A test device and method for testing the compressive performance of concrete

Abstract

The application belongs to the field of test devices and provides a test device and a test method for the compressive performance of concrete. The test device comprises a support platform, a test mechanism arranged at the middle part of the support platform, servo-controlled loading mechanisms arranged at both sides of the support platform and placed at one end inside the test mechanism, and electromagnetic pulse emission mechanisms arranged on both sides of the support platform and placed on the two servo-controlled loading mechanisms. The technical problem that the existing technology cannot carry out dynamic impact test research on rock-like materials such as concrete under dynamic and static combined load in the high-temperature water-cooled scene is solved.

Description

Technical Field

[0001] This invention belongs to the field of testing equipment, and particularly relates to a testing device and method for testing the compressive strength of concrete. Background Technology

[0002] When buildings suffer from fires or other disasters, the temperature of concrete rises rapidly and is then cooled by water during firefighting. During this process, complex physicochemical reactions occur within the concrete due to changes in temperature, water, and other environmental factors. These reactions degrade the mechanical properties of concrete, significantly impacting its load-bearing capacity and threatening the structural safety and stability of the building. Furthermore, during a fire, concrete not only bears the static load of the building's own weight but also often experiences dynamic disturbances caused by the collapse or explosion of other structures or objects within the building. The mechanical response of concrete and other rock-like solid materials under dynamic loads is often more complex, which is detrimental to the structural safety and stability. Therefore, it is necessary to conduct in-depth research on the dynamic mechanical response and failure characteristics of concrete and other building materials under high-temperature water cooling conditions, providing a theoretical basis and technical support for fire-resistant design of building structures and engineering safety analysis in firefighting scenarios.

[0003] Current research on the mechanical properties and failure characteristics of high-temperature water-cooled concrete under combined static and dynamic loading is very limited. This is mainly because existing technologies and testing equipment cannot easily and flexibly simulate the dynamic response of concrete materials under high-temperature water-cooling scenarios. Although there are existing testing devices for the mechanical properties and failure characteristics of rock-like materials in high-temperature environments under static or dynamic loads alone—for example, the utility model with patent number CN111024529.A, which uses a combined static and dynamic Hopkinson bar device to achieve real-time observation of material impact tests under high-temperature and combined static and dynamic loading conditions—this device cannot simulate the water-cooling scenario during firefighting. Furthermore, research on the mechanical properties of high-temperature concrete under water cooling typically involves heating, cooling, and loading separately in multiple devices, resulting in impact tests based on existing equipment that cannot accurately reflect the real-time failure process and changes in mechanical properties of concrete materials under simultaneous dynamic loading and high-temperature water cooling during firefighting. Therefore, it is necessary to innovate and improve existing devices used for conducting combined static and dynamic loading tests on concrete materials at high temperatures to overcome these technical difficulties. Summary of the Invention

[0004] The purpose of this invention is to provide a test device and method for the compressive strength of concrete, aiming to solve the technical problem that existing technologies cannot conduct dynamic impact tests on rock-like materials such as concrete under combined static and dynamic loads in high-temperature water-cooling scenarios.

[0005] The present invention is implemented as follows: a test device for the compressive strength of concrete, the test device comprising a support platform, a test mechanism disposed in the middle of the support platform, a servo-controlled loading mechanism disposed on both sides of the support platform with one end placed inside the test mechanism, and an electromagnetic pulse emitting mechanism disposed on both sides of the support platform and placed on the two servo-controlled loading mechanisms respectively.

[0006] A further technical solution of the present invention is: the testing mechanism includes a heating chamber support base disposed on the support platform and capable of translation relative to the support platform, and a heating chamber disposed on the heating chamber support base.

[0007] A further technical solution of the present invention is: the heating box includes a box body with heating function and consisting of a box shell, a lower insulation layer, a lower heating layer and a lower explosion-proof layer from the outside to the inside, and a box cover with heating function hinged to the box body and consisting of a box cover shell, an upper insulation layer, an upper heating layer and an upper explosion-proof layer from the outside to the inside.

[0008] A further technical solution of the present invention is: viewing windows are provided on the front and rear sides of the box, reserved through holes are provided on the left and right sides of the box, a drain outlet is provided at the bottom of the box, and a spray unit is provided on the box cover.

[0009] A further technical solution of the present invention is as follows: the spray unit includes at least one spray head disposed on the cover and penetrating the cover, and a flow rate regulating valve, a flow rate meter, a water pump and a water tank sequentially connected to the spray head via pipes; the lower heating layer and the upper heating layer are both made of thermally conductive material, and thermocouples are reserved therein; the viewing window includes a protective frame disposed on the box body and glass disposed on the protective frame.

[0010] A further technical solution of the present invention is as follows: the servo-controlled loading mechanism includes a hydraulic cylinder support base disposed on the support platform and movable relative to the support platform, a servo-controlled loading cylinder disposed on the hydraulic cylinder support base, a hydraulic piston rod disposed on the servo-controlled loading cylinder, a static loading frame contacting and connecting the hydraulic piston rod, a loading rod support base disposed on the support platform and movable relative to the support platform, a loading rod disposed on the loading rod support base with one end placed in the test mechanism and the other end placed in the static loading frame, and a flange ring disposed on the loading rod with its end face contacting the static loading frame.

[0011] A further technical solution of the present invention is: the electromagnetic pulse transmitting mechanism includes an electromagnetic pulse support base disposed on the support platform and capable of translation relative to the support platform, and an electromagnetic pulse excitation cavity disposed on the electromagnetic pulse support base and having its transmitting end in contact with the loading rod.

[0012] A further technical solution of the present invention is that the test device further includes a data acquisition mechanism disposed on the test mechanism and the servo control loading mechanism, and a monitoring mechanism disposed outside the test mechanism.

[0013] A further technical solution of the present invention is as follows: the data acquisition mechanism includes strain gauges disposed on the servo-controlled loading mechanisms on both sides for collecting strain signals, a temperature sensor disposed on the testing mechanism for collecting the internal temperature of the testing mechanism, and a synchronous high-speed recorder connected to the strain gauges and the temperature sensor for data recording and storage; the monitoring mechanism includes a high-speed camera for monitoring the entire process of sample cracking and failure, and at least one lighting lamp used in conjunction with the high-speed camera; the loading rod is a TC21 titanium alloy loading rod.

[0014] Another object of the present invention is to provide a method for testing the compressive strength of concrete, the method comprising the following steps:

[0015] Step S1: Install the test specimen in the test mechanism and control the servo control loading mechanism on both sides to apply a static preload of 20MPa to the test specimen. Wait until the static preload reaches the set value and remains stable.

[0016] Step S2: Control the testing mechanism to heat the test sample, stop heating when the temperature reaches the target temperature of 400℃, and maintain this temperature for at least 30 minutes;

[0017] Step S3: Control the testing mechanism to spray the test specimen, and control the electromagnetic pulse emission mechanisms on both sides to apply a half-sine incident stress wave with an amplitude of 300MPa and a duration of 200μs to the test specimen. The dynamic load is excited and output by the right end face of the electromagnetic pulse emission mechanisms on both sides. The dynamic load is transmitted to the test specimen in the form of stress wave through the loading rods on both sides to apply dynamic compressive load.

[0018] Step S4: During dynamic loading, when the dynamic load error of the two loading rods monitored by the strain gauges on both sides is less than the acceptable error range of the test, the test specimen is considered to have reached a dynamic stress equilibrium state during dynamic loading. According to the one-dimensional stress wave theory, the dynamic compressive strength σ of the test specimen during loading can be solved by the incident wave, reflected wave, and transmitted wave signals collected by the strain gauges on the loading rods according to the following formula:

[0019]

[0020] Where, ε 左透射 and ε 右透射A and E are the transmitted wave strain signals collected by the strain gauges on both sides; A and E are the cross-sectional areas and elastic moduli of the loading rods on both sides, respectively; F is the load output by the servo-controlled loading cylinder; A0 is the cross-sectional area of ​​the test specimen.

[0021] The beneficial effects of this invention are as follows: This testing device can heat and / or cool the sample by spraying water while simultaneously loading a dynamic and static combined load. It also considers a dynamic and static combined servo-controlled loading mechanism and heating and spraying units. Before and during the dynamic and static combined impact test, it can control both to heat and cool the sample simultaneously or separately. Existing technologies, when studying the performance of high-temperature concrete under water-cooled conditions, can only separate the heating and cooling processes in two separate devices, loading the high-temperature cooled sample after temperature treatment. This device can simulate the simultaneous heating and water-cooling of high-temperature concrete materials during firefighting, filling the technical gap in existing devices that cannot conduct dynamic and static combined compressive strength tests where sample heating and water cooling occur simultaneously. The electromagnetic pulse emission mechanism provides dynamic compressive load to the sample, which not only precisely controls and adjusts the amplitude and pulse width of the incident stress wave but also generates highly repeatable incident stress waves, overcoming the technical deficiency of existing devices that rely on mechanical impact to generate incident stress waves that are difficult to repeat and accurately produce fixed-characteristic incident waves. Furthermore, the bidirectional electromagnetic pulse emission mechanism can emit electromagnetic pulses from both sides of the test sample. The device provides a dynamic compressive load with the same incident stress wave amplitude and height, achieving stress balance on both sides of the specimen throughout the dynamic loading process. This ensures the accuracy and validity of the test data. During the test, the concrete specimen is placed in the testing mechanism of the testing device for impact compression testing. The testing mechanism is equipped with a transparent glass window, allowing real-time observation and recording of the dynamic strain field evolution, crack propagation, and specimen failure process on the side of the specimen through monitoring methods such as high-speed cameras. This facilitates a more comprehensive study of the impact compression failure process of concrete or other solid material specimens. It can also perform combined static and dynamic compressive loads on the specimen. The loading mechanism includes two independent loading mechanisms: a servo-controlled static loading mechanism and an electromagnetic pulse stress wave dynamic loading mechanism. During the test, the two mechanisms can be independently controlled to load the specimen separately. This simulates the situation in firefighting scenarios where concrete materials are subjected to the self-weight load of the building structure, as well as the impact load generated by surrounding structures or objects during a fire. This prevents potential secondary damage to the structure and allows for testing the compressive performance of concrete materials under combined static and dynamic loading. Attached Figure Description

[0022] Figure 1 This is a structural diagram of a test device for the compressive strength of concrete provided in an embodiment of the present invention;

[0023] Figure 2This is a plan view of a test device for the compressive strength of concrete provided in an embodiment of the present invention;

[0024] Figure 3 This is a structural diagram of the testing mechanism of a test device for testing the compressive strength of concrete provided in an embodiment of the present invention;

[0025] Figure 4 This is a three-view cross-sectional view of the testing mechanism of a test device for testing the compressive strength of concrete provided in an embodiment of the present invention;

[0026] Figure 5 This is a structural diagram of the spray unit of the testing mechanism of a test device for testing the compressive strength of concrete provided in an embodiment of the present invention;

[0027] Figure 6 This is a structural diagram and a cross-sectional view of the electromagnetic pulse transmitting mechanism of a test device for the compressive strength of concrete provided in an embodiment of the present invention;

[0028] Figure 7 This is a structural diagram of the upper heating layer, lower heating layer, and thermocouple of a concrete compressive strength testing device provided in an embodiment of the present invention. Detailed Implementation

[0029] Reference numerals: 1--Support platform, 2-Hydraulic cylinder support base, 3-Servo-controlled loading cylinder, 4-Hydraulic piston rod, 5-Static loading frame, 6-Electromagnetic pulse support base, 7-Electromagnetic pulse excitation chamber, 8-Flange ring, 9-Loading rod, 10-Loading rod support base, 11-Strain gauge, 12-Heating chamber support base, 20-Lighting lamp, 21-High-speed camera, 22-Box cover shell, 23-Box shell, 24-Thermocouple controller, 25-Glass, 26-Spray head, 27-Hinge, 28-Protective frame, 29-Bolt, 30-Temperature sensor, 31-Drain outlet, 32-Upper insulation layer, 33-Lower insulation layer, 34-Upper heating layer, 35-Lower heating layer, 36-Upper explosion-proof layer, 37-Thermocouple, 38-Lower explosion-proof layer, 39-Test specimen, 40-Flow rate regulating valve, 41-Flow rate gauge, 42-Water tank, 43-Water pump.

[0030] Figure 1-7This invention illustrates a testing apparatus for the compressive strength of concrete. The apparatus includes a support platform 1, a testing mechanism disposed in the middle of the support platform 1, servo-controlled loading mechanisms disposed on both sides of the support platform 1 with one end placed inside the testing mechanism, and electromagnetic pulse transmitting mechanisms disposed on both sides of the support platform 1 and mounted on the two servo-controlled loading mechanisms. This testing apparatus incorporates electromagnetic pulse transmitting mechanisms for dynamic electromagnetic pulse loading, servo-controlled loading mechanisms for static servo-controlled loading, and testing mechanisms for heating and spraying the test specimen 39 to provide static and dynamic (10) tests for concrete or other rock-like materials cooled by water at different temperatures. 1 s -1 ~10 2 s -1 Combined loads are used to obtain data such as the failure strength and deformation modulus of the high-temperature test specimen 39 under dynamic and static combined compressive loads when it is cooled by water or after being cooled by water. Then, by combining the methods of data acquisition and monitoring institutions, the dynamic response and failure law of concrete or other types of rock materials under high temperature and water cooling are analyzed, which provides a theoretical basis and technical support for the fire protection design of actual building structures and the engineering safety analysis in fire fighting scenarios.

[0031] Figure 3 , 4Figures 5 and 7 show that the testing mechanism includes a heating chamber support base 12 mounted on the support platform 1 and movable relative to the support platform 1, and a heating chamber mounted on the heating chamber support base 12. The heating chamber includes a chamber body with heating function, consisting of a chamber shell 23, a lower insulation layer 33, a lower heating layer 35, and a lower explosion-proof layer 38 from the outside to the inside, and a chamber cover with heating function hinged to the chamber body by hinge 27, consisting of a chamber cover shell 22, an upper insulation layer 32, an upper heating layer 34, and an upper explosion-proof layer 36 from the outside to the inside. Viewing windows are provided on the front and rear sides of the chamber body, reserved through holes are provided on the left and right sides of the chamber body, a drain outlet 31 is provided at the bottom of the chamber body, and a spray unit is provided on the chamber cover. The spray unit includes at least one spray head 26 disposed on the cover and penetrating the cover, and a flow rate regulating valve 40, a flow rate gauge 41, a water pump 42 and a water tank 43 connected in sequence to the spray head 26 via pipes; the lower heating layer 35 and the upper heating layer 34 are both made of thermally conductive material, and thermocouples 37 are pre-installed therein; the viewing window includes a protective frame 28 disposed on the box body, and a glass 25 disposed on the protective frame 28, the protective frame 28 and the glass 25 being fixed to the box body by bolts 29. The heating chamber support base 12 is located in the middle of the support platform 1. The servo-controlled loading mechanisms on both sides are symmetrically arranged around the heating chamber support base 12. The heating chamber support base 12 can be moved left and right along the axis of the support platform 1 and can be fixed in the required position. The heating layer is used to evenly transfer heat into the heating chamber. The explosion-proof layer is made of a high-hardness metal and protects the heating layer in case the test specimen 39 is damaged. The viewing window is used to observe the test specimen 39 during the test. The drain outlet 31 is used to drain the sprayed water. The reserved through hole allows the servo-controlled loading mechanisms on both sides to apply a certain axial pressure to the test specimen 39 and fix it in place. The heating chamber is located in the middle, and the thermocouple 37 is controlled by an external thermocouple controller 24 connected by wires. When the temperature is applied, the power of the thermocouple 37 is adjusted by operating the thermocouple controller 24 to heat the test sample 39 at the target rate. At the same time, the heating layer can also play a role in heat preservation. The water pump 43 in the spray unit provides the power required for water flow. The flow rate meter 41 displays the speed of the sprayed water flow. The spray head 26 is a metal spray head, and the spray speed of the water flow from the spray head 26 can be adjusted by the flow rate regulating valve 40. During cooling, the test sample 39 is cooled by spraying water through the spray unit, thereby realizing the heating and cooling of the test sample 39.

[0032] Figure 1 , 2The servo-controlled loading mechanism is shown to include a hydraulic cylinder support base 2 mounted on the support platform 1 and movable relative to the support platform 1, a servo-controlled loading cylinder 3 mounted on the hydraulic cylinder support base 2, a hydraulic piston rod 4 mounted on the servo-controlled loading cylinder 3, a static loading frame 5 connected to the hydraulic piston rod 4, a loading rod support base 10 mounted on the support platform 1 and movable relative to the support platform 1, a loading rod 9 mounted on the loading rod support base 10 with one end placed inside the test mechanism and the other end placed inside the static loading frame 5, and a flange ring 8 mounted on the loading rod 9 with its end face in contact with the static loading frame 5. The loading rod 9 is a TC21 titanium alloy loading rod with a length of 2000 mm and a diameter of 50 mm. In the servo-controlled loading mechanism on both sides, the servo-controlled loading cylinder 3 is fixed on the cylinder support base 2. The hydraulic piston rod 4 is the hydraulic actuation mechanism of the servo-controlled loading cylinder 3. Its end face is in free contact with the end face of the static loading frame 5. A flange ring 8 is provided near the end face of the static loading frame 5 on the hydraulic piston rod 4. The flange ring 8 is fixed on the loading rod 9 and plays the role of transmitting static load. The end face of the static loading frame 5 and the end face of the flange ring 8 are in free contact. When the servo-controlled loading mechanism on both sides is working, the servo-controlled loading cylinder 3 applies hydraulic driving force to the hydraulic piston rod 4, driving the hydraulic piston rod 4 to produce inward displacement, and applying static load to the static loading frame 5. The servo-controlled loading cylinder 3 transmits the load to the test specimen 39 in sequence through the hydraulic piston rod 4, the static loading frame 5, the flange ring 8 and the loading rod 9 to achieve static loading on both sides.

[0033] Figure 1 , 2 Figure 6 shows that the electromagnetic pulse transmitting mechanism includes an electromagnetic pulse support base 6 disposed on the support platform 1 and movable relative to the support platform 1, and an electromagnetic pulse excitation cavity 7 disposed on the electromagnetic pulse support base 6 with its transmitting end in contact with the loading rod 9. Both sides of the electromagnetic pulse transmitting mechanism include an electromagnetic pulse support base 6 and an electromagnetic pulse excitation cavity 7 placed thereon. The transmitting end faces of the electromagnetic pulse excitation cavities 7 on both sides are in close contact with the end faces of the loading rods 9 on both sides. During dynamic loading, the transmitting end faces of the electromagnetic pulse excitation cavities 7 on both sides excite and output the load. The load is transmitted to the loading rod 9 in the form of a stress wave via the end face of the loading rod 9. Subsequently, the incident stress wave propagates along the axial direction of the loading rod 9 to the test specimen 39, achieving dynamic loading.

[0034] Figure 1The experimental apparatus also includes a data acquisition mechanism mounted on the testing mechanism and the servo-controlled loading mechanism, and a monitoring mechanism mounted outside the testing mechanism. The data acquisition mechanism includes strain gauges 11 mounted on both sides of the servo-controlled loading mechanism for collecting strain signals, a temperature sensor 30 mounted on the testing mechanism for collecting the internal temperature of the testing mechanism, and a synchronous high-speed recorder (not shown) connected to the strain gauges 11 and the temperature sensor 30 for data recording and storage. The monitoring mechanism includes a high-speed camera 21 for monitoring the entire process of sample cracking and failure, and at least one illumination lamp 20 used in conjunction with the high-speed camera 21. Two strain gauges 11 are respectively attached to the middle surface of the loading rods 9 on both sides. During dynamic loading, stress waves will propagate in the loading rods 9 on both sides and generate strain. The strain gauges 11 are used to collect the strain signal at their location and transmit it to the synchronous high-speed recorder for recording and storage via shielded wires. The temperature sensor 30 is installed in the temperature sensor reserved channel of the heating box and is used to collect and output the temperature information inside the heating box. The high-speed camera 21 is axially positioned facing the center of the front window of the heating box, and lighting lamps 20 are placed on both sides to illuminate the test specimen 39. The lighting lamps 20, together with the high-speed camera 21, are used to monitor and transmit images of the entire cracking and failure process of the test specimen 39.

[0035] A method for testing the compressive strength of concrete, the method comprising the following steps:

[0036] Step S1: Install the test specimen in the test mechanism and control the servo control loading mechanism on both sides to apply a static preload of 20MPa to the test specimen. Wait until the static preload reaches the set value and remains stable.

[0037] Step S2: Control the testing mechanism to heat the test sample, stop heating when the temperature reaches the target temperature of 400℃, and maintain this temperature for at least 30 minutes;

[0038] Step S3: Control the testing mechanism to spray the test specimen, and control the electromagnetic pulse emission mechanisms on both sides to apply a half-sine incident stress wave with an amplitude of 300MPa and a duration of 200μs to the test specimen. The dynamic load is excited and output by the right end face of the electromagnetic pulse emission mechanisms on both sides. The dynamic load is transmitted to the test specimen in the form of stress wave through the loading rods on both sides to apply dynamic compressive load.

[0039] Step S4: During dynamic loading, when the dynamic load error of the two loading rods monitored by the strain gauges on both sides is less than the acceptable error range of the test, the test specimen is considered to have reached a dynamic stress equilibrium state during dynamic loading. According to the one-dimensional stress wave theory, the dynamic compressive strength σ of the test specimen during loading can be solved by the incident wave, reflected wave, and transmitted wave signals collected by the strain gauges on the loading rods according to the following formula:

[0040]

[0041] Where, ε 左透射 and ε 右透射 A represents the transmitted wave strain signal collected by the strain gauges on both sides; A and E represent the cross-sectional area and elastic modulus of the hydraulic loading rod, respectively; F represents the load output by the servo-controlled loading cylinder; and A0 represents the cross-sectional area of ​​the test specimen.

[0042] Example 1

[0043] First, install the servo-controlled loading mechanisms on both sides: Install the loading rod support base 10, electromagnetic pulse support base 6, and hydraulic cylinder support base 2 of the servo-controlled loading mechanisms on the support platform 1, symmetrically from the center to both ends, with the heating box support base 12 as the center. Fix the servo-controlled loading cylinders 3 and their hydraulic piston rods 4 on the hydraulic cylinder support base 2. Place the static loading frame 5 inside the hydraulic piston rod 4, with one end face of the static loading frame 5 freely contacting one end face of the hydraulic piston rod 4. Place the electromagnetic pulse support base 6 inside the static loading frame 5. Install the electromagnetic pulse excitation chamber 7 on the electromagnetic pulse support base 6. Place a 2000mm long, 50mm diameter TC21 titanium alloy loading rod parallel to the axial direction of the support platform 1 on the loading... On the rod support base 10, one end of the loading rod 9 extends into the interior of the static loading frame 5 through a pre-drilled through hole on the surface of the static loading frame 5, so that the end face of the flange ring 8 is in free contact with the end face of the static loading frame 5, and at the same time, the emitting end face of the electromagnetic pulse excitation cavity 7 is in free contact with the end face of the loading rod 9. Next, the test mechanism is installed: the heating box is installed on the heating box support base 12, so that the loading rods 9 on both sides pass through the reserved through holes into the heating box, and the loading rods 9 on both sides pass through the reserved through holes on both sides into the heating box. The water spray head 26 fixed on the upper part of the heating box cover is connected to the flow rate regulating valve 40, flow rate gauge 41, water pump 43, and water tank 42 in sequence through pipes. The thermocouple 37 in the heating box is connected to the thermocouple controller 24 and the power supply through wires. After the installation of the testing mechanism is completed, the data acquisition mechanism and the monitoring mechanism are connected: two strain gauges 11 are respectively attached to the middle surface of the loading rods 9 on both sides, the temperature sensor 30 is fixed in the heating box, the high-speed camera 21 is placed in the axial direction facing the center of the front window of the heating box, and the lighting lamps 20 are placed on both sides to illuminate the window. The high-speed camera 21 and the strain gauges 11 on both sides are connected to the synchronous high-speed recorder through shielded wires.

[0044] The installation of the testing apparatus is now complete, allowing for the heating, cooling, and loading of the test specimen 39. The concrete test specimen 39, with a height of 50 mm and a diameter of 50 mm, is clamped along its length between the two loading rods 9. After the testing apparatus is leveled and aligned to ensure that the test specimen 39 is collinear with the axes of other loading mechanisms, the servo-controlled hydraulic cylinders 3 on both sides are activated to apply a static preload of 20 MPa to the test specimen 39. The servo-controlled loading cylinders 3 on both sides apply hydraulic driving force to the hydraulic piston rod 4 and the static loading frame 5. The static pressure is transmitted to the test specimen 39 through the flange ring 8 and the loading rods 9, thus achieving static loading of the test specimen 39.

[0045] After the static preload reaches the set value and remains stable, the thermocouple controller 24 is controlled to heat the test specimen 39 with the thermocouple 37. The temperature is controlled by the heating chamber temperature information from the temperature sensor 30. When the temperature reaches the target temperature of 400℃, the heating is stopped. The heating chamber is maintained at this temperature by adjusting the thermocouple controller 24. After maintaining this temperature for at least 30 minutes, the flow rate regulating valve 40 is opened, and the water pump 43 is started to pump the water in the water tank 42 to the spray head 26 and finally spray it onto the test specimen 39. Then, the electromagnetic pulse excitation chambers 7 on both sides are controlled to simultaneously apply a half-sine incident stress wave with an amplitude of 300MPa and a duration of 200μs to the test specimen 39. The dynamic load is excited and output by the emitting end face of the electromagnetic pulse excitation chamber 7. The dynamic load is transmitted to the test specimen 39 in the form of stress wave through the loading rod 9 to perform dynamic compression load loading. This realizes the dynamic and static combined compression test of the high temperature concrete specimen when it is cooled by water in a simulated fire fighting scenario.

[0046] During dynamic loading, when the dynamic load error of the two loading rods 9 monitored by the strain gauges 11 at both ends is less than the acceptable error range of the test (e.g., 5%), it can be regarded that the test specimen 39 has reached a dynamic stress equilibrium state during dynamic loading. According to the one-dimensional stress wave theory, the dynamic compressive strength σ of the test specimen 39 during loading can be obtained by the following formula from the incident wave, reflected wave and transmitted wave signals collected by the strain gauges 11 on the loading rod 9.

[0047]

[0048] Where, ε 左透射 and ε 右透射 These are the transmitted wave strain signals collected by strain gauges 11 on both sides; A and E are the cross-sectional areas of the loading rod 9 (1963.5 mm²). 2 The modulus of elasticity is 107.8 GPa; F is the load output by the servo-controlled loading cylinder 3 (20 MPa); A0 is the cross-sectional area of ​​the test specimen 39 (1963.5 mm²). 2 ).

[0049] Example 2

[0050] Based on Example 1, the test apparatus is installed to heat, cool, and load the test specimen 39. The concrete test specimen 39, with a height of 50 mm and a diameter of 50 mm, is clamped along its length between the two loading rods 9. After the test device is leveled and aligned to ensure that the test specimen 39 is collinear with the axes of other loading mechanisms, the thermocouple controller 24 is controlled to heat the test specimen 39 with the thermocouple 37. The temperature is controlled by the temperature information of the heating chamber from the temperature sensor 30. When the temperature reaches the target temperature of 300℃, the heating is stopped. The temperature of the heating chamber is maintained by adjusting the thermocouple controller 24. After maintaining the temperature for 30 minutes, the flow rate regulating valve 40 is opened and the water pump 43 is started to pump the water in the water tank 42 to the water spray head 26 and finally spray it onto the test specimen 39. Then, the electromagnetic pulse excitation cavities 7 on both sides are controlled to synchronously apply a half-sine incident stress wave with an amplitude of 400MPa and a duration of 200μs to the test specimen 39. The dynamic load is excited and output by the emitting end face of the electromagnetic pulse excitation cavity 7. The dynamic load is transmitted to the test specimen 39 in the form of stress wave through the loading rod 9 to perform dynamic compression load loading. This realizes the dynamic compression test of the high temperature concrete specimen when it is cooled by water in a simulated fire fighting scenario.

[0051] During dynamic loading, when the dynamic load error of the two loading rods 9 monitored by the strain gauges 11 at both ends is less than the acceptable error range of the test (e.g., 5%), it can be considered that the test specimen 39 has reached a dynamic stress equilibrium state during the dynamic loading process. According to the one-dimensional stress wave theory, the dynamic compressive strength σ of the test specimen 39 during the loading process can be solved by the following formula based on the incident wave, reflected wave, and transmitted wave signals collected by the strain gauges 11 on the loading rod 9.

[0052]

[0053] Where, ε 左透射 and ε 右透射 These are the transmitted wave strain signals collected by strain gauges 11 on both sides; A and E are the cross-sectional areas of the loading rod 9 (1963.5 mm²). 2 The elastic modulus (107.8 GPa) is given by A0; A0 is the cross-sectional area of ​​test specimen 39 (1963.5 mm²). 2 ).

[0054] This testing apparatus can simultaneously heat and / or cool the specimen with a combination of dynamic and static loading. It incorporates a dynamic-static combined servo-controlled loading mechanism and heating and spraying units. Before and during the dynamic-static combined impact test, it can control the simultaneous or separate heating and cooling of the specimen. Existing technologies, when studying the performance of high-temperature concrete under water-cooling conditions, require separating the heating and cooling processes in two separate devices, loading the high-temperature cooled specimen after temperature treatment. This apparatus can simulate the simultaneous heating and water cooling of high-temperature concrete materials during firefighting, filling the technical gap in existing devices that cannot conduct dynamic-static combined compressive performance tests where specimens are simultaneously heated and cooled. The electromagnetic pulse emission mechanism provides dynamic compressive loads to the specimen, not only precisely controlling and adjusting the amplitude and pulse width of the incident stress wave, but also generating highly repeatable incident stress waves. This overcomes the technical deficiency of existing equipment that relies on mechanical impact to generate incident stress waves with difficulty in repeating and accurately producing fixed-characteristic incident waves. Furthermore, the bidirectional electromagnetic pulse emission mechanism can simultaneously provide loads from both sides of the test specimen. A dynamic compressive load with the same incident stress wave amplitude and height ensures stress balance on both sides of the specimen throughout the dynamic loading process, guaranteeing the accuracy and validity of the test data. During the test, the concrete specimen is placed in the testing mechanism of the testing device for impact compression testing. The testing mechanism is equipped with a transparent glass window, which allows for real-time observation and recording of the dynamic strain field evolution, crack propagation, and specimen failure process on the side of the specimen during the impact process through monitoring methods such as high-speed cameras. This facilitates a more comprehensive study of the impact compression failure process of concrete or other solid material specimens. The device can also perform combined static and dynamic compressive loads on the specimen. The loading mechanism includes two independent loading mechanisms: a servo-controlled static loading mechanism and an electromagnetic pulse stress wave dynamic loading mechanism. During the test, the two mechanisms can be independently controlled to load the specimen separately. This simulates the situation in firefighting scenarios where concrete materials are subjected to the self-weight load of the building structure, as well as the impact load generated by surrounding structures or objects during a fire. This prevents potential secondary damage to the structure and allows for testing the compressive performance of concrete materials under combined static and dynamic loading.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A testing apparatus for the compressive strength of concrete, characterized in that, The test apparatus includes a support platform, a test mechanism disposed in the middle of the support platform, servo-controlled loading mechanisms disposed on both sides of the support platform with one end placed inside the test mechanism, and electromagnetic pulse transmitting mechanisms disposed on both sides of the support platform and placed on the two servo-controlled loading mechanisms respectively. The test mechanism includes a heating chamber support base disposed on the support platform and movable relative to the support platform, and a heating chamber disposed on the heating chamber support base. The heating chamber includes a chamber body with heating function, consisting of a chamber shell, a lower insulation layer, a lower heating layer, and a lower explosion-proof layer from the outside to the inside, and a chamber cover with heating function hinged to the chamber body, consisting of a chamber cover shell, an upper insulation layer, an upper heating layer, and an upper explosion-proof layer from the outside to the inside. The chamber body has viewing windows on the front and rear sides, reserved through holes on the left and right sides, a drain outlet at the bottom of the chamber body, and a spray unit on the chamber cover. The spray unit includes at least one water nozzle disposed on the chamber cover and penetrating the chamber cover, and connected in sequence by pipes. The spray head includes a flow rate regulating valve, a flow rate gauge, a water pump, and a water tank; both the lower heating layer and the upper heating layer are made of thermally conductive materials and have thermocouples pre-installed within them; the viewing window includes a protective frame mounted on the housing and glass mounted on the protective frame; the servo-controlled loading mechanism includes a hydraulic cylinder support base mounted on the support platform and movable relative to the support platform, a servo-controlled loading cylinder mounted on the hydraulic cylinder support base, a hydraulic piston rod mounted on the servo-controlled loading cylinder, a static loading frame connected to the hydraulic piston rod, a loading rod support base mounted on the support platform and movable relative to the support platform, a loading rod mounted on the loading rod support base with one end inside the test mechanism and the other end inside the static loading frame, and a flange ring mounted on the loading rod with its end face contacting the static loading frame; the test device also includes a data acquisition mechanism mounted on the test mechanism and the servo-controlled loading mechanism, and a monitoring mechanism mounted outside the test mechanism.

2. The experimental apparatus according to claim 1, characterized in that, The electromagnetic pulse transmitting mechanism includes an electromagnetic pulse support base disposed on the support platform and movable relative to the support platform, and an electromagnetic pulse excitation cavity disposed on the electromagnetic pulse support base and having its transmitting end in contact with the loading rod.

3. The experimental apparatus according to claim 2, characterized in that, The data acquisition mechanism includes strain gauges mounted on the servo-controlled loading mechanisms on both sides for collecting strain signals, a temperature sensor mounted on the testing mechanism for collecting the internal temperature of the testing mechanism, and a synchronous high-speed recorder connecting the strain gauges and the temperature sensor for data recording and storage; the monitoring mechanism includes a high-speed camera for monitoring the entire process of sample cracking and failure, and at least one lighting lamp used in conjunction with the high-speed camera; the loading rod is a TC21 titanium alloy loading rod.

4. A method for testing the compressive strength of concrete, comprising using the apparatus as described in claim 3, characterized in that, The testing method includes the following steps: Step S1: Install the test specimen in the test mechanism and control the servo control loading mechanism on both sides to apply a static preload of 20MPa to the test specimen. Wait until the static preload reaches the set value and remains stable. Step S2: Control the testing mechanism to heat the test sample, stop heating when the temperature reaches the target temperature of 400℃, and maintain this temperature for at least 30 minutes; Step S3: Control the testing mechanism to spray the test specimen, and control the electromagnetic pulse emission mechanisms on both sides to apply a half-sine incident stress wave with an amplitude of 300MPa and a duration of 200μs to the test specimen. The dynamic load is excited and output by the right end face of the electromagnetic pulse emission mechanisms on both sides. The dynamic load is transmitted to the test specimen in the form of stress wave through the loading rods on both sides to apply dynamic compressive load. Step S4: During dynamic loading, when the dynamic load error of the two loading rods monitored by the strain gauges on both sides is less than the acceptable error range of the test, the test specimen is considered to have reached a dynamic stress equilibrium state during dynamic loading. According to the one-dimensional stress wave theory, the dynamic compressive strength σ of the test specimen during loading can be solved by the incident wave, reflected wave, and transmitted wave signals collected by the strain gauges on the loading rods according to the following formula: Where, ε 左透射 and ε 右透射 A and E are the transmitted wave strain signals collected by the strain gauges on both sides; A and E are the cross-sectional area and elastic modulus of the loading rods on both sides, respectively; F is the load output by the servo-controlled loading cylinder. A0 is the cross-sectional area of ​​the test specimen.

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