Non destructive testing can be divided into non destructive testing methods and semi destructive testing methods. Since the local damage caused by the semi damage detection method does not pose a threat to structural safety, from a macro perspective, the semi damage detection method can also be classified as non damage detection.

Non destructive testing methods

The non-destructive testing method is to measure the relevant physical quantities based on the relationship between the compressive strength of concrete and other physical quantities of concrete, without affecting the performance of the structure or component concrete. Then, according to the strength measurement curve, the standard strength conversion value of concrete is calculated, and the fixed value or characteristic strength of the standard value of concrete strength is finally obtained based on statistical principles. This type of method includes rebound method, ultrasonic pulse method, ray absorption and scattering method, maturity method, etc.

One is the rebound method

The rebound method refers to the method of using a rebound instrument to test the compressive strength of ordinary concrete structures or components. The implementation process is as follows: a spring driven heavy hammer is used to hit the surface of the concrete through a rebound rod (transmission rod), and the distance at which the heavy hammer rebounds (x in Figure 1) is measured. The rebound value (the ratio of rebound distance to the initial length of the spring) is used as an indicator related to strength, Convert the strength value of the concrete component from the established regression equation or calibration curve. The detection principle is shown in Figure 1.

The rebound method is easy to operate, fast and economical, and has considerable accuracy, so it is widely used in the field of concrete testing. However, there are many factors that affect the accuracy of rebound method strength measurement, such as instrument standard status, operating methods, on-site conditions, component selection, measurement area and point layout, and calculation methods. Therefore, in order to improve the accuracy of detection, it is necessary to strengthen the analysis of these influencing factors, and reasonably formulate and select formulas.

Split type direct reading+digital rebound instrument

The second is ultrasound method

The ultrasonic method is a method of estimating the strength of concrete by measuring the average speed of ultrasonic propagation within a distance measurement, as shown in Figure 2. In engineering, the method of establishing statistical strength curves related to the relationship between ultrasonic velocity and compressive strength of concrete in specimens is commonly used to detect and evaluate the mechanical properties of concrete.

There are many factors that affect the measurement of ultrasonic velocity in concrete, such as cross-sectional dimensions, temperature and humidity, reinforcement, aggregates, water cement ratio, age, pouring direction, and internal defects. Therefore, ultrasonic velocity is a comprehensive indicator that reflects its composition. This requires that when establishing a calibration curve, the technical conditions should be as close as possible to the actual testing environment, in order to understand the reasons that affect the measurement of ultrasonic velocity from the perspective of concrete material composition, Therefore, it can be excluded in actual testing.

Using ultrasonic method to detect concrete

Half damage detection method

The semi damage detection method is a method of directly conducting local destructive tests or drilling core samples on structures or components for destructive tests, and then converting the test values to the standard strength of structural concrete based on the correlation between the test values and the standard strength of structural concrete, to obtain the standard strength conversion value, and based on this, to calculate the estimated value or characteristic strength of structural concrete strength standard value. The semi destructive methods mainly include drilling core method, pulling out method, peeling method, breaking method, nail shooting method, and other methods.