The behavior heated-damaged reinforced concrete beams retrofitted with different CFRP strip length and number of transverse groove

The potential of recovering the flexural performance of thermally damaged concrete beams using carbon fiber reinforced polymer (CFRP) strips with groove technique was experimentally investigated. Twenty reinforced concrete beams (150 × 200 × 1100 mm) were cast then cured for 28 days in moist burlap. A set of thirty-nine beams were heated at 250 °C, 500 °C, and 750 °C for two hours using an electrical furnace, whereas those of the second set of thirteen beams were left in laboratory air (23 °C). Nevertheless, debonding and anchoring problems remain a challenge for the success of this technique. In this study, an innovative application was implemented in which CFRP strip length with different lengths was integrated as external flexural reinforcement for reinforced concrete beams by using the groove technique. The intent was to assess the contribution of the CFRP strips to the flexural strength and thus evaluate the effectiveness of using them as primary or supplemental flexural reinforcement before and after exposing to elevated temperature. The investigated parameters include the number of transverse grooves and different elevated temperatures. The mechanical performance of other beams was evaluated under a four-point loading test setup, including measurement of strain in CFRP strips and mid-span deflection. Moreover, cracking and failure modes were monitored and characterized. Intact/strengthened and heat-damaged/strengthened beams showed improved ultimate strength, ultimate deflection, stiffness, and toughness compared to control ones. Different performance indicators revealed the good potential of strengthened heat-damaged beams using CFRP strips with grooves. Furthermore, the results showed that the grooving method performs better than surface preparation without grooves. So that the strengthening with grooves prevents premature delaminating and some of the concrete shatters in the tension side, and the weakness of beams in debonding phenomena disappeared, and flexural failure became dominant failure mode with full attachment of CFRP strips with concrete.