Role of synthetic fibers in delaying steel corrosion cracks and improving bond with concrete

An experimental study was conducted to investigate the bond behavior betwee n corroding reinforcing steel and surrounding synthetic fiber reinforced co ncrete. Pullout concrete and fiber reinforced concrete specimens were prepa red at concrete cover to steel bar diameter ratios of 3.1 and 3.7 with thre e embedded lengths of 100, 200, and 300 mm. Fiber reinforced concrete was p repared using polypropylene at 0.15% and 0.30% or nylon fibers at 0.3% by m ix volume. After moist curing for 90 days, pullout specimens, originally co ntaminated by up to 11 kg/m(3) NaCl, were subjected to a special treatment to accelerate corrosion in steel. The bond stress-slippage relationship was evaluated at different corrosion levels. The findings indicated that the u se of fibers delayed initiation of cracking, due to steel corrosion, and im proved the ultimate bond strength at cracking and post-cracking stages. The percentage improvement in ultimate bond strength at the latter stages reac hed as high as 52% and 87%, respectively. It was noticed that, prior to cra cking, corrosion of steel bars resulted in an increase in bond strength, re gardless of the concrete cover to bar diameter ratio used, or whether fiber s were used or not. After cracking (due to steel corrosion), pullout specim ens prepared with polypropylene fibers showed better resistance than that o f corresponding ones with nylon fibers.