THE STUDY OF THE PROBLEM OF THE RELIABILITY ASSESSMENT OF THE CONCRETE STRENGTH BY NONDESTRUCTIVE METHODS
The quality of concrete and reinforced concrete structures largely depends on the reliability of concrete strength control. Determination of the strength of concrete can be made by standard methods (GOST 10180 Concrete. Methods for determining the strength of the control samples) by manufacturing and testing samples, but the reliability of the control of its strength and homogeneity of the standard samples is insufficient for a number of reasons: the volume of testing of standard samples does not exceed 0.01 % laid in the concrete structure, the conditions of vibration formation and hardening modes of samples and structures are different, standard methods can not determine the homogeneity of concrete in the product and the strength of its individual sections. When inspecting buildings and structures, standard concrete testing methods are not applicable at all. These disadvantages of the standard methods of testing the strength of concrete led to the development of nonestructive testing methods and methods associated with the testing of concrete in nonstandard samples extracted from the structure. Nondestructive control of concrete tempering and transfer strength allows to influence quickly the technological process of production of reinforced concrete products. For nondestructive testing of concrete strength, devices based on the methods of local destruction (separation with chipping, chipping ribs, separation of steel discs), impact on the concrete (shock impulse, elastic rebound, plastic deformation) and ultrasonic sounding are used. The main volumes of nondestructive testing of concrete strength are usually performed by highperformance devices after establishing the correlation of their indirect characteristics (basic dependence) with the actual strength of the controlled concrete. In contrast to the methods of local destruction devices based on the impactpulse impact on the concrete, have a much greater performance, but the control of the strength of concrete is carried out in the surface layer thickness 25...30 mm, which limits their use. In the cases mentioned above, it is necessary to clean the surface of the controlled areas of concrete or remove the damaged surface layer. The use of shockpulse and ultrasonic devices at the construction sites and during the inspection of the operated structures, when it is not possible to clarify the calibration dependence by testing the cubes in the press, is associated with significant errors in determining the strength of concrete. The article presents the results of studies to assess the calibration dependences in determining the strength of concrete by nondestructive methods. The reliability of concrete strength determination by ultrasonic method and shock pulse method applied to different concrete classes is estimated.