Information on the most widely used ASTM standards within the materials testing industry
Model: UTHT-225A
Concrete rebound test hammer is used to test the compressive strength of concrete and is the most widely used non-destructive testing instrument for concrete compressive strength on-site. It is the fastest, simplest, and most economical method to assess the quality and strength of concrete.
UTHT-225A Concrete Test Hammer is designed specifically for the non-destructive testing of concrete structures. This method has considerable advantages over conventional methods of assessing the compressive strength of concrete in that large areas can be tested in a very short time at a very low cost.
General Introduction
Concrete rebound test hammer is used to test the compressive strength of concrete and is the most widely used non-destructive testing instrument for concrete compressive strength on-site. It is the fastest, simplest, and most economical method to assess the quality and strength of concrete.
UTHT-225A Concrete Test Hammer is designed specifically for the non-destructive testing of concrete structures. This method has considerable advantages over conventional methods of assessing the compressive strength of concrete in that large areas can be tested in a very short time at a very low cost.
The HT225 is comparable with the Schmidt Hammer, Type N, this method of testing is covered by EN 12 504-2, ASTMC805, DIN 1048 and BS1881 part 202. These standards refer to assessment of the rebound hardness of concrete which is directly related to the compressive strengths of the material
being tested.
In order to make sure test hammer in good status, we should calibrate it regularly.
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| Rebound test hammer calibration anvil |
Hardness of steel core: HRC 60±2, The rebound value fall in the range of 80±2 (for test hammer with impact energy of 0.735J and 0.196J, it's calibrated value should be 74±2)
Main features
The basic principle of the rebound hammer is to use a spring to drive a heavy hammer, which strikes a plunger in direct contact with the concrete surface with constant kinetic energy. This causes local deformation of the concrete and absorbs part of the energy, while the remaining energy is converted into the rebound kinetic energy of the hammer. When all the rebound kinetic energy has been converted into potential energy, the hammer reaches its maximum rebound distance. The instrument displays the maximum rebound distance of the hammer as the rebound value (the ratio of the maximum rebound distance to the initial length of the spring).
The concrete strength value is the maximum stress that concrete can withstand under certain loading conditions and working environments. To accurately measure the strength of concrete, concrete specimens must be loaded to their failure limit, and the test value is obtained after the specimen is destroyed. The nondestructive testing method for structural concrete strength aims to obtain the failure stress value without damaging the structure or components. Therefore, it can only identify one or several functional values related to concrete strength that can be tested nondestructively. In practice, these are indirect estimates, and their agreement with the actual concrete strength depends on the correlation between the measured physical quantity and concrete strength. A commonly used nondestructive testing technique for concrete is the rebound method to measure strength.
Since the rebound hammer was invented in Switzerland in 1948, the rebound method has been in use for over 40 years. The rebound hammer operates based on the fundamental principle of the rebound method. The rebound method uses a spring-driven hammer that strikes the surface of the concrete through a transmission rod. The distance the hammer rebounds is measured, and the ratio of the rebound distance to the initial length of the spring is used as an indicator related to strength to estimate the concrete strength. Although other nondestructive testing methods have emerged, the rebound method remains advantageous in field applications due to its simple instrument structure, ease of operation, reasonably good correlation with concrete strength under certain conditions, and low testing cost. It is internationally recognized as one of the fundamental methods for nondestructive concrete testing.
When performing the impact test, the pointer slider stays at the starting position and does not move:
1. The pointer spring piece is broken. In this case, during the impact of the hammer, the spring piece cannot catch the hammer, causing the pointer slider to remain at the starting position.
Repair method: replace the spring piece.
2. The starting position of the impact hammer is not qualified, causing the pointer slider to remain at the starting position.
Repair method: adjust the position of the rear cover nut and set the hammer's release position to reach 100 divisions.
3. The opening angle of the pointer piece relative to the pointer shaft is too small. At this time, the friction during the hammer's impact is too low, preventing the pointer from sliding.
Repair method: remove the pointer assembly and appropriately increase the opening angle so it is within the specified range.
Rebound Hammer:
Rebound hammer does not bounce
1. The compression spring on the hook has come off, and the hook has no elasticity. Repair method: Install a new compression spring.
2. The tip of the hook is worn or broken, which also prevents the hook from functioning properly. Repair method: Install a new compression spring.
Tension Spring Stiffness:
Not within the specified range
The stiffness of the rebound tension spring is not within the specified range, resulting in a non-compliant rated value (when checking the stiffness of the rebound hammer tension spring).
Repair method: First, replace the rebound tension spring, then perform the check. If it passes, there is no need to replace the rebound hammer. Otherwise, continue replacing the rebound tension spring.
Main Technical Specification
| Measuring ranges | 10-70MPa |
| Impact energy | 2.207J (0.225Kgf.m) |
| Spring extension | 75±0.3mm |
| The static friction of pointer slider | 0.65N±0.15N |
| Radius of spherical tip | 25mm±1mm |
| The average rebound values on steel anvil | 80±2mm |
| Housing dimensions | Φ54*280mm |
| Weight | 1 kg |
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