotton wool for thermal insulation and maintenance.

[0075] After determining the crack control measures, the crack resistance characteristics of the bottom plate area were analyzed again, and the comparison results are as follows: Figure 5 shown.

[0076] It can be intuitively found from the figure that after taking crack control measures, no through cracks occurred in the bottom plate area, reducing the risk of large-volume concrete cracking in the bottom plate area, which meets the engineering requirements. This shows that the present invention can predict the risk of cracking in advance, and can greatly reduce the risk of structural through cracks by optimizing the use of materials, thereby improving the structural anti-seepage performance.

[0077] Although the above embodiments have described in detail the concepts and embodiments of the present invention with reference to the accompanying drawings, ordinary technicians in this field can recognize that various improvements and changes can still be made to the present invention without departing from the scope of the claims, so they are not described one by one here.< / x>

Claims

1. A method for analyzing the anti-permeability performance of concrete structures considering the multi-physical field coupling effect, characterized in that: The analytical method comprises the following steps: S1. Fully consider the mutual coupling between concrete hydration reaction, heat transfer and crack evolution, and establish a chemical-thermal-mechanical multi-field coupling model of concrete in the hydration process; S2. Combining phase field theory and multi-field coupling, a constitutive model that can consider the coupling of concrete age effect and damage effect is established; S3. Set boundary conditions and loading methods that simulate actual working conditions, use numerical simulation to solve the constructed multi-factor coupled phase field model, and simulate the internal damage and material degradation process of concrete in complex environments; S4. Based on the numerical simulation results, key parameters are extracted to evaluate the impermeability of concrete structures. In combination with actual working conditions, materials or construction processes are optimized to improve the crack resistance and impermeability of the project.

2. The method for analyzing the anti-permeability performance of concrete structures considering the multi-physical field coupling effect according to claim 1 is characterized in that: In step S1, in order to consider the shrinkage deformation effect of concrete during hydration, the total strain tensor ε of concrete is decomposed into mechanical strain ε m , thermal expansion strain ε t and the autogenous contraction strain ε a : e=e m +e t +e a ; Where, thermal expansion strain ε t and the autogenous contraction strain ε a are all second-order isotropic tensors, where the self-shrinkage deformation ε a It has a nonlinear relationship with the degree of hydration, expressed as: e a =-a a ξ(χ)I Where I is the second-order unit tensor; α a is a constant coefficient; χ0 is the initial hydration degree; χ ∞ is the final hydration degree; ξ(χ) is the truncated linear function, <x> :=max(x,0);< / x> Thermal expansion strain ε t It is related to the degree of change of early hydration temperature rise and later temperature drop, expressed as: e t =a t (θ-θ0)I; In the formula, α t is the coefficient of thermal expansion, which generally changes with age and temperature; Cement hydration reaction rate for: Where ω(d) is the energy degradation function, which reflects the effect of damage on the hydration reaction of concrete; A(χ) is the standardized chemical affinity; E a is the hydration activation energy; R is the universal gas constant; θ is the temperature; The heat conduction equation for cement hydration reaction is: Where ρ is the mass density of concrete; c is the specific heat capacity of concrete; J is the heat flow; γ is the heat released by cement hydration reaction; p ∞ is the latent heat of hydration reaction; The evolution of mechanical properties of early-age concrete is calculated using the following formula: Where f M (χ) is the mechanical properties of concrete when the degree of hydration is χ; It is the elastic modulus, tensile strength or breaking energy when the maximum hydration degree is reached.

3. The method for analyzing the anti-permeability performance of concrete structures considering the multi-physical field coupling effect according to claim 1 is characterized in that: In step S2, the cracking behavior of concrete is governed by the following governing equations of the displacement subproblem describing the force balance and the phase field subproblem describing the phase field evolution: In the formula, is the Laplace operator; σ is the stress; b is the volume uniform force; the volume where the material is located is Ω, and its external boundary is n is the normal vector of the boundary of the structure under consideration; t * is the value of stress on the corresponding structural boundary; Indicates the crack zone inside the material. and is the outer boundary of the crack zone and its normal vector. q is the crack phase field flux, Q is the crack phase field source, both are functions related to the phase field d (d = 0 means the material is intact, d = 1 means the material is cracked): Where l is the crack width characteristic parameter; c0 is the scale parameter; represents the derivative of the energy degradation function; represents the effective free energy release rate.

4. The method for analyzing the anti-permeability performance of concrete structures considering the multi-physical field coupling effect according to claim 1 is characterized in that: In step S3, the governing equations of the early-age concrete hydration model based on the integrated phase field theory are shown in the following table: In the table, is the Laplace operator; n is the normal vector of the boundary of the structure under consideration; b is the volume uniform force; q is the crack phase field flux; Q is the crack phase field source; u * ,t * ,θ * , J * are the values ​​of displacement, stress, temperature and heat flux on the corresponding structural boundaries; θ a is the air temperature, g is the convection / radiation coefficient related to the air temperature; The above control equations are discretized and solved by the finite element method. The obtained phase field distribution is the actual damage distribution caused by the cracks. Then, combined with the water environment in which the specific structure is located, leakage assessment is carried out.

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