Testing equipment and methods for deformation coefficient of concrete materials under seepage field

Abstract

The present invention discloses a deformation coefficient testing device for concrete materials under the action of a seepage field, comprising a formwork system, a concrete specimen, an anti-seepage system, a loading system, a measuring system and an acquisition system. The formwork system comprises a formwork base plate and two symmetrical side formworks, and the formwork base plate and the side formworks together constitute a pouring space for the concrete specimen. The anti-seepage system comprises a surface anti-seepage paint, a casing membrane and an anti-seepage glue, and the loading system is a concrete anti-seepage meter. The measuring system comprises a strain sensor, a temperature sensor and an osmotic pressure sensor. The input end of the acquisition system is connected to the strain sensor, the temperature sensor and the osmotic pressure sensor in the measuring system, and the output end is connected to a computer. The deformation coefficient testing device and the testing method for concrete materials under the action of a seepage field can test the deformation characteristics caused by pressure changes under the action of a seepage field of concrete materials, thereby making up for the deficiencies in the osmotic deformation parameters of hydraulic concrete.

Description

Technical Field

[0001] The invention relates to a testing device and a testing method for a permeability deformation coefficient of a concrete material, and in particular to a testing device and a testing method for a deformation coefficient of a concrete material under the action of a seepage field. Background Art

[0002] Hydraulic structures utilize a significant amount of concrete, and its properties are crucial for project safety and proper operation. While testing methods for thermal parameters such as calorific value, thermal conductivity, and linear expansion coefficient, as well as mechanical parameters such as elastic modulus and Poisson's ratio, and deformation properties such as volumetric deformation and creep are relatively mature, research on variations in concrete's internal seepage pressure and the resulting deformation characteristics is lacking. Engineering practice has shown that variations in concrete's internal seepage pressure can cause deformation. The paper "Study on Moisture-Induced Deformation of Concrete Fascias in Gongboxia Rockfill Dam" reports that some concrete structures experience an increase in moisture-induced deformation of 30 to 280 με after nine years of water-filled operation. The paper "Analysis of the Causes of the Discrepancy Between Stress Measurements and Elastic Calculations at the Heel of a High Arch Dam" points out that the dam's heel is permanently submerged in water, resulting in significantly greater pore water pressure at that location than elsewhere. Consequently, the compressive expansion deformation of concrete caused by pore water pressure is non-negligible. Therefore, accurately measuring deformation caused by variations in concrete seepage pressure is crucial for the construction and operation of concrete dams.

[0003] Patent CN107816936A uses a method of comparing before and after immersion in water to obtain swelling deformation, which can reflect the swelling deformation of concrete under conditions where it changes from dry to wet. It provides a method for obtaining the swelling deformation of hardened hydraulic concrete at non-standard temperatures, which can solve the problem of being unable to measure and separate the swelling deformation of concrete at non-standard temperatures. It can obtain the swelling deformation of hardened hydraulic concrete after immersion in water under real environmental conditions, but it cannot measure the material deformation characteristics under different osmotic pressure conditions under the action of the seepage field. Patent CN203133070U proposes a testing device for swelling deformation, which is mainly used to test the swelling (expansion rate) requirements of concrete at different ages. By using this testing device, tests can be performed according to different ages, and readings can also be taken once a day. A curve graph can be drawn and the range and pattern of swelling can be observed. However, it is also unable to consider the deformation characteristics under conditions of varying osmotic pressure. The paper "Experimental and Model Study on the Expansion and Deformation of Hydraulic Concrete Under the Influence of Water-Binder Ratio" investigated the expansion and deformation characteristics of hydraulic concrete under different water-binder ratios. Based on the concrete mix proportions of different dam sections, the expansion coefficients were measured under fully submerged conditions and at different water-binder ratios. However, the strain caused by changes in water pressure under the influence of the submerged seepage field was not considered. The paper "Experimental Study on the Expansion and Deformation of Hydraulic Concrete with Non-Standard Curing in Indoors" measured the expansion coefficient of concrete under different curing conditions. Two different curing conditions were designed: 1) indoor wrapped curing; 2) indoor unwrapped curing. However, the strain caused by changes in water pressure under the influence of the submerged seepage field was still not considered. The paper "Study on the Effect of Different Fly Ash Contents on the Waterproofing Performance of Concrete Roadbed" provides a general method for measuring the permeability coefficient of concrete. The water-permeable area of ​​the concrete specimen is divided and the remaining surface of the specimen is sealed with wax using epoxy resin. Using the HS-4 concrete impermeability tester, pressure was applied step by step from 0 MPA at the bottom of the specimen. Five specimens were selected from each group of mixes and the average value was taken as the concrete water permeability coefficient. However, this method did not measure and analyze the expansion coefficient under pressure changes.

[0004] A large amount of practical experience shows that under the action of long-term immersion, the dam, especially the upstream concrete, will have changes in concrete osmotic pressure and saturation due to the infiltration of reservoir water. The change of internal osmotic pressure may affect the strain measurement value. The use of specially designed anti-permeability instruments and strain gauges to carry out indoor tests on the influence of osmotic pressure (pore water pressure) on concrete strain stress, and combined with the concrete specimen micro-numerical test, the influence mechanism of osmotic pressure (pore water pressure) on concrete strain stress is studied. Through the research results on the influence of osmotic pressure on the measured values ​​of strain gauge groups, various types of strain gauge groups such as five-way, seven-way, and nine-way can be studied and optimized to calculate the stress of concrete measuring points. Therefore, the present invention tests the deformation characteristics caused by pressure changes under the action of the seepage field of concrete materials to make up for the shortcomings of hydraulic concrete swelling parameters. Summary of the Invention

[0005] The purpose of the present invention is to provide a deformation coefficient testing device and a testing method for concrete materials under the action of seepage field, so as to solve the above-mentioned multiple defects caused by the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A device for testing the deformation coefficient of concrete materials under the action of a seepage field comprises a template system, a concrete test piece, an anti-seepage system, a loading system, a measuring system and a collection system.

[0008] The formwork system includes a formwork base plate and two symmetrical side formworks, which are fastened to the formwork base plate with bolts to form a pouring space for the concrete specimen. The formwork base plate and side formworks can be made of steel or cast iron.

[0009] The anti-seepage system includes a surface anti-seepage paint, a membrane, and a high-strength sealant. The surface anti-seepage paint is evenly sprayed onto the sides of the concrete specimen. The anti-seepage paint is preferably an epoxy primer, epoxy midcoat, and epoxy topcoat. The bottom of the concrete specimen is enclosed in the membrane. The top of the sealing membrane is sealed with high-strength sealant at the point of contact with the concrete specimen. The membrane is then fixed to the loading system.

[0010] The loading system is a concrete impermeability tester.

[0011] The measurement system includes a strain sensor, a temperature sensor, and an osmotic pressure sensor. The sensors are preferably small, waterproof, and highly accurate. The input end of the acquisition system is connected to the strain sensor, temperature sensor, and osmotic pressure sensor in the measurement system, and the output end is connected to a computer.

[0012] Preferably, the base plate of the template system is disc-shaped, the upper part of the side template is a circular tube of equal diameter, and the lower part is a frustum of variable diameter, which is cut symmetrically along the vertical direction. The connection between the two side templates is a flange with screw holes, and the connection between the side template and the template base plate is a circular flange with screw holes.

[0013] Preferably, the upper portion of the mantle is a variable diameter circular tube with a smaller upper portion and a larger lower portion, and the lower portion is a circular flange with screw holes, which is fastened to the loading system via bolts. The inner dimensions of the mantle are the same as the inner dimensions of the lower portion of the formwork on the side of the formwork system, and the concrete specimen is tightly attached to the inner side of the mantle.

[0014] Preferably, the strain sensor, temperature sensor and osmotic pressure sensor are all long strips and are vertically buried in the middle of the concrete specimen. The connection between the wires and the sensors is sealed with high-strength sealant, preferably silicone rubber and epoxy resin.

[0015] A method for testing a deformation coefficient testing device of a concrete material under a seepage field, comprising the following steps:

[0016] Step 1: Design the concrete mix ratio and pour the concrete specimens. During the pouring process, embed the strain sensor, temperature sensor, and permeation pressure sensor before vibrating the concrete. Avoid damaging the sensors during the vibration process. After the concrete specimens are cured to initial setting, remove the formwork system and continue curing to the required age.

[0017] Step 2: After the concrete specimen is cured and formed, wipe the surface of the concrete specimen and spray the surface anti-seepage paint on the side of the concrete specimen. First, spray the anti-seepage paint primer, then spray the anti-seepage paint middle paint and top coat. Use high-strength sealant to seal the contact between the sensor wire and the concrete specimen. First, seal with silicone rubber to protect the sensor wire, and then seal with epoxy resin.

[0018] Step 3: Use a press to press the concrete specimen into the membrane, fasten the membrane to the loading system with bolts, and use high-strength sealant to seal the contact point between the top of the membrane and the concrete specimen.

[0019] Step 4: Saturate the concrete specimen with water and perform a pressure test under the action of the seepage field. Measure the temperature, pressure, and deformation. The pressure variation range must be at least greater than 0.4 MPa and the test must be repeated at least three times.

[0020] Step 5: Perform compression expansion coefficient analysis based on the test results to obtain the compression expansion coefficient;

[0021] Preferably, the method for analyzing the compression expansion coefficient based on the test results is as follows:

[0022] Calculate the temperature strain ε based on the temperature change measured by the temperature sensor T , and then calculate the expansion coefficient β of concrete under water pressure. The calculation formula is as follows:

[0023] ε w =ε-ε T -ε G

[0024] ε T =α·ΔT

[0025]

[0026] Where ε is the measured value of the strain gauge, ε T is the temperature strain of concrete, α is the linear expansion coefficient of concrete, ε w is the swelling deformation, ε G is its own volume deformation, ΔL is the micro deformation of the strain gauge, L is the strain gauge length, and ΔP is the changing pore water pressure.

[0027] Multiple Δε and ΔP of each concrete specimen are regressed and fitted to obtain the optimal solution as the result of the concrete specimen. Finally, the average value of the results of multiple concrete specimens is taken as the final result.

[0028] The advantages of the present invention are that the deformation coefficient testing equipment and testing method of concrete materials under the action of seepage field can test the deformation characteristics caused by pressure changes under the action of seepage field of concrete materials, filling the gap in the expansion parameters of hydraulic concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the present invention;

[0030] Figure 2 It is a structural schematic diagram of the template system of the present invention;

[0031] Figure 3 It is a schematic diagram of the top view of the template system of the present invention;

[0032] Among them: 1-formwork system, 2-concrete specimen, 3-anti-seepage system, 4-loading system, 5-measurement system, 6-acquisition system, 7-formwork base plate, 8-side formwork, 9-surface anti-seepage paint, 10-film, 11-high-strength sealant, 12-strain sensor, 13-temperature sensor, 14-seepage pressure sensor, 15-water pressure hole. DETAILED DESCRIPTION

[0033] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0034] like Figure 1 As shown, a deformation coefficient testing device for concrete materials under seepage field includes a formwork system 1, a concrete specimen 2, an anti-seepage system 3, a loading system 4, a measuring system 5 and a collection system 6.

[0035] The anti-seepage system 3 includes a surface anti-seepage paint 9, a membrane 10, and a high-strength sealant 11. The surface anti-seepage paint 9 is evenly sprayed onto the sides of the concrete specimen 2. The anti-seepage paint is preferably an epoxy primer and epoxy topcoat. The bottom of the concrete specimen 2 is enclosed in the membrane 10. The top of the sealing membrane 10 is sealed with high-strength sealant 11 at the point of contact with the concrete specimen 2. The membrane 10 is fixed to the loading system 4.

[0036] The loading system 4 is a concrete impermeability tester. The measurement system 5 includes a strain sensor 12, a temperature sensor 13, and a permeation pressure sensor 14. These sensors are preferably small, waterproof, and highly accurate. The input end of the acquisition system 6 is connected to the strain sensor 12, temperature sensor 13, and permeation pressure sensor 14 in the measurement system 5, and the output end is connected to a computer.

[0037] The upper portion of the mantle 10 is a variable diameter circular tube with a smaller upper portion and a larger lower portion. Its upper surface has an outer diameter of 195 mm and an inner diameter of 175 mm, while its lower surface has an outer diameter of 205 mm and an inner diameter of 185 mm. The lower portion is a circular flange with six screw holes, which is bolted to the loading system 4. The inner dimensions of the mantle 10 are identical to those of the lower portion of the side formwork 8 of the formwork system 1. The concrete specimen 2 is tightly attached to the inner side of the mantle 10. The mantle 10 is made of nickel-plated steel.

[0038] The strain sensor 12, temperature sensor 13 and penetration pressure sensor 14 are all long strips and are vertically buried in the middle of the concrete specimen 2. The connection between the wires and the sensors is sealed with high-strength sealant 11, preferably silicone rubber and epoxy resin.

[0039] like Figure 2 、 Figure 3 As shown, the formwork system 1 includes a formwork base plate 7 and two symmetrical side formworks 8. The two side formworks 8 are fastened to the formwork base plate 7 with bolts, and together they form a pouring space for the concrete specimen 2. The formwork base plate 7 and the side formworks 8 can be made of materials such as steel or cast iron. The base plate of the formwork system 1 is disc-shaped. The upper portion of the side formwork 8 is a 150mm long constant diameter circular tube with an outer diameter of 195mm and an inner diameter of 175mm. The lower portion is a 70mm long variable diameter circular tube. The upper surface is connected to the constant diameter circular tube, and the lower surface has an outer diameter of 205mm and an inner diameter of 185mm. It is cut symmetrically along the vertical direction. The connection between the two side formworks 8 is a flange with three screw holes on each side. The connection between the side formworks 8 and the formwork base plate 7 is a circular flange with six screw holes. The formwork system 1 is made of cast iron, which is easy to process and shape.

[0040] A method for testing a deformation coefficient testing device of a concrete material under a seepage field, comprising the following steps:

[0041] 1. Prepare concrete using the following mix ratio: 60kg gravel, 18.26kg cement, 10.4kg sand, 40kg sand, aggregate particle size, coarse aggregate 10-31.5mm, large particle size mainly accounts for 60%, fine aggregate is river sand with fineness modulus 2.7. Test process is as follows Figure 2 As shown, when the concrete specimen 2 is poured, the measuring system 5 is fixed to Figure 1The center of the mold shown in the figure was removed 24 hours after the concrete specimen 2 was formed. Measurement system 5 can be replaced with other high-precision, water-pressure-resistant, and cost-effective sensors. The larger the strain gauge length and the closer it fits the concrete, the smaller the measurement system 5. The dimensions of formwork system 1 and concrete specimen 2 can be as follows: concrete specimen 2 is 220 mm high, 175 mm in upper diameter, and 185 mm in lower diameter. Use a wire brush to remove the cement slurry film on both ends, then cure for 28 days.

[0042] 2. Use a dry towel to clean the surface of the concrete specimen 2. After standing for a while until the surface of the concrete specimen 2 is dry, spray the surface anti-seepage paint 9 on its side. Figure 3 As shown. First, spray a layer of water-based epoxy penetrating primer, spray once: first stir the primer component A evenly, then pour the primer component A and primer component B into an empty bucket according to the required ratio of 10:4 and stir electrically for 1 minute. 2 hours after the primer is applied, apply the water-based epoxy intermediate paint. The second step is to spray the water-based epoxy intermediate paint, and roll the intermediate paint twice: first stir the intermediate paint component A evenly, then pour the intermediate paint component A and intermediate paint component B into an empty bucket according to the required ratio of 5:1 and stir electrically for 1 minute. Depending on the specific situation, 5%-20% water can be added. 24 hours after the intermediate paint is rolled, apply the topcoat. The third step is to spray the water-based polyurethane topcoat, and spray the single-component topcoat 5 times: first stir the topcoat evenly, and apply the next coat after each coat is dry for 2 hours. During the spraying process, 5%-20% water can be added to adjust the viscosity to suit the spraying process. Note that the interface between the internal lead-out wires and the top surface should also be sealed with silicone rubber and epoxy resin glue;

[0043] 3. Immediately press the coated concrete specimen 2 into the membrane 10 on a uniaxial compressive strength testing machine, ensuring that the bottom surface of the concrete specimen 2 is flush with the bottom surface of the membrane 10. Since the top of the concrete specimen 2 is exposed, the coating can be inspected for wear and tear after the concrete specimen 2 is pressed in, and any damage can be repaired promptly. High-strength sealant 11 is then applied to the interface between the membrane 10 and the concrete specimen 2 to seal the coating. Once the coating reaches the required strength, start the test equipment and check that the instrument is functioning properly.

[0044] 4. First saturate the concrete specimen 2, e.g. Figure 1As shown, the pressure device applies water pressure through the water pressure hole 15, starting from 0.4MPa, and increasing the water pressure by 0.4MPa every 4 hours, and observing the end surface of the concrete specimen 2 at any time until water seeps from the top surface of the concrete specimen 2. After the concrete specimen 2 is saturated, the instrument is turned off. Anti-seepage paint 9 is applied to the top surface of the concrete specimen 2 to seal the entire concrete specimen 2. After the surface anti-seepage paint 9 solidifies, the instrument is turned on and the pressure is adjusted to 0.4MPa. After observing that the piezometer reading is stable, the measurement system 5 starts to collect data. The water pressure is increased by 0.4MPa every 4 hours. After 2MPa water pressure is applied for 4 hours, the experiment is stopped and data processing is performed;

[0045] 5. The strain measured by measurement system 5 is first eliminated by removing the temperature strain. Because the present invention is carried out under the action of a seepage field, the strain measured by measurement system 5 does not include the volume deformation caused by water absorption by the concrete. Therefore, after eliminating the temperature strain, only the strain caused by pore water pressure and the autogenous volume deformation of the concrete remain. The calculation formula for the expansion coefficient β of concrete under water pressure is as follows:

[0046] ε w =ε-ε T -ε G

[0047] ε T =α·ΔT

[0048]

[0049] Where ε is the measured value of the strain gauge, ε T is the temperature strain of concrete, α is the linear expansion coefficient of concrete, ε w is the swelling deformation, ε G is the volume deformation of the strain gauge, ΔL is the micro deformation of the strain gauge, L is the gauge length of the strain gauge, and ΔP is the changing pore water pressure. w and ΔP will change. Increasing the water pressure several times will result in several measurement results of the expansion coefficient. Therefore, multiple Δε and ΔP of each concrete specimen 2 are regressed and fitted to obtain the optimal solution as the result of the concrete specimen 2. Finally, the average value of the results of the six concrete specimens 2 is taken as the final result.

[0050] It is understood from common technical knowledge that the present invention may be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the embodiments disclosed above are, in all respects, merely illustrative and not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

Claims

1. A device for testing the deformation coefficient of concrete material under the action of seepage field, characterized in that: It includes a formwork system (1), a concrete specimen (2), an anti-seepage system (3), a loading system (4), a measurement system (5) and a collection system (6); The template system (1) comprises a template base plate (7) and two symmetrical side templates (8), wherein the two side templates (8) are fastened to the template base plate (7) by bolts, and together constitute a pouring space for the concrete specimen (2); the template system (1) has a disk-shaped base plate, the upper portion of the side template (8) is a uniform diameter circular tube, and the lower portion is a variable diameter frustum, which is cut symmetrically along the vertical direction, the connection between the two side templates (8) is a flange with screw holes, and the connection between the side template (8) and the template base plate (7) is a circular flange with screw holes; The anti-seepage system (3) includes a surface anti-seepage paint (9), a film (10) and a high-strength sealant (11), wherein the surface anti-seepage paint (9) is evenly sprayed on the side of the concrete specimen (2); the bottom of the concrete specimen (2) is installed in the film (10), and the top of the sealing film (10) is sealed and connected with the concrete specimen (2) with a high-strength sealant (11), and the film (10) is fixed on the loading system (4); the upper part of the film (10) is in the shape of a variable diameter circular tube with a small upper part and a large lower part, and the lower part is a circular flange with screw holes, which is fastened to the loading system (4) by bolts; the inner size of the film (10) is the same as the inner size of the lower part of the side template (8) of the template system (1), and the concrete specimen (2) is tightly attached to the inner side of the film (10); The loading system (4) is a concrete impermeability tester; The measurement system (5) includes a strain sensor (12), a temperature sensor (13), and a permeation pressure sensor (14) arranged in the concrete specimen (2); The input end of the acquisition system (6) is connected to the strain sensor (12), the temperature sensor (13) and the osmotic pressure sensor (14) in the measurement system (5), and the output end is connected to the computer; Calculate the temperature strain based on the temperature change measured by the temperature sensor (13) , and then calculate the expansion coefficient of concrete under water pressure. The expansion coefficient is also the compression coefficient β. The calculation formula is as follows: ； ； ； Where, is the measurement value of the strain sensor, is the temperature strain of concrete, is the linear expansion coefficient of concrete, It is swelling and deformation due to moisture. The deformation of its own volume, is the micro-deformation of the strain sensor, is the gauge length of the strain sensor, is the changing pore water pressure.

2. The deformation coefficient testing device for concrete materials under seepage field according to claim 1, characterized in that: The strain sensor (12), temperature sensor (13) and permeation pressure sensor (14) are all long strips and are vertically buried in the middle of the concrete specimen (2). The connection parts between the wires and each sensor are sealed with sealant.

3. The method for testing a deformation coefficient test device for concrete material under seepage field according to claim 1 or 2, characterized in that: The steps include: Step 1: Design a concrete mix ratio, cast a concrete specimen (2) in a formwork system (1), bury a strain sensor (12), a temperature sensor (13), and a permeation pressure sensor (14) during the casting process, and remove the formwork system (1) after curing the concrete specimen (2) until initial setting, and continue curing until the desired age; Step 2: After the concrete specimen (2) is cured and formed, the surface of the concrete specimen (2) is wiped, a surface anti-seepage paint (9) is sprayed on the side of the concrete specimen (2), and a high-strength sealant (11) is used to seal the contact between the sensor wire and the concrete specimen (2); Step 3: Press the concrete specimen (2) into the membrane (10), fasten the membrane (10) to the loading system (4) with bolts, and use high-strength sealant (11) to seal the contact between the top of the membrane (10) and the concrete specimen (2); Step 4: Pass water through the concrete specimen (2) and conduct a pressure test under the action of the seepage field, and measure the temperature, pressure and deformation. The pressure change range is at least greater than 0.4 MPa and is carried out for more than 3 times; Step 5: Perform compression expansion coefficient analysis based on the test results to obtain the compression expansion coefficient; The method for analyzing the compression coefficient is as follows: Calculate the temperature strain based on the temperature change measured by the temperature sensor (13) , and then calculate the compression expansion coefficient β of concrete under water pressure. The calculation formula is as follows: ； ； ； Where, is the measurement value of the strain sensor, is the temperature strain of concrete, is the linear expansion coefficient of concrete, It is swelling and deformation due to moisture. The deformation of its own volume, is the micro-deformation of the strain sensor, is the gauge length of the strain sensor, is the changing pore water pressure.

4. The method for testing a deformation coefficient test device for concrete material under seepage field according to claim 3, characterized in that: The multiple ∆ε and ∆P of each concrete specimen (2) are subjected to regression fitting to obtain the optimal solution as the compression-expansion coefficient result of the concrete specimen (2). Finally, the compression-expansion coefficient results of the multiple concrete specimens (2) are averaged as the final result.

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