A rebound hammer for non-destructive testing of UHPC compressive strength

Abstract

This utility model discloses a rebound hammer for non-destructive testing of UHPC compressive strength, belonging to the field of concrete engineering testing technology. It includes a hollow shell, an impact rod, an impact hammer, an impact spring, a guide rod, a hook assembly, and a switch. The impact rod is telescopically connected to one end of the shell. One end of the impact spring is fixed, and the other end is connected to the impact hammer. Both the impact hammer and the hook assembly are slidably connected to the guide rod. The hook assembly can slide along the guide rod and engage with the impact hammer. The switch controls the release of the impact hammer by the hook assembly. The free length of the impact spring is 134.4±0.5mm, and the impact length after stretching is 140.0±0.5mm. The wire diameter of the impact spring is greater than 1.5mm. The UHPC compressive strength regression equation is: ; the value of c ranges from -0.001 to -0.004, where is the average rebound value of the test area or specimen, is the average carbonation depth of the test area, and is the converted value of concrete strength in MPa. This enables non-destructive testing of the compressive strength of UHPC.

Description

Technical Field

[0001] This utility model relates to the field of concrete engineering testing technology, specifically to a UHPC compressive strength non-destructive testing rebound hammer. Background Technology

[0002] Concrete is a composite building material composed of cement, aggregates, water, and other materials, and it is the most widely used material in the construction engineering field. Concrete structural strength testing is a key technical means to ensure building safety, assess building durability, and guide construction decisions. Currently, concrete compressive strength testing methods are mainly divided into two categories: destructive testing and non-destructive testing, each with different application scenarios.

[0003] Destructive testing methods mainly include core drilling and standard block testing. Core drilling involves drilling cylindrical core samples from hardened concrete structures for strength testing. While this method provides relatively accurate strength data, it causes irreversible damage to the structure, potentially introducing cracks or stress concentrations, and thus reducing the structure's service performance. Standard block testing has limitations such as a limited number of test blocks and insufficient sample representativeness. Furthermore, the compaction and hardening conditions of the test blocks often differ from the actual structure, making it difficult to comprehensively reflect the overall strength status of the structure. In addition, destructive testing methods cannot effectively assess existing structures when concrete quality is questionable or when signs of structural deterioration appear.

[0004] In comparison, non-destructive testing (NDT) technology offers significant advantages by allowing for large-scale, multi-point strength assessments while maintaining structural integrity. NDT can rapidly evaluate concrete quality, providing timely feedback for engineering quality control, and also enables regular monitoring of existing structures to understand their performance evolution. From a techno-economic perspective, NDT is more economical and efficient than traditional destructive testing, significantly reducing testing costs and greatly improving testing efficiency.

[0005] Among existing non-destructive testing methods, the rebound hammer is the most widely used. Based on the mechanical principle that the degree of rebound of an elastic object is related to its surface hardness, the rebound hammer establishes a correlation with concrete strength by measuring the rebound height of a spring-driven hammer. The rebound hammer is characterized by its portability, ease of operation, rapid testing, and low cost. It can effectively assess concrete homogeneity, identify areas of insufficient strength, and provide a basis for further testing. Furthermore, the rebound hammer can reveal areas of inconsistent concrete quality, estimate in-situ compressive strength, and isolate areas damaged by environmental factors.

[0006] Based on the ultra-high strength and excellent durability of ultra-high performance concrete (UHPC), UHPC has shown great application potential in bridge engineering, precast components, marine engineering and other fields. The application of UHPC can significantly reduce the cross-sectional size of the structure, leave more usable space, reduce the self-weight of the building, and at the same time, its dense microstructure effectively blocks external penetration, significantly enhancing durability. However, the existing rebound hammer design is mainly for conventional strength concrete, and its application scope is limited to concrete with a compressive strength of less than 110MPa. When testing UHPC (compressive strength ≥120MPa), the following problems exist: (1) The hardness of UHPC is significantly higher than that of conventional concrete, which makes it difficult for the impact kinetic energy and spherical radius of the existing rebound hammer to produce sufficient deformation and energy absorption of the sample, thus failing to accurately reflect the actual mechanical properties of UHPC; (2) For the testing of conventional concrete, the small errors of the spring and spherical parameters of the existing rebound hammer affect the test results. The impact is negligible; however, for UHPC, parameters with smaller tolerances are required to ensure that data fluctuations are minimized and that the measurement results have scientific reference value. (3) Due to the ultra-high hardness of UHPC, the rebound value is significantly increased, which puts forward higher hardness requirements for the rebound hammer, impact rod and impact ball of the rebound hammer in order to achieve smaller plastic deformation and longer service life. (4) Due to the small energy absorption of UHPC, higher measurement standards are required to achieve smaller operating errors. However, existing rebound hammers lack auxiliary tools to limit operating errors, which affects the reliability of measurement data. Therefore, a rebound hammer for non-destructive testing of compressive strength of UHPC is needed. Utility Model Content

[0007] The purpose of this invention is to provide a rebound hammer for non-destructive testing of UHPC compressive strength, which solves the problems of low accuracy and high difficulty in operation of existing rebound hammers for measuring UHPC.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this utility model is as follows:

[0009] A UHPC compressive strength non-destructive testing rebound hammer includes a hollow shell, an impact rod, an impact hammer, an impact spring, a guide rod, a hook assembly, and a switch. The impact rod is telescopically connected to one end of the shell. One end of the impact spring is fixed, and the other end is connected to the impact hammer. The impact hammer and the hook assembly are both slidably connected to the guide rod. The hook assembly can slide along the guide rod and engage with the impact hammer. The switch is used to control the hook assembly to release the impact hammer. The impact kinetic energy on the impact rod is not less than 9.8J. The free length of the impact spring is 134.4±0.5mm, the impact length after tension is 140.0±0.5mm, and the stiffness is 1000±20N / m. The spring wire diameter of the impact spring is greater than 1.5mm to stably output sufficient impact energy, enabling rapid strength testing of concrete in the C120~C160 grade range.

[0010] Furthermore, it also includes a balance support, which is detachably connected to the housing. The balance support includes a sleeve, a balance spring, at least three legs, and a retaining ring. The sleeve has a groove on its outward-facing end, the balance spring is disposed in the groove, the at least three legs are slidably connected in the groove, and the retaining ring is disposed at the opening of the groove, and the retaining ring has at least three notches. Each leg is pushed outward through the notch by the balance spring. UHPC compressive strength regression equation:

[0011] ;

[0012] Wherein, the value of 'a' ranges from 0.4500 to 0.5000 (MPa), the value of 'b' ranges from 1.255 to 1.275 (dimensionless), and the value of 'c' ranges from -0.001 to -0.004 (mm). -1 ), The average rebound value (dimensionless) of the test area or test block. The average carbonization depth (mm) of the survey area. The value is a conversion of concrete strength in MPa. By increasing the kinetic energy on the impact rod and improving the stability of the shell, the compressive strength of UHPC can be tested. It is easy to use and has low measurement cost.

[0013] Furthermore, the inner wall of the sleeve is provided with an internal thread, and the outer wall of one end of the housing is provided with an external thread. The balance support is helically connected to the housing by the external thread and the internal thread, making it convenient to carry to the field for use.

[0014] Preferably, the device also includes an indicator and a scale. The indicator is slidably connected to the inner wall of the housing and can engage with the hammer in one direction. The scale is located on the outer wall of the housing and is used to measure the maximum rebound height of the hammer, thereby converting and reading the intensity value.

[0015] As an even better option, a reset spring and a limiting post are also included. The reset spring is located at the top inside the housing and is used to push the hook assembly to reset and return the indicator to its initial position. The limiting post is located in the middle of the reset spring and is used to limit the maximum stroke of the hammer and the hook assembly, ensuring that the preset position during measurement is accurate and controllable.

[0016] As an even better option, a buffer spring is also included, which is disposed inside the impact rod to buffer the impact force received by the rebound device and prevent the rebound value from fluctuating.

[0017] Furthermore, it also includes an anti-slip layer, which is disposed on the outer side wall of the housing. The anti-slip layer has a grip area that matches the palm of the hand, improving the comfort of use and making it suitable for repeated measurements.

[0018] Preferably, the balance support further includes a stop block, which is disposed in the groove near the opening of the groove, and the stop block pre-compresses the balance spring to prevent the support leg from wobbling in the groove.

[0019] As a better fit, the end face of the retaining ring is provided with a protrusion that extends into the groove to ensure the stability of the sliding of the support leg.

[0020] Furthermore, the hardness of the collision surface between the impact rod and the impact hammer is not less than HRC 65±2, the top of the impact rod is provided with an impact spherical surface, the hardness of the impact spherical surface is not less than HRC 70±2, which is much greater than the surface hardness of the specimen, and the measurement results are more accurate. The radius of the impact spherical surface is not greater than 30mm.

[0021] The beneficial effects of this utility model are as follows:

[0022] (1) The impact spring of the UHPC compressive strength non-destructive testing rebound tester can store an impact energy of not less than 9.8J for impacting the surface of the UHPC specimen. The radius of the impact sphere is limited, and the curvature radius design is limited to ensure that the surface of the UHPC specimen can generate sufficient deformation and energy absorption, thereby accurately reflecting its actual mechanical properties.

[0023] (2) The parameters of the impact spring and the spherical radius of the UHPC compressive strength non-destructive testing rebound hammer adopt smaller tolerance control requirements, which reduces the influence of parameter fluctuation on the measurement data and improves the reliability of the measurement data.

[0024] (3) The impact surface hardness of the impact rod and impact hammer of the UHPC compressive strength non-destructive testing rebound hammer is significantly higher than that of the existing rebound hammer, and the hardness of the impact ball surface is much higher than that of the UHPC specimen surface. This reduces the impact of the deformation of the rebound hammer components during repeated impacts on the measurement data, improves the measurement stability, and extends the service life of the equipment.

[0025] (4) The UHPC compressive strength non-destructive testing rebound hammer is equipped with a balance support on the shell. When using the rebound hammer, the balance support contacts the surface of the specimen, so that the impact rod on the rebound hammer can remain perpendicular to the surface of the specimen. This can achieve adaptive contact with the surface of the specimen, eliminate the fluctuation of the rebound value caused by the deviation of the operating posture, and significantly improve the reliability of the testing of ultra-high hardness materials. The three legs together determine a plane, and the difference between the specimen surface and the impact ball surface is compensated by the balance spring, which has strong applicability.

[0026] (5) The UHPC compressive strength non-destructive testing rebound instrument has an anti-slip layer on the outer wall of the shell. The anti-slip layer is made of a flexible high-friction material, and the grip area is suitable for hand operation, which reduces the difficulty of use. The anti-slip layer, together with the buffer spring that plays a buffering and energy absorption role, ensures the operational stability of high-intensity testing operations and reduces the fatigue intensity of the operator, making the equipment more adaptable to the continuous testing needs of complex engineering sites. Attached Figure Description

[0027] Figure 1 This is an assembly diagram of the UHPC compressive strength non-destructive testing rebound hammer and balance support provided by this utility model;

[0028] Figure 2 A cross-sectional structural diagram of the UHPC compressive strength non-destructive testing rebound hammer provided by this utility model;

[0029] Figure 3 A cross-sectional structural diagram of the balance support provided by this utility model;

[0030] Figure 4 The end face structure diagram of the balance support provided by this utility model.

[0031] Figure label:

[0032] 1. Housing; 2. Strike rod; 3. Strike spherical surface; 4. Strike tension spring; 5. Strike hammer; 51. Guide rod; 52. Indicator; 53. Scale line; 6. Hook assembly; 61. Return spring; 62. Limiting post; 7. Switch; 8. External thread; 9. Anti-slip layer; 101. Balance support; 10. Sleeve; 11. Protrusion; 12. Internal thread; 13. Balance spring; 14. Groove; 15. Stop block; 16. Retaining ring; 17. Support leg; 102. Buffer spring. Detailed Implementation

[0033] 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 in the application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present utility model.

[0034] like Figures 1-4 As shown, this embodiment discloses a UHPC compressive strength non-destructive testing rebound hammer, including a hollow shell 1, an impact rod 2, an impact hammer 5, an impact spring 4, a guide rod 51, a hook assembly 6, and a switch 7. One end of the shell 1 has an opening. The impact rod 2 is telescopically connected to one end of the shell 1 and can extend from the opening. One end of the impact spring 4 is fixed, and the other end is connected to the impact hammer 5. The guide rod 51 is axially arranged within the shell 1. The impact hammer 5 and the hook assembly 6 are both slidably connected to the guide rod 51. The hook assembly 6 can slide along the guide rod 51 and engage with the impact hammer 5. After being used for impact, the switch 7 is used to control the hook assembly 6 to release the impact hammer 5. The impact kinetic energy on the impact rod 2 is not less than 9.8J, preferably 9.8J, 9.9J, 10.0J and 10.1J. The free length of the impact spring 4 is 134.4±0.5mm, the impact length after stretching is 140.0±0.5mm, the stiffness is 1000±20N / m, and the wire diameter of the impact spring 4 is greater than 1.5mm, preferably 1.5mm, 1.6mm, 1.7mm and 1.8mm, to ensure a stable output of sufficient impact energy.

[0035] The regression equation for the compressive strength of UHPC was also obtained as follows: Where 'a' ranges from 0.4500 to 0.5000 (MPa), 'b' ranges from 1.255 to 1.275 (dimensionless), and 'c' ranges from -0.001 to -0.004 (mm). -1 ), The average rebound value (dimensionless) of the test area or test block. The average carbonation depth (mm) of the test area allows for rapid strength testing of concrete in the C120~C160 grade range.

[0036] Furthermore, it also includes a balance support 101, which is detachably connected to the housing 1 and has one end facing outwards. The balance support 101 includes a sleeve 10, a balance spring 13, at least three legs 17, and a retaining ring 16. The sleeve 10 has a groove 14 on its outward-facing end, and the balance spring 13 is disposed in the groove 14. The at least three legs 17 are slidably connected in the groove 14, with one end of each leg 17 abutting against the balance spring 13 and the other end facing outwards from the sleeve 10. The retaining ring 16 is disposed at the opening of the groove 14 and has at least three notches. Each leg 17 is pushed outwards through the notch by the balance spring 13, realizing the individual extension and retraction of the leg 17. The three legs 17 are axially balanced with the housing 1. By having the legs 17 contact the surface of the specimen first, it can be ensured that the impact rod 2 is perpendicular to the surface of the specimen, reducing operational errors and improving measurement accuracy. This allows the impact hammer 5 to transfer more energy to the impact rod 2, thereby expanding the application range of the rebound hammer.

[0037] Among them, at least three legs 17 are evenly distributed around the axis of the shell 1.

[0038] Furthermore, the inner wall of the sleeve 10 is provided with an internal thread 12, and the outer wall of one end of the housing 1 is provided with an external thread 8. The balance support 101 is helically connected to the housing 1 by the external thread 8 and the internal thread 12, so as to achieve a detachable connection. When measuring UHPC with lower strength, the balance support 101 can be removed to reduce the overall weight and make manual operation more convenient.

[0039] Preferably, it also includes an indicator 52 and a scale line 53. The indicator 52 is slidably connected to the inner wall of the housing 1 and can be engaged with the striking hammer 5 in one direction. The scale line 53 is set on the outer wall of the housing 1. The indicator 52 is engaged when the striking hammer 5 rebounds. The striking hammer 5 drives the indicator 52 to move upward. When the indicator 52 moves to the highest position of the scale line 53, the surface strength reading of the specimen can be read.

[0040] Preferably, it also includes a reset spring 61 and a limiting post 62. The reset spring 61 is located at the top inside the housing 1 and is used to push the hook assembly 6 to reset and return the indicator 52 to the initial position. The limiting post 62 is located in the middle of the reset spring 61 and is used to limit the maximum stroke of the hammer 5 and the hook assembly 6 to ensure that the preset position during measurement is accurate and controllable.

[0041] Preferably, it also includes a buffer spring 102, which is disposed inside the impact rod 2. The end face of the impact rod 2 is provided with a blind groove, and part of the buffer spring 102 falls into the blind groove to buffer the impact force received by the rebounder and prevent the rebound value from fluctuating and affecting its use.

[0042] Furthermore, it also includes an anti-slip layer 9, which is set on the outer side wall of the housing 1. The anti-slip layer 9 has a grip area that matches the palm of the hand. The grip area is the same shape as the palm of the hand, which improves the friction and comfort of holding it. It can meet the measurement of higher impact forces, and at the same time, the fatigue level is lower when used for a long time. It can be used for multi-point measurement.

[0043] Preferably, the anti-slip layer 9 is made of a flexible material and occupies at least 2 / 3 of the length of the housing 1, and is used to absorb vibration during the rebound and prevent the rebound device from slipping off the hand.

[0044] Preferably, the balance support 101 also includes a stop block 15. The stop block 15 is located in the groove 14 near the opening of the groove 14. The cross-section of the stop block 15 is set in an "L" shape. The stop block 15 pre-compresses the balance spring 13. The balance spring 13 is kept taut in the groove 14. The pressure of the balance spring 13 is kept stable by the support foot 17 and can apply pressure when in contact with the surface of the specimen to maintain the balance of the rebound hammer, thereby improving the accuracy of the impact measurement.

[0045] More preferably, the end face of the retaining ring 16 is provided with a protrusion 11, which extends into the groove 14. The protrusion 11 is used to restrict the stop block 15 from coming out of the groove 14. The retaining ring 16 is threadedly connected to the sleeve 10.

[0046] Furthermore, the top of the striking rod 2 is provided with a striking spherical surface 3. The hardness of the collision surface between the striking rod 2 and the striking hammer 5 is not less than HRC 65±2, the hardness of the striking spherical surface 3 is not less than HRC 70±2, and the radius of the striking spherical surface 3 is not greater than 30mm, preferably 24mm, 24.5mm, 25mm and 25.5mm. The striking spherical surface 3 is made of tungsten carbide alloy, which has a hardness much higher than that of the specimen surface, ensuring the accuracy of the measurement data.

[0047] This rebound hammer is suitable for strength testing of UHPC in the C120~C160 grade range. Based on the data obtained by the rebound hammer using standard methods and subsequent statistical analysis, a regression equation for the compressive strength of UHPC was established. The experimental data are shown in the table below:

[0048] Table 1-1 Test data on the correlation between concrete rebound value, concrete strength, and concrete carbonation depth

[0049]

[0050] This rebound hammer is suitable for strength testing of UHPC in the C120~C160 grade range. Practice has proven that the instrument has a small testing error and fully meets the accuracy requirements for on-site testing of UHPC compressive strength.

[0051] Based on the disclosure and teachings of the above specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, this utility model is not limited to the specific embodiments disclosed and described above, and any modifications and changes to this utility model should also fall within the protection scope of the claims of this utility model. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on this utility model.

Claims

1. A UHPC compressive strength non-destructive testing rebound hammer, comprising a hollow shell (1), a rebound rod (2), a rebound hammer (5), a rebound spring (4), a guide rod (51), a hook assembly (6), and a switch (7), wherein the rebound rod (2) is telescopically connected to one end of the shell (1), one end of the rebound spring (4) is fixed, and the other end is connected to the rebound hammer (5), the guide rod (51) is axially arranged in the shell (1), the rebound hammer (5) and the hook assembly (6) are both slidably connected to the guide rod (51), the hook assembly (6) can slide along the guide rod (51) and engage with the rebound hammer (5), and the switch (7) is used to control the hook assembly (6) to release the rebound hammer (5), characterized in that: The impact kinetic energy on the impact rod (2) is not less than 9.8J, the free length of the impact spring (4) is 134.4±0.5mm, the impact length after stretching is 140.0±0.5mm, the stiffness is 1000±20N / m, and the wire diameter of the impact spring (4) is greater than 1.5mm.

2. The UHPC compressive strength non-destructive testing rebound hammer according to claim 1, characterized in that: It also includes a balance support (101), which is detachably connected to the housing (1). The balance support (101) includes a sleeve (10), a balance spring (13), at least three legs (17), and a retaining ring (16). The sleeve (10) has a groove (14) on its outward-facing end. The balance spring (13) is disposed in the groove (14). At least three legs (17) are slidably connected in the groove (14). The retaining ring (16) is disposed at the opening of the groove (14) and has at least three notches. Each leg (17) is pushed outward through the notch by the balance spring (13). UHPC compressive strength regression equation: ； Wherein, the value of 'a' ranges from 0.4500 to 0.5000 (MPa), the value of 'b' ranges from 1.255 to 1.275 (dimensionless), and the value of 'c' ranges from -0.001 to -0.004 (mm). -1 ), The average rebound value (dimensionless) of the test area or test block. The average carbonization depth (mm) of the survey area. This is a converted value for concrete strength, in MPa.

3. The UHPC compressive strength non-destructive testing rebound hammer according to claim 2, characterized in that: The inner wall of the sleeve (10) is provided with an internal thread (12), and the outer wall of one end of the housing (1) is provided with an external thread (8). The balance support (101) is helically connected to the housing (1) by the external thread (8) and the internal thread (12).

4. The UHPC compressive strength non-destructive testing rebound hammer according to claim 1, characterized in that: It also includes an indicator (52) and a scale line (53), the indicator (52) being slidably connected to the inner wall of the housing (1) and the indicator (52) being able to engage with the hammer (5) in one direction, and the scale line (53) being disposed on the outer wall of the housing (1).

5. The UHPC compressive strength non-destructive testing rebound tester according to claim 1, characterized in that: It also includes a reset spring (62) and a limiting post (61), wherein the reset spring (62) is disposed at the top of the housing (1) and the limiting post (61) is disposed at the middle of the reset spring (62).

6. The UHPC compressive strength non-destructive testing rebound hammer according to claim 5, characterized in that: It also includes a buffer spring (102), which is disposed inside the impact rod (2).

7. The UHPC compressive strength non-destructive testing rebound hammer according to claim 1, characterized in that: It also includes an anti-slip layer (9), which is disposed on the outer side wall of the housing (1) and has a gripping area that matches the palm.

8. The UHPC compressive strength non-destructive testing rebound hammer according to claim 2, characterized in that: The balance support (101) also includes a stop (15), which is located in the groove (14) near the opening of the groove (14) and pre-compresses the balance spring (13).

9. The UHPC compressive strength non-destructive testing rebound hammer according to claim 2, characterized in that: The end face of the retaining ring is provided with a protrusion (11), which extends into the groove (14).

10. The UHPC compressive strength non-destructive testing rebound hammer according to any one of claims 1-9, characterized in that: The collision surface hardness of the impact rod (2) and the impact hammer (5) is not less than HRC 65±2. The top of the impact rod (2) is provided with an impact spherical surface (3). The hardness of the impact spherical surface (3) is not less than HRC 70±2. The radius of the impact spherical surface (3) is not greater than 30mm.

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