Rebound method for testing concrete strength

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The instrument, principle and method of rebound concrete for testing concrete strength, as well as the factors affecting the strength of testing, are introduced, and the most extensive, simple, and accurate method for determining concrete strength is provided for nondestructive testing.
Keywords: carbonization depth; rebound value; compressive strength; concrete
    There are many detection methods for on-site testing of concrete strength, such as core drilling method, pull-out method, indentation method, shooting method, rebound method, ultrasonic method, rebound ultrasonic comprehensive method, ultrasonic attenuation comprehensive method, ray method falling ball method, etc. The rebound method and ultrasonic rebound method are the most widely used non-destructive testing methods.

The relationship curve established between the compressive strength of concrete test blocks and the parameters of nondestructive testing (ultrasonic sound velocity value, rebound value, pull-out force, etc.) is called the strength curve, which is the basis for estimating the concrete strength of nondestructive testing. The strength curve is divided into three types: unified strength curve, regional strength curve and special (calibrated) strength curve according to the source of the material.

The method of detecting the compressive strength of ordinary concrete structural members by using a rebound instrument (a direct-acting hammer type instrument) is referred to as the rebound method.
The following focuses on the rebound method for testing concrete strength.

1 Detection principle and characteristics
1.1 Principle
    Because there is a correlation between the compressive strength of concrete and its surface hardness, the rebound hammer of the rebound meter is hit by a certain elastic force on the concrete surface, and its rebound height (rebound value read by the rebound meter) It is proportional to the hardness of the concrete surface. Therefore, the rebound value
According to the surface hardness of concrete, the compressive strength of concrete can be estimated based on the surface hardness.

1.2 Features

    The rebound method is used to test the compressive strength of concrete. Although the detection accuracy is not high, the equipment is simple, easy to operate, quick to test, and low in testing cost, and does not damage the normal use of concrete. There are many factors that affect the accuracy of the rebound method, such as operating methods, instrument performance, and climatic conditions. For this reason, you must master the correct operation method, pay attention to the maintenance and calibration of the rebound meter.

   "Technical Specifications for Testing the Compressive Strength of Concrete by the Rebound Method" (JGJ / T23-2001) stipulates that the age of the concrete measured by the rebound method is 7 d to 1000 d, which is not applicable to the surface and internal quality with obvious differences or internal existence The detection of defective concrete components and concrete made by special molding processes greatly limits the detection range of the rebound method. In addition, due to the large strength base of high-strength concrete, even if the relative error is only 15%,Its absolute error will also be very large and make the test result meaningless.