ACOUSTIC EMISSION TECHNIQUE APPLIED FOR MONITORING AND INSPECTION OF CEMENTITIOUS STRUCTURES ENCAPSULATING ALUMINIUM

The acoustic emission (AE) technique and data analysis have been applied to detect and characterise the corrosion of aluminium and its impact on the mechanical stability of encapsulating cementitious systems. To that purpose laboratory scale samples prepared by ordinary Portland cement (OPC) and blast furnace slag (BFS)/OPC to mass ratio 7:3 with encapsulated aluminium rods were monitored for AE. The cumulative number of signals generated by piezoelectric broadband transducers attached to the samples and recorded by a computer-controlled AE system provided initial indication for the active corrosion process and damage development within the cementitious structures. Additional analysis based on the time domain parameters of the recorded AE signals (in relation to the visual and optical microscopy observations) was used to conclude on the potential AE sources active on micro and macro scale. According to their frequency characteristics the AE signals collected were divided into two main groups. The first group consisted of a large number of signals with two major frequency components distributed respectively below and above 100 kHz. The second group comprised of fewer resonance-like signals with a single frequency component at 34 kHz. Wavelet transformation was subsequently applied for frequency-time analysis. Calculation of the cross-correlation function in time domain was performed to assess the similarity of the acquired AE signals and therefore to conclude on the potential sources activity in time and space. The AE technique was shown as a potential tool for monitoring of the aluminium corrosion development associated with accumulation of structural damage within the encapsulating cementitious structures.

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