A model calculation method for determining chloride ion diffusion coefficient of concrete
By soaking concrete specimens in deionized water and detecting the concentration of chloride ion leaching liquid, combining the one-dimensional diffusion model and Fick's second law, the problem of insufficient accuracy in determining chloride ion diffusion coefficient in the existing technology is solved, achieving convenience and Accurate measurement results are suitable for concrete durability design.
Patent Information
- Application Number
- CN202110844407.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-07-26
- Publication Date
- 2024-12-24
- Estimated Expiration
- 2041-07-26
AI Technical Summary
The prior art lacks accuracy when determining the diffusion coefficient of concrete chloride ion. The natural diffusion method has a long period, and the non-stable electromigration method requires the action of an electric field and the color-developing reagent affects the results, so an accurate diffusion coefficient cannot be obtained.
By placing the concrete specimens with chloride ions inside soaking in deionized water, the chloride ion concentration at different diffusion times is detected, the chloride ion diffusion coefficient is calculated using the one-dimensional diffusion model and Fick's second law, and cumbersome layered grinding is omitted The powder is soaked and titrated to test the titer test step, and only the titration is required to detect the chloride ion concentration in the leaching solution.
It achieves a more convenient and accurate determination of concrete chloride ion diffusion coefficient, which is suitable for durability design and life prediction, and is of great significance for actual on-site application.
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Figure CN113776990B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of measuring chloride ion diffusion coefficient of concrete, and in particular to a model calculation method for measuring chloride ion diffusion coefficient of concrete. Background Art
[0002] Steel corrosion caused by chloride ions is a key issue in the durability design of concrete. The life of the structure depends on the speed and concentration of chloride ions entering the concrete. The chloride ion diffusion coefficient is the most important indicator for measuring the transmission speed of chloride ions in concrete. There are many laboratory measurement methods used to determine the chloride ion diffusion migration coefficient, including natural diffusion method, non-steady-state electromigration test method, etc. The natural diffusion method allows the concrete sample to be immersed in the chloride solution for a longer time, and the non-steady-state electromigration test can accelerate the rapid penetration of chloride ions in concrete through the action of the electric field. The chloride ion diffusion coefficient can be measured by the above laboratory methods.
[0003] Traditional chloride ion migration tests are based on the prediction of Fick's second law, and theoretical methods have certain limitations. The natural diffusion method has a long cycle and cannot be used in practical engineering applications. The non-steady-state electromigration method requires an electric field, and different ions will interact with each other under the action of the electric field. The chloride ion diffusion concentration curve measured after the test deviates greatly from the theoretical model. The colorimetric reagent used has an effect on the sample containing chloride ions, and it is impossible to obtain an accurate diffusion coefficient.
[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention
[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a model calculation method for measuring the chloride ion diffusion coefficient of concrete, aiming to solve the problem that the existing measurement method cannot obtain an accurate diffusion coefficient.
[0006] The technical solution of the present invention is as follows:
[0007] A model calculation method for determining the chloride ion diffusion coefficient of concrete, comprising the following steps:
[0008] The concrete specimens doped with chloride ions were placed in deionized water and soaked;
[0009] After soaking for a predetermined time, detecting the chloride ion concentration in the deionized water at different diffusion times, and replacing the deionized water after each detection;
[0010] According to the chloride ion concentration at different diffusion times, determine the relationship between chloride ion concentration and diffusion time;
[0011] The chloride ion diffusion flux was calculated based on the one-dimensional chloride ion diffusion model and Fick's second law.
[0012] The chloride ion diffusion coefficient is calculated based on the relationship between the chloride ion concentration and the diffusion time and the chloride ion diffusion flux.
[0013] Optionally, the concrete specimen is in the shape of a cube, and the side length of the cube is 100 mm;
[0014] Three groups of concrete specimens doped with chloride ions are set up, and three concrete specimens in each group are placed in deionized water for immersion; the average value of the chloride ion diffusion coefficients of the three groups of concrete specimens is taken as the chloride ion diffusion coefficient of the concrete.
[0015] Optionally, the step of placing the concrete specimen doped with chloride ions in deionized water for immersion specifically comprises: sealing the five faces of the cubic concrete specimen with epoxy resin, placing the specimen with the exposed face facing upward for immersion in deionized water, maintaining the water level 5 cm higher than the exposed face of the concrete specimen, and the spacing between adjacent concrete specimens being greater than or equal to 20 mm.
[0016] Optionally, the process of detecting the chloride ion concentration in the deionized water at different diffusion times includes: detecting the chloride ion concentration in the deionized water according to the immersion days of the concrete specimen, and the immersion days for each detection are 1d, 1-3d, 3-6d, 6-9d, 9-14d, 14-21d, 21-28d, and 28-35d respectively.
[0017] Optionally, the one-dimensional diffusion model of chloride ions is as follows:
[0018]
[0019] Among them, J is the chloride ion diffusion flux, D is the chloride ion diffusion coefficient, C is the chloride ion concentration in the concrete specimen, and x is the chloride ion diffusion direction in the concrete specimen.
[0020] Optionally, the Fick's second law is as follows:
[0021]
[0022] Where D is the chloride ion diffusion coefficient, C is the chloride ion concentration in the concrete specimen, x is the chloride ion diffusion direction in the concrete specimen, and t is the diffusion time.
[0023] Optionally, the chloride ion diffusion model obtained from equations (1) and (2) is:
[0024]
[0025] Among them, C i is the chloride ion concentration obtained by the i-th detection, i = 1, 2, 3, ... N, and t is the diffusion time.
[0026] Optionally, according to the determined relationship between chloride ion concentration and diffusion time, the change rate of chloride ion concentration and diffusion time under the corresponding diffusion time is obtained as follows:
[0027]
[0028] Wherein, K is the rate of change of chloride ion concentration and diffusion time at the corresponding diffusion time, and t is the diffusion time.
[0029] Optionally, the chloride ion diffusion coefficient is obtained from equations (3) and (4):
[0030]
[0031] Beneficial effect: The present invention soaks the concrete specimen mixed with chloride ions in deionized water, collects and detects the chloride ion concentration dissolved in deionized water at different diffusion times, fits the two-dimensional graph of chloride ion concentration-diffusion time of the concrete specimen by approximating the one-dimensional saturated diffusion model and Fick's second law, and obtains the chloride ion diffusion coefficient using the corresponding chloride ion concentration-diffusion time change rate and diffusion flux. Compared with the existing layered grinding test method, the method of the present invention omits the cumbersome layered grinding and then soaking titration test steps, and only needs to titrate the chloride ion concentration in the leachate, which can more conveniently measure the chloride ion diffusion coefficient of concrete, and perform durability design and life prediction on concrete structures mixed with chloride ions (such as seawater and sea sand concrete), which is of great significance for actual on-site application. In addition to being able to more conveniently measure the chloride ion diffusion coefficient of concrete, the method of the present invention can also more accurately measure the chloride ion diffusion coefficient of concrete. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 A schematic flow chart of a model calculation method for determining chloride ion diffusion coefficient of concrete provided by an embodiment of the present invention;
[0033] Figure 2 A schematic diagram of a device for measuring chloride ion diffusion coefficient of concrete provided in an embodiment of the present invention. DETAILED DESCRIPTION
[0034] The present invention provides a model calculation method for determining the chloride ion diffusion coefficient of concrete. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.
[0035] Combination Figure 1 As shown, an embodiment of the present invention provides a model calculation method for determining the chloride ion diffusion coefficient of concrete, which includes the following steps:
[0036] S1. Soak the concrete specimen doped with chloride ions in deionized water;
[0037] S2, after soaking for a predetermined time, detecting the chloride ion concentration in the deionized water at different diffusion times, and replacing the deionized water after each detection;
[0038] S3. Determine the relationship between chloride ion concentration and diffusion time according to the chloride ion concentration at different diffusion times;
[0039] S4. Calculate the chloride ion diffusion flux based on the one-dimensional chloride ion diffusion model and Fick's second law;
[0040] S5. Calculate the chloride ion diffusion coefficient according to the relationship between the chloride ion concentration and the diffusion time and the chloride ion diffusion flux.
[0041] In this embodiment, the concrete specimen mixed with chloride ions is placed in deionized water for immersion. By collecting and detecting the chloride ion concentration dissolved in deionized water at different diffusion times, the two-dimensional graph of chloride ion concentration-diffusion time of the concrete specimen is fitted by approximating the one-dimensional saturated diffusion model and Fick's second law, and the chloride ion diffusion coefficient is obtained by using the corresponding chloride ion concentration-diffusion time change rate and diffusion flux. Compared with the existing layered grinding test method, the method of this embodiment omits the cumbersome layered grinding and then soaking titration test steps, and only needs to titrate the chloride ion concentration in the leachate, which can more conveniently and accurately measure the chloride ion diffusion coefficient of concrete, and carry out durability design and life prediction for concrete structures mixed with chloride ions (such as seawater and sea sand concrete), which is of great significance for actual on-site application. In addition to being able to more conveniently measure the chloride ion diffusion coefficient of concrete, the method of this embodiment can also more accurately measure the chloride ion diffusion coefficient of concrete.
[0042] It should be noted that the concrete specimen doped with chloride ions described in this embodiment may be a concrete specimen that already contains chloride ions, or may be a concrete specimen that has been corroded by chloride ions.
[0043] Ordinary concrete does not contain chloride ions. Currently, the chloride ion diffusion coefficient is mainly calculated by natural immersion to allow chloride ions to penetrate into the concrete, and then using the color development principle that the reagent silver nitrate reacts with chloride ions to form silver chloride precipitate.
[0044] The above method proposed in this embodiment is aimed at concrete mixed with chloride ions, especially seawater and sea sand concrete containing chloride ions. The diffusion coefficient is calculated by leaching chloride ions outward. The above method can be used to conveniently and accurately measure the chloride ion diffusion coefficient of seawater and sea sand concrete.
[0045] In step S1, in one embodiment, the concrete specimen is in a cubic shape, and the side length of the cube is 100 mm, which is the size of a standard chloride ion penetration test.
[0046] In one embodiment, 3 groups of concrete specimens doped with chloride ions are set up, and each group of 3 concrete specimens is placed in deionized water for immersion; the average value of the chloride ion diffusion coefficients of the 3 groups of 3 concrete specimens is taken as the chloride ion diffusion coefficient of the concrete. That is to say, 3 groups of concrete specimens are set up, and each group of 3 concrete specimens is subjected to leaching test, and the chloride ion diffusion coefficient of each concrete specimen is measured, and the average value of the chloride ion diffusion coefficients of the 3 concrete specimens in each group is taken as the chloride ion diffusion coefficient of the group of concrete, and the average value of the chloride ion diffusion coefficients of the 3 groups of concrete specimens is taken as the final chloride ion diffusion coefficient of the concrete, which is conducive to improving the accuracy of the calculation results.
[0047] In one embodiment, the step of placing the concrete specimen doped with chloride ions in deionized water for immersion specifically comprises: sealing the five surfaces of the cubic concrete specimen with epoxy resin, placing the specimen with the exposed surface facing upward for immersion in deionized water, keeping the water level 5 cm higher than the exposed surface of the concrete specimen, and the spacing between adjacent concrete specimens being greater than or equal to 20 mm. In this embodiment, the concrete specimen has only one exposed surface, and the remaining surfaces are sealed with epoxy resin to ensure that the diffusion of chloride ions is carried out only in one-dimensional direction.
[0048] In step S2, after soaking for a predetermined time (i.e., after a certain diffusion time, such as 1 day), the concentration of chloride ions dissolved in the deionized water at different times (days) is collected and detected. In order to ensure that the concentration collected from the deionized water each time is the diffused chloride ion concentration, the deionized water needs to be replaced after each detection.
[0049] In one embodiment, the process of detecting the chloride ion concentration in the deionized water under different diffusion times includes: the concrete specimen is tested for the chloride ion concentration in the deionized water according to the number of days of immersion (i.e., diffusion time), and the number of days of immersion for each test is 1d, 1-3d, 3-6d, 6-9d, 9-14d, 14-21d, 21-28d, and 28-35d. In other words, the first test is performed after 1d of immersion, the second test is performed after 1-3d of immersion, the third test is performed after 3-6d of immersion, the fourth test is performed after 6-9d of immersion, the fifth test is performed after 9-14d of immersion, the sixth test is performed after 14-21d of immersion, the seventh test is performed after 21-28d of immersion, and the eighth test is performed after 28-35d of immersion. It should be noted that the number of days of immersion in two adjacent tests is different.
[0050] In one embodiment, the one-dimensional diffusion model of chloride ions (one-dimensional saturated water diffusion model) is as follows:
[0051]
[0052] Among them, J is the chloride ion diffusion flux, D is the chloride ion diffusion coefficient, C is the chloride ion concentration in the concrete specimen, and x is the chloride ion diffusion direction in the concrete specimen.
[0053] In this embodiment, the diffusion of chloride ions satisfies Fick's second law. In one embodiment, the Fick's second law is as follows:
[0054]
[0055] Where D is the chloride ion diffusion coefficient, C is the chloride ion concentration in the concrete specimen, x is the chloride ion diffusion direction in the concrete specimen, and t is the diffusion time.
[0056] In one embodiment, the chloride ion diffusion model obtained by integral transformation of equations (1) and (2) is:
[0057]
[0058] Among them, C i is the chloride ion concentration obtained by the i-th detection, i = 1, 2, 3, ... N, and t is the diffusion time.
[0059] In this embodiment, the two-dimensional graph of chloride ion concentration at different diffusion times is fitted to obtain the change rate of chloride ion concentration and diffusion time at the corresponding diffusion time. In one embodiment, according to the determined relationship between chloride ion concentration and diffusion time, the change rate of chloride ion concentration and diffusion time at the corresponding diffusion time is obtained as follows:
[0060]
[0061] Wherein, K is the rate of change of chloride ion concentration and diffusion time at the corresponding diffusion time, and t is the diffusion time.
[0062] In one embodiment, assuming that the diffusion distance from the concrete surface to the deionized water is a small amount, the chloride ion diffusion coefficient is obtained from equations (3) and (4):
[0063]
[0064] The present embodiment provides a model calculation method for determining the chloride ion diffusion coefficient of concrete, which first performs a dechlorination water leaching test, then collects and detects the chloride ion concentration dissolved in the deionized water at different diffusion times according to the leaching test, and calculates the chloride ion diffusion coefficient according to the diffusion flux and the chloride ion concentration-diffusion time relationship diagram through an approximate one-dimensional saturated diffusion model and Fick's second law. The present embodiment can also calculate the distribution of free chloride ion concentration in concrete through a numerical model based on the chloride ion diffusion coefficient model and the diffusion coefficient, and perform durability design and life prediction for concrete structures mixed with chloride ions and corroded.
[0065] Based on the above method, the embodiment of the present invention also provides a device for measuring the chloride ion diffusion coefficient of concrete, such as Figure 2 As shown, it includes: a leaching chamber 1, a water inlet box 2 for injecting deionized water into the leaching chamber 1, a water seepage box 3 for automatically allowing deionized water above a predetermined height to flow out and recovering the outflowing deionized water, and a water outlet pipe 4 arranged at the bottom end of one side of the leaching chamber 1.
[0066] In one embodiment, the device further comprises: a temperature and humidity sensor 5 disposed on the top of the leaching chamber 1. The temperature and humidity sensor 5 is added to ensure that the chloride ion leaching test is performed under certain temperature and humidity conditions.
[0067] Furthermore, the temperature and humidity sensors are provided with two, namely Figure 2 The temperature and humidity sensor 5 and the temperature and humidity sensor 6 in the leaching chamber 1 are provided. The two temperature and humidity sensors can avoid experimental errors, and when one of the temperature and humidity sensors is inaccurate or fails to measure, the other one can be used for measurement, effectively ensuring that the chloride ion leaching test is carried out under certain temperature and humidity conditions. The temperature and humidity sensor 6 is arranged side by side with the temperature sensor 5 and is arranged at the same end of the top of the leaching chamber 1, and the water inlet box 2 is arranged at the other end of the top of the leaching chamber 1.
[0068] In one embodiment, the water inlet tank 2 is an automatic induction water inlet tank.
[0069] In one embodiment, the water inlet tank 2 is disposed on the top of the leaching chamber 1 .
[0070] In one embodiment, the bottom of the water inlet box 2 has a water inlet 7 , and the water inlet 7 passes through the top of the leaching chamber 1 .
[0071] In this embodiment, an automatic induction water inlet tank 2 is arranged on the top of the leaching chamber 1, which can conveniently inject deionized water required for the chloride ion leaching test.
[0072] In one embodiment, a water seepage pipe 8 is provided at the top of one side of the leaching chamber 1 , and the water seepage box 3 is connected to the leaching chamber 1 through the water seepage pipe 8 .
[0073] In this embodiment, Figure 2 As shown, when the leaching test is carried out, the water level in the leaching chamber 1 is maintained at 5 cm above the exposed surface of the concrete specimen 10. When the water level is more than 5 cm above the exposed surface of the concrete specimen, the seepage pipe 8 can allow deionized water above a predetermined height (such as 5 cm) to automatically flow into the seepage box 3 to save resources and ensure efficient utilization.
[0074] In one embodiment, a water valve 9 is provided on the water outlet pipe 4. After the leaching test reaches a specified number of days, the water is collected, and the deionized water after the test is collected by opening the water valve 9, and then chloride ion titration is performed to measure the chloride ion concentration.
[0075] In one embodiment, the leaching chamber 1 is a square structure or a ring structure.
[0076] The present invention will be further described below by means of specific examples.
[0077] Use Figure 2 The method for determining the chloride ion diffusion coefficient of concrete using the device shown is as follows:
[0078] The concrete containing chloride ions is immersed in deionized water, wherein the chloride ion concentration in the concrete containing chloride ions is uniformly distributed. The chloride ion leaching test in concrete is a one-dimensional diffusion process, and the concentration of chloride ions leached in the concrete under different immersion days (i.e., diffusion time) is collected and detected.
[0079] The two-dimensional graph of chloride ion concentration-diffusion time is fitted, and the corresponding concentration-time change rate is obtained as follows: Wherein, K is the rate of change of chloride ion concentration and diffusion time at the corresponding diffusion time, and t is the diffusion time.
[0080] The chloride ion diffusion coefficient is calculated based on the chloride ion concentration-diffusion time change rate and the diffusion model:
[0081]
[0082] The chloride ion diffusion coefficient was calculated based on the chloride ion concentration-diffusion time change rate and the diffusion model: the sample side length of test block 1 is L = 100 mm, the chloride ion concentration-diffusion time change rate when the leaching time is t = 35 days is 44.48, and the chloride ion concentration after 35 days of leaching is 0.2083%. Substituting into the chloride ion diffusion coefficient model, the chloride ion diffusion coefficient D is calculated to be 1.9×10 -4 mm 2 / d.
[0083] The chloride ion diffusion coefficient was calculated based on the chloride ion concentration-diffusion time change rate and diffusion model: the chloride ion concentration-diffusion time change rate of the sample of test block 2 when the side length L = 100 mm and the leaching time t = 35 days was 166.23, and the chloride ion leaching concentration after 35 days of leaching was 1.0444%. Substituting into the chloride ion diffusion coefficient model, the chloride ion diffusion coefficient D = 5.1×10 -5 mm 2 / d.
[0084] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.
Claims
1. A model calculation method for determining the chloride ion diffusion coefficient of concrete, characterized in that: The following steps are involved: The concrete specimens doped with chloride ions were placed in deionized water and soaked; After soaking for a predetermined time, detecting the chloride ion concentration in the deionized water at different diffusion times, and replacing the deionized water after each detection; According to the chloride ion concentration at different diffusion times, determine the relationship between chloride ion concentration and diffusion time; The chloride ion diffusion flux was calculated based on the one-dimensional chloride ion diffusion model and Fick's second law. Calculating the chloride ion diffusion coefficient according to the relationship between the chloride ion concentration and the diffusion time and the chloride ion diffusion flux; The one-dimensional diffusion model of chloride ions is as follows: Wherein, J is the chloride ion diffusion flux, D is the chloride ion diffusion coefficient, C is the chloride ion concentration in the concrete specimen, and x is the chloride ion diffusion direction in the concrete specimen; The Fick's second law is as follows: Where D is the chloride ion diffusion coefficient, C is the chloride ion concentration in the concrete specimen, x is the chloride ion diffusion direction in the concrete specimen, and t is the diffusion time; The chloride ion diffusion model obtained from equations (1) and (2) is: Among them, C i is the chloride ion concentration obtained by the i-th detection, i = 1, 2, 3, ... N, t is the diffusion time; According to the determined relationship between chloride ion concentration and diffusion time, the change rate of chloride ion concentration and diffusion time under the corresponding diffusion time is obtained: Where K is the rate of change of chloride ion concentration and diffusion time at the corresponding diffusion time, and t is the diffusion time; The chloride ion diffusion coefficient is obtained from equations (3) and (4):
2. The model calculation method for determining the chloride ion diffusion coefficient of concrete according to claim 1, characterized in that: The concrete specimen is in the shape of a cube, and the side length of the cube is 100 mm; Three groups of concrete specimens doped with chloride ions are set up, and three concrete specimens in each group are placed in deionized water for immersion; the average value of the chloride ion diffusion coefficients of the three groups of concrete specimens is taken as the chloride ion diffusion coefficient of the concrete.
3. The model calculation method for determining the chloride ion diffusion coefficient of concrete according to claim 2, characterized in that: The step of placing the concrete specimen doped with chloride ions in deionized water for immersion specifically comprises: sealing the five faces of the cubic concrete specimen with epoxy resin, placing the specimen with the exposed face facing upward for immersion in deionized water, keeping the water level 5 cm higher than the exposed face of the concrete specimen, and the spacing between adjacent concrete specimens being greater than or equal to 20 mm.
4. The model calculation method for determining the chloride ion diffusion coefficient of concrete according to claim 1, characterized in that: The process of detecting the chloride ion concentration in the deionized water at different diffusion times includes: the concrete specimen is tested for the chloride ion concentration in the deionized water according to the number of immersion days, and the number of immersion days for each test is 1d, 1-3d, 3-6d, 6-9d, 9-14d, 14-21d, 21-28d, and 28-35d.
5. The model calculation method for determining the chloride ion diffusion coefficient of concrete according to claim 1, characterized in that: The concrete specimen mixed with chloride ions is seawater and sea sand concrete.