Simplified concrete freeze-thaw damage simulation method

Abstract

The invention discloses a simplified concrete freeze-thaw damage simulation method which comprises the following steps: establishing a concrete mesoscopic model, and obtaining internal temperature field distribution of concrete under the action of freeze-thaw cycle; the concrete internal damage evolution law under the freezing and thawing cycle effect is researched, and the mapping relation between damage dissipated energy and loading time is established; the residual compressive strength of the concrete after different freeze-thaw damages is explored based on restart analysis, and when the error between a strength simulation value and an experimental value is less than 3%, the damage dissipated energy corresponding to the current restart analysis is recorded; and establishing a relationship between damage dissipated energy and freezing and thawing cycle times, obtaining residual compressive strength of the concrete under other freezing and thawing cycle times based on restart analysis, and establishing a concrete freezing and thawing damage evaluation model. Results show that the concrete freeze-thaw damage under the unknown freeze-thaw cycle number can be obtained based on limited freeze-thaw damage test data, manpower and material resource consumption is greatly reduced, and accurate prediction of the concrete freeze-thaw damage is achieved.

Description

Technical Field

[0001] The invention relates to a simplified concrete freeze-thaw damage simulation method, belonging to the technical field of concrete durability performance evaluation. Background Art

[0002] When pore water freezes in concrete during freeze-thaw cycles, it expands by one-ninth of its volume, subjecting the pore walls to significant crystallization pressure. When this pressure exceeds the tensile strength of concrete, concrete damage occurs, significantly reducing its service life. Therefore, studying the evolution of concrete damage under freeze-thaw cycles and developing freeze-thaw damage evaluation methods are of great research significance. Conventional freeze-thaw cycle testing of concrete requires the production of a large number of specimens to investigate the evolution of their relative dynamic elastic modulus, mass loss rate, and residual compressive strength, consuming significant manpower and material resources. Furthermore, existing numerical models often simulate concrete freeze-thaw damage by coupling moisture, temperature, stress, and damage fields. These models consider numerous factors, making them unsuitable for practical engineering applications. Therefore, a simplified method for simulating freeze-thaw damage in concrete is urgently needed. Summary of the Invention

[0003] Purpose of the invention: In view of the defects of the prior art, the purpose of the present invention is to provide a simplified method for simulating freeze-thaw damage of concrete, so as to solve the problems that the existing concrete freeze-thaw damage test research is time-consuming and labor-intensive, and the numerical model is too complex to be applied in engineering.

[0004] Technical solution: The simplified concrete freeze-thaw damage simulation method of the present invention is characterized by comprising the following steps:

[0005] (1) Establish a concrete microscopic model and obtain the temperature field distribution inside the concrete under freeze-thaw cycles based on Fick's law;

[0006] (2) Based on sequential coupling, the internal damage evolution law of concrete under freeze-thaw cycles is studied, and the mapping relationship between damage dissipation energy and loading time is established;

[0007] (3) Based on the restart analysis, the residual compressive strength of concrete after different freeze-thaw damage is investigated. When the relative error between the strength simulation value and the experimental value is less than 3%, the damage dissipation energy corresponding to the current restart analysis is recorded;

[0008] (4) Establish the relationship between damage dissipation energy and the number of freeze-thaw cycles, and based on this, obtain the damage dissipation energy of concrete under other freeze-thaw cycles;

[0009] (5) Based on the restart analysis, the residual compressive strength of concrete at other freeze-thaw cycles is obtained, and a concrete freeze-thaw damage evaluation model is established.

[0010] Furthermore, in step (1), the concrete micro-model is established based on the Monte Carlo method using ABAQUS software.

[0011] Furthermore, in step (1), the concrete mesoscopic model is a mesoscopic-scale model including aggregate, interface transition zone, mortar matrix and pores.

[0012] Furthermore, the aggregate volume fraction in the concrete mesoscopic model is 40% and the porosity is 1.17%.

[0013] Furthermore, in step (1), the density, thermal conductivity, and specific heat capacity of the aggregate, interface transition zone, mortar matrix, and pores need to be set during the temperature field simulation.

[0014] Furthermore, in step (2), the sequential coupling is to use the simulation results of the temperature field in step (1) as a predefined field to explore the damage and degradation process of the concrete specimen during the cooling process. In particular, in order to further simplify the numerical model, only the effect of the continuous freezing and expansion of pore water on the specimen during a single cooling process is considered.

[0015] Furthermore, in step (2), the damage dissipation energy can be directly output by the finite element analysis software.

[0016] Furthermore, the finite element analysis software is ABAQUS software, ANSYS software or COMSOL software.

[0017] Furthermore, in step (3), the restart analysis is to use the stress and damage distribution of the specimen in step (2) as a predefined field to explore the residual compressive strength of concrete after freeze-thaw cycles.

[0018] Furthermore, in step (5), the freeze-thaw damage evaluation model is established based on the attenuation of the residual compressive strength, and the calculation formula is as follows:

[0019]

[0020] Where: D is freeze-thaw damage, f0 is the initial compressive strength of concrete, f FT It is the residual compressive strength of concrete after freeze-thaw cycles.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] This paper proposes a simplified method for simulating freeze-thaw damage in concrete. Compared with traditional experimental studies, it significantly reduces the use of manpower and material resources. Compared with existing numerical models, the simulation steps are greatly simplified while achieving higher accuracy. Overall, this method can determine freeze-thaw damage in concrete under an unknown number of freeze-thaw cycles based on limited freeze-thaw damage test data, significantly reducing the use of manpower and material resources and enabling accurate prediction of freeze-thaw damage in concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the four-phase mesoscopic model of concrete;

[0024] Figure 2 This is the specimen boundary temperature diagram during the freeze-thaw cycle simulation;

[0025] Figure 3 This is the temperature field distribution diagram when the temperature at the center of the specimen is the lowest;

[0026] Figure 4 This is the mapping relationship between damage dissipation energy and loading time;

[0027] Figure 5 This is the mechanical composition of the bonding crack unit;

[0028] Figure 6 Insert schematic diagram for bond crack element;

[0029] Figure 7 Schematic diagram of boundary condition settings during compressive strength simulation;

[0030] Figure 8 is the relationship between damage dissipation energy E and the number of freeze-thaw cycles N;

[0031] Figure 9 The relationship between the experimental value and the simulated value of the residual compressive strength of concrete after different freeze-thaw cycles;

[0032] Figure 10 The relationship between the experimental value and the simulated value of freeze-thaw damage of concrete after different freeze-thaw cycles;

[0033] Figure 11 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0035] Example 1:

[0036] (1) Based on the Monte Carlo method, a four-phase microscopic model of concrete including aggregate, mortar, interface transition zone and pores was generated in ABAQUS software (e.g. Figure 1As shown), the aggregate volume fraction is 40% (calculated based on the test mix ratio) and the porosity is 1.17%. The specific steps for generating the micro-model are as follows: ① Generate the aggregate library: Use a random convex function to randomly generate 6-10 polygons of 5-31mm until the area ratio of 40% is met. ② Aggregate placement: Aggregates in the aggregate library are placed in order from large to small. When there is no specimen boundary or other aggregate boundary inside the aggregate, the placement requirement is met. Otherwise, the placement is repeated until all aggregates in the aggregate library are placed. ③ Generate the pore library: Use a random function to randomly generate circular pores with a diameter of 1-2mm until the pore area ratio of 1.17% is met. ④ Pore placement: First, the interference between the pores and the specimen boundary and the placed aggregates is judged, and then the interference between the pores is judged. The former judgment is similar to step ③, and the latter is achieved by judging whether the distance between the centers of the two pores is greater than the sum of the radii of the two centers. Specifically, when the distance between the two circle centers is greater than the sum of the two radii, the delivery requirement is met, otherwise the delivery is repeated.

[0037] (2) Based on the Heat transfer analysis step in ABAQUS software, the temperature field distribution inside the specimen under the action of freeze-thaw cycles was analyzed. During the simulation, the boundary temperature of the specimen was Figure 2 As shown, it is output by the freeze-thaw tester (the temperature of the coolant). The parameter settings of each microscopic component of concrete required in this step are shown in Table 1. The comparison between the experimental value and the simulated value of the temperature at the center of the specimen is shown in Table 1. Figure 2 As shown, Figure 3 It is the temperature field distribution when the temperature at the center of the specimen is the lowest.

[0038] Table 1 Parameter settings of each mesoscopic component of concrete during simulation

[0039] aggregate mortar Porosity COH-Mortar COH-pore COH-Interface <![CDATA[Density (kg / m 3 )]]> 2750 2300 1000 / / / Thermal conductivity (W / (m·K)) 2.75 0.89 0.6 / / / Specific heat capacity (J / (kg·K)) 800 2730 2100 / / / Elastic modulus (MPa) 65000 31000 600 / / / Poisson's ratio 0.15 0.2 0.35 / / / Forward stiffness (MPa / mm) 31000 23250 15500 Tangential stiffness (MPa / mm) 31000 23250 15500 Tensile strength (MPa) 3 2.25 1.5 Shear strength (MPa) 30 22.5 15 Tensile breaking energy (N / m) 30 22.5 15 Shear fracture energy (N / m) 300 300 150

[0040] (3) The temperature field data obtained in step (2) is used as a predefined field (only considering the influence of the temperature drop process, i.e. Figure 2 The Dynamic, Explicit analysis step in ABAQUS was used to explore the effect of continuous freezing of pore water on the internal damage of the specimen during the cooling process, and the mapping relationship between damage dissipation energy and loading time was established (such as Figure 4 During the simulation, zero-thickness bond crack units were inserted inside the mortar, around the pores, and in the interface transition zone. The damage constitutive model was adopted as follows: Figure 5 The insertion process of the bonding crack unit is shown in Figure 6 As shown below: Assume that the element and node numbers before the concrete mesh information is re-edited are as follows: Figure 6 As shown in (a), Figure 6In (a), units ③ and ④ are aggregate units, and ① and ② are mortar units. After embedding bonding units with a thickness of 0 between mortar units and between aggregate and mortar units, Figure 6 As shown in (b), the node numbers are reorganized: node 1 is split into 1 and 10, node 2 is split into 2 and 4, node 3 is split into 5 and 7, and node 5 is split into 3, 6, and 9. Units ①, ②, ③, and ④ are composed of the new nodes. The parameter settings for each concrete mesoscopic component required in this step are shown in Table 1.

[0041] (4) Based on the restart analysis, the freeze-thaw damage of concrete after different loading times is used as a predefined field to explore its effect on the compressive strength of concrete. In particular, when the relative error between the strength simulation value and the experimental value is less than 3%, the damage dissipation energy corresponding to the current restart analysis is recorded. The boundary conditions in the numerical simulation process are as follows: Figure 7 As shown in Figure 1, the degrees of freedom of the bottom of the specimen are all constrained, the left and right ends of the specimen are free ends, and after coupling the top of the specimen with the reference point, a downward displacement load is applied to the reference point.

[0042] (5) Based on the method described in step (4), the damage dissipation energy of the specimen after 25, 50 and 75 freeze-thaw cycles was obtained in turn, and the relationship between the damage dissipation energy E and the number of freeze-thaw cycles N was established based on nonlinear regression analysis (e.g. Figure 8 As shown), that is, E = 0.3968N.

[0043] (6) Based on the relationship between the damage dissipation energy E and the number of freeze-thaw cycles N obtained in step (5), the damage dissipation energy of the specimen after 100, 125, and 150 freeze-thaw cycles was further obtained, as shown in Table 2.

[0044] Table 2 Damage dissipation energy of specimens after different freeze-thaw cycles

[0045] Number of freeze-thaw cycles 100 125 150 Damage dissipation energy (mJ) 39.68 49.60 59.52

[0046] (7) Based on the damage dissipation energy shown in Table 2, the residual compressive strength of the specimens after 100, 125, and 150 freeze-thaw cycles was obtained based on the restart analysis (e.g. Figure 9 The boundary conditions of this process are consistent with those of step (4).

[0047] (8) Based on the residual compressive strength of the specimens after 0, 25, 50, 75, 100, 125 and 150 freeze-thaw cycles obtained by numerical simulation, the freeze-thaw damage of the specimens after different freeze-thaw cycles was calculated using the following formula (e.g. Figure 10 As shown). Figure 10 It can be seen that the simulated values of concrete freeze-thaw damage after different freeze-thaw cycles are in good agreement with the experimental values, which proves the rationality of this method.

[0048]

[0049] Where: D is freeze-thaw damage, f0 and f FT They are the initial compressive strength of concrete and the residual compressive strength after freeze-thaw cycles. Figure 11 shown.

Claims

1. A simplified concrete freeze-thaw damage simulation method, characterized in that: The following steps are involved: (1) Establish a concrete microscopic model and obtain the temperature field distribution inside the concrete under freeze-thaw cycles based on Fick's law; (2) Based on sequential coupling, the internal damage evolution law of concrete under freeze-thaw cycles is studied, and the mapping relationship between damage dissipation energy and loading time is established; (3) Based on the restart analysis, the residual compressive strength of concrete after different freeze-thaw damage is investigated. When the relative error between the strength simulation value and the experimental value is less than 3%, the damage dissipation energy corresponding to the current restart analysis is recorded; (4) Establish the relationship between damage dissipation energy and the number of freeze-thaw cycles, and based on this, obtain the damage dissipation energy of concrete under other freeze-thaw cycles; (5) Based on the restart analysis, the residual compressive strength of concrete at other freeze-thaw cycles is obtained, and a concrete freeze-thaw damage evaluation model is established.

2. The simplified concrete freeze-thaw damage simulation method according to claim 1, characterized in that: The concrete micro-model is established based on the Monte Carlo method using ABAQUS software.

3. The simplified concrete freeze-thaw damage simulation method according to claim 1, characterized in that: In step (1), the concrete mesoscopic model is a mesoscopic model including aggregate, interface transition zone, mortar matrix and pores.

4. The simplified concrete freeze-thaw damage simulation method according to claim 3, characterized in that: The aggregate volume fraction in the concrete mesoscopic model is 40% and the porosity is 1.17%.

5. The simplified concrete freeze-thaw damage simulation method according to claim 1, characterized in that: In step (1), the density, thermal conductivity, and specific heat capacity of the aggregate, interface transition zone, mortar matrix, and pores need to be set during the temperature field simulation.

6. The simplified concrete freeze-thaw damage simulation method according to claim 1, characterized in that: In step (2), the damage dissipation energy can be directly output by the finite element analysis software.

7. The simplified concrete freeze-thaw damage simulation method according to claim 6, characterized in that: The finite element analysis software is ABAQUS, ANSYS or COMSOL.

8. The simplified concrete freeze-thaw damage simulation method according to claim 1, characterized in that: In step (4), the relationship between damage dissipation energy and the number of freeze-thaw cycles is obtained by multivariate nonlinear fitting.

9. The simplified concrete freeze-thaw damage simulation method according to claim 1, characterized in that: In step (5), the freeze-thaw damage evaluation model is established based on the attenuation of residual compressive strength, and the calculation formula is as follows: Where: D is freeze-thaw damage, f0 is the initial compressive strength of concrete, f FT It is the residual compressive strength of concrete after freeze-thaw cycles.

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