The basic principle of the rebound method is to detect the compressive strength of concrete: there is a certain relationship between the hardness of the concrete surface and the ultimate strength of the concrete. relation. In this way, the surface hardness of concrete can be tested by a rebound hammer, and the strength of concrete can be indirectly measured in combination with the carbonation depth of concrete.
However, the accuracy of the results obtained by this detection method is low. It is not suitable for components with obvious quality differences between the surface and content, and the result is greatly affected by many factors such as the raw materials of the concrete itself, construction technology, and curing conditions.
The verification period for the rebound hammer is half a year.
1. Before the new Schmidt concrete test hammer is used;
2. Exceeding the validity period of the verification;
3. The difference between the rebound value displayed by the digital rebound hammer and the pointer direct reading value is greater than 1;
4. After maintenance, the fixed value of the steel anvil rate is unqualified;
5. Suffer severe impact or other damage.
Quantity of sampling components
For components to be tested in batches, the number of random inspections should not be less than 30% of the total number of components in the same batch, and the number of components should not be less than 10. When the number of components in the inspection batch is greater than 30, the number of sampling components can be adjusted appropriately, but it must not be less than the minimum sampling quantity specified in the current relevant national standards.
Survey area layout requirements
1. For general components, the number of survey areas should not be less than 10.
The number of survey areas can be appropriately reduced, but not less than 5:
The number of inspected members is more than 30 and the deduced strength of individual members does not need to be provided; the member whose dimension in one direction of the shear member is less than 4.5m and the dimension in the other direction is less than 0.3m;
2. The distance between two adjacent measurement areas should not be greater than 2m, and the distance between the measurement area and the end of the component or the edge of the construction joint should not be greater than 0.5m, and should not be less than 0.2m;
3. The measurement area should be selected on the side of the concrete pouring where the rebound hammer is in the horizontal direction. When this requirement cannot be met, the hammer can also be placed on the concrete pouring surface or bottom in a non-horizontal direction;
4. The measurement area should be selected on the two symmetrical measurable surfaces of the component. If it cannot be arranged on the symmetrical measurable surface, it can also be arranged on the same measurable surface, and it should be evenly distributed. The survey area must be arranged in the important parts and weak parts of the components, and the embedded parts should be avoided;
5. The area of the survey area should not be larger than 0.04 square meters;
6. The surface of the measurement area should be the original concrete slurry surface, which should be clean and smooth, and there should be no loose layer, laitance, grease, coating, honeycomb, and pockmarked surface;
7. Thin-walled and small components that vibrate during bullet strikes should be fixed;
8. The survey area should be marked with a clear number, and it is advisable to draw a schematic diagram of the survey area layout and describe the appearance quality on the recording paper.
rebound hammer test values and carbonization depth measurement
1. When measuring the rebound hammer test values, the axis of the rebound hammer should always be perpendicular to the concrete testing surface, and the pressure should be applied slowly to obtain accurate readings and reset quickly.
2. 16 rebound values should be recorded in each measuring area, and the rebound hammer test values reading of each measuring point is accurate to 1. The measuring points should be evenly distributed within the survey area, and the clear distance between two adjacent measuring points should not be less than 20mm; the distance between the measuring point and the exposed steel bars and embedded parts should not be less than 30mm. The measuring point should not be on air holes or exposed stones, and the same measuring point should only be bounced once.
3. After the rebound hammer test values is measur
nization depth value should be measured at a representative position. The measuring point table should not be less than 30% of the number of component measurement areas, and the average value is the carbonization depth of each measurement area of the component. value. When the extreme difference in carbonation depth value is greater than 2.0mm, the carbonation depth value should be measured in each measurement area.
rebound hammer test values calculation
1. Remove 3 maximum values and 3 minimum values from the 16 rebound values in the survey area, and take the arithmetic mean value of the remaining 10 rebound hammer test values;
2. When detecting the side of concrete pouring in a non-horizontal state, the average rebound hammer test values of the measurement area should be corrected for the angle;
3. When detecting the top or bottom surface of concrete pouring in the horizontal direction, the average rebound hammer test values of the measurement area should be corrected for the detection surface;
4. When the rebound tester is in a non-horizontal direction and the test surface is a non-concrete pouring side, the rebound value should be corrected for the angle first, and then the corrected value should be corrected for the pouring surface
Strength conversion and estimation
The strength value of concrete at the current age of the survey area is obtained from the average rebound hammer test values and carbonation depth value of the survey area through the strength measurement curve or the strength conversion table of the survey area.
About Coring Corrections
1. The situation that needs to be corrected is significantly different from the following applicable conditions:
(1) The cement, sand, admixtures, admixtures, and mixing water used in ordinary concrete conforms to the relevant current national standards;
(2) Adopt ordinary molding process;
(3) Use templates that comply with current national standards;
(4) After steam curing, it has been naturally cured for more than 7 days after leaving the pool, and the concrete surface is in a dry state;
(5) The natural conservation age is 14 to 1000 days;
(6) The compressive strength is (10-60) MPa.
2. Correction method
Drill concrete core samples on the component: 6 pieces, 100mm, aspect ratio 1. Core samples should be drilled in the survey area, and only one core sample should be processed for each core sample. When the test block is corrected under the same conditions: the number of test blocks is 6, 150mm.