Testing method of concrete strength

1, strength detection by core drilling method

The basic principle of core drilling method is to drill a core sample in a representative concrete structure, then finish machining such as sawing and grinding, and then measure its compressive strength. The strength of concrete with strength exceeding 10MPa and age exceeding 14d can generally be detected by core drilling method. However, drilling core will have a certain impact on concrete structure. Therefore, in order to ensure the performance of concrete structures, the designer's consent must be obtained before adopting this method. It should be noted that the size of core samples, the number and location of coring should meet the specific requirements. In addition, the core drilling method can effectively detect the local damage of concrete and truly and reliably reflect the situation of the specimen. At the same time, through the observation and detection of core samples, we can understand and master the internal situation of local concrete, such as the distribution of aggregate and the size of cracks. However, this method also has some shortcomings, such as high labor intensity, high detection cost and certain damage to the structure.

2, rebound method to detect strength

Rebound method is a method to estimate the compressive strength of concrete by measuring the hardness of concrete surface with the help of rebound instrument. On the basis of not destroying the structural members, the concrete strength of the structure is detected by rebound instrument, so as to judge the concrete strength, the position and defects of steel bars. The rebound method has the characteristics of simplicity, flexibility, high detection efficiency and low cost. However, compared with test block method and core drilling method, its accuracy is relatively poor. In the process of determining the strength of concrete by rebound method, some strength curves are needed to effectively judge the strength. For some special parts of concrete or concrete made by special molding technology, it is necessary to carry out corresponding testing through special strength curves to ensure the effectiveness of the testing results. It should be noted that if concrete is affected by external factors (fire, frostbite, chemical corrosion, etc.). ), the surface and internal quality are very different, so this method can not be used for the strength detection of concrete.

3, ultrasonic testing method to detect strength

Ultrasonic testing method can detect the density, uniformity, crack depth, surface damage layer thickness and other indicators of concrete, and make a more accurate judgment, so this method has been widely used in various industries. In the process of applying this method, there are many factors that affect the sound speed, such as cement dosage, cement variety, aggregate variety and particle size, water content, sand content and so on. Moreover, different materials have different ages and moisture contents, so the sound propagation speed will be different, which makes it difficult to ensure the reliability of concrete strength measurement results. Therefore, at this stage, ultrasonic method and rebound method are usually used comprehensively.