Experimental study on the effects of dynamic loading and seawater attack on bond behavior between basalt fiber reinforced polymer bars and seawater sea-sand concrete

Coastal and marine constructions are continually subjected to dynamic loads during long-term service life. Therefore, the present research investigated the effects of dynamic loads and marine environment exposure on the bond behavior of basalt fiber reinforced polymer (BFRP) bars embedded in seawater sea-sand concrete (SSC). Both static and dynamic pull-out velocities, exposure duration, and environment temperature were considered to examine the bond behavior. The scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and low-field nuclear magnetic resonance (LF-NMR) were applied to reveal the deterioration mechanism of the bond behavior. Both the bond behavior and bond mechanism were analyzed based on interface failure morphology and bond stress-slip relationship. It was found that the bond strength declined with exposure temperature and duration mainly owing to the surface deterioration of the bar embedded in SSC under exposure condition. The bond strength diminished with the increasing pull-out velocity, and both dynamic loading rates and exposure conditions altered the bond mechanisms from being controlled by the shear strength of interface between the bars and SSC to the interlaminar shear properties of bar surface fiber layer. The bond stiffness initially increased and then decreased with the pull-out velocities. At last, the bond strength retentions after 50 years of service in various environments and loading rates were predicted. This study provides a valuable insight for the design and application of BFRP bar reinforced SSC in marine constructions.