Bond behavior of flexible braided AFRP tendons in high-performance concrete based on pull-out and beam tests

AFRP tendons are manufactured in both rigid and flexible form, where flexible AFRP tendons could be coiled and utilized as external prestressed tendons with significant curvature. This study investigates the bond behavior of flexible AFRP tendons in high-performance concrete (HPC) by examining the effects of tendon types, tendon diameter, concrete types, and test methods. Results show that pull-out failures are prone to occur in specimens with AFRP tendon, whereas splitting failures are prone to occur in specimens with steel tendon. The bond stresses for AFRP tendons reach maximum value within a slippage range of 4.5-10.5 mm, while for steel tendons, the maximum bond stresses occur within a larger slippage range of 17-44 mm. The bond strength of steel tendons is 1.12-1.26 times higher than that of AFRP tendons. Normal concrete (NC) specimens with splitting failure produced maximum 7.1 % higher bond strength compared to HPC. On the other hand, the pull-out failure is determined by the interlaminar shear strength of AFRP tendons, leading to comparable bond strength between NC and HPC. A 5 % difference in bond strength exists between pull-out tests and beam tests with similar failure modes. For AFRP tendons, changing the diameter from 13 mm to 15 mm increases the bonding strength by +6 % to -17 %, which is basically consistent with the existing research that the bonding strength decreases as the diameter increases. This study presented a formula for AFRP tendon bond strength, considering concrete strength, types, tendon diameter, and test methods. The proposed model outperforms existing ones with an average of 0.99 and a variance of 0.13.