Recovering flexural performance of thermally damaged concrete beams using NSM CFRP strips

- Exposure of beams to 600 °C for 2 h degraded their mechanical properties.
- Flexural behavior of post-heated beams with NSM CFRP strips was recovered.
- Ductility was recovered for heat-damaged beams with NSM CFRP strips.
- Heat-damaged had significantly reduced bond strength between concrete and NSM CFRP.
- End-concrete cover peeling off was the dominant failure mode for repaired and strengthened beams.

The potential of recovering the flexural performance of thermally damaged concrete beams using near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) strips was experimentally investigated. Twenty reinforced concrete beams (150 × 250 × 1400 mm) were cast then cured for 28 days in moist burlap. A set of ten beams were heated at 600 °C for 2 h using an electrical furnace whereas those of the second set were left in laboratory air. Four pairs of beams from each set were repaired/strengthened at their tension side using similar configurations of NSM CFRP strips. Duplicate beams of each set were tested as controls. The mechanical performance of different beams was evaluated under four-point loading test setup including measurement of strain in NSM CFRP strips and slippage between NSM CFRP strips and concrete. Moreover, cracking and failure modes were monitored and characterized. Intact/strengthened and heat-damaged/repaired beams showed improved load capacity and toughness, yet experienced reductions in ductility and toughness as compared to control ones. Different performance indicators revealed good potential of repairing heat-damaged beams using NSM CFRP strips. End-cover separation failure mode was observed for both strengthened as well as repaired beams. Analytical predictions of ultimate load capacity for different beams confirmed experimentally obtained results.

The potential of recovering flexural performance of thermally damaged concrete beams using near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) strips was satisfactory when enough development lengths beyond critical stress region were provided. Intact/strengthened and heat-damaged/repaired beams showed improved load capacity and toughness, yet experienced reductions in ductility and toughness as compared to control ones.162