Damage Research On Steam-Curing GFRP Reinforced Precast Concrete Components In High-Speed Railway

The steam-curing precast concrete component with advantages of short construction period,less environmental pollution,convenient construction and low costhas been widely popularized and applied in the structure of high-speed railway project.According to statistics,it is a key issue that the service life of steam-curing precast concrete component greatly differs with the design life,which not only causes serious economic losses,but also can’t meet the requirements of high-speed railway construction for the safe development in China.In order to fundamentally solve the corrosive problem of steel embedded in steam-curing concrete components and improve the service life ofsteam-curing concrete component,glass fiber reinforced plastic(GFRP)bars with the corrosion resistance and superior cost-effective were used in the steam-curing precast concrete through completely or partly replacing for steel.However,domestic and foreign research on steam-curing precast concrete is relatively simple,which mainly concentrates on the damage of steam-curing concrete.Meanwhile,it is lack of the researches on the damage of reinforcement material embedded in steam-curing concrete components,the bond performance damage between steam-curing concrete and GFRP bars and the design method of steam-curing precast concrete components,causing the great error between the actual performance and design performance of steam-curing precast concrete components.Therefore,in order to improve the durability and reduce the design errors of steam-curing precast concrete components,the damage of steam-curing GFRPreinforced precast concrete components were studied.Firstly,the damage experimental study on steam-curing concrete,GFRP bars embedded in steam-curing concrete and the bond performance were carried out from the perspective of macroscopically and microcosmic respectively.Subsequently,the damage mechanism of the underlying relationship was analyzed.The damage evolution process of GFRP reinforced concrete beams was analyzed from the perspective of energy dissipationby using the finite element method.The results showed that the early strength of steam-curing concrete was higher and the damage of GFRP bars embedded in steam-curing concrete reinforced concrete was significantly lower than that of steel bars.It was verified that the method of using the GFRP bars in the concrete structure for completely or partly replacing for steel to solve the corrosion problem of steel bars were feasible.However,the changes of later strength,capillary water absorption and pore distribution leaded to the reduction of durability of steam-curing concrete andaccelerated the damage speed of GFRP bars and bond performance between steam-curing concrete and GFRP bars.The damage level of tensile properties of internal GFRP bars was decrease with the increase of diameter.The closer to the concrete surface,the thinner the thickness of the protective layer,the more obvious the tensile properties of GFRP bar was displayed.The bond performance was also related to the diameter and thickness of the protective layer.In addition,the maximum bond strengthand the interface fracture energy increased with the increase of the thickness and diameter of the protective layer.Secondly,On the basis of damage test,the prediction model of the strength of steam-curing concrete,tensile strength of GFRP bar embedded in the steam-curing concrete and bonding strength were established respectively.In the prediction model of steam-curing concrete,the strength of concrete conditioned 28 days and the curing age were regarded as a quantitative value and a variable value,respectively.In addition,the prediction model of tensile strength of GFRP bar embedded in the steam-curing concrete was established based on the Fick diffusion law with the introduction of steam curing damage factor,termed as λ and β.The prediction models of bonding strength between the steam-curing concrete and the GFRP bars considered the influences of steam-curing temperature damage,bonding length and thickness of protective layer,respectively.Finally,the bonding strength prediction model involved with the relationship of four parties was established.All about strength damage prediction model were in normal circumstances the strength as the base to reduce the design difficulties of steam-curing precast concrete components,due to dispense with the performance test of steam-curing precast concrete components.Finally,the property damage was embodied in the structural design of steam-curing concrete,forming as a final foothold.Based on the damage experimental investigations,the finite element model analysis and the performance prediction models,the appropriately modifyingwas conducted for the calculations including the normal section bearing capacity,flexural stiffness and crack width.According to the the characteristics of surface damage and low elastic modulus of GFRP bars,the suggestions of the minimal concrete cover thickness,the maximum allowable values of cracks and the reinforcement principle of GFRP bars were proposed.The actual design theory and method were provided for steam-curing precast concrete components to reduce the error between the service life and design life.