Recovering shear capacity of heat-damaged beams using NSM-CFRP strips

The potential of recovering shear capacity of heat-damaged beams using near surface mounted (NSM)-carbon fiber reinforced polymer (CFRP) strips was investigated in this work. Twenty-two under-reinforced concrete beams with shear reinforcement deficiency (150 × 250 × 1400) were cast and heat-treated for two hours in an electric furnace; under different temperatures (300, 500, and 600 °C). Later, control beams were strengthened, whereas post-heated ones repaired with NSM-CFRP strips, directed vertically across the depth of the beams and at different spacing values ranging from 100 to 200 mm. The mechanical behavior of the beams was evaluated under three-point loading test setup; with data collected and analyzed for the characteristics of the relationships between load and deflection or slippage (between concrete and reinforcing steel). Cracking and failure modes were monitored and characterized, as well. The experimental results indicated that the efficiency of repairing heat-damaged reinforced concrete beams using NSM-CFRP strips depended mainly upon damage level and spacing between NSM-CFRP strips. The result showed that using NSM-CFRP allowed restoring load capacity of the beams, damaged at 300 and 500 °C; but not so for those, post-heated to 600 °C. The latter achieved an utmost load capacity recovery of about 91% of original value. Lowering spacing between the CFRP strips contributed to increasing shear load capacity of repaired beams as long as peeling-off failure of the concrete cover across the depth of beam's soffits was avoided. The flexural stiffness was not recovered for heat-damaged and repaired beams whereas toughness and ductility were noticeably improved.