Study On The Durability Of BFRP Bars By Using An Accelerating Simulated Marine Immersion Environment

Steel corrosion in the reinforced concrete structure of marine engineering is the problem which needs to be solved as soon as possible.Fiber reinforced reinforced polymer bars(FRP bars)are used to substitute steel bars to solve this problem with the advantages of light weight,high strength and high-corrosion resistance.Comparing with other kinds of fiber,basalt fiber has high temperature resistance,environmental protection and low price.The durability of BFRP bars in the marine engineering attracks many researchers' attention while most researches are about the bare BFRP bars immersed in the corrosion solution with little data about the durability(degradation performance and thesis)of the BFRP bars wrapped in concrete in the corrosion solution.According to the shortcomings of current researches,the durability of the bare BFRP bars and the BFRP bars wrapped in concrete mortar of different diameters in the accelerated simulated marine immersion environment is studied and the future tensile strength retention within 20 years is predicted in this paper.The accelerated marine immersion environment contains different corrosion solution(seawater,alkaline solution and water)and temperature(room temperature,40°C and 60°C).The study on degradation mechanism of BFRP bars includes mechanics degradation of BFRP bars(tensile strength,elastic modulus,transverse shear strength,apparent horizontal shear strength),micro structure of BFRP bars and micro structure of the interfacial layer between concrete mortar and concrete mortar,which is compared by GFRP bars.The conclusions are as follows:(1)For basalt fiber bars in corrosive environment,setting concrete mortar accelerates the degradation rate of BFRP bars in the early stage,which is attributed to the alkaline concrete mortar.The concrete mortar prevents the BFRP bars from external corrosive media with alkaline material,which is reducing over time.This slows down the mechanical degradation rate of the BFRP bars wrapped in concrete mortar in the late stage.(2)The larger the diameter of concrete mortar is,the more alkaline material exists in concrete mortar.The strength retention of BFRP bars wrapped in the concrete mortar of 45 mm diameter are almostly lower than the BFRP bars wrapped in the concrete mortar of 27 mm diameter under the same conditions during the 180-day immersion period.To the BFRP bars wrapped in concrete mortar of 45mm/27 mm diameter and immersed in seawater for 180 days,their tesile strength reduces by 34.8%/28.1%(room temperature),43.1%/30.1%(40°C)and 45.9%/38.8%(60°C).(3)For the BFRP bars wrapped in concrete mortar in corrosive environment,the material in the interface between BFRP bars and concrete mortar changs due to the external corrosive environment(immersion solution temperature,solution type,thickness of concrete mortar).Sulfate attack is found in the specimens in seawater.C–S–H gel is found in the seriously degenerated BFRP specimens which means the fiber has been corrosed due to the alkali aggregate reaction or attack of hydroxy ions on the siliconoxygen bonds.The indications of alkali-aggregate reaction have been proved in the interface between BFRP bars and concrete mortar.