Concrete chlorine salt erosion model construction method suitable for salt-fresh water intersection area

Abstract

The invention discloses a concrete chlorine salt erosion model construction method suitable for a salt-fresh water intersection area, and belongs to the technical field of concrete erosion, and the concrete chlorine salt erosion model construction method suitable for the salt-fresh water intersection area comprises the following steps: S1, determining the time-varying distribution characteristics of the chlorine salt concentration of the salt-fresh water intersection area; s2, acquiring chlorine salt erosion rules of the concrete test piece at different test ages; s3, constructing a time-varying model of the chloride ion concentration on the surface of the concrete; s4, constructing a time-varying model of the concrete chloride ion diffusion coefficient based on the Fick second law analytical solution; and S5, constructing a concrete chlorine salt erosion double-time-varying numerical model in a saturated state. According to the method, the actual service environment of the concrete structure in the river-sea intersection area can be better reflected, the durability of the concrete structure in the river-sea intersection area can be accurately predicted, a more reliable basis is provided for durability design of the salt and fresh water intersection area, and high-quality construction of the concrete structure in the salt and fresh water intersection area is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete erosion, and particularly relates to a method for constructing a concrete chloride erosion model applicable to the salt - fresh water confluence area. Background Art

[0002] Reinforced concrete structures have become the most common composite structures in modern transportation infrastructure due to their advantages such as strong plasticity, high bearing capacity, and low cost. However, the service life of reinforced concrete structures in the marine environment is much lower than the designed service life. The reason is that in addition to suffering from conventional impacts, abrasions and other factors, reinforced concrete structures in the marine environment also face the risk of chloride erosion. When chloride ions penetrate the concrete protective layer and accumulate a certain concentration on the steel bar surface, they will damage the passivation film of the steel bar under the action of oxygen, causing steel bar corrosion. After corrosion, the volume of the steel bar product expands, causing rust - induced cracks in the concrete and reducing the service life of the structure.

[0003] With the establishment of the chloride transport model for concrete structures in the marine environment, the chloride erosion law of concrete structures in this environment has been basically clarified. However, there is little research on the durability of concrete structures in the salt - fresh water confluence area. The chloride concentration in the service environment of concrete in the salt - fresh water confluence area changes irregularly due to seasonal influences such as tides and wind directions, and the chloride concentration in this area is much lower than that in the marine environment. The chloride transport model for concrete structures in the marine environment is not applicable to the durability design of concrete in the river - sea confluence area. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a method for constructing a concrete chloride erosion model applicable to the salt - fresh water confluence area, which can be applicable to the chloride erosion law of concrete structures in the river - sea confluence area, thereby providing technical support for the durability design of concrete structures in the salt - fresh water confluence area.

[0005] The method for constructing a concrete chloride erosion model applicable to the salt - fresh water confluence area according to an embodiment of the present invention includes:

[0006] S1: Obtain the seasonal variation law of chloride concentration in the estuary area, and determine the time - varying distribution characteristics of chloride concentration in the salt - fresh water confluence area according to the seasonal variation law of chloride concentration;

[0007] S2: Obtain concrete specimens, and conduct immersion tests on the concrete specimens according to the time - varying distribution characteristics to obtain the distribution law of chloride concentration on the concrete surface and chloride ions inside;

[0008] S3: Construct a time - varying model of chloride concentration on the concrete surface according to the distribution law of chloride concentration on the concrete surface and chloride ions inside;

[0009] S4: Construct a time-varying model of the chloride diffusion coefficient of concrete based on the analytical solution of Fick's second law;

[0010] S5: According to the time-varying model of the chloride concentration on the concrete surface and the time-varying model of the chloride diffusion coefficient of concrete, construct a double-time-varying numerical model for the chloride salt erosion of concrete in a saturated state.

[0011] The method for constructing a chloride salt erosion model of concrete applicable to the saltwater-freshwater confluence area according to the embodiments of the present invention has at least the following beneficial effects: obtaining the variation laws of chloride salt concentration and astronomical tide changes in the outer sea in a typical saltwater-freshwater confluence area to provide an environmental background for subsequent concrete erosion research, obtaining erosion data of concrete in different chloride salt environments through indoor concrete immersion tests, and then quantifying the accumulation process of chloride ions on the concrete surface by constructing a time-varying model of the chloride concentration on the concrete surface. Then, construct a time-varying model of the chloride diffusion coefficient of concrete to describe the diffusion behavior of chloride ions inside the concrete. Finally, propose a double-time-varying numerical model that considers the periodic change of environmental corrosion media and is applicable to the saltwater-freshwater confluence area, so as to realize the prediction of the long-term erosion behavior of concrete in a chloride salt environment, better reflect the actual service environment of concrete structures in the river-sea confluence area, provide a more reliable basis for the durability design of the saltwater-freshwater confluence area, and improve the high-quality construction of concrete structures in the saltwater-freshwater confluence area.

[0012] According to some embodiments of the present invention, it further includes S6: Based on the double-time-varying numerical model of the chloride salt erosion of concrete in a saturated state, construct a numerical simulation model considering the surface chloride concentration and the chloride diffusion coefficient to complete the model accuracy analysis by comparing the simulated data with the measured data.

[0013] According to some embodiments of the present invention, in S1, obtaining the seasonal variation law of the chloride salt concentration in the estuary area includes: selecting no less than three estuary areas as monitoring areas, collecting water samples once in each season; synchronously collecting astronomical tide data in the monitoring areas during the sampling period; continuously collecting water samples and measuring the chloride salt concentration in each water sample; combining the collected astronomical tide data to record the chloride salt concentration in the corresponding water sample.

[0014] According to some embodiments of the present invention, for waters with a water depth exceeding 5 meters, stratified sampling is carried out at three points on the surface layer, middle layer and bottom layer in the vertical direction.

[0015] According to some embodiments of the present invention, in S2, the immersion test on the concrete specimens according to the time-varying distribution characteristics is implemented through the following steps: Based on the time-varying distribution characteristics of the chloride salt concentration in the brackish-freshwater confluence area, the highest concentration, the intermediate concentration, and the lowest concentration are selected as the chloride salt concentrations of the immersion solution; The five surfaces of the concrete specimens are coated with epoxy resin for sealing, and one surface is reserved as the exposed surface; Prepare high-chloride-salt-concentration solution, medium-chloride-salt-concentration solution, and low-chloride-salt-concentration solution, place the sealed concrete specimens in a container, and conduct cyclic immersion tests with different chloride salt concentrations according to the seasonal change law of the chloride salt concentration.

[0016] According to some embodiments of the present invention, the concentration of the immersion solution is detected monthly, and the concentration fluctuation range of the immersion solution is controlled not to exceed ±0.05%.

[0017] According to some embodiments of the present invention, in S3, obtaining the distribution law of the chloride ion concentration on the concrete surface and the internal chloride ions at different test ages includes: Taking out the concrete specimens at different test ages; Using the powder grinding method to conduct stratified sampling on the concrete specimens at different ages; Using the chemical titration method to determine the chloride ion content in each layer of concrete powder sample, and obtaining the chloride salt concentration of each layer of concrete powder sample; Based on the chloride salt concentration of the concrete powder samples at different ages, obtaining the erosion law of the chloride salt in the concrete specimens at different ages.

[0018] According to some embodiments of the present invention, in S4, the time-varying model of the concrete chloride ion diffusion coefficient is determined through the following steps: Setting boundary conditions and initial conditions for the preset Fick's second law to obtain the analytical formula of Fick's second law; Obtaining the apparent chloride ion diffusion coefficient, substituting the apparent chloride ion diffusion coefficient into the analytical formula of Fick's second law, and establishing a time-varying model of the concrete chloride ion diffusion coefficient.

[0019] According to some embodiments of the present invention, the time-varying model of the concrete chloride ion diffusion coefficient is:

[0020]

[0021] In the formula: C(x,t) is the chloride ion concentration in the depth x of the concrete specimen after soaking for t, C s is the chloride ion concentration on the concrete surface, C i is the initial chloride ion concentration of the concrete, D e is the concrete chloride ion diffusion coefficient, x is the depth from the concrete immersion surface, t is the immersion time, and erf is the error function.

[0022] According to some embodiments of the present invention, the chloride ion diffusion coefficient is determined by the following steps: obtaining the water-binder ratio of the concrete, the mass fraction of fly ash, and the mass fraction of slag; calculating the time decay coefficient of the concrete in the wet-dry alternate area; obtaining the exposure time, and calculating the chloride ion diffusion coefficient of the concrete corresponding to the exposure time based on the time decay coefficient.

[0023] According to some embodiments of the present invention, the deformation formula of the chloride ion diffusion coefficient is:

[0024]

[0025] In the formula: is the apparent chloride ion diffusion coefficient of the concrete corresponding to the exposure time t i ; is the apparent chloride ion diffusion coefficient of the concrete corresponding to the concrete curing time t1, and n is the time decay coefficient.

[0026] According to some embodiments of the present invention, data verification is performed on the calculation results of the chloride ion diffusion coefficient of the concrete and the chloride ion concentration on the concrete surface: taking the arithmetic mean of the calculation results of three specimens of the same batch; if the deviation of the calculation result of any specimen from the median exceeds 20% of the mean value, then the median value is taken as the final value; if the deviations of the calculation results of two specimens from the median both exceed 20% of the mean value, then it is determined that the set of data is invalid and a new test is carried out.

[0027] The additional aspects and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

[0029] Figure 1 is a schematic flow chart of a method for constructing a concrete chloride salt erosion model applicable to the salt-fresh water confluence area in this specific embodiment;

[0030] Figure 2 is a graph of the seasonal variation law of chloride salt concentration;

[0031] Figure 3 is a graph of the variation law of surface chloride ion concentration;

[0032] Figure 4 is a comparison graph of concrete chloride salt distribution under different value-taking conditions. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] In the description of the present invention, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc., is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0034] In the description of the present invention, the meaning of "several" is one or more, the meaning of "multiple" is more than two. Understanding greater than, less than, exceeding, etc. does not include the original number, and understanding "above", "below", "within", etc. includes the original number. If there is a description of "first", "second", etc., it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0035] In the description of the present invention, unless otherwise clearly defined, words such as "set", "install", "connect", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0036] Please refer to Figure 1 , this embodiment discloses a method for constructing a concrete chloride erosion model applicable to the salt - fresh water confluence area, including:

[0037] S1: Obtain the seasonal variation law of chloride concentration in the estuary area, and determine the time - varying distribution characteristics of chloride concentration in the salt - fresh water confluence area according to the seasonal variation law of chloride concentration.

[0038] S2: Obtain concrete specimens, and conduct immersion tests on the concrete specimens according to the time - varying distribution characteristics to obtain the distribution law of chloride ion concentration on the concrete surface and chloride ions inside.

[0039] S3: Construct a time - varying model of chloride ion concentration on the concrete surface according to the distribution law of chloride ion concentration on the concrete surface and chloride ions inside.

[0040] S4: Construct a time - varying model of concrete chloride diffusion coefficient based on the analytical solution of Fick's second law.

[0041] S5: Construct a double - time - varying numerical model of concrete chloride erosion in the saturated state according to the time - varying model of chloride ion concentration on the concrete surface and the time - varying model of concrete chloride diffusion coefficient.

[0042] According to the variation law of chloride salt concentration and the variation law of astronomical tides in the open sea in the typical brackish water convergence area, an indoor concrete immersion test is carried out, and then a double-time-varying numerical model of concrete chloride salt erosion under saturated state is constructed and corrected, so as to propose a concrete chloride salt erosion model that takes into account the periodic change of environmental corrosion medium and is applicable to the brackish water convergence area, which can better reflect the actual service environment of concrete structures in the river-sea convergence area, accurately predict the durability of concrete structures in the river-sea convergence area, provide a more reliable basis for the durability design of the brackish water convergence area, and improve the high-quality construction of concrete structures in the brackish water convergence area.

[0043] It should be noted that Fick's second law, that is, Fick's second law, states that: the diffusion mass flow rate through a unit cross-sectional area perpendicular to the diffusion direction per unit time is proportional to the concentration gradient at that cross-section, that is, the greater the concentration gradient, the greater the diffusion flux.

[0044] In some specific embodiments of the present invention, it further includes S6: Based on the double-time-varying numerical model of concrete chloride salt erosion under saturated state, a numerical simulation model considering the surface chloride ion concentration and chloride ion diffusion coefficient is constructed to complete the model accuracy analysis by comparing the simulated data with the measured data.

[0045] In some specific embodiments of the present invention, in S1, obtaining the seasonal variation law of chloride salt concentration in the estuary area includes: selecting no less than three estuary areas as monitoring areas, collecting water samples once in each season and accumulating water samples for no less than 1 year, synchronously collecting the astronomical tide data in the monitoring area during the sampling period, continuously collecting water samples, measuring the chloride salt concentration in each water sample, and recording the chloride salt concentration in the corresponding water sample in combination with the collected astronomical tide data.

[0046] Specifically, for waters with a water depth exceeding 5 meters, stratified sampling is carried out at three points on the vertical direction, namely the surface layer, the middle layer and the bottom layer.

[0047] In some specific embodiments of the present invention, in S2, the immersion test on the concrete specimens is carried out according to the time-varying distribution characteristics through the following steps: Based on the time-varying distribution characteristics of chloride salt concentration in the brackish water convergence area, the highest concentration, the intermediate concentration and the lowest concentration are selected as the chloride salt concentrations of the immersion solution. To ensure that chloride ions are transmitted into the concrete specimens in a one-dimensional manner, five sides of the concrete specimens are coated with epoxy resin for sealing, and one side is reserved as the exposed surface. High-chloride-concentration solution, medium-chloride-concentration solution and low-chloride-concentration solution are prepared, and the sealed concrete specimens are placed in a container, and cyclic immersion tests with different chloride salt concentrations are carried out according to the seasonal variation law of chloride salt concentration.

[0048] Specifically, the concrete specimens are selected with the mix proportions of typical bridges, piers and other structures, prepared and subjected to standard curing for 28 days.

[0049] It should be noted that the containers for holding solutions in indoor tests are relatively small, and there is no external chloride salt supplement. As chloride ions enter the interior of the concrete and water evaporates, etc., the chloride ion concentration will change. Therefore, it is necessary to supplement chloride salt in a timely manner to keep the solution in a basically constant state. In some specific embodiments of the present invention, the concentration of the soaking solution is detected monthly, and the fluctuation range of the concentration of the soaking solution is controlled not to exceed ±0.05%.

[0050] In some specific embodiments of the present invention, in S3, obtaining the surface chloride ion concentration and the internal chloride ion distribution law of concrete at different test ages includes: taking out concrete specimens at different test ages, using the grinding powder method to conduct stratified sampling on the concrete specimens at different ages, using the chemical titration method to determine the chloride ion content in each layer of concrete powder samples, obtaining the chloride salt concentration of each layer of concrete powder samples, and obtaining the erosion law of chloride salt in concrete specimens at different ages based on the chloride salt concentration of concrete powder samples at different ages.

[0051] Specifically, the chemical titration method is used to obtain the chloride ion content in the concrete powder sample, and the calculation formula is as follows:

[0052]

[0053] In the formula: is the mass percentage of acid-soluble chloride ions in hardened concrete in the cementitious material (accurate to 0.001%), is the molar concentration of the silver nitrate standard solution, V1 is the dosage of the silver nitrate standard solution, V2 is the dosage of the silver nitrate standard solution in the blank test, 0.03545 is the millimolar mass of chloride ions, m is the mass of the concrete mortar sample, m m is the dosage of the mortar material excluding coarse aggregate in the concrete mix, m B is the dosage of the cementitious material per cubic meter of concrete in the concrete mix.

[0054] In some specific embodiments of the present invention, in S4, constructing the time-varying model of the concrete chloride diffusion coefficient is determined through the following steps: setting boundary conditions and initial conditions for the preset Fick's second law to obtain the analytical formula of Fick's second law, obtaining the apparent chloride diffusion coefficient, and substituting the apparent chloride diffusion coefficient into the analytical formula of Fick's second law to establish the time-varying model of the concrete chloride diffusion coefficient.

[0055] Specifically, the time-varying model of the concrete chloride diffusion coefficient is:

[0056]

[0057] In the formula: C(x,t) is the chloride ion concentration in the depth x of the concrete after soaking the specimen for t, C sis the chloride ion concentration on the concrete surface, C i is the initial chloride ion concentration of the concrete, D e is the chloride ion diffusion coefficient of the concrete, x is the depth from the immersed surface of the concrete, t is the immersion time, and erf is the error function.

[0058] In some specific embodiments of the present invention, the chloride ion diffusion coefficient is determined by the following steps: obtaining the water-binder ratio, mass fraction of fly ash, and mass fraction of slag of the concrete, calculating the time decay coefficient of the concrete in the wet-dry alternate area, obtaining the exposure time, and calculating the chloride ion diffusion coefficient of the concrete corresponding to the exposure time based on the time decay coefficient.

[0059] Specifically, the deformation formula of the chloride ion diffusion coefficient is:

[0060]

[0061] In the formula: is the apparent chloride ion diffusion coefficient of the concrete corresponding to the exposure time t i and is the apparent chloride ion diffusion coefficient of the concrete corresponding to the concrete curing time t1, and n is the time decay coefficient.

[0062] In some specific embodiments of the present invention, data verification is performed on the calculation results of the chloride ion diffusion coefficient and the chloride ion concentration on the concrete surface: taking the arithmetic mean of the calculation results of three specimens of the same batch, if the deviation of the calculation result of any specimen from the median exceeds 20% of the mean, then the median is taken as the final value, and if the deviations of the calculation results of two specimens from the median both exceed 20% of the mean, then the group of data is determined to be invalid and the test is repeated.

[0063] The following uses a specific embodiment to illustrate the construction method of the concrete chloride salt erosion model applicable to the saltwater-freshwater confluence area.

[0064] S1: Obtain the seasonal variation law of the chloride salt concentration in the estuary area, and determine the time-varying distribution characteristics of the chloride salt concentration in the saltwater-freshwater confluence area according to the seasonal variation law of the chloride salt concentration.

[0065] Continuously track the change law of chloride ions at the Pearl River Estuary, select three areas at the Pearl River Estuary as monitoring areas, and collect water samples once each season. Among them, for waters with a water depth exceeding 5 meters, stratified sampling is carried out at three points on the vertical direction, namely the surface layer, middle layer, and bottom layer. During the sampling period, synchronously collect the astronomical tide data of the monitoring area, and combine the collected astronomical tide data to measure and record the chloride salt concentration in the collected water samples, and obtain the change of the chloride salt concentration in the water samples at the Pearl River Estuary in one year, as Figure 2 shown.

[0066] S2: Obtain concrete specimens, and conduct immersion tests on the concrete specimens according to the time-varying distribution characteristics to obtain the chloride ion concentration on the concrete surface and the distribution law of chloride ions inside.

[0067] The immersion test on the concrete specimens according to the time-varying distribution characteristics is implemented through the following steps:

[0068] Based on the time-varying distribution characteristics of the chloride salt concentration in the salt-freshwater confluence area, select the highest concentration, medium concentration, and lowest concentration as the chloride salt concentrations of the immersion solution;

[0069] Coat five sides of the concrete specimens with epoxy resin for sealing, and leave one side as the exposed surface;

[0070] Prepare high-chloride-salt-concentration solution, medium-chloride-salt-concentration solution, and low-chloride-salt-concentration solution. Place the sealed concrete specimens in a container and conduct cyclic immersion tests with different chloride salt concentrations according to the seasonal change law of chloride salt concentration.

[0071] The chloride salt concentration at the Pearl River Estuary shows seasonal changes, basically between 1000 and 10000 mg / L. Based on this, select the chloride salt concentrations of the immersion solution as 1000 mg / L, 6000 mg / L, and 10000 mg / L, and conduct indoor cyclic tests with the three concentrations as the high-chloride-salt-concentration solution, medium-chloride-salt-concentration solution, and low-chloride-salt-concentration solution respectively. The cyclic steps are as follows:

[0072] Prepare concrete specimens. Adopt the conventional C30 concrete mix ratio to prepare 100×100×100 cube specimens. After demolding for 1 day, send them to the curing room and take them out after curing for 28 d;

[0073] Use epoxy resin to seal the concrete specimens, and leave one side uncoated with epoxy resin as the exposed surface;

[0074] Put the concrete specimens coated with epoxy resin into the immersion tank, prepare a 10000 mg / L solution and immerse the concrete in it to conduct the immersion experiment;

[0075] Replace the solution every 7 days, and conduct the immersion test in a cycle of high-medium-low-medium.

[0076] Specifically, detect the concentration of the immersion solution every month, and control the concentration fluctuation range of the immersion solution not to exceed ±0.05%.

[0077] S3: Construct a time-varying model of the chloride ion concentration on the concrete surface according to the chloride ion concentration on the concrete surface and the distribution law of chloride ions inside.

[0078] Take out the concrete specimens after the 1st, 3rd, 5th, 7th, 10th, 12th, 14th, 16th, 18th, and 20th cycles respectively;

[0079] The concrete specimens were sampled layer by layer using a grinding method, with each layer having a thickness of 1 mm;

[0080] The chemical titration method was used to calculate the chloride ion content in the concrete powder sample based on the volume of silver nitrate consumed, and the chloride salt concentration of each layer of concrete powder sample was obtained. The calculation formula is as follows:

[0081]

[0082] In the formula, is the mass percentage of acid-soluble chloride ions in hardened concrete in the cementitious material (accurate to 0.001%); is the molar concentration of the silver nitrate standard solution, V1 is the amount of the silver nitrate standard solution used, V2 is the amount of the silver nitrate standard solution used in the blank test, 0.03545 is the millimolar mass of chloride ions, m is the mass of the concrete mortar sample, m m is the amount of mortar material in the concrete mix ratio excluding coarse aggregates, m B is the amount of cementitious material per cubic meter of concrete in the concrete mix ratio. As Figure 3 shown, Figure 3 is the graph of the change law of surface chloride ion concentration. Its ordinate is the surface chloride ion concentration of concrete, and its abscissa is the number of test days. Based on the chloride salt concentration of concrete powder samples at different ages, the erosion law of chloride salt in concrete specimens at different ages is obtained.

[0083] Based on Figure 3 the erosion law of chloride salt in concrete specimens at different ages, with the help of SPASS software and using the least squares method for fitting, a piecewise function of the time-varying law of surface chloride ion concentration is obtained, and then a time-varying model of concrete surface chloride ion concentration is constructed. The result is shown in the following formula:

[0084]

[0085] In the formula: C(x,t) is the chloride ion concentration in the concrete at depth x after soaking the specimen for t.

[0086] S4: Based on the analytical solution of Fick's second law, a time-varying model of concrete chloride diffusion coefficient is constructed.

[0087] The preset Fick's second law is used to describe the diffusion state of chloride ions:

[0088]

[0089] In the formula: C is the chloride ion concentration at a distance x from the concrete surface after exposure for time t, and D is the concrete chloride diffusion coefficient;

[0090] Boundary conditions and initial conditions are set for the preset Fick's second law to obtain the analytical formula of Fick's second law:

[0091]

[0092] Where: C(x,t) is the chloride ion concentration in the concrete at depth x after soaking the specimen for t, C s is the chloride ion concentration on the concrete surface, C i is the initial chloride ion concentration of the concrete, D e is the chloride ion diffusion coefficient of the concrete, x is the depth from the concrete soaking surface, t is the soaking time, and erf is the error function;

[0093] Obtain the chloride ion diffusion coefficient, and the deformation formula of the chloride ion diffusion coefficient is:

[0094]

[0095] Where: is the apparent chloride ion diffusion coefficient of the concrete corresponding to the exposure time t i of the concrete, is the apparent chloride ion diffusion coefficient of the concrete corresponding to the concrete curing time t1, and n is the time decay coefficient.

[0096] Substitute the apparent chloride ion diffusion coefficient into the analytical formula of Fick's second law to establish a time-varying model of the concrete chloride ion diffusion coefficient:

[0097]

[0098] Where: C(x,t) is the chloride ion concentration in the concrete at depth x after soaking the specimen for t, Cs is the chloride ion concentration on the concrete surface, C i is the initial chloride ion concentration of the concrete, D a,28 is the chloride ion diffusion coefficient of the concrete cured for 28 days, x is the depth from the concrete soaking surface, t is the soaking time, t2 is the exposure time, and erf is the error function.

[0099] S5: According to the time-varying model of the concrete surface chloride ion concentration and the time-varying model of the concrete chloride ion diffusion coefficient, construct a double-time-varying numerical model of concrete chloride salt erosion in the saturated state.

[0100] Substitute the formula of the time-varying model of the concrete surface chloride ion concentration into the formula of the time-varying model of the concrete chloride ion diffusion coefficient to obtain the double-time-varying numerical model of concrete chloride salt erosion in the saturated state:

[0101]

[0102] S6: Based on the dual time-varying numerical model of chloride-salt corrosion of concrete under saturated state, a numerical simulation model considering the surface chloride ion concentration and chloride ion diffusion coefficient is constructed to complete the model accuracy analysis by comparing the simulation data with the measured data.

[0103] Based on the established dual time-varying mathematical model, a numerical simulation model considering the surface chloride ion concentration and chloride ion diffusion coefficient was constructed with the help of Comsol finite element numerical simulation software. The distribution law of chloride ions in concrete under the measured values, dual time-varying model and single concentration surface chloride ion concentration model was compared. The results are shown in Fig. Figure 4 As shown. Figure 4 It can be clearly seen that under conventional values, the predicted chloride distribution law is quite different from the measured value. This is mainly because under different concentration cycles, there will be a convection zone in the chloride ion distribution on the concrete surface. The conventional practice is to remove this part of the data, resulting in a decrease in the chloride ion content. It can be seen that the dual time-varying numerical model of chloride corrosion of concrete under saturated state proposed by this method is more targeted and has higher fitting accuracy. It can better reflect the actual service environment of concrete structures in the river-sea confluence area, accurately predict the durability of concrete structures in the river-sea confluence area, and provide a more reliable basis for the durability design of the salt-fresh water confluence area.

[0104] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for constructing a concrete chloride corrosion model suitable for the intersection of salt and fresh water, characterized in that: include: S1: Obtain the seasonal variation law of chloride concentration in the estuary area, and determine the time-varying distribution characteristics of chloride concentration in the salt-fresh water confluence area based on the seasonal variation law of chloride concentration; S2: Obtain concrete specimens and conduct immersion tests on the concrete specimens according to the time-varying distribution characteristics to obtain the chloride ion concentration on the concrete surface and the distribution law of chloride ions inside the concrete; S3: Based on the chloride ion concentration on the concrete surface and the distribution law of chloride ions inside, a time-varying model of chloride ion concentration on the concrete surface is constructed; S4: Construct a time-varying model of chloride ion diffusion coefficient in concrete based on the analytical solution of Fick's second law; S5: Based on the time-varying model of chloride ion concentration on the concrete surface and the time-varying model of chloride ion diffusion coefficient of concrete, a dual time-varying numerical model of chloride erosion of concrete under saturated state is constructed.

2. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 1, characterized in that: It also includes S6: Based on the dual time-varying numerical model of chloride-salt corrosion of concrete under saturated state, a numerical simulation model considering the surface chloride ion concentration and chloride ion diffusion coefficient is constructed to complete the model accuracy analysis by comparing the simulation data with the measured data.

3. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 2, characterized in that: In S1, the seasonal variation of chloride concentration in the estuary area is obtained including: No fewer than three estuary areas were selected as monitoring areas, and water samples were collected once in each season; Synchronously collect astronomical tidal data in the monitoring area during the sampling period; Continuously collect water samples and measure the chloride concentration in each water sample; Combined with the collected astronomical tidal data, the chloride concentration in the corresponding water samples is recorded.

4. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 3, characterized in that: For waters with a depth of more than 5 meters, stratified sampling is carried out at three points in the vertical direction: surface, middle and bottom layers.

5. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 1, characterized in that: In S2, the immersion test of concrete specimens is carried out according to the time-varying distribution characteristics through the following steps: Based on the time-varying distribution characteristics of chloride concentration in the salt-fresh water confluence area, the highest concentration, the middle concentration and the lowest concentration were selected as the chloride concentration of the immersion solution. Five sides of the concrete specimen were sealed with epoxy resin, and the other side was kept as an exposed surface; High chloride concentration solution, medium chloride concentration solution and low chloride concentration solution were prepared, sealed concrete specimens were placed in containers, and cyclic immersion tests with different chloride concentrations were carried out according to the seasonal variation law of chloride concentration.

6. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 5, characterized in that: The concentration of the soaking solution was tested monthly and the concentration fluctuation range of the soaking solution was controlled to be no more than ±0.05%.

7. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 1, characterized in that: In S3, the chloride ion concentration on the concrete surface and the distribution of chloride ions inside the concrete at different test ages are obtained, including: Concrete specimens were taken out at different test ages; The grinding method was used to sample concrete specimens of different ages in different layers. The chloride ion content in each layer of concrete powder sample is determined by chemical titration method to obtain the chloride salt concentration of each layer of concrete powder sample; Based on the chloride concentration of concrete powder samples at different ages, the chloride corrosion law of concrete specimens at different ages was obtained.

8. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 1, characterized in that: In S4, the time-varying model of chloride ion diffusion coefficient of concrete is determined by the following steps: Set boundary conditions and initial conditions for the preset Fick's second law to obtain the analytical formula of Fick's second law; The apparent diffusion coefficient of chloride ions was obtained and substituted into the analytical formula of Fick's second law to establish a time-varying model of chloride ion diffusion coefficient in concrete.

9. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 8, characterized in that: The time-varying model of chloride ion diffusion coefficient in concrete is: Where: C(x,t) is the chloride ion concentration of concrete at depth x after the specimen has been immersed for t, C s is the chloride ion concentration on the concrete surface, C i is the initial chloride ion concentration of concrete, D e is the diffusion coefficient of chloride ions in concrete, x is the depth from the concrete immersion surface, t is the immersion time, and erf is the error function.

10. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 9, characterized in that: The chloride diffusion coefficient of concrete is determined by the following steps: Obtain the water-binder ratio of concrete, the mass fraction of fly ash and the mass fraction of slag; The time attenuation coefficient of concrete in the dry-wet alternating area is calculated; The exposure time is obtained, and based on the time attenuation coefficient, the chloride ion diffusion coefficient of the concrete corresponding to the exposure time is calculated.

11. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 10, characterized in that: The deformation formula of the chloride ion diffusion coefficient of concrete is: Where: Corresponding exposure time t i The apparent diffusion coefficient of chloride ions in concrete is is the apparent diffusion coefficient of chloride ions in concrete corresponding to the concrete curing time t1, and n is the time attenuation coefficient.

12. The method for constructing a concrete chloride corrosion model suitable for a salt-fresh water confluence area according to claim 9, characterized in that: Data verification of the calculation results of the chloride ion diffusion coefficient of concrete and the chloride ion concentration on the concrete surface: Take the arithmetic mean of the calculation results of three specimens in the same batch; If the calculated result of any specimen deviates from the mean value by more than 20%, the mean value shall be taken as the final value; If the deviation between the calculated results of the two specimens and the middle value exceeds 20% of the average value, the data set is deemed invalid and the test is repeated.

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