Method for evaluating multi-ion transmission in concrete based on diffusion coefficient time-varying rule

Abstract

The invention discloses a method for evaluating multi-ion transmission in concrete based on a diffusion coefficient time-varying rule, and belongs to the technical field of durability of concrete structures, and the method comprises the following steps: building a concrete structure internal moisture transmission model; establishing an ion diffusion coefficient time-varying model in the concrete structure; respectively obtaining water saturation and diffusion coefficients corresponding to chloride ions, sulfate ions and calcium ions according to the water transmission model and the ion diffusion coefficient time-varying model, and establishing a multi-ion coupling transmission model based on the water saturation and the diffusion coefficients. The method for evaluating the multi-ion transmission in the concrete based on the diffusion coefficient time-varying rule disclosed by the invention reveals the durability degradation rule of the concrete structure in the marine environment, and lays a theoretical foundation for developing durability design of the concrete structure and predicting the service life of the concrete structure.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete durability, and in particular relates to a method for evaluating multi-ion transmission in concrete based on the time-varying law of diffusion coefficient. Background Art

[0002] Concrete durability design and evaluation evaluates the ion transport behavior in concrete from the perspective of chemical damage. The model has been greatly improved compared to the simple chloride ion transport model, but the influence of water saturation is not considered. Water is a carrier of ion transport, and its saturation has a great influence on the ion concentration distribution in concrete, which is an influencing factor that cannot be ignored. The size of the diffusion coefficient is determined by the porosity, and the influencing factors are relatively single, which is inconsistent with reality.

[0003] For example, the patent application publication number CN 111310360A, entitled "A method for assessing the transport of concrete damage under sulfate attack in the splash zone", establishes a damage constitutive model under sulfate attack based on the damage to the concrete structure caused by the chemical reaction between sulfate ions and material components in the concrete. It also establishes a relationship between the stress and porosity of the concrete damage process, and then establishes a relationship between the porosity and the ion diffusion coefficient, thereby obtaining the ion diffusion coefficient after damage. Finally, a sulfate ion transport model based on the relationship between the porosity and the ion diffusion coefficient affected by chemical damage is established. The type of corrosive ions is single, and it is rather one-sided to describe the ion corrosion behavior of concrete in service under actual marine environments.

[0004] Another example is the patent application publication number CN 112414902A, entitled "Chloride ion transport assessment method in concrete considering sulfate chemical damage effect", which establishes a chloride ion transport model inside concrete under sulfate, taking into account ion activity, temperature gradient, diffusion term and reaction term; establishes a chloride ion transport model inside concrete under temperature field; finally, establishes a chloride ion transport model inside concrete under the coupling of sulfate and temperature field from three aspects: pore structure, cracks and bonding effect. However, the ion activity measurement technology is limited, making it difficult to accurately obtain relevant data; while considering the effect of the chemical reaction of chloride ions and sulfate ions on porosity, the effect of calcium dissolution is more significant, and the effect of water transport is not considered. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficients.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0007] The present invention provides a method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient, comprising the following steps:

[0008] Establish a model of moisture transfer inside concrete structures;

[0009] Establish a time-varying model of ion diffusion coefficient in concrete structures;

[0010] The water saturation and the diffusion coefficients corresponding to chloride ions, sulfate ions and calcium ions are obtained respectively according to the water transport model and the ion diffusion coefficient time-varying model, and a multi-ion coupling transport model is established based on the water saturation and the diffusion coefficients.

[0011] Furthermore, the formula of the moisture transfer model is expressed as:

[0012]

[0013] Where Θ is the water saturation, t is the exposure time, x is the distance to the exposed end surface of the concrete, K(Θ) is the hydraulic conductivity, and K s is the saturated hydraulic conductivity, l is the constitutive constant, m is the constant parameter measured by adsorption-desorption test, and Ψ is the capillary potential.

[0014] Furthermore, the formula of the time-varying model of the ion diffusion coefficient is expressed as:

[0015]

[0016] Where i is the ion type, and its value is Cl - , and Ca 2+ , D i is the ion diffusion coefficient that varies with time, D i,0 The hydration age of concrete is t hydration,0 The ion diffusion coefficient measured at t hydration is the hydration age of concrete, m t is the time decay factor.

[0017] Furthermore, the relationship between the water saturation and the capillary potential conforms to the following model:

[0018]

[0019] In the formula, a, m, and n are constant parameters measured by adsorption-desorption experiments;

[0020] The partial derivative function of the capillary potential with respect to water saturation is expressed as follows:

[0021]

[0022] Furthermore, establishing a multi-ion coupling transport model based on the water saturation and the diffusion coefficient includes the following steps:

[0023] A concrete internal calcium dissolution model under the influence of water saturation and time-varying calcium ion diffusion coefficient was established;

[0024] A sulfate ion transport model in concrete under the influence of water saturation and time-varying sulfate ion diffusion coefficient was established.

[0025] A chloride ion transport model inside concrete under the coupling effects of water saturation, calcium dissolution and sulfate ions was established.

[0026] Furthermore, the concrete internal calcium dissolution model is expressed as:

[0027]

[0028]

[0029] In the formula, is the solid calcium ion concentration at a depth x from the concrete surface when the exposure time is t, is the liquid calcium ion concentration at a depth x from the concrete surface at exposure time t, is the calcium ion diffusion coefficient, C CSH0 is the initial calcium silicate hydrate gel content, C CH0 is the initial calcium hydroxide content, C satu is the saturated liquid calcium ion concentration, is the liquid phase calcium ion concentration corresponding to the rapid decalcification of hydrated calcium silicate gel. D is the liquid phase calcium concentration corresponding to the complete dissolution of calcium hydroxide and the beginning of the dissolution of calcium silicate hydrate gel. Θ is the water diffusion coefficient.

[0030] Furthermore, the sulfate ion transport model inside the concrete is expressed as:

[0031]

[0032] In the formula, is the sulfate ion concentration, is the sulfate ion diffusion coefficient.

[0033] Furthermore, the chloride ion transmission model inside concrete is:

[0034]

[0035] In the formula, is the chloride ion concentration, is the chloride ion diffusion coefficient.

[0036] Furthermore, the water diffusion coefficient D Θ The formula is:

[0037]

[0038] Where a, m, and n are constant parameters measured by adsorption-desorption experiments.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The multi-ion transport evaluation method in concrete based on the time-varying law of diffusion coefficient provided by the present invention establishes the chloride ion transport mechanism in the concrete pore fluid under the action of chlorine-sulfur coupling corrosion from the two aspects of water saturation and time-varying diffusion coefficient, and reasonably characterizes the concrete calcium dissolution process and the porosity change law caused by it, comprehensively considers the influence of water saturation and time-varying diffusion coefficient on the internal ion transport process of long-term service concrete in marine environment, reveals the durability degradation law of concrete structure in marine environment, and lays a theoretical foundation for carrying out durability design of concrete structure and predicting its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flow chart of the multi-ion transport evaluation method in concrete based on the time-varying law of diffusion coefficient;

[0042] Figure 2 It is a comparison diagram of the simulation results of the model of the present invention and the results of Experiment 1;

[0043] Figure 3 It is a comparison chart between the simulation results of the model of the present invention and the results of Experiment 2. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0045] Example

[0046] like Figure 1 As shown, the present invention provides a method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient, comprising the following steps:

[0047] Step 1: Establish a moisture transfer model inside the concrete structure.

[0048] The degree of concrete saturation is a necessary condition for the occurrence of concrete durability degradation and the basis for the establishment of many failure mechanisms and models. The value of saturation is determined by the following calculation model:

[0049]

[0050] Among them, θ is the water saturation, θ is the moisture content inside the concrete under corrosive environment, and θr is the residual moisture content of concrete in dry environment, θ s is the moisture content of concrete under saturated conditions;

[0051] The relationship between saturation and capillary potential fits the following model:

[0052]

[0053] Among them, Ψ is the capillary potential, a, m, and n are constant parameters measured by adsorption-desorption experiments;

[0054] The partial derivative function of capillary potential with respect to saturation is expressed as follows:

[0055]

[0056] The hydraulic conductivity coefficient K(θ) is expressed as follows:

[0057]

[0058] Among them, K s is the saturated hydraulic conductivity, l is the constitutive constant, and m is the constant parameter measured by adsorption-desorption test;

[0059] Combining the above parameters, the concrete internal moisture transmission model is established, as shown in the following formula:

[0060]

[0061] Where t is the exposure time, and x is the distance to the exposed end surface of the concrete;

[0062] Step 2: Establish a time-varying model of ion diffusion coefficient in concrete structure.

[0063] The chloride ion diffusion coefficient of concrete was measured when the hydration age reached 28 days. Sulfate ion diffusion coefficient and calcium ion diffusion coefficient The ion diffusion coefficient at different hydration ages t is expressed as follows:

[0064]

[0065] Among them, i is the ion type, which can represent Cl - , and D i is the ion diffusion coefficient that varies with time, D i,0 The hydration age of concrete is t hydration,0 The ion diffusion coefficient measured at t hydration is the hydration age of concrete, m tis the time decay factor;

[0066] Step 3: According to the water transport model and the ion diffusion coefficient time-varying model, the water saturation and the diffusion coefficients corresponding to chloride ions, sulfate ions and calcium ions are respectively obtained, and a multi-ion coupling transport model is established based on the water saturation and the diffusion coefficients.

[0067] For concrete structures that have been exposed to water environments such as the ocean for a long time, the cement hydration products inside the concrete are easily corroded under the action of water. The corrosion increases the porosity of the concrete, deteriorates the microstructure, and accelerates the transmission process of ions inside the concrete. Therefore, firstly, a concrete internal calcium dissolution model under the influence of water saturation and time-varying calcium ion diffusion coefficient is established, as shown in the following formula:

[0068]

[0069]

[0070] in, is the solid calcium ion concentration at a depth x from the concrete surface at exposure time t, is the liquid calcium ion concentration at a depth x from the concrete surface when the exposure time is t, is the calcium ion diffusion coefficient, C CSH0 is the initial calcium silicate hydrate gel content, C CH0 is the initial calcium hydroxide content, C satu is the saturated liquid calcium ion concentration, is the liquid phase calcium ion concentration corresponding to the rapid decalcification of hydrated calcium silicate gel. D is the liquid phase calcium concentration corresponding to the complete dissolution of calcium hydroxide and the beginning of the dissolution of calcium silicate hydrate gel. Θ is the water diffusion coefficient.

[0071] Secondly, the sulfate ion transport model inside concrete under the influence of water saturation and time-varying sulfate ion diffusion coefficient is established:

[0072]

[0073] in, is the sulfate ion concentration, is the sulfate ion diffusion coefficient.

[0074] Finally, a chloride ion transport model inside concrete under the coupling effects of water saturation, calcium dissolution and sulfate ions was established.

[0075]

[0076] in, is the chloride ion concentration, is the chloride ion diffusion coefficient.

[0077] In order to prove the effectiveness of the technical solution of the embodiment of the present invention, the multi-ion transport evaluation method in concrete based on the time-varying law of diffusion coefficient of the present invention is verified as follows in combination with specific embodiments.

[0078] Li Jianqiang and others conducted a real sea exposure test at Xiaomai Island in Qingdao and studied the distribution law of surface chloride ion concentration of concrete in the tidal zone when the corrosion age reached 13 months.

[0079] Xu Mei et al. measured the distribution of chloride ion content at different depths in the concrete of a tidal zone of a dock in Dalian Port that had been in service for 11 years.

[0080] In this simulation, the PDE (partial differential equation) module of COMSOL finite element software was used to simulate the one-dimensional chloride ion diffusion process under the coupling of chlorine-sulfur corrosion and calcium dissolution when the concrete exposure age reached 13 months and 11 years. The surface chloride ion concentration and the 28d chloride ion diffusion coefficient are shown in Table 1, respectively.

[0081] Comparison of the measured results with the simulation results Figure 2 and Figure 3 As shown in the figure, the experimental data are in good agreement with the simulation data, indicating that the model can be used to predict the distribution of chloride ion concentration in concrete under actual marine corrosion environment.

[0082] Table 1

[0083] Data Source Surface chloride ion concentration / % 28d chloride ion diffusion coefficient Experiment 1: Qingdao Wheat Island 1 <![CDATA[2×10 -11 m 2 / s]]> Experiment 2: Dalian Port 0.8 <![CDATA[1.5×10 -11 m 2 / s]]>

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient, characterized in that: The steps include: Establish a model of moisture transfer inside concrete structures; Establish a time-varying model of ion diffusion coefficient in concrete structures; The water saturation and the diffusion coefficients corresponding to chloride ions, sulfate ions and calcium ions are obtained respectively by using a water transport model and an ion diffusion coefficient time-varying model, and a multi-ion coupling transport model is established based on the water saturation and the diffusion coefficients.

2. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to claim 1 is characterized in that: The formula of the moisture transfer model is expressed as: Where Θ is the water saturation, t is the exposure time, x is the distance to the exposed end surface of the concrete, K(Θ) is the hydraulic conductivity, and K s is the saturated hydraulic conductivity, l is the constitutive constant, m is the constant parameter measured by adsorption-desorption test, and Ψ is the capillary potential.

3. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to claim 2 is characterized in that: The formula of the time-varying model of ion diffusion coefficient is expressed as: Where i is the ion type, and its value is Cl - 、SO4 2- and Ca 2+ , D i is the ion diffusion coefficient that varies with time, D i,0 The hydration age of concrete is t hydration,0 The ion diffusion coefficient measured at t hyration is the hydration age of concrete, m t is the time decay factor.

4. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to claim 2 is characterized in that: The relationship between water saturation and capillary potential conforms to the following model: In the formula, a, m, and n are constant parameters measured by adsorption-desorption experiments; The partial derivative function of the capillary potential with respect to water saturation is expressed as follows:

5. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to any one of claims 2 to 4, characterized in that: Establishing a multi-ion coupling transport model based on the water saturation and the diffusion coefficient includes the following steps: A concrete internal calcium dissolution model under the influence of water saturation and time-varying calcium ion diffusion coefficient was established; A sulfate ion transport model in concrete under the influence of water saturation and time-varying sulfate ion diffusion coefficient was established. A chloride ion transport model inside concrete under the coupling effects of water saturation, calcium dissolution and sulfate ions was established.

6. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to claim 5, characterized in that: The concrete internal calcium dissolution model is expressed as: In the formula, is the solid calcium ion concentration at a depth x from the concrete surface when the exposure time is t, D is the liquid calcium ion concentration at a depth x from the concrete surface at exposure time t, Ca2+ is the calcium ion diffusion coefficient, C CSH0 is the initial calcium silicate hydrate gel content, C CH0 is the initial calcium hydroxide content, C satu is the saturated liquid calcium ion concentration, is the liquid phase calcium ion concentration corresponding to the rapid decalcification of hydrated calcium silicate gel. D is the liquid phase calcium concentration corresponding to the complete dissolution of calcium hydroxide and the beginning of the dissolution of calcium silicate hydrate gel. Θ is the water diffusion coefficient.

7. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to claim 6, characterized in that: The concrete internal sulfate ion transport model is expressed as: In the formula, is the sulfate ion concentration, is the sulfate ion diffusion coefficient.

8. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to claim 7, characterized in that: The concrete internal chloride ion transmission model: In the formula, C Cl- is the chloride ion concentration, D Cl- is the chloride ion diffusion coefficient.

9. The method for evaluating multi-ion transport in concrete based on the time-varying law of diffusion coefficient according to claim 6, characterized in that: The water diffusion coefficient D Θ The formula is: Where a, m, and n are constant parameters measured by adsorption-desorption experiments.

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