A device for testing the frost heave stress of a cement-based material pore solution

Abstract

The utility model discloses a cement base material hole solution frost heaving stress testing arrangement, including low temperature thermostat, low temperature thermostat both sides are installed with export refrigerant pipeline, install the liquid valve on export refrigerant pipeline, export refrigerant pipeline is connected with steel bottle side top, the outer chamber is arranged to the steel bottle inboard periphery, the inner chamber is arranged to the steel bottle inboard center, export refrigerant pipeline top end and outer chamber top intercommunication, the inner chamber top installs the piston, the bottle lid center is provided with piezoelectric stress sensor, low temperature thermostat and piezoelectric stress sensor all with data acquisition instrument electric connection. This cement base material hole solution frost heaving stress testing arrangement can simulate the ice expansion process of hole solution under the closed environment, the size of frost heaving stress is measured, and the cement base material hole solution frost heaving stress is measured in real time, high precision and full automation, which is convenient for analyzing the freezing damage process and principle of concrete from the theoretical level.

Description

Technical Field

[0001] This utility model relates to the technical field of concrete frost resistance testing equipment, specifically a device for testing the frost heave stress of pore solutions in cement-based materials. Background Technology

[0002] Freeze-thaw damage, as one of the major types of concrete defects, is particularly prominent in the "Three Norths" region of my country. Concrete projects in this area are subjected to long-term freeze-thaw cycles, leading to surface erosion and internal cracking of cement-based materials, resulting in reduced durability, protective layer detachment, and shortened structural service life. Premature repairs impose a significant economic burden. At sub-zero temperatures, the crystallization and expansion of pore solutions in relatively closed pores is the main cause of freeze damage to cement-based materials. Due to differences in the components of cement-based materials such as cement and admixtures, as well as capillary water absorption components, the solutes in the pore solutions of cement-based materials vary under different service environments. The freeze-thaw stress generated by the crystallization of these pore solutions at sub-zero temperatures also varies, resulting in different degrees of damage to cement-based materials. By "designing" the solute composition of the pore solutions to reduce the freeze-thaw stress caused by crystallization, freeze damage to cement-based materials can be significantly reduced.

[0003] Currently, specialized equipment is rarely used in the study of frost heave stress in pore solutions. Researchers often use indirect measurements or simplified models. For example, they build simple devices using gantry cranes, gas cylinders, traditional diaphragm stress sensors, temperature sensors, and high and low temperature test chambers (or refrigerators) to test frost heave stress. Existing simple devices face four main problems:

[0004] Firstly, there is the issue of stress transmission. The deformation of traditional diaphragm-type stress sensors can cause errors, leading to a decrease in accuracy.

[0005] Secondly, the simple device uses a piston-type bottle cap and a traditional diaphragm-type stress sensor, which inevitably leads to leakage of the test liquid and poor repeatability and regularity of the measured values.

[0006] Third, the cooling effect of simple devices in low-temperature test chambers (or refrigerators) is affected by the high-frequency vibration of the cooling equipment itself, which reduces the degree of crystallization of the solution.

[0007] Fourth, simple devices placed directly in the refrigerator can cause problems such as localized overcooling and uneven freezing. Utility Model Content

[0008] To address the problems existing in the prior art, this utility model provides a device for testing the frost heave stress of pore solutions in cement-based materials.

[0009] To achieve the above objectives, this utility model provides the following technical solution: a freezing heave stress testing device for pore solutions of cement-based materials, comprising a low-temperature constant temperature bath, outlet refrigerant conduits installed on both sides of the low-temperature constant temperature bath, an outlet valve installed on the outlet refrigerant conduit, the outlet refrigerant conduit being connected to the top of the side of a steel cylinder, an outer cavity provided on the outer edge of the inner side of the steel cylinder, an inner cavity provided at the center of the inner side of the steel cylinder, the top of the outlet refrigerant conduit communicating with the top of the outer cavity, a piston installed at the top of the inner cavity, a bottle cap installed at the top of the steel cylinder, a piezoelectric stress sensor disposed at the center of the bottle cap, the low-temperature constant temperature bath and the piezoelectric stress sensor being electrically connected to a data acquisition instrument, an inlet refrigerant conduit installed at the bottom of the outer cavity, an inlet valve installed on the inlet refrigerant conduit, and the inlet refrigerant conduit being connected to the low-temperature constant temperature bath.

[0010] Preferably, both the cylinder and the cap are made of 440C martensitic stainless steel. The cylinder is a cylinder with a diameter of 74mm and a height of 145mm. The cap is 40mm high and includes a non-stopper part and a threaded stopper part. The upper non-stopper part of the cap is 20mm high and 74mm in diameter, and the lower stopper part is 20mm high and 54mm in diameter.

[0011] Preferably, the outer cavity and the inner cavity form a double-layer cavity storage system, wherein the outer cavity is a circulating refrigerant cavity and the inner cavity is a sample cavity;

[0012] The outer cavity is 75mm high. The outer cavity cross-section is uniformly wrapped around the outer side of the inner cavity in the form of a ring. The width of the ring of the outer cavity cross-section is 10mm. The wall thickness between the ring of the outer cavity cross-section and the inner cavity is 10mm. The distance between the ring of the outer cavity cross-section and the outer surface of the cylinder is 10mm. Refrigerant outlets are reserved on both sides of the upper end of the outer cavity. The refrigerant outlets of the outer cavity are slightly higher than the upper surface of the inner cavity. The diameter of the outlet refrigerant conduit connected to the outer cavity is 10mm. A refrigerant inlet is reserved at the lower end of the outer cavity. The diameter of the inlet refrigerant conduit connected to the lower end of the outer cavity is 15mm.

[0013] The inner cavity has a diameter of 14 mm and a height of 60 mm. The surface of the inner cavity is hydrophilic by etching micron / nano-scale pores. The etching method on the surface of the inner cavity is either femtosecond laser or nanosecond laser.

[0014] Preferably, the piston and the piezoelectric stress sensor constitute a stress sensing system;

[0015] The piston is made of tungsten carbide and is a cylinder with a diameter of 24 mm and a height of 15 mm. The piston has a reserved space of 24 mm in diameter and 15 mm in height above the inner cavity.

[0016] The piezoelectric stress sensor is embedded in the bottle cap, with the height of the piezoelectric stress sensor being the same as that of the bottle cap, the diameter of the piezoelectric stress sensor being the same as that of the piston, the bottom of the piezoelectric stress sensor completely overlapping with the top of the piston, the range of the piezoelectric stress sensor being 0 to 50 kN, and the accuracy of the piezoelectric stress sensor being no less than ±0.1%.

[0017] Preferably, the data acquisition instrument and its matching temperature stress acquisition channel constitute a data acquisition system. The data acquisition instrument synchronously records the freezing expansion stress of the solution in the inner cavity and the temperature of the cold medium in the low-temperature constant temperature bath. The data acquisition instrument records data once every 10 seconds.

[0018] Preferably, the low-temperature thermostatic bath, the outlet refrigerant conduit, the inlet refrigerant conduit, the inlet valve, and the outlet valve constitute a freezing system, and the outlet refrigerant conduit is symmetrically distributed about the center of the low-temperature thermostatic bath.

[0019] Preferably, the temperature range of the low-temperature constant temperature bath is -30℃ to 0℃, the fluctuation is ≤0.05℃, the resolution is 0.01℃, the bath volume is 30L, and the pump flow rate is 13L / min. The outer surfaces of the outlet refrigerant conduit and the inlet refrigerant conduit connected to the low-temperature constant temperature bath are covered with thermal insulation foam. The refrigerant in the low-temperature constant temperature bath is an ethylene glycol solution, and the freezing point of the refrigerant in the low-temperature constant temperature bath is not higher than -35℃.

[0020] Compared with the prior art, the beneficial effects of this utility model are:

[0021] 1. Dual-cavity design: The combination of a dual-cavity design and an externally connected low-temperature constant temperature bath ensures the uniformity of the temperature field within the inner cavity and sample cavity during the cooling process. This effectively prevents the problems of rapid "ice shell" formation at the edge of the solution in traditional measuring devices, which hinders internal moisture migration, and stress distribution distortion caused by an axial / radial temperature difference >5℃.

[0022] 2. Anti-interference design of rigid piston measurement system: The piston is made of tungsten carbide (elastic modulus 710GPa) and the deformation is less than 0.001mm. At the same time, the piston surface is coated with polytetrafluoroethylene sealing material to reduce friction. The traditional diaphragm stress sensor is replaced with a piezoelectric stress sensor, which reduces the error caused by the elastic absorption of frost heave stress.

[0023] 3. Realistically simulate the sealed environment inside the pores of cement-based materials: By adopting a combination of piston and piezoelectric stress sensor, a better sealing design is achieved, eliminating errors caused by deformation and leakage of diaphragm sensor, and more accurately recording the changes in frost heave stress and temperature, thus improving the feasibility of improving the frost resistance of concrete based on "pore solution design". Attached Figure Description

[0024] Figure 1 This is a front view structural diagram of the present invention;

[0025] Figure 2 This is a frontal cross-sectional view of the present invention.

[0026] Figure 3 This utility model Figure 2 Schematic diagram of the cross-sectional structure of section aa;

[0027] Figure 4 This is a bottom view schematic diagram of the piezoelectric stress sensor and bottle cap structure of this utility model.

[0028] In the diagram: 1. Low-temperature thermostatic bath; 2. Outlet refrigerant conduit; 3. Inlet valve; 4. Gas cylinder; 5. Outer cavity; 6. Inner cavity; 7. Outlet valve; 8. Piston; 9. Piezoelectric stress sensor; 10. Bottle cap; 11. Data acquisition instrument; 12. Inlet refrigerant conduit. Detailed Implementation

[0029] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0030] Please see Figure 1-4 This utility model provides a technical solution: a freezing heave stress testing device for cement-based material pore solutions, comprising a low-temperature constant temperature bath 1, an outlet refrigerant conduit 2, an inlet valve 3, a steel cylinder 4, an outer cavity 5, an inner cavity 6, an outlet valve 7, a piston 8, a piezoelectric stress sensor 9, a bottle cap 10, a data acquisition instrument 11, and an inlet refrigerant conduit 12. Outlet refrigerant conduits 2 are installed on both sides of the low-temperature constant temperature bath 1, and outlet valves 7 are installed on the outlet refrigerant conduits 2. The outlet refrigerant conduits 2 are connected to the top side of the steel cylinder 4, and the inner side of the steel cylinder 4... An outer cavity 5 is provided on the outer edge, and an inner cavity 6 is provided at the center of the inner side of the cylinder 4. The top of the outlet refrigerant conduit 2 is connected to the top of the outer cavity 5. A piston 8 is installed at the top of the inner cavity 6. A bottle cap 10 is installed at the top of the cylinder 4. A piezoelectric stress sensor 9 is provided at the center of the bottle cap 10. The low-temperature constant temperature bath 1 and the piezoelectric stress sensor 9 are both electrically connected to the data acquisition instrument 11. An inlet refrigerant conduit 12 is installed at the bottom of the outer cavity 5. An inlet valve 3 is installed on the inlet refrigerant conduit 12. The inlet refrigerant conduit 12 is connected to the low-temperature constant temperature bath 1.

[0031] In this example, both the cylinder 4 and the cap 10 are made of 440C martensitic stainless steel. The cylinder 4 is a cylinder with a diameter of 74mm and a height of 145mm. The cap 10 is 40mm high and consists of two parts: a non-capping part and a threaded capping part. The upper non-capping part of the cap 10 is 20mm high and 74mm in diameter, while the lower capping part is 20mm high and 54mm in diameter.

[0032] The outer cavity 5 and the inner cavity 6 form a double-layer cavity storage system. The outer cavity 5 is the circulating refrigerant cavity, and the inner cavity 6 is the sample cavity.

[0033] The outer cavity 5 is 75mm high. The cross-section of the outer cavity 5 is uniformly wrapped around the outer side of the inner cavity 6 in the form of a ring. The width of the ring of the outer cavity 5 is 10mm. The wall thickness between the ring of the outer cavity 5 and the inner cavity 6 is 10mm. The distance between the ring of the outer cavity 5 and the outer surface of the cylinder 4 is 10mm. Refrigerant outlets are reserved on both sides of the upper end of the outer cavity 5. The refrigerant outlets of the outer cavity 5 are slightly higher than the upper surface of the inner cavity 6. The diameter of the outlet refrigerant conduit 2 connected to the outer cavity 5 is 10mm. A refrigerant inlet is reserved at the lower end of the outer cavity 5. The diameter of the inlet refrigerant conduit 12 connected to the lower end of the outer cavity 5 is 15mm.

[0034] The diameter and height of the inner cavity 6 are 14mm and 60mm, respectively. The surface of the inner cavity 6 is hydrophilic by etching micron / nano-scale pores. The etching method on the surface of the inner cavity 6 is either femtosecond laser or nanosecond laser.

[0035] Piston 8 and piezoelectric stress sensor 9 constitute a stress sensing system;

[0036] Piston 8 is made of tungsten carbide. Piston 8 is a cylinder with a diameter of 24mm and a height of 15mm. Piston 8 has a reserved space of 24mm in diameter and 15mm in height above the inner cavity 6.

[0037] The piezoelectric stress sensor 9 is embedded in the bottle cap 10. The height of the piezoelectric stress sensor 9 is the same as that of the bottle cap 10. The diameter of the piezoelectric stress sensor 9 is the same as that of the piston 8. The bottom of the piezoelectric stress sensor 9 is completely overlapped with the top of the piston 8. The range of the piezoelectric stress sensor 9 is 0 to 50 kN. The accuracy of the piezoelectric stress sensor 9 is not less than ±0.1%.

[0038] The data acquisition system consists of the data acquisition instrument 11 and its matching temperature stress acquisition channel. The data acquisition instrument 11 synchronously records the freezing expansion stress of the solution in the inner cavity 6 and the temperature of the cooling medium in the low temperature constant temperature bath 1. The data acquisition instrument 11 records data once every 10 seconds.

[0039] The cryogenic constant temperature bath 1, the outlet refrigerant conduit 2, the inlet refrigerant conduit 12, the liquid inlet valve 3, and the liquid outlet valve 7 constitute a freezing system. The outlet refrigerant conduit 2 is symmetrically distributed about the center of the cryogenic constant temperature bath 1.

[0040] The low-temperature thermostatic bath 1 has an adjustable temperature range of -30°C to 0°C, a fluctuation degree ≤ 0.05°C, a resolution of 0.01°C, a bath volume of 30L, and a pump flow rate of 13L / min. The outer surfaces of the outlet refrigerant conduit 2 and the inlet refrigerant conduit 12 connected to the low-temperature thermostatic bath 1 are coated with thermal insulation foam. The refrigerant medium in the low-temperature thermostatic bath 1 is ethylene glycol solution, and the freezing point of the refrigerant medium in the low-temperature thermostatic bath 1 is not higher than -35°C.

[0041] Working principle: The pore solution is extracted by a cement-based material pore solution pressing device or a self-prepared simulated pore solution is used as the test sample. After the pore solution is pressed or prepared, the test shall be carried out immediately to prevent component change caused by contact between the sample and air;

[0042] Weigh and extract 9.231 ml of the sample, slowly inject the sample into the inner cavity 6 along the inner wall of the inner cavity 6, place the piston 8 and tighten the bottle cap 10, so that the inner cavity 6, the piston 8 and the piezoelectric stress sensor 9 remain in a straight line;

[0043] In advance, fill 25L-30L of ethylene glycol solution with a freezing point not higher than -35°C into the low-temperature thermostatic bath 1 as the refrigerant medium, start the low-temperature thermostatic bath 1 and the data acquisition instrument 11 according to the set temperature. When the temperature of the solution in the low-temperature thermostatic bath 1 reaches the set temperature, open the inlet valve 3 and the outlet valve 7 to allow the refrigerant medium to quickly fill the outer cavity 5, and start the circulation of the refrigerant medium by the circulating pump matched with the low-temperature thermostatic bath 1 to ensure uniform temperature reduction in the inner cavity 6-inner cavity 6. The low-temperature thermostatic bath 1 automatically adjusts the temperature to always keep the temperature at or infinitely close to the set temperature,

[0044] The data acquisition instrument 11 records the temperature of the circulating refrigerant medium in the low-temperature thermostatic bath 1 and the pore solution icing expansion stress in the inner cavity 6-inner cavity 6 read by the piezoelectric stress sensor 9 in real time, and the test is ended after the frost heave stress reaches the peak and stabilizes;

[0045] When the test is finished, turn off the low-temperature thermostatic bath 1 first, and after the temperature of the refrigerant medium drops to room temperature, disassemble the device one by one, clean the pore solution to be tested, and recover the refrigerant medium. Be careful of frostbite caused by the refrigerant medium during the test. This is the working principle of the frost heave stress testing device for pore solution of cement-based materials.

[0046] Although the embodiments of the present utility model have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principle and spirit of the present utility model, and the scope of the present utility model is defined by the appended claims and their equivalents.

Claims

1. A device for testing the frost heave stress of a cement-based material pore solution, comprising a low-temperature constant temperature bath (1), characterized in that: The low-temperature constant temperature bath (1) is equipped with outlet refrigerant conduits (2) on both sides. The outlet refrigerant conduits (2) are equipped with liquid outlet valves (7). The outlet refrigerant conduits (2) are connected to the top of the side of the cylinder (4). The outer edge of the inner side of the cylinder (4) is provided with an outer cavity (5). The center of the inner side of the cylinder (4) is provided with an inner cavity (6). The top of the outlet refrigerant conduits (2) is connected to the top of the outer cavity (5). The top of the inner cavity (6) is equipped with a piston (8). The top of the cylinder (4) is equipped with a bottle cap (10). The center of the bottle cap (10) is provided with a piezoelectric stress sensor (9). The low-temperature constant temperature bath (1) and the piezoelectric stress sensor (9) are electrically connected to the data acquisition instrument (11). The bottom of the outer cavity (5) is equipped with an inlet refrigerant conduit (12). The inlet refrigerant conduit (12) is equipped with a liquid inlet valve (3). The inlet refrigerant conduit (12) is connected to the low-temperature constant temperature bath (1).

2. The device for testing the frost heave stress of a cement-based material pore solution according to claim 1, characterized in that: The steel cylinder (4) and the bottle cap (10) are both made of 440C martensitic stainless steel. The steel cylinder (4) is a cylinder with a diameter of 74mm and a height of 145mm. The bottle cap (10) is 40mm high. The bottle cap (10) includes a non-stopper part and a threaded stopper part. The upper non-stopper part of the bottle cap (10) is 20mm high and 74mm in diameter. The lower stopper part of the bottle cap (10) is 20mm high and 54mm in diameter.

3. The device for testing the frost heave stress of a cement-based material pore solution according to claim 1, characterized in that: The outer cavity (5) and the inner cavity (6) form a double-layer cavity storage system. The outer cavity (5) is a circulating refrigerant cavity, and the inner cavity (6) is a sample cavity. The outer cavity (5) is 75mm high. The cross section of the outer cavity (5) is uniformly wrapped around the outer side of the inner cavity (6) in the form of a ring. The width of the ring of the outer cavity (5) is 10mm. The wall thickness between the ring of the outer cavity (5) and the inner cavity (6) is 10mm. The wall thickness between the ring of the outer cavity (5) and the outer surface of the cylinder (4) is 10mm. Refrigerant outlets are reserved on both sides of the upper end of the outer cavity (5). The refrigerant outlet of the outer cavity (5) is slightly higher than the upper surface of the inner cavity (6). The diameter of the outlet refrigerant conduit (2) connected to the outer cavity (5) is 10mm. A refrigerant inlet is reserved at the lower end of the outer cavity (5). The diameter of the inlet refrigerant conduit (12) connected to the lower end of the outer cavity (5) is 15mm. The diameter and height of the inner cavity (6) are 14 mm and 60 mm, respectively. The surface of the inner cavity (6) is hydrophilic by etching micron / nano-scale pores. The etching method on the surface of the inner cavity (6) is either femtosecond laser or nanosecond laser.

4. The device for testing the frost heave stress of a cement-based material pore solution according to claim 1, characterized in that: The piston (8) and the piezoelectric stress sensor (9) together form a stress sensing system; The piston (8) is made of tungsten carbide and is a cylinder with a diameter of 24 mm and a height of 15 mm. The piston (8) has a reserved space of 24 mm in diameter and 15 mm in height above the inner cavity (6). The piezoelectric stress sensor (9) is embedded in the bottle cap (10). The height of the piezoelectric stress sensor (9) is the same as that of the bottle cap (10). The diameter of the piezoelectric stress sensor (9) is the same as that of the piston (8). The bottom of the piezoelectric stress sensor (9) is completely overlapped with the top of the piston (8). The range of the piezoelectric stress sensor (9) is 0 to 50 kN. The accuracy of the piezoelectric stress sensor (9) is not less than ±0.1%.

5. The device for testing the frost heave stress of a cement-based material pore solution according to claim 1, characterized in that: The data acquisition instrument (11) and its matching temperature stress acquisition channel constitute a data acquisition system. The data acquisition instrument (11) synchronously records the freezing expansion stress of the solution in the inner cavity (6) and the temperature of the cold medium in the low temperature constant temperature bath (1). The data acquisition instrument (11) records data once every 10 seconds.

6. The device for testing the frost heave stress of a cement-based material pore solution according to claim 1, characterized in that: The low-temperature thermostatic bath (1), the outlet refrigerant conduit (2), the inlet refrigerant conduit (12), the liquid inlet valve (3), and the liquid outlet valve (7) constitute a freezing system. The outlet refrigerant conduit (2) is symmetrically distributed about the center of the low-temperature thermostatic bath (1).

7. The device for testing the frost heave stress of a cement-based material pore solution according to claim 1, characterized in that: The temperature range of the low-temperature constant temperature bath (1) is -30℃ to 0℃, the fluctuation is ≤0.05℃, the resolution is 0.01℃, the tank volume is 30L, and the pump flow rate is 13L / min. The outer surfaces of the outlet refrigerant conduit (2) and the inlet refrigerant conduit (12) connected to the low-temperature constant temperature bath (1) are covered with heat-insulating foam. The refrigerant in the low-temperature constant temperature bath (1) is an ethylene glycol solution, and the freezing point of the refrigerant in the low-temperature constant temperature bath (1) is not higher than -35℃.

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