Experimental Research On Durability Of FRP Reinforced Sea Sand Concrete Beams

With the country on the coastal and island construction and development,in some areas of river sand shortage is very serious,both from the economic and social benefits must reduce the exploitation of river sand resources,will look to the sea sand resources.But the sea sand contains chlorine ions will cause corrosion of steel.In recent years,domestic and foreign scholars have proposed the use of fiber reinforced plastic bar(FRP bar)instead of steel used in concrete structure to solve the problem of steel corrosion.In this paper,FRP reinforced beams are studied,including basalt fiber reinforced plastic bar(BFRP bar),carbon fiber reinforced plastic bar(CFRP bar)and Steel FRP composite bar(SFCB).Good bond behavior between FRP and sea sand concrete is the fundamental issue of reinforced concrete,therefore bond behavior between FRP and sea sand concrete was firstly studied in this paper.50 pull-out specimens were made and tested in the experiment in order to obtain short-term and long-term bond behavior between FRP bar and concrete.5%NaCl solution was made to simulate sea water and two different corrosion conditions which were wet-dry cycling with sea water at 40 ℃ and sea water immersion at 50 ℃ were used in the test in 3 and 6 months.Bond slip curve of each specimen and the ultimate bond strength of specimens were investigated in this paper.Bending property of FRP reinforced sea sand concrete beams was experimentally studied next.20 sea sand concrete beams were made to study the short-term flexural properties of FRP beams and the long-term flexural properties of FRP beams under the action of wet-dry cycling with salt solution.The long-term degradation rule of FRP reinforced sea sand concrete beams was analyzed about the aspects of failure mode,bearing capacity,ductility and crack development.From the bond test,the following conclusions can be conducted:The bond strength between SFCB and sea sand concrete was not changed or even increased during the 6-month period,and the bond strength between BFRP bar and sea sand concrete was fluctuating.50 ℃ salt solution immersion,6 months of age,SFCB and sea sand concrete bond strength changed little.But the bond strength between BFRP bar and sea sand concrete was degraded.In addition,all FRP bars under immersion had a lower bond strength than the wet-dry cycling environment.From the flexural test,the following conclusions can be conduted:the mechanic properties of FRP reinforced sea sand concrete beams were similar to river sand concrete beams.For the non-corroded specimen,the load deflection curve of BFRP and CFRP bar were obviously linearly eveloped.SFCB reinforced sea sand concrete beams had stable secondary stiffness.After wet-dry cycling and immersion corrosion,the majority of BFRP and CFRP beams had the same failure of bending with shearing or shearing,and a small amount of bending failure occured.The SFCB beams were mostly damaged by concrete crushed,but after 6 months of immersion,bending failure occured with the bar fractured.It is found by comparing immersion and wet-dry cycle in 3 to 6-month-old that BFRP,CFRP and SFCB ultimate load and ductility decline in varying degrees,and under the same age,the immersion capacity was lower than that of the wet-dry cycling.The degradation of BFRP stirrup and concrete interface was the main reason for the change of FRP beam failure mode and decline of limit load.The beam yield and ultimate load obtained by the calculation formula of the flexural capacity of the SFCB beam given in this chapter are in good agreement with the experimental results.At the same time,the formula of crack width of reinforced concrete beam is modified,and the formula of crack width before yield of sea sand concrete beam is obtained.The width of the crack calculated by the formula is in good agreement with the experimental results.