Formulation of the problem. Operation of buildings and structures is based on periodic assessment of the condition of structures. The procedure for determining the strength of concrete by non-destructive methods requires a certain preparation of the concrete surface of the structure and sampling in order to calibrate the devices. During sampling, the samples may be damaged, in addition the surface of the cylinders does not meet the requirements for normalized test conditions. Part of the cores

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... uring selection is being destroyed, which reduces the representativeness of the results of determining the physical and mechanical properties of concrete. The purpose of the article is to find out the possibilities to increase the reliability of determining the physical and mechanical properties of concrete. Results. In the conditions of a real object, core samples were taken to study the concrete strength of the damaged area. Samples that did not meet the normalized parameters were prepared for testing using a repair mixture Mapegrout Thixotropic. Testing of the recovered core samples showed that the repair mixture adhered well to the surface of the core. The nature of the destruction in the restored and normalized samples is similar. Conclusions. Studies have shown that: the application of the existing method of determining the strength of concrete for slab structures limits the possibility of using core samples taken from structures; the use of Mapegrout Thixotropic repair mixture allows to carry out tests according to the normative method of damaged concrete samples or samples rejected due to size mismatch; reliable assessment of the deformable properties of concrete cores in many cases is impossible; the existing methodology needs to be improved or replaced by an alternative one; quantitative assessment of the rheological properties of the concrete mixture used for the manufacture of concrete structure is possible on the basis of comparing the deformable and strength characteristics of concrete structure, which requires formalization of the procedure and standardization.