At one of the Latvian hydroelectric power plants, according to the project, it was planned to replace the turbines and at the same time renovate the concrete of the turbine compartment structures. To this end, the old, damaged concrete was removed (to a depth of 60 cm), new reinforcement was laid and concreted with new concrete. This object is important for the national economy, so it was necessary to ensure quality control of construction work and materials used. To control the strength of concrete, usually at the same time as concreting the structure, cube specimens are made from the same concrete mixture. This method cannot fully guarantee an objective control, since the manufacturing technology and hardening conditions of the control samples differ from real conditions. To obtain more objective results, it would be necessary to drill core samples from the hardened concrete for their subsequent testing. Drilling out a large number of samples is laborious and undesirable, since reinforcing bars can be damaged due to the dense reinforcement of the structure. Investigation the concrete mechanical properties have been performed non-destruction method applying ultrasound equipment.