Non-destructive method for determining the strength of concrete based on immersion and extraction of steel nails

Introduction. The method of concrete strength control based on immersion of a steel dowel into concrete due to the energy of a powder charge has been used since the 60s of the last century. Since the early 2000s, the method has been supplemented by the definition of the dowel pullout force from concrete and the definition of an indirect characteristic in the form of the ratio of the pullout force to the depth of immersion of the dowel.

The object of the present research was a method for determining the strength of concrete based on measuring the depth of immersion and the pulling force of a dowel nail installed in concrete.

Aim: to develop requirements for testing by the proposed method, allowing its use as a non-destructive method for testing the strength of concrete.

Materials and methods. The following research methods are used in this work: analysis of available regulatory documents and technical literature on this issue; collection and analysis of the results of previously conducted research using mathematical statistics methods, development of a research program and assignment of parameters, the value of which must be controlled when performing research; performance of own tests and research; analysis of the obtained results of the performed research using methods of mathematical statistics; analysis of the influence of various factors on the result of research, exclusion of non-influencing factors; development of recommendations for the use of the studied control method.

Results. The limitations for the application of the investigated method and the factors that have the most significant impact on the accuracy of the method are revealed: the power spread of the powder charge, the parameters of the indenter (plugged dowel), the criteria for the quality of the dowel installation; a method for rejecting of low-quality results and processing test results has been developed. The factors that do not have a significant impact on the test results have been identified.

Conclusions. Taking into account the identified limitations, a method has been developed for determining the strength of concrete by the magnitude of the local destruction force of concrete when pulling out a dowel nail immersed in concrete, and proposals have been made for inclusion in the State Standard R "Concretes. Determination of the strength by the depth of immersion of the dowel-nail".

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