Flexural capacity and serviceability evaluation on seawater sea-sand concrete beams reinforced by BFRP bars and TRE composite in the dry-wet environment

To promote the durability and serviceability of offshore structures, the bearing capacity and serviceability of BFRP-reinforced seawater sea-sand concrete (SWSSC) beams with textile reinforced ECC (TRE) to retard deformation and cracking under chloride dry-wet cycles were investigated. A total of a BFRP-reinforced SWSSC beam and nine TRE composite beams were designed. The dry-wet cycles, thickness, fabrication method and shape of TRE composite layer as factors the on the bearing capacity, deflection and crack behavior, curvature and ductility of beams with TRE composite were analyzed. TRE composite layer still can visibly increase the cracking moment of BFRP-reinforced SWSSC beams even in the dry-wet conditions, but the improvement effect on the ultimate moment was noteless. The bearing moments of composite beams increased with the TRE thickness and the dry-wet cycles. The failure modes for composite beams with the same reinforced radio of FRP bars under dry wet environment changed from failure in shear cross zone to failure in pure bending zone with the increase of the thickness of TRE composite layer. The development of deformation and cracks for beams with TRE composite was significantly distinct from that for BFRP-reinforced SWSSC beams, attributed to the bonding properties of the composite layer to concrete, which with the TRE composite subjected to service moments can be judged by the curvature of 0.00375/d, below the curvature of 0.005/d. The fine cracks in TRE composite beams developed sequentially throughout the pure bending of beams. The dry-wet environment can reduce the deflection by increasing the stiffness of beams. Under service moment, the neutral axis height of TRE composite beam was clearly superior to that of BFRP-reinforced SWSSC beam. The variation trend of ductility index on energy and deformation was different. And the ductility of TRE composite beams declined as the increasing dry-wet cycles, regardless of the energy or deformation.