Freeze-thaw cycle test method for foundation concrete influenced by underground water

Abstract

The invention discloses a freezing and thawing cycle test method for foundation concrete influenced by underground water, which is characterized by comprising the following steps of: fixing a concrete test piece in a simulation box, and burying the concrete test piece in a simulation soil body material; the underground water infiltration condition is simulated by relying on infiltration water at the lower part of the simulation box; pressure is applied to the concrete test piece according to the pressure bearing size of building foundation concrete, and preparation work is completed; during the test, cold air is introduced for cooling until the permeated water body is frozen, after a period of time, the concrete test piece is heated by applying electric heat radiation above the concrete test piece until the frozen water body is unfrozen, and the freezing and thawing cycle is repeatedly formed until the end of the test time, so that the performance change of the building foundation concrete influenced by freezing and thawing is obtained. According to the invention, the freeze-thaw soil environment can be simulated more truly and reliably, and the freeze-thaw durability of the foundation concrete structure under the infiltration action of underground water is obtained; the method can be better used for building foundation safety assessment guidance, and the building safety performance in the freeze-thaw environment is improved.

Description

[0001] This application is a divisional invention application of the patent application number 202211270480.4, filed on October 18, 2022, entitled "A Test Method for Freeze-Thaw Cycle of Foundation Concrete Affected by Groundwater". Technical Field

[0002] This invention relates to the field of concrete freeze-thaw performance research technology, specifically to a freeze-thaw cycle test method for foundation concrete affected by groundwater. Background Technology

[0003] Freeze-thaw cycles refer to the physical and geological processes and phenomena that occur when soil layers freeze and thaw due to temperatures dropping below or rising above zero degrees Celsius. In the cold regions of eastern and western my country, due to seasonal and diurnal temperature variations, the surface soil is often subject to periodic freeze-thaw cycles. In these areas, the concrete foundations of buildings are constantly exposed to the hazards of cyclical freeze-thaw cycles, potentially leading to structural safety issues. Specifically, during the freezing process, the water in the soil freezes into ice, creating numerous ice layers and ice mirrors. This causes relative displacement of soil particles, resulting in soil expansion—a phenomenon known as frost heave. The outward manifestations of frost heave include uniform or uneven bulging, swelling, and cracking of the soil layer; after thawing, significant subsidence occurs, causing substantial damage to structures. Generally, when water in the soil freezes, its volume increases by approximately 9%, causing the foundation soil to expand outwards. For foundations containing groundwater, the depth of the groundwater determines the water content within the foundation. Foundations below the groundwater level have a higher water content and are more susceptible to frost heave damage. The resulting cracks can lead to foundation cracking, which in turn affects the strength and deformation of the foundation. Therefore, it is necessary to study the freeze-thaw degradation of foundation soil structures at different groundwater levels.

[0004] Generally, the maximum depth at which surface temperature changes affect the temperature of soil and rock masses is approximately 2.5 m. This effect changes downwards, with the temperature gradually increasing from top to bottom. This influences the soil structure's susceptibility to freeze-thaw cycles. Simultaneously, the contact between groundwater and soil affects the soil's susceptibility to freeze-thaw cycles. The soil-water interface experiences frost heave when frozen, a phenomenon not observed at non-water-soil interfaces. Most existing freeze-thaw testing methods do not consider these factors. For example, CN114486512A disclosed a concrete durability testing device under the coupled effects of load and multiple environmental factors. This device can realistically simulate various environmental conditions, enabling concrete durability testing under the coupled effects of load and multiple environmental factors, providing fundamental equipment for systematic and comprehensive research on concrete durability under these conditions. However, this device still cannot simulate the freeze-thaw durability performance of soil under groundwater infiltration.

[0005] Therefore, how to provide a test method that can better simulate the freeze-thaw soil environment and obtain the freeze-thaw durability performance of foundation concrete structures under the influence of groundwater infiltration has become a problem that needs to be further considered and solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the technical problem to be solved by this invention is: how to provide a groundwater-affected freeze-thaw cycle test method for foundation concrete that can better simulate the freeze-thaw soil environment and obtain the freeze-thaw durability performance of foundation concrete structures under the influence of groundwater; so as to guide the safety assessment of building foundations and improve the safety performance of buildings in freeze-thaw environments.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for testing the freeze-thaw cycle of foundation concrete affected by groundwater is characterized by the following steps: First, concrete specimens are prepared according to the performance requirements of the foundation concrete of the building to be tested. The concrete specimens are then fixed in a simulation chamber. Second, the soil conditions of the foundation concrete construction environment are simulated by embedding the concrete specimens in simulated soil material. Third, water is infiltrated into the lower part of the simulation chamber to simulate the actual groundwater immersion of the foundation concrete. Fourth, pressure is applied to the concrete specimens according to the bearing capacity of the foundation concrete (which can be calculated), completing the preparation work. During the test, cold air is introduced to cool the infiltrated water until it freezes. After maintaining this state for a period, the frozen water is heated by applying electrothermal radiation above the concrete specimens until it thaws. This process is repeated for a period to form a freeze-thaw cycle. At the end of the freeze-thaw test, the concrete specimens are removed and their performance is tested. The results are compared with untested identical concrete specimens to obtain the performance change parameters of the foundation concrete affected by the freeze-thaw environment.

[0008] The experimental method of this invention better simulates the conditions under which a building's foundation concrete structure is buried by soil and infiltrated by groundwater. It also simulates the actual freeze-thaw cycle, where ice forms at night due to cold winds and thaws during the day due to solar radiation. This allows for a more accurate simulation of the actual freeze-thaw conditions on building foundation concrete. The changes in performance parameters obtained after the experiment better reflect the impact of actual freeze-thaw conditions on performance. This method can be better used for safety monitoring of actual building concrete foundations or for pre-construction safety performance assessments, thereby improving building safety.

[0009] Furthermore, the ambient temperature of the test environment, which was cooled by introducing cold air, was determined based on the lowest nighttime temperature of the building foundation concrete in the local spring and autumn seasons.

[0010] In this way, simulations using extreme environmental parameters allow the test results to be better used for safety assessments.

[0011] Furthermore, the temperature used for heating by electrothermal radiation during the experiment was determined based on the highest daytime temperature of the building foundation concrete in the local spring and autumn seasons.

[0012] In this way, simulations using extreme environmental parameters allow the test results to be better used for building safety assessments.

[0013] Furthermore, in the preparation of concrete specimens, cylindrical specimens are obtained by pouring the foundation concrete of the building to be tested according to the same concrete formula.

[0014] In this way, the test results of concrete specimens can better reflect the actual performance changes of building foundation concrete under the influence of freeze-thaw cycles, thus improving the reliability of the test.

[0015] Furthermore, the simulated soil material is prepared using gravel, silt, and clay to simulate the actual soil conditions surrounding the concrete foundation of a building. A better option is to directly excavate the actual soil surrounding the concrete foundation of the building to obtain the simulated soil material, which contains the corresponding microorganisms, thus maintaining the consistency of the influence of rock microorganisms on the concrete.

[0016] This allows for a better simulation of actual conditions and improves the reliability of the experiment.

[0017] Furthermore, when the depth of the simulation chamber (referring to the depth that can be used for testing) is greater than the depth of groundwater immersion in the foundation concrete of the building to be tested, the depth of water seepage at the bottom of the simulation chamber is consistent with the actual depth of groundwater immersion; when the depth of the simulation chamber (referring to the depth that can be used for testing) is less than the depth of groundwater immersion in the foundation concrete of the building to be tested, the simulation chamber is sealed and pressurized by introducing gas, and the water pressure at the bottom of the simulation chamber is measured to make it consistent with the actual water pressure at the lowest point of the foundation concrete of the building to be tested (the actual water pressure value can be obtained through actual testing or calculation).

[0018] In this way, when the concrete foundation of the building to be tested is deeply infiltrated by groundwater, a smaller simulation chamber can be used to simulate a deeper infiltration situation, greatly expanding the application range of the test. When using a pressure-based simulation method, the height of the concrete specimen can be set to match the test depth of the simulation chamber. Then, the simulated soil material is covered to the same height as the concrete specimen. Finally, the water seepage depth in the lower part of the simulation chamber is sufficient to leave 5-10cm of uninfiltrated soil material above. This better simulates the actual situation of the concrete specimen being infiltrated by groundwater.

[0019] Furthermore, a single freeze-thaw cycle lasts 24 hours, including 12 hours of freezing and 12 hours of thawing; the number of freeze-thaw cycles is set to 7, 15, 30, 60, or 90 times according to the study, corresponding to a time of 7, 15, 30, 60, or 90 days.

[0020] This is because periods shorter than seven days are insufficient to reflect changes, while periods longer than 90 days are too long to be meaningful for testing. This method, by completing the freeze-thaw test within a limited timeframe and then analyzing the performance parameters of the concrete specimens, allows for the estimation of performance changes after extended freeze-thaw cycles, thus guiding practical safety monitoring.

[0021] Furthermore, after the freeze-thaw test period, the concrete specimens are removed and subjected to uniaxial compression tests or triaxial compression tests to test the mechanical properties of the concrete specimens after being subjected to freeze-thaw cycles, including compressive strength and elastic modulus parameters. The mechanical property parameters of the unfrozen concrete specimens are compared to obtain the degree of deterioration of the mechanical properties of the building foundation concrete under the influence of the freeze-thaw environment.

[0022] This experimental method relies on a foundation concrete freeze-thaw cycle test system, which includes a simulation chamber with an openable top cover. A specimen positioning device is located in the lower middle part of the simulation chamber, and a pressure application device is positioned directly above the positioning device. A water supply pipe with a switch valve is connected to the lower middle side of one end of the simulation chamber, and the other end of the water supply pipe is connected to a water storage tank. A drainage pipe with a switch valve is connected downwards to the bottom of the other end of the simulation chamber. The system also includes a refrigeration evaporator located at the top of the simulation chamber, with a built-in fan and an air inlet and outlet for creating internal circulation within the simulation chamber. The refrigeration evaporator is connected to an external compressor located outside the simulation chamber to form a refrigeration cycle system. Furthermore, it includes an electric heating element fixed to the inner surface of the top cover of the simulation chamber, and a groundwater depth adjustment simulation device for simulating groundwater depth regulation within the simulation chamber.

[0023] Thus, in the aforementioned apparatus, the specimen positioning device facilitates the temporary positioning of concrete specimens to simulate soil burial, the pressure application device applies pressure to the concrete specimens to simulate actual pressure conditions, the water tank and drainage pipes facilitate the injection and discharge of simulated groundwater, and the groundwater depth adjustment device controls and adjusts the groundwater depth to match the actual situation. A refrigeration cycle system provides cooling and freezing to the simulation chamber, and an electric heating tube thaws the frozen soil through electrothermal radiation, thus better simulating the actual freeze-thaw conditions of building concrete foundations. Therefore, the above-mentioned experimental system is well-suited for the aforementioned simulation test methods, is simple, reliable, and effective in operation, and can significantly improve the convenience and simulation effect of the experiment, as well as the accuracy of the test results.

[0024] Furthermore, the specimen positioning device includes a positioning ring located in the middle, the inner diameter of which is 1-10 mm larger than the outer diameter of the specimen. The periphery of the positioning ring is fixed to the inner wall of the simulation chamber by horizontally set fixing rods. This structure is simple and facilitates the placement and positioning of the specimen.

[0025] Furthermore, the pressure application device includes a pressure head positioned above the positioning ring, with a retractable pressure rod connecting the pressure head to a hydraulic tank. The hydraulic tank is fixedly mounted on the inner wall of the simulation chamber via a support arm, and the hydraulic tank is connected to a control oil tank outside the simulation chamber via hydraulic pipelines.

[0026] This allows for easy control of the hydraulic tank via the oil tank, enabling the pressure head to extend downwards and apply pressure to the concrete specimen positioned within the positioning ring, thus simulating its actual working stress conditions.

[0027] Furthermore, a specimen pressure detection sensor is installed on the lower surface of the indenter. This facilitates the detection of the magnitude of the pressure applied to the concrete specimen.

[0028] Furthermore, a mesh screen is installed on the upper surface of the drainage pipe. This prevents mud and sand from leaking out with the water during drainage.

[0029] Furthermore, there are four evaporators arranged at the four corners of the top of the simulation chamber. This makes the cooling process faster and more uniform.

[0030] Furthermore, the simulation chamber is made of a transparent material. This facilitates observation of the test conditions inside the simulation chamber.

[0031] Furthermore, the simulation chamber is equipped with a vertical scale on at least one side. This facilitates the observation of groundwater levels.

[0032] Furthermore, the groundwater depth adjustment simulation device includes a water collection trough located inside the side of the simulation box where the water pipeline is located. The water collection trough is set along the overall length of the side wall of the simulation box where the water pipeline is located. The height of the upper surface of the water collection trough is not lower than the height of the specimen positioning device. The retaining wall on the side of the water collection trough facing the specimen positioning device is set as a movable retaining wall. The two sides of the movable retaining wall can be slidably engaged in the retaining wall groove. The movable retaining wall is connected to a retaining wall up and down movement control mechanism.

[0033] In this way, when water is introduced into the pipeline to simulate groundwater, the water can first be transported to the collection tank, and then the movable retaining wall can be raised to the preset groundwater depth. This allows the water in the collection tank to flow out from a fixed height below the movable retaining wall, forming groundwater. This method of groundwater simulation is more convenient and reliable, and the accuracy of groundwater depth can be better controlled.

[0034] Furthermore, on the side of the movable retaining wall where the specimen positioning device is located, a supporting grid and sponge material fixed to the supporting grid are also fixed outwards in sequence. This can effectively prevent sand from entering the water collection tank and affecting the lifting and lowering control of the movable retaining wall, without hindering the outward flow of water in the water collection tank. At the same time, it can also prevent the direct flow of water from the water collection tank from impacting the sand and affecting the test.

[0035] Furthermore, the retaining wall moving control mechanism includes retaining wall racks vertically fixed at both ends of one side of the movable retaining wall. The two retaining wall racks are respectively engaged with a retaining wall control gear located at the same horizontal height. The two retaining wall control gears are fixed on a retaining wall control shaft set at the same horizontal level. The two ends of the retaining wall control shaft are rotatably mounted on the simulation box, and one end extends out of the simulation box and is provided with a retaining wall control rotating handle.

[0036] This design allows for easy movement of the retaining wall along its sliding groove by rotating a control handle, which in turn engages with the retaining wall control gears and racks. The structure is simple, stable, and reliable.

[0037] Furthermore, a scale is installed on the side of the simulation chamber at the location of the movable retaining wall. This allows for a direct visual observation of the height to which the movable retaining wall is lifted, facilitating precise control of the depth at which groundwater is released.

[0038] Furthermore, the groundwater depth adjustment simulation device includes a baffle plate located inside the simulation box on the side away from the water supply pipeline and spaced parallel to that side. The two ends of the baffle plate are slidably engaged with the baffle plate grooves on the inner side wall of the simulation box. A baffle plate sinkhole is provided downward at the bottom of the simulation box below the baffle plate. The baffle plate is connected to a baffle plate up-and-down movement control mechanism. The baffle plate up-and-down movement control mechanism can control the baffle plate to extend upward or retract downward into the baffle plate sinkhole. After the baffle plate extends upward, it forms a drainage cavity on the side away from the water supply pipeline. The drainage pipeline is located on the bottom surface of the drainage cavity.

[0039] In this way, when simulating groundwater, the baffle plate can be extended upwards to the depth of the groundwater to be simulated (or slightly below the simulated groundwater depth by 1-5 cm to offset the water level exceeding the baffle plate in the test area). Only when the water in the simulation chamber reaches the height of the baffle plate can it flow over the baffle plate into the drainage chamber and be discharged through the drainage pipe. This better ensures that the groundwater depth in the test area meets the simulation requirements. Furthermore, as can be seen from the above process, when the baffle plate and the retaining wall are used together, the retaining wall controls the outflow depth of water in the collection tank, while the baffle plate blocks the water and ensures that the water-infiltrated depth in the test area meets the requirements, thus achieving a more accurate simulation of groundwater depth. More specifically, during the freeze-thaw cycle test, when the groundwater is frozen, the operation is relatively simple; only the water supply pipe needs to be shut off. However, when the groundwater is thawed, since the freeze-thawed areas are usually mountainous environments, the groundwater is usually in a slow-flowing subsurface state after thawing. Therefore, when the water-retaining plate and the water-retaining wall are used together, by controlling the upper end of the water-retaining plate to extend lower than the lower end of the water-retaining wall by leaving a gap (i.e., the groundwater depth to be simulated) by a distance (usually 1-5cm), and at the same time opening the water supply pipe to supply water according to the actual subsurface flow velocity and flow rate of the groundwater to be simulated, the slow-flowing subsurface state of the groundwater can be better simulated while ensuring that sufficient groundwater depth is maintained. Especially when the groundwater simulation depth in the simulation chamber is insufficient and it is necessary to increase the air pressure inside the chamber to increase the simulated groundwater depth, the combined use of the retaining wall and the retaining plate can better ensure that, even with increased air pressure (the water flow will not be pushed away by the high pressure), sufficient groundwater depth can still be maintained, simulating a good subsurface flow state. Simultaneously, the increased air pressure can be better applied to the groundwater in the area between the retaining plate and the retaining wall, thus creating a stronger water pressure effect at the bottom of the test area and better achieving the effect of increasing the simulated water depth through air pressure. Furthermore, when increasing air pressure to enhance the simulation, the drainage pipes can be closed to prevent air leakage when the pressure is high. At this time, water can be stored in the drainage cavity area formed by the retaining plate to meet the subsurface flow simulation requirements of the test area.

[0040] Furthermore, on the side of the baffle plate facing the water pipeline, a support grid and sponge material fixed on the support grid are also fixed outward in sequence.

[0041] This design effectively prevents sand and soil from entering and affecting the control of the water baffle's raising and lowering, without obstructing the flow of water. It also prevents the sand and soil used in the experiment from being washed away by the water flow, thus avoiding disruption to the experiment.

[0042] Furthermore, the water baffle moving up and down control mechanism includes water baffle racks vertically fixed at both ends of one side of the water baffle. The two water baffle racks respectively mesh with a water baffle control gear located at the same horizontal height. The two water baffle control gears are fixed on a water baffle control shaft set at the same horizontal level. The two ends of the water baffle control shaft are rotatably mounted on the simulation box, and one end extends out of the simulation box and is provided with a water baffle control rotating handle.

[0043] This design allows for easy control of the baffle plate by rotating the control handle. The engagement of the control gear and the baffle plate rack drives the baffle plate to move up and down along its groove. The structure is simple, stable, and reliable.

[0044] Furthermore, a scale is installed on the side of the simulation chamber at the location of the water baffle. This allows for a direct visual indication of the height to which the water baffle is lifted, facilitating precise control of the groundwater depth.

[0045] Furthermore, the groundwater depth regulation simulation device also includes a sealing strip and a top cover pressing and sealing mechanism installed between the top cover and the body of the simulation box, as well as a water pressure detection sensor located at the bottom of the simulation box and a gas pressure delivery pipe connected to the simulation box, the gas pressure delivery pipe being connected to a gas compressor outside the simulation box.

[0046] In this way, when the simulation chamber cannot accurately simulate the depth of groundwater, the top cover can be sealed using a sealing strip and a top cover clamping mechanism. Then, air pressure is introduced into the simulation chamber via a pneumatic compressor and air supply pipeline. Under the combined action of air and water pressure, the water pressure at the bottom of the simulation chamber is detected by a water pressure sensor, ensuring it matches the actual groundwater pressure at the bottom of the building's foundation concrete. This maintains the freeze-thaw cycle test under realistic water pressure conditions, simulating deeper groundwater infiltration and thus expanding the scope of experimental applications. The top cover clamping mechanism can be implemented using existing mechanisms such as bolt fixing or quick-connect clip fixing; the specific structure is not detailed here.

[0047] More specifically, when the above-mentioned test system is used for a specific test (taking the groundwater depth as an example that meets the simulation depth of the simulation chamber), first, the top cover of the simulation chamber is opened, and then the prepared concrete specimen is positioned and erected in the simulation chamber using the specimen positioning device. The vertical positioning of the concrete specimen is maintained, and the pressure head is controlled to extend downward and press against the upper end of the concrete specimen until the test pressure reaches the test pressure. Then, the simulated soil material is poured into the simulation chamber until the concrete specimen is buried around it. Then, the baffle plate is adjusted to extend upward from the baffle plate sink to 0-5cm below the preset water depth. Then, the switch valve on the water supply pipeline is opened to inject water from the water storage tank into the water collection tank. The movable retaining wall of the water collection tank is controlled to rise upward until the lower end is exposed to the preset water depth position, so that the water in the water collection tank flows outward from the lower end until the water flows over the baffle plate and flows into the drainage pipe. Then, the water supply pipeline is closed, and the drainage pipe is closed when the water level in the water collection tank drops to the height of the lower end of the movable retaining wall. The refrigeration cycle system is activated to cool the interior of the simulation chamber, causing the simulated soil material to freeze. The ambient temperature inside the simulation chamber is then maintained at the lowest nighttime temperature of the building foundation concrete in spring and autumn in the local area until the freezing period ends (usually 12 hours). The refrigeration cycle system is then turned off, and the electric heating element is activated to raise the temperature inside the simulation chamber and thaw it. The temperature inside the simulation chamber is then maintained at the highest daytime temperature of the building foundation concrete in spring and autumn in the local area until the thawing period ends (usually 12 hours). The freeze-thaw cycle is then repeated until the end of the test period. The top cover of the simulation chamber can then be opened, the concrete specimens removed, and their performance tested to obtain the characteristic parameters of performance changes.

[0048] In summary, this invention can more realistically and reliably simulate the freeze-thaw soil environment and obtain the freeze-thaw durability performance of foundation concrete structures under the influence of groundwater infiltration; it can be better used to guide the safety assessment of building foundations and improve the safety performance of buildings in freeze-thaw environments. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the rock mass freeze-thaw cycle test system used in the implementation of this invention.

[0050] Figure 2 for Figure 1 A schematic diagram of the structure of a standalone groundwater depth regulation simulation device.

[0051] Figure 3 for Figure 1 A schematic diagram of the structure of the control mechanism for the vertical movement of the retaining wall from the side view.

[0052] Figure 4 for Figure 1 A schematic diagram of the structure of the control mechanism for the up-and-down movement of the water baffle plate, viewed from the side.

[0053] Figure 5 for Figure 1 A schematic diagram of the structure of the independent pressure application device. Detailed Implementation

[0054] The present invention will now be described in further detail with reference to specific embodiments.

[0055] Detailed Implementation: A method for testing the freeze-thaw cycle of foundation concrete affected by groundwater, wherein: concrete specimens are prepared according to the performance requirements of the foundation concrete of the building to be tested, and the concrete specimens are fixed in a simulation box; the soil conditions of the construction environment of the foundation concrete are simulated, and the concrete specimens are embedded in the simulated soil material; water seeps into the lower part of the simulation box to simulate the actual groundwater immersion of the foundation concrete; pressure is applied to the concrete specimens according to the bearing capacity of the foundation concrete (which can be obtained through calculation), and the preparation work is completed; during the test, cold air is introduced to cool the seeping water until it freezes, and after maintaining this state for a period of time, the frozen water is heated by applying electric heating radiation above the concrete specimens until it thaws, and this process is repeated for a period of time to form a freeze-thaw cycle. At the end of the freeze-thaw test, the concrete specimens are taken out and their performance is tested. The results are compared with the same untested concrete specimens to obtain the performance change parameters of the foundation concrete affected by the freeze-thaw environment.

[0056] The experimental method of this invention better simulates the conditions under which a building's foundation concrete structure is buried by soil and infiltrated by groundwater. It also simulates the actual freeze-thaw cycle, where ice forms at night due to cold winds and thaws during the day due to solar radiation. This allows for a more accurate simulation of the actual freeze-thaw conditions on building foundation concrete. The changes in performance parameters obtained after the experiment better reflect the impact of actual freeze-thaw conditions on performance. This method can be better used for safety monitoring of actual building concrete foundations or for pre-construction safety performance assessments, thereby improving building safety.

[0057] The ambient temperature for the test, which was cooled by introducing cold air, was determined based on the lowest nighttime temperature of the building's foundation concrete in spring and autumn in the local area.

[0058] In this way, simulations using extreme environmental parameters allow the test results to be better used for safety assessments.

[0059] The temperature used for heating by electrothermal radiation during the test was determined based on the highest daytime temperature of the building foundation concrete in the local spring and autumn seasons.

[0060] In this way, simulations using extreme environmental parameters allow the test results to be better used for building safety assessments.

[0061] When preparing concrete specimens, cylindrical specimens are obtained by pouring the foundation concrete of the building to be tested according to the same concrete formula.

[0062] In this way, the test results of concrete specimens can better reflect the actual performance changes of building foundation concrete under the influence of freeze-thaw cycles, thus improving the reliability of the test.

[0063] In the experiment, the simulated soil material was prepared using gravel, silt, and clay to mimic the actual soil conditions surrounding the concrete foundation of a building. A better option would be to directly excavate the actual soil surrounding the concrete foundation of the building to obtain the simulated soil material, which contains the corresponding microorganisms and can maintain the consistency of the influence of rock microorganisms on concrete.

[0064] This allows for a better simulation of actual conditions and improves the reliability of the experiment.

[0065] During the test, when the depth of the simulation chamber (referring to the depth that can be used for the test) is greater than the depth of groundwater immersion in the foundation concrete of the building to be tested, the depth of water seepage at the bottom of the simulation chamber is consistent with the actual depth of groundwater immersion; when the depth of the simulation chamber (referring to the depth that can be used for the test) is less than the depth of groundwater immersion in the foundation concrete of the building to be tested, the simulation chamber is sealed and pressurized by introducing gas, and the water pressure at the bottom of the simulation chamber is measured to make it consistent with the actual water pressure at the lowest point of the foundation concrete of the building to be tested (the actual water pressure value can be obtained through actual measurement or calculation).

[0066] In this way, when the concrete foundation of the building to be tested is deeply infiltrated by groundwater, a smaller simulation chamber can be used to simulate a deeper infiltration situation, greatly expanding the application range of the test. When using a pressure-based simulation method, the height of the concrete specimen can be set to match the test depth of the simulation chamber. Then, the simulated soil material is covered to the same height as the concrete specimen. Finally, the water seepage depth in the lower part of the simulation chamber is sufficient to leave 5-10cm of uninfiltrated soil material above. This better simulates the actual situation of the concrete specimen being infiltrated by groundwater.

[0067] Specifically, one freeze-thaw cycle lasts 24 hours, including 12 hours of freezing and 12 hours of thawing; the number of freeze-thaw cycles is set to 7, 15, 30, 60 or 90 times according to the study, and the corresponding time is 7, 15, 30, 60 or 90 days.

[0068] This is because periods shorter than seven days are insufficient to reflect changes, while periods longer than 90 days are too long to be meaningful for testing. This method, by completing the freeze-thaw test within a limited timeframe and then analyzing the performance parameters of the concrete specimens, allows for the estimation of performance changes after extended freeze-thaw cycles, thus guiding practical safety monitoring.

[0069] After the freeze-thaw test is completed, the concrete specimens are taken out and subjected to uniaxial compression tests or triaxial compression tests to test the mechanical properties of the concrete specimens after being subjected to freeze-thaw cycles, including compressive strength and elastic modulus parameters. The mechanical property parameters of the unfrozen concrete specimens are compared to obtain the degree of deterioration of the mechanical properties of the building foundation concrete under the influence of the freeze-thaw environment.

[0070] In practice, this experimental method relies on Figure 1-5 The system described herein is a freeze-thaw cycle test system for foundation concrete. The system includes a simulation chamber 1 with an openable top cover 2. A specimen positioning device is located in the lower middle part of the simulation chamber 1, and a pressure application device is positioned directly above the positioning device. A water supply pipe 4 with a switch valve is connected to the lower middle side of one end of the simulation chamber, and the other end of the water supply pipe 4 is connected to a water storage tank 5. A drainage pipe 6 with a switch valve is connected downwards to the bottom of the other end of the simulation chamber 1. The system also includes a refrigeration evaporator 7 located on the upper part of the simulation chamber. The refrigeration evaporator 7 has a built-in fan and an air inlet and outlet for creating internal circulation within the simulation chamber. The refrigeration evaporator 7 is connected to an external compressor 8 located outside the simulation chamber to form a refrigeration cycle system. The system also includes an electric heating tube 9 fixed to the inner surface of the top cover of the simulation chamber. Finally, it includes a groundwater depth adjustment simulation device for simulating groundwater depth adjustment within the simulation chamber.

[0071] Thus, in the aforementioned apparatus, the specimen positioning device facilitates the temporary positioning of concrete specimens to simulate soil burial, the pressure application device applies pressure to the concrete specimens to simulate actual pressure conditions, the water tank and drainage pipes facilitate the injection and discharge of simulated groundwater, and the groundwater depth adjustment device controls and adjusts the groundwater depth to match the actual situation. A refrigeration cycle system provides cooling and freezing to the simulation chamber, and an electric heating tube thaws the frozen soil through electrothermal radiation, thus better simulating the actual freeze-thaw conditions of building concrete foundations. Therefore, the above-mentioned experimental system is well-suited for the aforementioned simulation test methods, is simple, reliable, and effective in operation, and can significantly improve the convenience and simulation effect of the experiment, as well as the accuracy of the test results.

[0072] The specimen positioning device includes a positioning ring 10 located in the middle. The inner diameter of the positioning ring 10 is 1-10 mm larger than the outer diameter of the specimen. The periphery of the positioning ring is fixed to the inner wall of the simulation chamber by horizontally set fixing rods. This structure is simple and facilitates the placement and positioning of the specimen.

[0073] The pressure device includes a pressure head 11 positioned above the positioning ring. The pressure head 11 is connected to a hydraulic tank 12 via a retractable pressure rod. The hydraulic tank 12 is fixedly mounted on the inner wall of the simulation box 1 via a support arm 13. The hydraulic tank 12 is connected to a control oil tank 3 outside the simulation box via hydraulic pipes.

[0074] This allows for easy control of the hydraulic tank via the oil tank, enabling the pressure head to extend downwards and apply pressure to the concrete specimen positioned within the positioning ring, thus simulating its actual working stress conditions.

[0075] The lower surface of the pressure head 11 is equipped with a specimen pressure detection sensor 14, which facilitates the detection of the magnitude of the pressure applied to the concrete specimen.

[0076] The upper surface of the drainage pipe is equipped with a mesh screen. This prevents mud and sand from leaking out with the water during drainage.

[0077] The system includes four evaporators positioned at the four corners of the top of the simulation chamber. This ensures faster and more even cooling.

[0078] The simulation chamber 1 is made of transparent material. This allows for easy observation of the test conditions inside the simulation chamber.

[0079] The simulation chamber 1 is equipped with a vertical scale 15 on at least one side. This facilitates the observation of the groundwater level.

[0080] The groundwater depth adjustment simulation device includes a water collection trough 16 located inside the side of the simulation box where the water pipeline is located. The water collection trough 16 is set along the overall length of the side wall of the simulation box where the water pipeline is located. The height of the upper surface of the water collection trough is not lower than the height of the specimen positioning device. The retaining wall on the side of the water collection trough facing the specimen positioning device is set as a movable retaining wall 17. The two sides of the movable retaining wall can be slidably engaged in the retaining wall groove 18. The movable retaining wall 17 is connected to a retaining wall up and down movement control mechanism.

[0081] In this way, when water is introduced into the pipeline to simulate groundwater, the water can first be transported to the collection tank, and then the movable retaining wall can be raised to the preset groundwater depth. This allows the water in the collection tank to flow out from a fixed height below the movable retaining wall, forming groundwater. This method of groundwater simulation is more convenient and reliable, and the accuracy of groundwater depth can be better controlled.

[0082] Among them, on the side of the movable retaining wall 17 facing the specimen positioning device, a supporting grid 19 and sponge material fixed on the supporting grid are also fixed outward in sequence. In this way, it can isolate sand from entering the water collection tank and affecting the lifting and lowering control of the movable retaining wall, but does not hinder the water in the water collection tank from flowing outward. At the same time, it can also prevent the water flowing directly out of the water collection tank from impacting the sand and soil and affecting the test.

[0083] The retaining wall moving control mechanism includes retaining wall racks 20 fixed vertically at both ends of one side of the movable retaining wall. The two retaining wall racks 20 respectively mesh with a retaining wall control gear 21 located at the same horizontal height. The two retaining wall control gears 21 are fixed on a retaining wall control shaft 22 set at the same horizontal level. The two ends of the retaining wall control shaft 22 are rotatably mounted on the simulation box, and one end extends out of the simulation box and is provided with a retaining wall control rotating handle 23.

[0084] This design allows for easy movement of the retaining wall along its sliding groove by rotating a control handle, which in turn engages with the retaining wall control gears and racks. The structure is simple, stable, and reliable.

[0085] The scale on the side of the simulation chamber is located at the position of the movable retaining wall. This allows for a direct visual reading of the height to which the movable retaining wall is raised, facilitating precise control of the depth at which groundwater is released.

[0086] The groundwater depth adjustment simulation device includes a baffle plate 25 located inside the simulation box away from the direction of the water supply pipeline and spaced parallel to that side. The two ends of the baffle plate 25 are slidably engaged with the baffle plate groove 26 on the inner side wall of the simulation box. A baffle plate sink 27 is provided downward at the bottom of the simulation box below the baffle plate 25. The baffle plate 26 is connected to a baffle plate up-and-down movement control mechanism. The baffle plate up-and-down movement control mechanism can control the baffle plate to extend upward or retract downward into the baffle plate sink 27. After the baffle plate extends upward, it forms a drainage cavity on the side away from the direction of the water supply pipeline. The drainage pipeline is located on the bottom surface of the drainage cavity.

[0087] In this way, when simulating groundwater, the baffle plate can be extended upwards to the depth of the groundwater to be simulated (or slightly below the simulated groundwater depth by 1-5 cm to offset the water level exceeding the baffle plate in the test area). Only when the water in the simulation chamber reaches the height of the baffle plate can it flow over the baffle plate into the drainage chamber and be discharged through the drainage pipe. This better ensures that the groundwater depth in the test area meets the simulation requirements. Furthermore, as can be seen from the above process, when the baffle plate and the retaining wall are used together, the retaining wall controls the outflow depth of water in the collection tank, while the baffle plate blocks the water and ensures that the water-infiltrated depth in the test area meets the requirements, thus achieving a more accurate simulation of groundwater depth. More specifically, during the freeze-thaw cycle test, when the groundwater is frozen, the operation is relatively simple; only the water supply pipe needs to be shut off. However, when the groundwater is thawed, since the freeze-thawed areas are usually mountainous environments, the groundwater is usually in a slow-flowing subsurface state after thawing. Therefore, when the water-retaining plate and the water-retaining wall are used together, by controlling the upper end of the water-retaining plate to extend lower than the lower end of the water-retaining wall by leaving a gap (i.e., the groundwater depth to be simulated) by a distance (usually 1-5cm), and at the same time opening the water supply pipe to supply water according to the actual subsurface flow velocity and flow rate of the groundwater to be simulated, the slow-flowing subsurface state of the groundwater can be better simulated while ensuring that sufficient groundwater depth is maintained. Especially when the groundwater simulation depth in the simulation chamber is insufficient and it is necessary to increase the air pressure inside the chamber to increase the simulated groundwater depth, the combined use of the retaining wall and the retaining plate can better ensure that, even with increased air pressure (the water flow will not be pushed away by the high pressure), sufficient groundwater depth can still be maintained, simulating a good subsurface flow state. Simultaneously, the increased air pressure can be better applied to the groundwater in the area between the retaining plate and the retaining wall, thus creating a stronger water pressure effect at the bottom of the test area and better achieving the effect of increasing the simulated water depth through air pressure. Furthermore, when increasing air pressure to enhance the simulation, the drainage pipes can be closed to prevent air leakage when the pressure is high. At this time, water can be stored in the drainage cavity area formed by the retaining plate to meet the subsurface flow simulation requirements of the test area.

[0088] Among them, the side of the water baffle 25 facing the water pipeline is also provided with a support grid 28 and sponge material fixed on the support grid.

[0089] This design effectively prevents sand and soil from entering and affecting the control of the water baffle's raising and lowering, without obstructing the flow of water. It also prevents the sand and soil used in the experiment from being washed away by the water flow, thus avoiding disruption to the experiment.

[0090] The water baffle moving up and down control mechanism includes water baffle racks 29 vertically fixed at both ends of one side of the water baffle. The two water baffle racks 29 respectively mesh with a water baffle control gear 30 located at the same horizontal height. The two water baffle control gears 30 are fixed on the same horizontally arranged water baffle control shaft 31. The two ends of the water baffle control shaft 31 are rotatably mounted on the simulation box, and one end extends out of the simulation box and is provided with a water baffle control rotating handle 32.

[0091] This design allows for easy control of the baffle plate by rotating the control handle. The engagement of the control gear and the baffle plate rack drives the baffle plate to move up and down along its groove. The structure is simple, stable, and reliable.

[0092] The simulation chamber features a scale on its side, near the water-retaining plate. This allows for a clear visual indication of the height the water-retaining plate is raised, facilitating precise control of the groundwater depth.

[0093] The groundwater depth regulation simulation device also includes a sealing strip and a top cover pressing and sealing mechanism 35 installed between the top cover 2 and the body 1 of the simulation box, as well as a water pressure detection sensor (not shown in the figure) located at the bottom of the simulation box and a gas pressure transmission pipeline 36 connected to the simulation box. The gas pressure transmission pipeline is connected to a gas compressor (not shown in the figure) outside the simulation box.

[0094] In this way, when the simulation chamber cannot accurately simulate the depth of groundwater, the top cover can be sealed using a sealing strip and a top cover clamping mechanism. Then, air pressure is introduced into the simulation chamber via a pneumatic compressor and air supply pipeline. Under the combined action of air and water pressure, the water pressure at the bottom of the simulation chamber is detected by a water pressure sensor, ensuring it matches the actual groundwater pressure at the bottom of the building's foundation concrete. This maintains the freeze-thaw cycle test under realistic water pressure conditions, simulating deeper groundwater infiltration and thus expanding the scope of experimental applications. The top cover clamping mechanism can be implemented using existing mechanisms such as bolt fixing or quick-connect clip fixing; the specific structure is not detailed here.

[0095] More specifically, when the above-mentioned test system is used for a specific test (taking the groundwater depth as an example that meets the simulation depth of the simulation chamber), first, the top cover of the simulation chamber is opened, and then the prepared concrete specimen is positioned and erected in the simulation chamber using the specimen positioning device. The vertical positioning of the concrete specimen is maintained, and the pressure head is controlled to extend downward and press against the upper end of the concrete specimen until the test pressure reaches the test pressure. Then, the simulated soil material is poured into the simulation chamber until the concrete specimen is buried around it. Then, the baffle plate is adjusted to extend upward from the baffle plate sink to 0-5cm below the preset water depth. Then, the switch valve on the water supply pipeline is opened to inject water from the water storage tank into the water collection tank. The movable retaining wall of the water collection tank is controlled to rise upward until the lower end is exposed to the preset water depth position, so that the water in the water collection tank flows outward from the lower end until the water flows over the baffle plate and flows into the drainage pipe. Then, the water supply pipeline is closed, and the drainage pipe is closed when the water level in the water collection tank drops to the height of the lower end of the movable retaining wall. The refrigeration cycle system is activated to cool the interior of the simulation chamber, causing the simulated soil material to freeze. The ambient temperature inside the simulation chamber is then maintained at the lowest nighttime temperature of the building foundation concrete in spring and autumn in the local area until the freezing period ends (usually 12 hours). The refrigeration cycle system is then turned off, and the electric heating element is activated to raise the temperature inside the simulation chamber and thaw it. The temperature inside the simulation chamber is then maintained at the highest daytime temperature of the building foundation concrete in spring and autumn in the local area until the thawing period ends (usually 12 hours). The freeze-thaw cycle is then repeated until the end of the test period. The top cover of the simulation chamber can then be opened, the concrete specimens removed, and their performance tested to obtain the characteristic parameters of performance changes.

Claims

1. A method for testing the freeze-thaw cycle of foundation concrete affected by groundwater, characterized in that, Concrete specimens were prepared according to the performance requirements of the foundation concrete of the building to be tested, and the concrete specimens were fixed in a simulation box. The soil conditions of the foundation concrete construction environment were simulated by embedding the concrete specimens in the simulated soil material. Water was introduced into the lower part of the simulation box to simulate the actual situation of the foundation concrete being wetted by groundwater. Pressure was applied to the concrete specimens according to the bearing capacity of the foundation concrete to complete the preparation work. During the test, cold air was introduced to cool the water until it froze. After maintaining this state for a period of time, the frozen water was heated by applying electric heating radiation above the concrete specimens until it thawed. This process was repeated for a period of time to form a freeze-thaw cycle. After the freeze-thaw test was completed, the concrete specimens were taken out and their performance was tested. The specimens were compared with the same untested concrete specimens to obtain the performance change parameters of the foundation concrete affected by the freeze-thaw environment. This experimental method relies on a foundation concrete freeze-thaw cycle test system, which includes a simulation chamber with an openable top cover. A specimen positioning device is located in the lower middle part of the simulation chamber, and a pressure application device is positioned directly above the positioning device. A water supply pipe with a switch valve is connected to the lower middle side of one end of the simulation chamber, and the other end of the water supply pipe is connected to a water storage tank. A drainage pipe with a switch valve is connected downwards to the bottom of the other end of the simulation chamber. The system also includes a refrigeration evaporator located at the top of the simulation chamber, with a built-in fan and an air inlet and outlet for internal circulation within the simulation chamber. The refrigeration evaporator is connected to an external compressor located outside the simulation chamber to form a refrigeration cycle system. Furthermore, it includes an electric heating element fixed to the inner surface of the top cover of the simulation chamber, and a groundwater depth adjustment simulation device for simulating groundwater depth regulation within the simulation chamber. The groundwater depth regulation simulation device includes a baffle plate located inside the simulation box away from the direction of the water supply pipeline and spaced parallel to that side. The two ends of the baffle plate can be slidably engaged in the baffle plate groove on the inner side wall of the simulation box. A baffle plate sinkhole is provided at the bottom of the simulation box below the baffle plate. The baffle plate is connected to a baffle plate up-and-down movement control mechanism. The baffle plate up-and-down movement control mechanism can control the baffle plate to extend upward or retract downward into the baffle plate sinkhole. After the baffle plate extends upward, it forms a drainage cavity on the side away from the direction of the water supply pipeline. The drainage pipeline is set at the bottom surface of the drainage cavity. On the side of the baffle plate facing the water pipeline, a support grid and sponge material fixed on the support grid are also fixed outward in sequence; The baffle plate vertical movement control mechanism includes baffle plate racks fixed vertically at both ends of one side of the baffle plate. The two baffle plate racks are respectively engaged with a baffle plate control gear located at the same horizontal height. The two baffle plate control gears are fixed on a baffle plate control shaft set at the same horizontal level. The two ends of the baffle plate control shaft are rotatably mounted on the simulation box, and one end extends out of the simulation box and is provided with a baffle plate control rotating handle.

2. The freeze-thaw cycle test method for foundation concrete affected by groundwater as described in claim 1, characterized in that, The ambient temperature for the test, which was cooled by introducing cold air, was determined based on the lowest nighttime temperature of the building's foundation concrete in spring and autumn in the local area. The temperature used for heating by electrothermal radiation during the test was determined based on the highest daytime temperature of the building foundation concrete in the local spring and autumn seasons.

3. The method for freeze-thaw cycle testing of foundation concrete affected by groundwater as described in claim 1, characterized in that, When preparing concrete specimens, cylindrical specimens are obtained by pouring the foundation concrete of the building to be tested according to the same concrete formula. The simulated soil material was prepared using gravel, silt, and clay to simulate the actual soil conditions around the concrete foundation of a building.

4. The freeze-thaw cycle test method for foundation concrete affected by groundwater as described in claim 1, characterized in that, When the depth of the simulation chamber (referring to the depth that can be used for testing) is greater than the depth of groundwater immersion in the foundation concrete of the building to be tested, the water penetration depth at the bottom of the simulation chamber is consistent with the actual groundwater immersion depth; when the depth of the simulation chamber is less than the depth of groundwater immersion in the foundation concrete of the building to be tested, the simulation chamber is sealed and pressurized with gas, and the water pressure at the bottom of the simulation chamber is measured to make it consistent with the actual water pressure at the lowest point of the foundation concrete of the building to be tested.

5. The freeze-thaw cycle test method for foundation concrete affected by groundwater as described in claim 1, characterized in that, One freeze-thaw cycle lasts 24 hours, including 12 hours of freezing and 12 hours of thawing; the number of freeze-thaw cycles is set to 7, 15, 30, 60 or 90 times according to the study, and the corresponding time is 7, 15, 30, 60 or 90 days. After the freeze-thaw test is completed, the concrete specimens are removed and subjected to uniaxial compression tests or triaxial compression tests to test the mechanical properties of the concrete specimens after the freeze-thaw cycle, including compressive strength and elastic modulus parameters. The mechanical property parameters of the unfrozen concrete specimens are compared to obtain the degree of deterioration of the mechanical properties of the building foundation concrete under the influence of the freeze-thaw environment.

6. The method for freeze-thaw cycle testing of foundation concrete affected by groundwater as described in claim 1, characterized in that, The specimen positioning device includes a positioning ring located in the middle. The inner diameter of the positioning ring is 1-10 mm larger than the outer diameter of the specimen. The periphery of the positioning ring is fixed to the inner wall of the simulation chamber by horizontally set fixing rods. The pressure application device includes a pressure head positioned above the positioning ring. The pressure head is connected to a hydraulic tank via a retractable pressure rod. The hydraulic tank is fixedly mounted on the inner wall of the simulation chamber via a support arm. The hydraulic tank is connected to a control oil tank outside the simulation chamber via hydraulic pipelines. A specimen pressure detection sensor is installed on the lower surface of the pressure head.

7. The method for freeze-thaw cycle testing of foundation concrete affected by groundwater as described in claim 1, characterized in that, The upper surface of the drainage pipe is covered with a mesh screen.

8. The method for freeze-thaw cycle testing of foundation concrete affected by groundwater as described in claim 1, characterized in that, There are four refrigeration evaporators, which are located at the four corners of the top of the simulation chamber.

9. The method for freeze-thaw cycle testing of foundation concrete affected by groundwater as described in claim 1, characterized in that, The simulation chamber is made of transparent material.

10. The method for testing the freeze-thaw cycle of foundation concrete affected by groundwater as described in claim 1, characterized in that, The simulation chamber has a vertical scale on at least one side.

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