Durability Study Of Sea Water And Sea Sand Concrete Beams Reinforced With BFRP Bars

In view of the rapid development of the coastal economy and the implementation of the national marine strategy,many buildings need to be built in our coastal areas.The traditional steel concrete structure affects the construction time,not only increases the cost,However,if the traditional FRP structure is strengthened,the degradation of sandstone natural resources and the shortage of fresh water resources will be intensified.BFRP(Basalt-fiber Reinforced Polymer)is a new environmental protection high performance composite material in civil engineering.As a new structural system,its durability in the marine environment needs further study.In this paper,the durability of BFRP reinforced sea sand concrete beams in simulated seawater immersion environment is explored and studied.The results of this study will provide data and theoretical support for further development of practical application of basalt fiber.The main research contents and achievements of this paper are as follows:(1)The static behavior evolution of BFRP reinforced sea sand concrete beams in simulated sea water immersion environment is studied by comparing alkali solution and water immersion.The results show that a dense and thick calcium film and a thin salt film will form on the surface of beams immersed in alkali solution and sea water,which will hinder the corrosion of external corrosion solution;The concentration of ions inside and outside the concrete can cause the filtration pressure,and the water is easy to be immersed in the sea sand of the concrete.Because of the obstruction of calcium film,the corrosion time of beams immersed in alkali solution is delayed,and the ultimate load of specimens immersed in simulated seawater,water and alkali environment at 180 days is reduced by 34.5%,28.8% and 6.7%,respectively.The contact area between BFRP reinforcement and sea sand concrete increases after water absorption expansion,and the mechanical bite force increases.After immersion for 360 days,the ultimate strength of simulated seawater,aqueous solution and alkali environment decreased by 51%,53% and 47%,respectively.There are many uncorroded cracks in the beam,the width of the cracks is small,the development of the cracks is mostly oblique cracks,and shear compression failure occurs.However,with the increase of leaching time,the crack width increases under the same load,which is basically longitudinal crack,and the crack decreases after corrosion,In the end,the destruction of the model is a transformation.(2)The fatigue behavior of the concrete beam strengthened by BFRP reinforcement after simulated seawater immersion is studied,and the fatigue life,deflection change,strain change of reinforcement and concrete and crack development law are analyzed.The results show that the fatigue damage is accumulating and the material properties are deteriorating under the cyclic load.The bond slip between the BFRP reinforcement and the concrete makes the crack width gradually larger,the crack extends upward,the residual deformation is accumulating,the overall stiffness is decreasing.When the strain of BFRP is close to the strain corresponding to the ultimate load,the shear failure occurs.The higher the stress level,the faster the fatigue damage accumulation and the shorter the fatigue life.Compared with the beam without corrosion,the residual deformation accumulated faster after simulated seawater immersion corrosion,and the overall performance of the structure became "soft".The adjusted strength formula accurately reflects the reduction of the test beam strength,and the embedded S-N curve can well predict the fatigue life.