Purpose and Scope of Application

1.1 This method is applicable to the rapid evaluation of the compressive strength of ordinary concrete for cement concrete pavements and other structures on site, and the thickness of cement concrete tested shall not be less than 100mm and the humidity shall not be less than 10 ° C.

1.2The rebound hammer test results can be used as a reference for the strength of the test block, cannot be used as a substitute for the strength evaluation of concrete, and is not suitable as the final basis for arbitration tests or project acceptance.

2.Instruments and materials

The following instruments and materials are required for this method:

1) Rebound hammer machine: Pointer direct reading concrete rebound instrument also can use digital rebound hammer test

The rebound instrument shall meet the following standards:

A. During a horizontal rebound, the nominal kinetic energy of the rebound instrument is 2.207J at the moment the hammer is unhooked.

B. At the moment of collision between the impact hammer and the impact rod, the impact tension spring is in a free state, and the starting point of the impact hammer should be at the zero point of the scale.

C. On a steel drill with a Rockwell hardness of HRC60 ± 2, the calibration value of the rebound instrument should be 80 ± 2.

2) Phenolphthalein alcohol solution at a concentration of 1%.

3) Portable grinding wheel.

4) Steel drill: Rockwell hardness HRC60 ± 2.

5) Others: tape measure, steel ruler, chisel, hammer, brush, etc.

3.Verification and maintenance of langry concrete test hammer

3.1 In case of any of the following circumstances, the concrete strength test hammer shall be sent to the verification unit for verification. The qualified rebound instrument shall have a verification certificate with a validity period of half a year.

1) The cumulative number of shots exceeds 6000;

2) Spring seat, spring rod, buffer pressure spring, center guide rod, guide flange, hammer, pointer shaft, pointer piece, pointer block, hook, zero adjustment screw, etc

After replacing one of the necessary parts;

3) The front end of the spring is not at the original hole position of the spring seat or the zero adjustment screw is loose;

4) Suffer from severe impact or other damage.

3.2 If one of the following conditions occurs to the rebound hammer test apparatus, a calibration test should be conducted on a steel drill;

1) Before and after component testing, if testing is carried out for several consecutive days, it can be determined once a day after testing is completed;

2) When there is doubt about the rebound hammer test result during the measurement process.

If the calibration test results are not within the specified range of 80 ± 2, the spring back instrument should be routinely maintained before calibration. If the calibration is still not qualified, a verification sheet should be submitted

Bit test.

3.3 Calibration steps of langry concrete test hammer

The calibration test of the rebound instrument should be carried out at a room humidity of 20 ± 5 ℃. When calibrating, the steel anvil should be firmly placed on a rigid concrete floor, with the rebound meter downward

During the rebound stroke, the rebound rod should be rotated four times, each time about 90 º, and the rebound value of the last three consecutive times with stable readings should be averaged 3-5 times

Is the rated value.

4 Measurement steps

4.1 Survey area and survey point layout

1) When a cement concrete pavement is used, a concrete slab is taken as a sample, and the selection of the sample is determined by the random sampling method. The number of test areas for each sample should not be less than

10, and the spacing between two adjacent survey areas should not be greater than 2m; The measurement area should be evenly distributed on the measurable surface of the sample and should avoid the edges and corners of the plate.

2) For other concrete structures, the test area should be away from the reinforcement set near the inner protective layer of the concrete. The test area should have two basic pairs on the two opposite surfaces of the sample

If this requirement cannot be met, only one test surface is allowed for a test area.

3) The surface of the survey area should be clean, dry, and flat, without joints, finishing layers, paint layers, laitance, oil stains, as well as honeycomb and pockmarked surfaces. If necessary, grinding wheels can be used to remove them

Sundries and irregularities on the surface, and polished surfaces should be free of residual dust or debris.

4) The area of a survey area should not be less than 200mm × 200mm, 16 measurement points should be measured in each measurement area, and the spacing between two adjacent measurement points should not be less than 3cm. Measuring point distance

The distance between the edges or joints of the pavement shall be not less than 5 cm.

5) For hardened concrete aged over 3 months, the carbonation depth of the concrete surface layer should be measured to cor

value, or after the carbonation layer is polished off with a grinding wheel

Conduct measurement, but the polished ones shall not be mixed together for calculation or compared with the strength of the test block (not polished).

4.2 Determination of rebound hammer test result

During the test, the axis of the langry concrete test hammer should always be perpendicular to the concrete pavement, and the specific operation should meet the following requirements:

1) Hold the rebound rod of the rebound hammer equipment against the concrete surface, gently press the instrument to release the button, slowly extend the rebound rod, and hang the hammer on the hook;

2) Slowly and evenly apply pressure to the concrete surface with the rebound instrument. After the rebound hammer is unhooked and impacts the rebound rod, the rebound hammer will drive the pointer backward until it reaches a certain position

The scale line of the pointer block indicates a certain rebound value on the scale;

3) Continue to hold the rebound hammer equipment against the concrete surface, take readings, and record the rebound value. If conditions are not conducive to reading, press the button, lock the movement, and move the rebound meter

Read elsewhere, accurate to 1 unit.

4) Gradually depressurize the rebound hammer test equipment, extend the rebound rod from the casing, hang the rebound hammer on the hook, and wait for the next use.

4.3 Determination of carbonization depth

1) For concrete with an age of more than 3 months, after measuring the rebound value, the carbonation depth of the concrete can be measured at a selected location on each measurement area. When adjacent survey areas

When the concrete soil quality or rebound value is basically similar to it, the carbonation depth value measured in the survey area can also represent the carbonation depth value of the adjacent survey area.

2) When measuring the carbonation depth value, a hole with a diameter of about 15 mm can be formed on the surface of the measurement area using a suitable tool (its depth is slightly greater than the carbonation depth of the concrete)

After that, use a brush to remove the powder and debris in the hole (liquid washing is not allowed), and immediately sprinkle a 1% phenolphthalein alcohol solution on the edge of the inner wall of the hole, and then use steel Measure the vertical distance from the surface of the concrete to the representative intersection point where the deep part does not change color (the non-carbonated part turns purple-red) 1-2 times with a ruler, and this distance is the concrete's carbonization depth value shall be measured and read to 0.5mm each time.