Acoustic emission and flexural behaviour of RC beams strengthened with UHPC overlay

• Damaged reinforced beams are strengthened with UHPC overlay.
• Composite beams failed monolithically with no debonding and strength improvement up to 30%.
• The failure of composite beams is studied at five different damage levels.
• Visual observations during testing are corroborated with AE parameters.
• The effect of UHPC overlay thickness and reinforcement ration on AE parameters is detailed.

Reinforced concrete beams with reinforcement ratios of 0.57%, 0.89% and 1.30% are cast and after subjecting to flexural damage strengthened with ultra high performance concrete (UHPC) overlays of thickness of 10, 15 and 20 mm. The composite retrofitted beams acted monolithically under bending without debonding. The damaged beams were able to regain its origin flexural capacity with 10 mm overlay. The increase in load carrying capacity of beams with 15 mm and 20 mm overlay is 24% and 35% for beams with reinforcement ratio of 0.57%, 11.57% and 18.45% for 0.89% reinforcement ratio and 10.60% and 15.12% for beams with 1.3% reinforcement ratio. During mechanical testing, acoustic emission (AE) parameters are analyzed for five levels of damage, which are formation of hair line crack, visible crack in UHPC overlay, yielding of main bars and finally crushing of composite beams. From parametric studies between rise angle and average frequency, it is found that AE analysis can be successfully used to determine crack movement and classify damage level of retrofitted beams.