Durability Study Of BFRP Bars And Their Reinforced Concrete Beam Immersed In Seawater

Basalt Fiber Reinforced Polymer(BFRP) bars, as a new type of composite materials, have been used in coastal projects by many countries to replace steel bars. BFRP bars possess high strength and alkali-resistance, they stay in seawater(SS) and sea sand(SC) environment without being rusted like steel bars, and to be seen as a substitute of steel bars used in future reinforced concrete structures. In view of investigating the properties of BFRP bars, bond strength between BFRP bars and concrete, and shear performance of BFRP bar reinforced concrete beam in seawater environment, the research work includes three following contents:1) Degradation of BFRP bars’ mechanical properties, including tensile property, flexural property, shear property and in-plane shear property. Samples include BFRP bars that immersed in simulated seawater with a temperature of 20°C/40°C/60°C; and wrapped in mortar immersed in simulated seawater with a temperature of 20°C have been tested.2) Bonding property of BFRP bars and SSSC concrete: Pull-out experiments of BFRP bar SSSC concrete and normal concrete immersed in outdoor seawater environment have been conducted.3) Degradation of BFRP bar reinforced concrete beam: Experiment of shear performance degradation of BFRP bar reinforced concrete beam has been conducted.Based on the experiments, the main results are listed as follow:1) Higher the soaking temperature, greater the degradation. After six months of seawater immersing, tensile and in-plane shear strength decreased by 39%/38%, respectively, shear strength decreased by 23%, flexural strength decreased by 14%, due to erosion of water molecules and alkali solution to the matrix. Reasons to the different falling range are: tensile strength depends mainly on residual quantity of resin, flexural strength depends mainly on bond stress between matrix and fiber, shear strength depends mainly on the strength of resin, and in-plane shear strength depends mainly on internal porosity;2) Initial bond strength of BFRP bar–SWSSC is higher, because chloride accelerated the dissolution and reprecipitation of calcium hydroxide, increased contact area between cement grain and water, accelerated early reaction. Seawater in concrete have a corrosion effect on the matrix, causing friction between BFRP bars and concrete bond strength decreased, therefore, bond strength decreased.3) The loading procedure can be divided into four stages: elastic stage, cracking stage, shear stress dominating stage, failure stage. Load-deflection curve has a high rigidity stage in the beginning and then a low rigidity stage until failure, due to a sudden redistribution of stress after crack. BFRP bar RC beam behaved as shear-compression failure while steel bar RC beam behaved as flexural failure with the same ratio of longitudinal and stirrup reinforcement. The maximum load of BFRP bar RC beam decreased by 18.2% after soaking in seawater for six months, the result meet the requirement of ACI/ASTM standard.