Time-frequency characterization of acoustic emission signals from bending damage of corroded reinforced concrete beams in high- temperature saline environment

To analyze the crack development characteristics of corroded reinforced concrete (RC) beams in high-temperature saline environment flexural failure, and to explore the degradation laws of beams' flexural performance after high-temperature corrosion, as well as the time-frequency characteristics of the acoustic emission signals during flexural failure; employing electrochemical acceleration corrosion and four-point bending tests, combined with acoustic emission technology, establishes a connection between the flexural failure process of concrete beams under three conditions: unrusted (RC-1), rusted at room temperature (CRC-1), and rusted at high temperature (GRC-1). Additionally, the study uses the Abaqus finite element numerical analysis method to simulate and verify the flexural failure process of the concrete beams under three conditions. The experimental results indicate that high-temperature conditions exacerbate the corrosion of the beam body compared to room-temperature conditions. Specifically, the corrosion rate of steel reinforcement increases by 2.25 %, and rust expansion cracks appear earlier under high-temperature conditions. The yield load of the beam is advanced under high-temperature conditions and corrosion, and the ultimate bending capacity of the beam decreases, the ultimate bending capacity of the beam CRC-1 and GRC-1 under corrosion conditions decreases by 6.7 % and 14.4 %, respectively, compared with that of the beam RC-1 under non-corrosion condition. Under high temperature and corrosion conditions, the level of bending failure cracks is basically concentrated below 1/2 of the beam height, and the development level of the cracks is greatly limited. As the degree of rusting increases, the proportions of AE signal RA in the beams of RC-1, CRC-1, and G-1 are 77.6 %, 81.96 %, and 90.8 %, respectively, showing an increasing trend, and the proportion of shear cracks in the beams increases. The common characteristics of the amplitude distribution at each stage of bending damage of reinforced concrete beams are mainly reflected in the amplitude peaks in the frequency bands 4–6 kHz, 13.5–16 kHz, and 53–57 kHz. When the beam reaches the yield stage the amplitude peaks in the high-frequency band rise abruptly, indicating that the internal reinforcement of the beam has yielded and the structure is about to become unstable as it enters failure stage. This can be used as an important basis for monitoring the extent of internal damage to the structure using time-frequency transformation of acoustic emission signals. As the level of rust expansion cracks inside the beams continues to intensify and the initial damage of the structure increases, the fitted slope of the seismic mechanics b a values RC-1 (-1.91e-5) > CRC-1 (-2.51e-5) > GRC-1 (-2.99e-5), the level of negative values of the fitted slopes increases, and the damage process of the beam structure accelerates, and the structural ductility and flexural bearing capacity decrease. • Rusting of beams using high-temperature (up to 60°C) electrified accelerated corrosion tests. • Numerical simulations were carried out to verify the variation of bending damage in concrete beams with different degrees of rusting. • The GMM clustering analysis of acoustic emission RA-AF signals was performed using Matlab digital analysis software, which improved the accuracy of internal damage identification in beams. • FFT time-frequency transforms are applied to the time-domain waveforms of beams at different stages of damage to study the frequency-domain characteristics at different stages of bending damage. This provides an important reference for the time-frequency monitoring of damage inside the structure.