Acoustic emission-based damage assessment of CFRP-repaired pre-cracked corroded reinforced concrete beams under flexural loading

Service cracks in reinforced concrete (RC) beams facilitate chloride ingress, accelerating reinforcement corrosion and structural deterioration. Evaluating the combined influence of cracking, corrosion, and repair on structural performance remains challenging. This study investigates the flexural behaviour of pre-cracked, corroded RC beams and the ability of externally bonded carbon fibre-reinforced polymer (CFRP) sheets to restore their structural capacity. Acoustic emission (AE) monitoring was used to relate the structural response to the corresponding damage evolution. Beams were pre-cracked to 65% of their ultimate capacity, subjected to accelerated corrosion targeting 10%, 15%, and 20% mass loss, and tested under three-point bending with continuous AE monitoring. The combined action of pre-cracking and corrosion reduced stiffness and load-bearing capacity, while the AE response captured the associated damage evolution throughout the loading process. Gaussian-filtered b -value trends identified the transition from distributed microcracking to localised macro-crack growth in all specimens. The sharpest and earliest drop in the b -value occurred in the pre-cracked corroded beams immediately after pre-crack reopening. CFRP repair restored the load capacity of the 10% and 15% corroded specimens to at least that of the uncorroded control specimen. This recovery was reflected in the AE response, with the repaired beams absorbing nearly three times the cumulative absolute energy of the unrepaired specimens and exhibiting more distributed cracking due to CFRP confinement. RA-AF classification confirmed a progressive shift from tensile to shear-dominated fracture with increasing corrosion severity. The combined mechanical and AE evidence provides a physically grounded basis for assessing residual capacity and repair effectiveness in deteriorating RC structures.