The paper discusses fast Fourier transform (FFT) parameters of acoustic emission signals acquired during the hydro-abrasive erosion(HAE) of five different concrete mixtures. The FFT-peak amplitude as well as the FFT-peak frequency shows some pronounced relationshipsto the depth of penetration and to the fracture behavior of the investigated materials. Correlation statistics is used to separate threedistinguished fracture ranges during HAE: intergranular erosion, mixed-mode fracture, and transgranular fracture. It is concluded thatFFT-peak amplitude and FFT-peak frequency of the acoustic emission signals can be used for the on-line control of HAE-processes.