Non-destructive evaluation of the concrete structure damage

The present paper deals with an experimental study of the frequency inspection method applicability to the concrete structure integrity damage assessment. Our research has addressed to three groups of specimens which differed from each other in the structure quality, because of different concrete ageing conditions, were subjected to the degradation. Our objective consisted in determining how the freeze-thaw cycle application induced degradation depends on the structure initial quality. The measurement results of the specimens (the best structure quality) which had undergone degradation showed no frequency spectra changes and no predominant frequency shifts. Specimen groups of which quality was inferior due to the lack of water during the ageing process showed a shift of the predominant frequencies toward higher frequencies. However, it was an upward shift which we are interpreting as a symptom of the specimen structure improvement – contrary to our expectations. The structure integrity improvement is in our opinion due to the additional hydration of mixed cement grains in consequence of specimen soaking in water in the course of the freeze-thaw cycles. It was verified that this method is appropriate to concrete structure changes assessment.

Key words: concrete ageing conditions, structure integrity, micro-cracks, frequency inspection