A high-throughput measurement method for deformation damage of concrete specimen caused by calcium dissolution based on digital image correlation method

Abstract

The present application belongs to the technical field of concrete durability test, and particularly relates to a high-throughput measurement method for deformation and damage of a concrete test piece caused by calcium dissolution based on a digital image correlation method.The present application combines the digital image correlation method (DIC) with the high-throughput measurement concept, and realizes integrated measurement of deformation and damage of the concrete test piece during the calcium dissolution process.Through high-throughput acquisition of DIC images before and after the dissolution, the test efficiency is greatly improved; meanwhile, the macroscopic deformation calculation is combined with the microscopic damage model optimization, so that the overall deformation result of the test piece is obtained, and the damage degree is accurately quantified through the calcium dissolution damage factor.

Description

Technical Field

[0001] This invention belongs to the field of concrete durability testing technology, specifically a high-throughput measurement method for calcium dissolution deformation damage of concrete specimens based on digital image correlation. Background Technology

[0002] Calcium dissolution is a common form of concrete failure in hydraulic engineering projects. The successive dissolution of cement hydration products such as CH and CSH leads to increased porosity, decreased mechanical properties, and reduced durability in hydraulic concrete. The deterioration of material properties and structure caused by calcium dissolution has long been considered a fundamental and important technical issue.

[0003] Currently, researchers have conducted extensive studies on reducing the rate of calcium dissolution and the performance loss after dissolution, including the amount of deformation of specimens after dissolution and the sources of deformation. However, the methods for evaluating dissolution deformation are relatively rudimentary, such as using length comparators and calipers, which have limited accuracy. This has led to ongoing debate among scientists regarding whether the initial deformation in dissolution is expansion or contraction. Furthermore, there is currently no unified evaluation index for dissolution damage. The evaluation of dissolution performance often requires multiple indicators, such as loss of mechanical properties, dissolution depth, and mass loss. These indicators sometimes show contradictory patterns, lacking a powerful quantitative evaluation index. Traditional methods such as length comparators and calipers can only be used to evaluate the change in specimen length caused by calcium dissolution, and cannot assess the damage to the microstructure of concrete. This leaves scientists without sufficient theoretical support for improving and protecting concrete against calcium dissolution.

[0004] Therefore, it is necessary to quantify the calcium dissolution deformation and micro-damage of cement-based materials to provide quantitative indicators for improving the calcium dissolution performance of cement-based materials. Summary of the Invention

[0005] To avoid and overcome the technical problems existing in the prior art, the present invention provides a high-throughput measurement method for calcium dissolution deformation damage of concrete specimens based on digital image correlation, which can quantify the microscopic damage of calcium dissolution deformation more accurately.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A high-throughput measurement method for calcium dissolution deformation damage in concrete specimens based on digital image correlation includes the following measurement steps:

[0008] S1. Prepare speckled specimens for calcium dissolution deformation damage testing;

[0009] S2. Calcium dissolution deformation test was carried out on the speckled specimen, and the surface speckled DIC images of the speckled specimen before and after calcium dissolution deformation were obtained by high-throughput method.

[0010] S3. Calculate the strain of the speckled specimen before and after calcium dissolution deformation using the surface speckled DIC image, select the micro-damage model, and optimize the micro-damage model based on the strain.

[0011] S4. Calcium dissolution deformation of speckled specimens was measured using the optimized micro-damage model.

[0012] As a further technical solution of the present invention, the sub-steps of step S1 are as follows:

[0013] S11. Prepare block concrete specimens and cut and grind the concrete specimens into multiple square sheet specimens of a set thickness.

[0014] S12. Seal the lower surface of the square sheet-like specimen;

[0015] S13. Coat the upper surface of the square sheet specimen with black speckled spots to prepare a speckled specimen.

[0016] As a further technical solution of the present invention, the sub-steps of step S2 are as follows:

[0017] S21. Before conducting the calcium dissolution deformation test on the speckled specimen, use a DIC device to photograph the upper surface of the speckled specimen to obtain a surface speckled DIC image before calcium dissolution deformation, and divide the surface speckled DIC image into multiple sub-regions by grid division.

[0018] S22. Seal the upper surface of the speckled specimen and immerse it in a calcium dissolving chemical solution for a set period of time to allow the calcium dissolving chemical solution to dissolve into the specimen along its circumference.

[0019] S23. Each time the soaking time reaches the corresponding dissolution age, the following imaging operation shall be performed until imaging of all dissolution ages is completed.

[0020] Imaging procedure: Remove the speckled specimen from the calcium dissolution chemical solution and remove the seal on its upper surface. Then, use a DIC device to photograph the upper surface to obtain a speckled DIC image of the surface at the corresponding dissolution age. After that, seal the upper surface again and continue to immerse it in the calcium dissolution chemical solution.

[0021] As a further technical solution of the present invention, the sub-steps of step S3 are as follows:

[0022] S31. Establish a plane coordinate system OXY with the two perpendicular sides of the upper surface of the speckled specimen as coordinate axes;

[0023] S32. Using the surface speckle DIC images before and after calcium dissolution deformation, calculate the strain of each sub-region at different dissolution ages. The corresponding calculation formulas are as follows:

[0024] ;

[0025] ;

[0026] ;

[0027] ;

[0028] ;

[0029] In the formula, U This indicates the displacement of the current sub-region center point along the positive X-axis; V This indicates the displacement of the current sub-region center point along the positive Y-axis; express U Rate of change in the positive direction of the X-axis; express V Rate of change in the positive direction of the Y-axis; This indicates the strain of the current sub-region in the positive X-axis direction; This shows the strain of the current sub-region in the positive Y-axis direction; This represents the sum of the strains of the current sub-region in the positive X-axis and positive Y-axis directions; This indicates the maximum principal strain in the current sub-region; This represents the minimum principal strain of the current subregion;

[0030] S33. The micro-damage model adopts the Mazars model, and the Mazars model is optimized based on the maximum principal strain and the minimum principal strain. The optimized Mazars model is expressed as follows:

[0031] ;

[0032] ;

[0033] ;

[0034] In the formula, Indicates calcium dissolution damage factor; Indicates the first m Equivalent tensile strain of each sub-region; Indicates the first m The area of ​​each sub-region; This indicates that the speckled specimen has a solution age of [missing information]. The tensile strain threshold at that time; The summation symbol; This indicates that the speckled specimen has a solution age of [missing information]. Dissolution depth x Tensile strength at the point; This indicates that the speckled specimen has a solution age of [missing information]. Dissolution depth x The elastic modulus at that point.

[0035] As a further technical solution of the present invention: tensile strength The calculation formula is as follows:

[0036] ;

[0037] ;

[0038] In the formula, This indicates the tensile strength of the area in the speckled specimen where calcium dissolution has not occurred. This indicates the tensile strength at the edge of the speckled specimen. b Indicates the edge tensile strength attenuation coefficient; h This indicates that the speckled specimen has a solution age of [missing information]. The depth of dissolution at that time x ∈[0, h ]; This indicates that the speckled specimen has a solution age of [missing information]. The dissolution depth is 0.5. h Tensile strength at the point, a Indicates the attenuation coefficient of tensile strength in the middle section; Indicates the depth of dissolution x Related switching functions; Indicates when the dissolution depth When the time condition is met, the value is 1; otherwise, it is 0. Indicates when the dissolution depth When the time condition is met, the value is 1; otherwise, it is 0. Indicates the length of the speckled specimen.

[0039] As a further technical solution of the present invention: elastic modulus The calculation formula is as follows:

[0040] ;

[0041] In the formula, This indicates the elastic modulus of the region in the speckled specimen where calcium dissolution has not occurred. This indicates the elastic modulus at the edge of the speckled specimen. Indicates the edge modulus attenuation coefficient; This indicates that the speckled specimen has a solution age of [missing information]. The dissolution depth is 0.5. h The elastic modulus at that point, This represents the coefficient of elastic modulus attenuation in the middle section.

[0042] As a further technical solution of the present invention: before calculating the strain of the speckled specimen before and after calcium dissolution deformation, it is necessary to calculate the overall deformation and the average value of the overall deformation of each speckled specimen in the positive Y-axis direction when it reaches the current dissolution age; if the relative error between the overall deformation of a speckled specimen and the average value of the overall deformation is greater than a set value, the overall deformation measurement of each speckled specimen is invalid, and the measurement should be repeated or a new speckled specimen should be made; otherwise, it is valid and can be used for subsequent strain calculation.

[0043] As a further technical solution of the present invention, the overall deformation calculation is as follows:

[0044] ;

[0045] ;

[0046] ;

[0047] In the formula, This represents the average displacement of the first edge parallel to the Y-axis in the current speckle specimen. This represents the first edge of the first edge parallel to the Y-axis on the current speckle specimen. Displacement of each sub-region along the positive Y-axis; This represents the total number of sub-regions in the first edge parallel to the Y-axis on the current speckle specimen; This represents the average displacement of the second side parallel to the Y-axis in the current speckle specimen. This represents the first edge of the second side parallel to the Y-axis on the current speckle specimen. Displacement of each sub-region along the positive Y-axis; This represents the total number of sub-regions on the second side parallel to the Y-axis of the current speckle specimen; This indicates the overall deformation of the speckled specimen on the Y-axis.

[0048] As a further technical solution of the present invention: the area of ​​the speckled spots on the upper surface of the speckled specimen accounts for one-half.

[0049] As a further technical solution of the present invention: before and after taking a speckled DIC image of the surface using a DIC device, the speckled specimen is located in the same shooting position with the same posture.

[0050] Compared with the prior art, the beneficial effects of the present invention are:

[0051] 1. This invention combines digital image correlation (DIC) with high-throughput measurement, achieving integrated measurement of deformation and damage during calcium dissolution in concrete specimens. High-throughput acquisition of DIC images before and after dissolution significantly improves testing efficiency. Simultaneously, by combining macroscopic deformation calculation with microscopic damage model optimization, it obtains both the overall deformation results of the specimen and accurately quantifies the degree of damage through dissolution damage factors, balancing comprehensiveness and depth of measurement. This provides an efficient and systematic solution for studying the calcium dissolution performance of concrete.

[0052] 2. By referring to standard molding, cutting, and grinding to control the thickness of the specimens, the standardization and consistency of the specimens were ensured; the sealing design of the upper and lower surfaces ensures that the dissolution effect proceeds from the circumference to the inside, reducing interference factors; and the preparation of uniform and irregular black speckles lays the foundation for the accurate identification and matching of subsequent DIC images, improves the reliability of image analysis, and ensures the quality of measurement data from the source.

[0053] 3. Equipment debugging and calibration ensured the stability of the DIC system; the operation of soaking the specimens for 24 hours and keeping them moist effectively eliminated measurement errors caused by differences in dryness and humidity, and improved the comparability of data; the high-throughput mode of dual-camera lenses synchronously acquiring multiple specimens in the same field of view within 2 minutes not only greatly improved the testing efficiency, but also avoided environmental interference caused by acquisition at different times, ensuring the consistency and reliability of image data before dissolution.

[0054] 4. Sealing the upper surface of the specimen before dissolution can prevent non-target areas from participating in the dissolution reaction, ensuring the directionality and stability of the dissolution process; the precise preparation of chemical reagents provides a controllable corrosion environment for accelerating dissolution, which can simulate the effect of long-term calcium dissolution of concrete in a short time, significantly shortening the test cycle, while ensuring the scientific nature and repeatability of the dissolution process.

[0055] 5. By removing the seal, acquiring images, and then resealing to continue the etching process, dynamic monitoring of the same specimen at different etching ages was achieved, ensuring the continuity of the data over time. The high-throughput acquisition method was used, maintaining efficiency advantages in multiple measurements. Furthermore, multiple measurements of the same specimen can more accurately reflect the gradual nature of the etching process, providing a complete data chain for analyzing the damage evolution law.

[0056] 6. In addition to calculating the overall deformation of the specimen, the maximum and minimum principal strains in the two-dimensional XY plane were obtained, accurately revealing the strain distribution characteristics after dissolution. This refined analysis can clearly locate areas of concentrated deformation, reveal the influence of dissolution on the internal stress and strain of concrete, and provide richer information for understanding the deformation mechanism.

[0057] 7. Mechanical property data were obtained by simultaneously molding mortar specimens, providing a reliable experimental basis for the micro-damage model; the micro-damage model was optimized for the characteristics of calcium dissolution, improving the applicability of the model; the final calculated dissolution damage factor realized the correlation between micro-damage and macro-performance, which can both qualitatively analyze the damage distribution and quantitatively judge the degree of damage, making the damage evaluation more scientific and convincing. Attached Figure Description

[0058] Figure 1 This is a flowchart illustrating the overall implementation of the present invention.

[0059] Figure 2 This is a flowchart illustrating the preparation process of the speckled specimen in this invention.

[0060] Figure 3 This is a schematic diagram of the installation structure of the speckled specimen in this invention.

[0061] Figure 4 This is a displacement diagram on the X-axis of the speckled specimen of the present invention after 28 days of etching.

[0062] Figure 5 This is a displacement diagram of the speckled specimen in this invention on the Y-axis after 28 days of etching.

[0063] Figure 6 This is a diagram showing the maximum principal strain distribution of the speckled specimen in this invention after 28 days of etching.

[0064] Figure 7 This is a diagram showing the minimum principal strain distribution of the speckled specimen in this invention after 28 days of etching.

[0065] Figure 8 This is a damage diagram of the speckled specimen of the present invention after 28 days of etching.

[0066] Figure 9 This is a schematic diagram of the gradient decay model of the mechanical properties of calcium dissolution in the speckled specimen in this embodiment of the invention.

[0067] Figure 10 This is a spatial distribution diagram of the calcium dissolution damage field based on the DIC and optimized Mazars models in an embodiment of the present invention.

[0068] In the figure: 1. Scattered speckle specimen; 2. Vibration damping table; 3. Positioning screws; 4. Field of view. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] Please see Figure 1 This embodiment presents a high-throughput measurement method for calcium dissolution deformation damage in concrete specimens based on digital image correlation, including the following:

[0071] I. Preparation of speckled specimens for calcium dissolution deformation damage testing

[0072] First, cubic concrete specimens were prepared according to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete GB / T50081—2002". After demolding, the cubic concrete specimens were cured for 28 days in a standard curing environment of 20±2℃ and RH≥95%. Then, a high-speed cutting machine was used to cut the cubic concrete specimens into square sheet specimens with a thickness of 1cm. When preparing the square sheet specimens, three specimens were selected from the middle of the cubic concrete specimen, with smooth surfaces, uniform aggregate distribution, and no large pores. The surfaces of these three specimens were then polished for later use.

[0073] Next, the lower surface of the square sheet-like specimen was sealed with a sealant such as epoxy resin to ensure that the calcium dissolution direction proceeded from the periphery of the specimen inwards, rather than from the lower surface, which would interfere with the dissolution results. (See...) Figure 2 .

[0074] Finally, the upper surface of the square sheet specimen is cleaned and sprayed with white matte paint as a speckle background. The spray should be as thin as possible while covering the aggregate and slurry to avoid glare during image acquisition. Then, uniform, irregular black speckles are prepared on the specimen surface using black matte paint. The speckle size should be approximately 4-6 image pixels, and the speckles should be irregular with a coverage of about 50%. The speckles should have good contrast and not emit light. The size of the speckles should meet the requirements of the software for raster calculations on the specimen surface while also being recognizable by the camera; this needs to be controlled based on the measurement field of view, camera resolution, and specimen size.

[0075] II. Obtaining surface speckle DIC images of speckle specimens before calcium dissolution and deformation using a high-throughput method.

[0076] First, the DIC equipment was debugged, calibrated, and tested. The angle between the two DIC cameras was adjusted to 30°, the working distance to 600mm, and the camera distance to 160mm. Throughout the subsequent shooting process, the camera was kept stationary. The light source was adjusted so that the specimen was not exposed and the speckled spots on the specimen surface could be clearly identified. A 12×9 12mm calibration plate was used to calibrate the displacement resolution, which was 0.5μm. The influence of speckled specimen movement on the displacement test should be less than 5μm. The equipment was placed in a constant temperature room at 20℃.

[0077] Next, the prepared speckled specimen was immersed in water for 24 hours to ensure that the surface speckled spots collected before and after calcium dissolution deformation of the speckled specimen remained in the same moist state, thus avoiding measurement errors caused by differences in the dryness and humidity of the speckled specimen.

[0078] Then, remove the speckled specimens that have been soaked for 24 hours, let them air dry and cover them with a damp towel, and wait for DIC image acquisition.

[0079] Finally, the speckle pattern on the upper surface of the speckle specimen was acquired using a dual-camera DIC device. High-throughput image acquisition was employed, meaning multiple speckle specimens were acquired simultaneously within the same field of view. The number of speckle specimens acquired was determined by both the field of view and the size of the specimens, ensuring that all specimens were within the acquisition field of view to effectively improve testing efficiency. Figure 3 As shown, speckle specimens 1 are placed sequentially on the vibration damping table 2, and the positions of each speckle specimen 1 are fixed using positioning screws 3. Multiple positioning screws 3 cooperate to form multiple small squares, and each speckle specimen 1 is sequentially engaged in its corresponding square, achieving circumferential positioning, and all speckle specimens 1 are located within the defined field of view 4. The sampling time for speckle specimens should be controlled within 2 minutes to prevent the influence of moisture loss on the specimens, or the influence of drying shrinkage caused by prolonged exposure to air on the test results.

[0080] III. Accelerated calcium dissolution of speckled specimens

[0081] First, the upper surface of the speckle specimen, after the initial speckle distribution data has been collected, is sealed. The upper surface of the speckle specimen is sealed using plastic wrap and silicone sealant, such as... Figure 2 As shown, plastic wrap was used to cover the upper surface of the speckled specimen, and then silicone sealant was used to seal the perimeter of the upper surface of the specimen. The silicone sealant is very easy to remove and will not damage the speckled surface.

[0082] Next, a 6 mol / L ammonium chloride solution was prepared to accelerate calcium dissolution. Besides ammonium chloride, ammonium nitrate solution can also be used to accelerate calcium dissolution. Compared to deionized water, its acceleration rate can be increased by 300 times. The ratio of solution to the area of ​​the etched surface of the specimen was 8 mL / cm². 2 This ensures that the specimens maintain a certain calcium dissolution rate throughout the corrosion period.

[0083] Finally, the speckled specimen, with both the upper and lower surfaces sealed, was placed in a 6 mol / L ammonium chloride solution for calcium etching. Since both the upper and lower surfaces of the speckled specimen were sealed, calcium etching would proceed from the periphery of the plate-like specimen towards the center, accelerating the calcium etching process. The chemical reagents and specimen were placed in a constant temperature room at 20°C.

[0084] IV. Obtaining DIC images of the surface of speckle specimens after calcium dissolution and deformation using high-throughput methods.

[0085] First, to ensure effective observation of the deformation of the speckled specimens in both the early and late stages of calcium dissolution, the specimens immersed in ammonium chloride solution were removed at dissolution ages of 1, 3, 7, 14, 28, and 42 days, and the plastic wrap and silicone sealant on their surface were removed. Then, the specimens were covered with a damp towel to avoid the influence of drying shrinkage on their deformation.

[0086] Next, without moving the DIC equipment or changing the relevant parameters, high-throughput DIC images of the speckled surface of the speckled specimen after calcium dissolution deformation were acquired using the DIC equipment. During acquisition, the specimen remained fixed in the position determined by the positioning screws and was not allowed to be moved to other positions; the positions of the speckled specimens in the same batch were not to be changed.

[0087] Then, seal the upper surface of the speckled specimen again with plastic wrap and glass glue. The whole process should be carried out as soon as possible, and a damp towel should be used to ensure a moist environment for the speckled specimen.

[0088] Finally, the speckled specimens were immersed in an accelerated calcium dissolution chemical solution to continue calcium dissolution, and images were repeatedly acquired during the next dissolution period.

[0089] V. Calculate the strain of the speckled specimen before and after dissolution.

[0090] First, the deformation data of the speckled specimens before and after calcium dissolution were analyzed using DIC testing software to calculate the overall deformation of the speckled specimens. The overall deformation of the speckled specimens can be determined by determining the displacement of the boundary before and after calcium dissolution deformation. The overall deformation of each group of specimens requires the average value of three parallel specimens to be the overall deformation data of calcium dissolution for that group of specimens. An error exceeding 15% is considered an invalid test result.

[0091] The calculation formulas are shown in formulas (1) to (3):

[0092] (1);

[0093] (2);

[0094] (3);

[0095] In the formula, This represents the average displacement of the first edge parallel to the Y-axis in the current speckle specimen. This represents the first edge of the first edge parallel to the Y-axis on the current speckle specimen. Displacement of each sub-region along the positive Y-axis; This represents the total number of sub-regions in the first edge parallel to the Y-axis on the current speckle specimen; This represents the average displacement of the second side parallel to the Y-axis in the current speckle specimen. This represents the first edge of the second side parallel to the Y-axis on the current speckle specimen. Displacement of each sub-region along the positive Y-axis; This represents the total number of sub-regions on the second side parallel to the Y-axis of the current speckle specimen; This indicates the overall deformation of the speckled specimen on the Y-axis.

[0096] Next, the calculation of the maximum and minimum principal strains of the speckled specimen in the two-dimensional XY plane is given by formulas (4) to (8):

[0097] (4);

[0098] (5);

[0099] (6);

[0100] (7);

[0101] (8);

[0102] In the formula, U This indicates the displacement of the current sub-region center point along the positive X-axis; V This indicates the displacement of the current sub-region center point along the positive Y-axis; express U Rate of change in the positive direction of the X-axis; express V Rate of change in the positive direction of the Y-axis; This indicates the strain of the current sub-region in the positive X-axis direction; This shows the strain of the current sub-region in the positive Y-axis direction; This represents the sum of the strains of the current sub-region in the positive X-axis and positive Y-axis directions; This indicates the maximum principal strain in the current sub-region; This represents the minimum principal strain of the current subregion.

[0103] Using Matlab software, the displacement field, maximum principal strain field, and minimum principal strain field of each sub-region of the speckle specimen in the positive X-axis and positive Y-axis directions were plotted, and the overall deformation data of each speckle specimen were statistically analyzed. Figures 4-8 The figure shows the displacement fields in the positive X-axis and positive Y-axis directions of the speckle specimen in this embodiment, as well as the maximum principal strain, minimum principal strain, and damage field.

[0104] Figure 4 The figure shows the strain contour plot of the speckle specimen along the X-axis. Blue indicates that the speckle has moved in the negative X-axis direction, and yellow indicates that the speckle has moved in the positive X-axis direction. Figure 4 This indicates that the speckled specimen underwent shrinkage during the etching process.

[0105] Figure 5 The figure shows the strain contour plot of the speckle specimen along the Y-axis. Blue indicates that the speckle has moved in the negative Y-axis direction, and yellow indicates that the speckle has moved in the positive Y-axis direction. Figure 5 This indicates that the speckled specimen underwent shrinkage during the etching process.

[0106] Figure 6 The maximum principal strain contour map shows that yellow represents the tensile strain region and blue represents the compressive strain region. The dissolution proceeds from the outside to the inside, and the maximum principal strains, tensile strain and compressive strain, advance into the interior of the specimen as the dissolution progresses. The extreme value regions are distributed on the surface of the speckled specimen.

[0107] Figure 7 The minimum principal strain distribution cloud map shows the tensile strain zone in yellow and the compressive strain zone in blue. The minimum principal strain map can be used to distinguish between the aggregate zone and the mortar zone. Similar to the maximum principal strain, the minimum principal strain, tensile strain and compressive strain, advance into the interior of the specimen as the erosion progresses. The extreme value region is distributed on the surface area of ​​the speckled specimen.

[0108] Figure 8 Medium gray represents aggregate, white represents mortar, and yellow and red represent different degrees of dissolution damage. Dissolution damage exists in the dissolution area of ​​the speckled specimen. The damage progresses from the outside to the inside, mainly distributed in the transition zone between the aggregate and aggregate interfaces and between aggregates. The maximum damage is mainly distributed on the surface of the speckled specimen. As it moves inward, the dissolution damage gradually decreases, and there is no damage in the undissolved area inside.

[0109] Then, the Mazars model was selected as the micro-damage model and optimized. The Mazars model was used to calculate the damage caused by calcium dissolution in the speckled specimen, as shown in formulas (9) to (11):

[0110] (9);

[0111] (10);

[0112] (11);

[0113] In the formula, This represents the calcium dissolution damage factor, i.e., the tensile strain of the speckled specimen. The area of ​​the region; Indicates the tensile strength of cement-based materials; Indicates the elastic modulus of cement-based materials; Indicates the first m Equivalent tensile strain of each sub-region; Indicates the first m The area of ​​each sub-region.

[0114] Because calcium dissolution causes a significant decrease in the mechanical properties of cement paste, both tensile strength and elastic modulus fluctuate greatly. Therefore, the tensile strain threshold of cement-based materials is affected. It is not a constant value and requires optimization of the Mazars model, as shown in formulas (12) and (13):

[0115] (12);

[0116] (13);

[0117] In the formula, Indicates the first m Equivalent tensile strain of each sub-region; Indicates the first m The area of ​​each sub-region; This indicates that the speckled specimen has a solution age of [missing information]. The tensile strain threshold at that time; The summation symbol; This indicates that the speckled specimen has a solution age of [missing information]. Dissolution depth x Tensile strength at the point; This indicates that the speckled specimen has a solution age of [missing information]. Dissolution depth x The elastic modulus at that point.

[0118] Finally, based on existing research, the mechanical properties of the etched zone exhibit a gradient decrease due to the dissolution of CH and CSH gels. Therefore, let the compressive strength of the un-etched zone be... The elastic modulus is The edge strength of the speckled specimen is The edge elastic modulus of the speckled specimen is The speckled specimen at the dissolution age was... The depth of dissolution at that time was h At a dissolution depth of 0.5 h The tensile strength at the position is The elastic modulus is . This represents the coefficient of elastic modulus attenuation in the middle section. This represents the edge modulus attenuation coefficient. This represents the attenuation coefficient of the tensile strength in the middle section. This represents the edge tensile strength attenuation coefficient.

[0119] Based on this, it can be inferred that the speckled specimen had a dissolution age of [missing information]. At that time, the overall compressive strength of the speckled specimen The integral can be performed by referring to formula (14) to obtain the overall elastic modulus. The integral can be performed by referring to formula (15):

[0120] (14);

[0121] (15);

[0122] Integrating equations (14) and (15), we can see that the dissolution age is... At that time, the overall strength and elastic modulus of the speckled specimen are shown in formulas (16) and (17), respectively:

[0123] (16);

[0124] (17);

[0125] Therefore, the solution age can be deduced as follows: Dissolution depth Tensile strength at the point and elastic modulus It can be calculated using formulas (18) to (20):

[0126] (18);

[0127] (19);

[0128] (20);

[0129] In the formula, Indicates the depth of dissolution x Related switching functions; Indicates when the dissolution depth When the time condition is met, the value is 1; otherwise, it is 0. Indicates when the dissolution depth When the time condition is met, the value is 1; otherwise, it is 0. Indicates the length of the speckled specimen.

[0130] like Figure 9 As shown in the figure, the three-dimensional gradient decay law of the mechanical properties of concrete after calcium dissolution is revealed: from the edge of the specimen ( x =0) to the undissolved core area ( The compressive strength (red) and elastic modulus (blue) show a three-stage gradual change, namely the severely attenuated area at the edge ( Performance increases linearly to and ), Central Transition Zone ( (constant performance) and uncorroded areas ( Restore original value and Key parameter: thickness Defining the calculation boundary and the solution depth Over time, the attenuation coefficient b , β It is much less than 1, which quantitatively characterizes the degree of dissolution damage and provides a physical basis for the gradient damage model (Equations 18-19), and realizes the quantification of damage depth for the first time.

[0131] like Figure 10 As shown in the figure, the spatial distribution of calcium dissolution damage based on the optimized Mazars model and DIC technology is illustrated: in the damage field of the color-mapped model, the red area represents a high damage region ( ) Densely distributed at the edge of the specimen, and Figure 9 The edge attenuation zone strictly corresponds; the blue low-damage zone ( Located within the undissolved core. (Through dynamic threshold) Related dissolution depth h The damage gradient law (edge ​​> center > core) and model reliability were empirically verified (the 28-day calcium dissolution damage factor was 129 μm·m). -1 This fills the gap in the precise spatial measurement of concrete corrosion damage, providing a direct basis for durability design and protection.

[0132] The compressive strength, elastic modulus, and dissolution depth of the speckled specimens at different dissolution ages were measured. Based on the measured data, a set of equations was constructed using formulas (18) to (20). The specific values ​​of the relevant parameters were obtained by solving the equations and fitting them, as shown in Table 1.

[0133] Table 1 Parameter Values

[0134] ;

[0135] Substituting the fitted parameters into formulas (18) to (20), the tensile strength and elastic modulus at different dissolution depths can be calculated, as shown in Table 2:

[0136] Table 2 Tensile Strength and Modulus of Elasticity

[0137] ;

[0138] VI. Calculate the dissolution loss factor using a microscopic damage model

[0139] Based on the optimized Mazars model, the calcium dissolution damage factor was calculated using Matlab software. Note that Image-J was used to binarize the specimen cross-section, removing the aggregate region and calculating only the damage amount of the mortar portion in the speckled specimen. The corresponding damage field was then plotted for qualitative and quantitative assessment of the specimen's dissolution damage. Figure 8 The image shows the damage field distribution of the 28-day corrosion damage of the test specimen in this case. It can be seen that the corrosion damage is more significant around the perimeter of the specimen, while no significant damage is observed in the center. The calculated corrosion damage factor at a corrosion age of 28 days is 129 μm·m. -1 .

[0140] Therefore, the present invention uses digital image correlation to measure the deformation of cement-based materials caused by calcium dissolution, which improves the measurement accuracy and allows for intuitive observation and characterization of non-uniform stress and strain at different dissolution ages.

[0141] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-throughput measurement method for calcium dissolution deformation damage in concrete specimens based on digital image correlation, characterized in that, The measurement steps include the following: S1. Prepare speckled specimens for calcium dissolution deformation damage testing; S2. Calcium dissolution deformation test was carried out on the speckled specimen, and the surface speckled DIC images of the speckled specimen before and after calcium dissolution deformation were obtained by high-throughput method. S3. Calculate the strain of the speckled specimen before and after calcium dissolution deformation using the surface speckled DIC image, select the micro-damage model, and optimize the micro-damage model based on the strain. S4. Calcium dissolution deformation of speckled specimens was measured using the optimized micro-damage model. The sub-steps of step S2 are as follows: S21. Before conducting the calcium dissolution deformation test on the speckled specimen, use a DIC device to photograph the upper surface of the speckled specimen to obtain a surface speckled DIC image before calcium dissolution deformation, and divide the surface speckled DIC image into multiple sub-regions by grid division. S22. Seal the upper surface of the speckled specimen and immerse it in a calcium dissolving chemical solution for a set period of time to allow the calcium dissolving chemical solution to dissolve into the specimen along its circumference. S23. Each time the soaking time reaches the corresponding dissolution age, the following imaging operation shall be performed until imaging of all dissolution ages is completed. Imaging procedure: Remove the speckled specimen from the calcium dissolution chemical solution and remove the seal on its upper surface. Then, use a DIC device to take a picture of its upper surface to obtain a speckled DIC image of the surface at the corresponding dissolution age. After that, seal the upper surface again and continue to immerse it in the calcium dissolution chemical solution. The sub-steps of step S3 are as follows: S31. Establish a plane coordinate system OXY with the two perpendicular sides of the upper surface of the speckled specimen as coordinate axes; S32. Using the surface speckle DIC images before and after calcium dissolution deformation, calculate the strain of each sub-region at different dissolution ages. The corresponding calculation formulas are as follows: ； ； ； ； ； In the formula, U This indicates the displacement of the current sub-region center point along the positive X-axis; V This indicates the displacement of the current sub-region center point along the positive Y-axis; express U Rate of change in the positive direction of the X-axis; express V Rate of change in the positive direction of the Y-axis; This indicates the strain of the current sub-region in the positive X-axis direction; This shows the strain of the current sub-region in the positive Y-axis direction; This represents the sum of the strains of the current sub-region in the positive X-axis and positive Y-axis directions; This indicates the maximum principal strain in the current sub-region; This represents the minimum principal strain of the current subregion; S33. The micro-damage model adopts the Mazars model, and the Mazars model is optimized based on the maximum principal strain and the minimum principal strain. The optimized Mazars model is expressed as follows: ； ； ； In the formula, Indicates calcium dissolution damage factor; Indicates the first m Equivalent tensile strain of each sub-region; Indicates the first m The area of ​​each sub-region; This indicates that the speckled specimen has a solution age of [missing information]. t The tensile strain threshold at that time; Σ The summation symbol; This indicates that the speckled specimen has a solution age of [missing information]. t Dissolution depth x Tensile strength at the point; This indicates that the speckled specimen has a solution age of [missing information]. Dissolution depth x The elastic modulus at that point; tensile strength The calculation formula is as follows: ； ； In the formula, This indicates the tensile strength of the area in the speckled specimen where calcium dissolution has not occurred. This indicates the tensile strength at the edge of the speckled specimen. b Indicates the edge tensile strength attenuation coefficient; h This indicates that the speckled specimen has a solution age of [missing information]. The depth of dissolution at that time x ∈[0, h ]; This indicates that the speckled specimen has a solution age of [missing information]. t The dissolution depth is 0.

5. h Tensile strength at the point, a Indicates the attenuation coefficient of tensile strength in the middle section; Indicates the depth of dissolution x Related switching functions; Indicates when the dissolution depth When the time condition is met, the value is 1; otherwise, it is 0. Indicates when the dissolution depth When the time condition is met, the value is 1; otherwise, it is 0. Indicates the length of the speckled specimen; elastic modulus The calculation formula is as follows: ； In the formula, This indicates the elastic modulus of the region in the speckled specimen where calcium dissolution has not occurred. This indicates the elastic modulus at the edge of the speckled specimen. Indicates the edge modulus attenuation coefficient; This indicates that the speckled specimen has a solution age of [missing information]. t The dissolution depth is 0.

5. h The elastic modulus at that point, This represents the coefficient of elastic modulus attenuation in the middle section.

2. The high-throughput measurement method for calcium dissolution deformation damage of concrete specimens based on digital image correlation according to claim 1, characterized in that, The sub-steps of step S1 are as follows: S11. Prepare block concrete specimens and cut and grind the concrete specimens into multiple square sheet specimens of a set thickness. S12. Seal the lower surface of the square sheet-like specimen; S13. Coat the upper surface of the square sheet specimen with black speckled spots to prepare a speckled specimen.

3. The high-throughput measurement method for calcium dissolution deformation damage of concrete specimens based on digital image correlation according to claim 2, characterized in that, Before calculating the strain of speckled specimens before and after calcium dissolution deformation, it is necessary to calculate the overall deformation and average overall deformation of each speckled specimen in the positive Y-axis direction when it reaches the current dissolution age. If the relative error between the overall deformation and the average overall deformation of a speckled specimen is greater than the set value, the overall deformation measurement of that speckled specimen is invalid, and the measurement should be repeated or a new speckled specimen should be made. Otherwise, it is valid and can be used for subsequent strain calculations.

4. The high-throughput measurement method for calcium dissolution deformation damage of concrete specimens based on digital image correlation according to claim 3, characterized in that, The overall deformation is calculated as follows: ； ； ； In the formula, This represents the average displacement of the first edge parallel to the Y-axis in the current speckle specimen. This represents the first edge of the first edge parallel to the Y-axis on the current speckle specimen. Displacement of each sub-region along the positive Y-axis; This represents the total number of sub-regions in the first edge parallel to the Y-axis on the current speckle specimen; This represents the average displacement of the second side parallel to the Y-axis in the current speckle specimen. This represents the first edge of the second side parallel to the Y-axis on the current speckle specimen. Displacement of each sub-region along the positive Y-axis; This represents the total number of sub-regions on the second side parallel to the Y-axis of the current speckle specimen; This indicates the overall deformation of the speckled specimen on the Y-axis.

5. A high-throughput measurement method for calcium dissolution deformation damage of concrete specimens based on digital image correlation according to claim 4, characterized in that, The area of ​​the speckled spots on the upper surface of the specimen is one-half.

6. A high-throughput measurement method for calcium dissolution deformation damage of concrete specimens based on digital image correlation according to claim 5, characterized in that, Before and after taking DIC images of the surface speckle pattern using a DIC device, the speckle specimens were positioned in the same orientation at the same shooting location.

Images