A method for evaluating multi-ion transport in concrete considering saturation and porosity

Abstract

The present invention discloses a method for evaluating multi-ion transmission in concrete considering saturation and porosity, comprising the following steps: constructing a concrete internal moisture transmission model; constructing a concrete internal calcium dissolution model under the influence of moisture saturation; constructing a sulfate ion transmission reaction model in concrete under the influence of moisture saturation and calcium dissolution; constructing a chloride ion transmission reaction model in concrete under the coupling of moisture saturation, calcium dissolution and sulfate ions. The method for evaluating multi-ion transmission in concrete considering saturation and porosity provided by the present invention comprehensively considers the influence of moisture saturation, porosity change and chemical reaction between ions on the internal ion transmission process of long-term service concrete in marine environment, establishes a chloride ion transmission model in concrete under the joint action of chlorine-sulfur coupling erosion and calcium dissolution, and reveals the durability degradation law of concrete structure in marine environment.

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 transport in concrete taking saturation and porosity into consideration. Background Art

[0002] Existing technologies mainly evaluate 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 none of them considers the influence of water saturation. 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.

[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] For example, the patent application publication number CN 112414902A, entitled "Evaluation Method of Chloride Ion Transport in Concrete Considering Sulfate Chemical Damage Effect", establishes a chloride ion transport model inside concrete under the action of sulfate, which considers ion activity, temperature gradient, diffusion term and reaction term; establishes a chloride ion transport model inside concrete under the action of 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, and it is difficult to accurately obtain relevant data; while considering the effect of 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 taking into account saturation and porosity.

[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 considering saturation and porosity, comprising the following steps:

[0008] Construct a model of moisture transport inside concrete;

[0009] Construct a model of calcium dissolution inside concrete under the influence of water saturation;

[0010] Construct a model of sulfate ion transport reaction in concrete under the influence of water saturation and calcium dissolution;

[0011] A chloride ion transport reaction model inside concrete under the coupling effects of water saturation, calcium dissolution and sulfate ions was constructed.

[0012] Furthermore, the concrete internal moisture transmission model is expressed as:

[0013]

[0014] Where Θ is the water saturation, t is the exposure time, x is the distance to the exposed end surface of the concrete, 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.

[0015] Furthermore, the concrete internal calcium dissolution model is expressed as:

[0016]

[0017] 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 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, x 1 is the liquid phase calcium ion concentration corresponding to the rapid decalcification of hydrated calcium silicate gel, x 2 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.

[0018] Furthermore, the sulfate ion transport reaction model inside the concrete is expressed as:

[0019]

[0020] In the formula, is the sulfate ion concentration, is the sulfate ion diffusion coefficient, is the concentration of sulfate ions in chemically bound form, The calcium aluminate (including C3 A.C 4 AH 13 and ) concentration, C CA is the aluminate concentration, C gypsum is the gypsum concentration, k 1 k is the chemical reaction rate coefficient of sulfate ion reaction to form gypsum, 2 is the chemical reaction rate coefficient of aluminate and gypsum to form ettringite, H t is the influence coefficient of temperature on the chemical binding ability of sulfate ions and chloride ions, E b is the binding activation energy, T is the temperature, T ref is the reference temperature, R is the ideal gas constant, and q is the equivalent stoichiometric coefficient of the chemical reaction between sulfate ions and aluminate.

[0021] Furthermore, the chloride ion transport reaction model inside the concrete is expressed as:

[0022]

[0023] In the formula, is the chloride ion concentration, is the chloride ion diffusion coefficient, is the concentration of chloride ions in chemically bound form, Chloride ions in physically bound form, is the concentration of aluminate consumed by the chemical reaction of chloride ions, k cb is the chemical reaction rate constant of chloride ion, k e is the mass transfer coefficient between the liquid phase and the solid phase, f s is the coefficient of influence of sulfate ion concentration on the binding capacity of chloride ions, and δ is the equivalent stoichiometric coefficient of the chemical reaction between chloride ions and aluminate.

[0024] Furthermore, the value of the water saturation is expressed by a formula model as follows:

[0025]

[0026] Where θ is the moisture content of concrete in an aggressive environment, r is the residual moisture content of concrete in dry environment, θ s is the moisture content of concrete under saturated conditions;

[0027] The relationship between water saturation and capillary potential conforms to the formula model:

[0028]

[0029] In the formula, a, m, and n are constant parameters measured by adsorption-desorption experiments;

[0030] Moreover, the partial derivative function of capillary potential to water saturation is expressed by the formula model as follows:

[0031]

[0032] Furthermore, the water diffusion coefficient D Θ The formula model is expressed as:

[0033]

[0034] Furthermore, the chloride ion diffusion coefficient Sulfate ion diffusion coefficient and calcium ion diffusion coefficient The formula model is expressed as:

[0035]

[0036] In the formula, i is the ion type, which can represent Cl - 、SO 4 2- and Ca 2+ , D i,min is the minimum diffusion coefficient of ion i when the pores are filled with products, D i,0 is the initial diffusion coefficient of ion i, β D is the shape factor, which takes a value of 1.5. is the porosity of concrete, is the initial porosity of concrete, D min / D 0 The value is 0.2.

[0037] Furthermore, the porosity of concrete and initial porosity of concrete The formula is:

[0038]

[0039]

[0040] α=1-0.5[(1+1.67τ) -0.6 +(1+0.29τ) -0.48 ]

[0041] In the formula, is the change in concrete pore volume caused by calcium dissolution, is the change in concrete pore volume caused by chemical reaction, f c is the volume fraction of cementitious material in concrete, w / c is the water-cement ratio, α is the degree of cement hydration, and τ is the concrete curing time.

[0042] Furthermore, the change in concrete pore volume is expressed as follows:

[0043]

[0044]

[0045]

[0046]

[0047] In the formula, c AFt is the concentration of aluminate consumed by sulfate chemical reaction, c CA0 is the initial aluminate concentration, α s is the volume change produced when the unit molar concentration of ettringite is generated, c Fs is the concentration of aluminate consumed by the chemical reaction of chloride ions, β s V is the volume change produced when the unit molar concentration of Friedel salt is generated. CH is the molar volume of solid calcium hydroxide.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention provides a method for evaluating multi-ion transport in concrete taking into account saturation and porosity, studies the chloride ion transport mechanism in concrete pore fluid under the action of chlorine-sulfur coupling corrosion, reasonably characterizes the progress of concrete calcium dissolution and the porosity change law caused by it, comprehensively considers the influence of water saturation, porosity change and chemical reaction between ions on the internal ion transport process of long-term service concrete in marine environment, establishes a chloride ion transport model in concrete under the combined action of chlorine-sulfur coupling corrosion and calcium dissolution, reveals the durability degradation law of concrete structure under 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

[0050] Figure 1 A flowchart of a method for evaluating multi-ion transport in concrete considering saturation and porosity provided by an embodiment of the present invention;

[0051] Figure 2 A schematic diagram of the distribution of free chloride ion concentration in concrete under chlorine-sulfur coupling corrosion provided by an embodiment of the present invention;

[0052] Figure 3 A schematic diagram of the effect of saturation on free chloride ion concentration distribution under chlorine-sulfur coupling corrosion provided by an embodiment of the present invention;

[0053] Figure 4A schematic diagram of porosity distribution under chlorine-sulfur coupling corrosion provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0054] 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.

[0055] Example

[0056] like Figure 1 As shown, an embodiment of the present invention provides a method for evaluating multi-ion transport in concrete taking into account saturation and porosity, such as Figure 4 As shown, the following steps are included:

[0057] Step 1: Establish a concrete internal moisture transfer model;

[0058] Step 2: Establish a model of calcium dissolution inside concrete under the influence of water saturation;

[0059] Step 3, establishing a sulfate ion transport reaction model in concrete under the influence of water saturation and calcium dissolution;

[0060] Step 4: Establish a chloride ion transport reaction model inside concrete under the coupling effects of water saturation, calcium dissolution and sulfate ions.

[0061] Specifically, the following is a detailed introduction to this solution with reference to specific cases:

[0062] 1. Step 1: Perform the following operations:

[0063] 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:

[0064]

[0065] Among them, θ is the water saturation, θ is the moisture content inside the concrete under corrosive environment, and θ r is the residual moisture content of concrete in dry environment, θ s is the moisture content of concrete under saturated conditions;

[0066] The relationship between saturation and capillary potential fits the following model:

[0067]

[0068] Among them, Ψ is the capillary potential, a, m, and n are constant parameters measured by adsorption-desorption experiments;

[0069] The partial derivative function of capillary potential with respect to saturation is expressed as follows:

[0070]

[0071] The hydraulic conductivity coefficient K(θ) is expressed as follows:

[0072]

[0073] 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;

[0074] Establishing the model of moisture transport inside concrete:

[0075]

[0076] Where t is the exposure time, and x is the distance to the exposed end surface of the concrete;

[0077] Step 2:

[0078] The water saturation is introduced into the calcium ion transport model in concrete, and the internal calcium dissolution model of concrete under the influence of water saturation is established:

[0079]

[0080] in, is the calcium ion diffusion coefficient, is the liquid phase calcium ion concentration, is the solid phase calcium ion concentration, D Θ is the water diffusion coefficient;

[0081] The water diffusion coefficient can be expressed as:

[0082]

[0083] The volume increments produced by chemical reactions of different reactants are shown in Table 1:

[0084] Table 1 Pore volume increment caused by sulfate chemical reaction and chloride chemical reaction

[0085]

[0086] The change in pore volume caused by calcium dissolution and chemical reaction can be expressed as follows:

[0087]

[0088]

[0089]

[0090]

[0091] Among them, c AFt is the concentration of aluminate consumed by sulfate chemical reaction, c CA0 is the initial aluminate concentration, α s is the volume change produced when the unit molar concentration of ettringite is generated, c Fs is the concentration of aluminate consumed by the chemical reaction of chloride ions, β s V is the volume change produced when the unit molar concentration of Friedel salt is generated. CH is the molar volume of solid calcium hydroxide.

[0092] Concrete porosity and initial porosity of concrete There are the following statements:

[0093]

[0094]

[0095] α=1-0.5[(1+1.67τ) -0.6 +(1+0.29τ) -0.48 ]

[0096] in, is the change in concrete pore volume caused by calcium dissolution, is the change in concrete pore volume caused by chemical reaction, f c is the volume fraction of cementitious materials in concrete, w / c is the water-cement ratio, α is the degree of cement hydration, and τ is the concrete curing time;

[0097] The calcium ion diffusion coefficient is affected by the porosity and can be expressed as:

[0098]

[0099] in, is the minimum diffusion coefficient of calcium ions when the pores are filled with products, is the initial diffusion coefficient of calcium ions, β D is the shape factor, which takes a value of 1.5. is the porosity of concrete, is the initial porosity of concrete, D min / D 0 The value is 0.2;

[0100] The solid phase calcium concentration can be obtained according to the solid-liquid equilibrium equation:

[0101]

[0102] in, 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 when the exposure time is t, 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, x 1 is the liquid phase calcium ion concentration corresponding to the rapid decalcification of hydrated calcium silicate gel, x 2 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;

[0103] Step 3:

[0104] Sulfate ions in the corrosive environment penetrate into the concrete under the combined action of convection and diffusion, and react chemically with calcium ions dissolved from cement hydration products. Therefore, a sulfate ion transport reaction model inside concrete under the influence of water saturation and calcium dissolution is established:

[0105]

[0106] in, is the sulfate ion concentration, is the sulfate ion diffusion coefficient, is the concentration of sulfate ions in chemically bound form;

[0107] The sulfate ion diffusion coefficient is affected by the porosity and can be expressed as:

[0108]

[0109] in, is the minimum diffusion coefficient of sulfate ions when the pores are filled with products, is the initial diffusion coefficient of sulfate ions;

[0110] Considering the influence of temperature on chemical reactions, the temperature influence coefficient is introduced:

[0111] H t =exp[E b / R·(1 / T-1 / T ref )]

[0112] Among them, H t is the influence coefficient of temperature on the chemical binding ability of sulfate ions and chloride ions, E b is the binding activation energy, T is the temperature, Tref is the reference temperature, R is the ideal gas constant;

[0113] Sulfate ions generate gypsum through chemical reactions, and the concentration of sulfate ions consumed through chemical reactions is:

[0114]

[0115] Among them, k 1 is the chemical reaction rate coefficient of sulfate ion reaction to form gypsum;

[0116] Gypsum further reacts with aluminate to form ettringite. The concentration of aluminate consumed by the chemical reaction is:

[0117]

[0118] Among them, C gypsum is the gypsum concentration, k 2 is the chemical reaction rate coefficient of aluminate and gypsum to form ettringite, The calcium aluminate (including C 3 A.C 4 AH 13 and ) concentration, C CA is the aluminate concentration;

[0119] Gypsum is generated by the reaction of sulfate ions and calcium ions, and is consumed by the reaction with aluminate, so the concentration of gypsum changes as follows:

[0120]

[0121] Where q is the equivalent stoichiometric number of the chemical reaction between sulfate ions and aluminate;

[0122] Step 4:

[0123] The corrosion process of chloride ions inside concrete is very complicated. It is the mass transfer process of charged particles in the pore fluid of porous media. The corrosion depth is related to the pore water saturation and chloride ion concentration distribution inside the concrete, and a series of physical and chemical effects occur, including diffusion and convection. At the same time, there is a competitive effect between the binding reaction of chloride ions and sulfate ions. Therefore, a chloride ion transport reaction model inside concrete under the coupling of water saturation, calcium dissolution and sulfate ions is established:

[0124]

[0125] in, is the chloride ion concentration, is the chloride ion diffusion coefficient, is the concentration of chloride ions in chemically bound form, Chloride ions in physically bound form;

[0126] The chloride ion diffusion coefficient is affected by the porosity and can be expressed as:

[0127]

[0128] in, is the minimum diffusion coefficient of chloride ions when the pores are filled with products, is the initial diffusion coefficient of chloride ions;

[0129] Considering the effect of sulfate ion on the binding capacity of chloride ion, the influence coefficient f of sulfate ion concentration on the binding capacity of chloride ion is introduced. s :

[0130]

[0131] The change in ion or substance concentration caused by chemical reaction or physical adsorption during chloride ion corrosion is:

[0132]

[0133] is the concentration of aluminate consumed by the chemical reaction of chloride ions, k cb is the chemical reaction rate constant of chloride ion, k e is the mass transfer coefficient between the liquid phase and the solid phase, δ is the equivalent stoichiometric coefficient of the chemical reaction between chloride ions and aluminate;

[0134] In order to prove the effectiveness of the solution of the present invention, the above transmission model is verified as follows:

[0135] 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 erosion and calcium dissolution for 14 months. The initial conditions and boundary conditions were set as follows:

[0136]

[0137] The values ​​of relevant parameters in the model are shown in Table 2.

[0138] Table 2 Parameters in the diffusion-reaction model

[0139]

[0140] Real sea exposure tests were carried out on plain concrete and hydrophobic concrete at Xiaomaidao exposure station (latitude 36°03'N, longitude 120°25'E) in the southeast of Qingdao, Shandong Province.

[0141] In the test, the test block used four continuous surfaces sealed with epoxy resin to ensure one-dimensional ion transmission and was placed in the tidal zone of the marine environment. After the exposure age reached 14 months, the concrete was ground and the solution was prepared according to the "Technical Specifications for Testing and Inspection of Concrete for Water Transport Engineering" (JTS / T236-2019), and the chloride ion content was determined using IC technology.

[0142] Comparison of the measured results with the simulation results Figure 2 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.

[0143] Figure 3 The influence of saturation parameters on the simulation results of chloride ion concentration distribution is demonstrated.

[0144] Figure 4 The effects of calcium dissolution and chemical reaction on the porosity of concrete are demonstrated.

[0145] 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 considering saturation and porosity, characterized in that: The steps include: Construct a model of moisture transport inside concrete; Construct a model of calcium dissolution inside concrete under the influence of water saturation; Construct a model of sulfate ion transport reaction in concrete under the influence of water saturation and calcium dissolution; Construct a reaction model of chloride ion transport in concrete under the coupling effects of water saturation, calcium dissolution and sulfate ions; The concrete internal moisture transmission 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 concrete, K s is the saturated hydraulic conductivity, l is the constitutive constant, m is a constant parameter measured by adsorption-desorption experiment, Ψ is the capillary potential; The concrete internal calcium dissolution model is expressed as: ； In the formula, The exposure time is t Time distance concrete surface x Solid-phase calcium concentration at depth, The exposure time is t Time distance concrete surface x The liquid calcium concentration at depth, is the calcium ion diffusion coefficient, is the initial calcium silicate hydrate gel content, is the initial calcium hydroxide content, is the saturated liquid calcium ion concentration, x 1 is the liquid phase calcium ion concentration corresponding to the rapid decalcification of hydrated calcium silicate gel. x 2 is the liquid phase calcium concentration corresponding to when calcium hydroxide is completely dissolved and hydrated calcium silicate gel begins to dissolve, D Θ is the water diffusion coefficient; The concrete internal sulfate ion transport reaction model is expressed as: ； In the formula, is the sulfate ion concentration, is the sulfate ion diffusion coefficient, is the concentration of sulfate ions in chemically bound form, Calcium aluminate (including C3A, C4AH) consumed by sulfate chemical reaction 13 and C4ASH 12 )concentration, C CA is the aluminate concentration, C gypsum is the gypsum concentration, k 1 is the chemical reaction rate coefficient of sulfate ion reaction to generate gypsum, k 2 is the chemical reaction rate coefficient of aluminate reacting with gypsum to form ettringite, H t is the influence coefficient of temperature on the chemical binding ability of sulfate ions and chloride ions, E b is the binding activation energy, T is the temperature, T ref is the reference temperature, R is the ideal gas constant, q is the equivalent stoichiometric number of the chemical reaction between sulfate ions and aluminate; The concrete internal chloride ion transport reaction model is expressed as: ； In the formula, is the chloride ion concentration, is the chloride ion diffusion coefficient, is the concentration of chloride ions in chemically bound form, Chloride ions in physically bound form, is the concentration of aluminate consumed by the chemical reaction of chloride ions, k cb is the chemical reaction rate constant of chloride ion, k e is the mass transfer coefficient between the liquid and solid phases, f s is the influence coefficient of sulfate ion concentration on chloride ion binding capacity, δ It is the equivalent stoichiometric coefficient of the chemical reaction between chloride ions and aluminate.

2. The method for evaluating multi-ion transport in concrete considering saturation and porosity according to claim 1, characterized in that: The value of the water saturation is expressed by the formula model as follows: ； In the formula, θ is the moisture content of concrete in an aggressive environment, θ r is the residual moisture content of concrete in a dry environment, θ s is the moisture content of concrete under saturated conditions; The relationship between water saturation and capillary potential conforms to the formula model: ； In the formula, a , m , n is a constant parameter measured by adsorption-desorption test; In addition, the partial derivative function of capillary potential to water saturation is expressed by the formula model: 。 3. The method for evaluating multi-ion transport in concrete considering saturation and porosity according to claim 2, characterized in that: The water diffusion coefficient D Θ The formula model is expressed as: 。 4. The method for evaluating multi-ion transport in concrete considering saturation and porosity according to claim 3, characterized in that: The chloride ion diffusion coefficient , sulfate ion diffusion coefficient and calcium ion diffusion coefficient The formula model is expressed as: ； In the formula, i is the ion type, representing , and , D i,min When the pores are filled with products, the ions i The minimum diffusion coefficient, D i,0 For ions i The initial diffusion coefficient, β D is the shape factor, which takes a value of 1.

5. φ is the porosity of concrete, φ 0 is the initial porosity of concrete, D min / D 0 The value is 0.

2.

5. The method for evaluating multi-ion transport in concrete considering saturation and porosity according to claim 4, characterized in that: Concrete porosity φ and initial porosity of concrete φ 0 is expressed as: ； In the formula, is the change in concrete pore volume caused by calcium dissolution, is the change in concrete pore volume caused by chemical reaction. f c is the volume fraction of cementitious materials in concrete, w / c is the water-to-binder ratio, α is the cement hydration degree, τ It is the curing time of concrete.

6. The method for evaluating multi-ion transport in concrete considering saturation and porosity according to claim 5, characterized in that: The change in concrete pore volume is expressed as: ； In the formula, is the concentration of aluminate consumed by sulfate chemical reaction, c CA0 is the initial aluminate concentration, α s is the volume change produced when the unit molar concentration of ettringite is generated, c Fs is the concentration of aluminate consumed by the chemical reaction of chloride ions, β s is the volume change produced when the unit molar concentration of Friedel salt is generated, V CH is the molar volume of solid calcium hydroxide.

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