Study On The Bonding Performance Of BFRP Rebar-Polypropylene Fiber Concrete In Seawater

The new material composed of basalt fiber composite material(BFRP)and polypropylene fiber concrete has good durability such as impermeability,toughness and fatigue resistance.It is expected to solve the problem of poor durability of reinforced concrete,and has broad application prospects in coastal and saline soil areas.The bonding performance of BFRP rebar and polypropylene fiber concrete will directly affect the cooperative bearing,so the research of bonding performance is the basis of application.Aiming at the bond performance between BFRP rebar and polypropylene fiber concrete in seawater,the degradation rule of the bond performance is obtained through the central pull-out test,and the bond-slip constitutive relationship of BFRP rebar-polypropylene fiber concrete is obtained based on the existing research.The following aspects are proposed:(1)Through the basic mechanical performance test,the mass loss,compressive strength and splitting tensile strength of the polypropylene fiber concrete test block under different immersion periods are obtained.After 90 days,the quality of the specimens decreased by 3.9%,the compressive strength decreased by 24.9%,and the splitting tensile strength decreased by 28.5%.It is found that the specimens all exhibit ductile failure,and the fibers at the cracks are stretched,which can prevent and slow down the development of cracks.(2)The failure form,failure load and loading end displacement of each group of specimens are obtained through the center pull test,and the bond strength and the complete stress-slip curve are calculated.Analyzing the bond strength of each group of specimens found that: The specimens with smaller BFRP rib diameter and shorter bonding length have greater bonding stress and higher utilization rate of bonding performance within a certain range;90 days later,the bond strength is reduced by about28%,and through the stress-slip curves of each group,it is found that seawater immersion mainly affects the drop and attenuation stage of stress.(3)Based on the existing bond-slip constitutive relationship,the bond-slip of the BFRP tendon-polypropylene fiber concrete is divided into five stages: micro-slip,rise,fall,attenuation,and residual.And the physical meaning and geometric characteristics of each stage are explained.The stress and displacement expressions of each stage are obtained through data fitting,and the correlation coefficients are all above 0.9.The fitting curve and the test curve can be matched with high precision.Analysis of the fitting parameters found that the fitting parameters in the ascending phase remained basically unchanged,while the parameters in the descent phase and the attenuation phase were weakened,which confirmed that seawater immersion mainly affected the descending and attenuation phases.The constitutive relationship model proposed is more complete and clearer,which can accurately describe the bond slip of BFRP rebar-polypropylene fiber concrete.