| Fiber reinforced polymer(FRP)has the ability of resisting chloride ion erosion.Therefore,FRP bars are considered as an ideal solution to steel corrosion.In addition,there are a lot of seawater and sea sand in the marine environment.If local materials can be obtained,the shortage of fresh water and excessive exploitation of river sand will be effectively alleviated.In recent years,the combination of FRP bars and seawater and sea sand concrete(SWSSC)has attracted extensive attention of scholars at home and abroad,and become a research hotspot.However,FRP bars are not immune to all engineering environments,and there are still durability problems in the marine environment.The lack of durability evolution rule and evolution mechanism hinders the application of the composite structure in practical engineering.Therefore,it is of great significance to study the durability of FRP bars reinforced SWSSC structure in the marine environment.Considering that the actual structure is in the state of stress in the service stage,the bond durability of glass fiber reinforced polymer(GFRP)bars and SWSSC and the flexural durability of FRP bars reinforced SWSSC beams under the coupled effects of seawater immersion and sustained load.(1)Firstly,the bond durability of GFRP bars and SWSSC was studied under the coupled effects of seawater immersion and sustained load.The effects of aging time,sustained load,and reinforcement diameter on bond durability were analyzed.The results showed that the pull-out failure of GFRP bars with a diameter of 12 mm occurred before and after the coupled effects of seawater immersion and sustained load.The ultimate bond strength increased first and then decreased with the aging time,and decreased with the sustained load from 0% to 25% of the ultimate pull-out load.Before and after the coupled effects of seawater immersion and sustained load,the failure mode of GFRP bars with a diameter of 16 mm was mainly caused by concrete splitting,and a few of them was pull-out failure.The ultimate bond strength increased with the aging time,and decreased with the sustained load from 0% to 25% of the ultimate pull-out load.Under the same aging time and sustained load,the ultimate bond strength of GFRP bars with a diameter of 16 mm was always lower than that with a diameter of 12 mm.(2)Secondly,the durability of flexural behaviors of GFRP bars reinforced SWSSC beams was studied under the coupled effects of seawater immersion and sustained load.The effects of aging time and sustained load on the durability of flexural behaviors of the beams were analyzed.The results showed that the failure modes of GFRP bars reinforced SWSSC beams changed from concrete crushed to GFRP bars ruptured under the coupled effects of seawater immersion and sustained load.The ultimate flexural capacity decreased with the aging time and also decreased with the sustained load from 0% to 40% of the ultimate load.The flexural stiffness of the beams increased first and then decreased with the aging time.Moreover,the flexural stiffness increased with the increase of sustained load.The maximum crack width of the beams decreased first and then increased with the aging time.The number of cracks decreased with the aging time and also decreased with the increase of sustained load.(3)Thirdly,the durability of flexural behaviors of steel-FRP composite bars(SFCBs)reinforced SWSSC beams was studied under the coupled effects of seawater immersion and sustained load.The effects of the aging time and sustained load on the durability of flexural behaviors of the beams were analyzed.The results showed that the failure modes of SFCBs reinforced SWSSC beams changed from the SFCBs yielding and then concrete crushed to the outer fiber ruptured of SFCBs under the coupled effects of seawater immersion and sustained load.The yield load and ultimate load of the beams increased first and then decreased with the aging time.Moreover,the yield load and ultimate load decreased with the sustained load from 0% to 40% of the ultimate load.The flexural stiffness of all the beams increased first and then decreased with the aging time.Moreover,the flexural stiffness increased with the increase of sustained load.The crack width of the beams decreased first and then increased with the aging time.The number of cracks decreased with the aging time and also decreased with the increase of sustained load.(4)Finally,the safety reserve of GFRP bars reinforced SWSSC beams and SFCBs reinforced SWSSC beams under the coupled effects of seawater immersion and sustained load was evaluated by the overall performance factor.The results showed that the overall performance factor decreased with the aging time,and also decreased with the sustained load from 0% to 40% of ultimate load.In addition,the degradation mechanism of flexural durability of FRP bars reinforced SWSSC beams was analyzed under the coupled effects of seawater immersion and sustained load.The results showed that both the degradation of mechanical properties of materials and the degradation of bond properties were the main reasons for the degradation of durability of beams.The microcracks on the surface of FRP bars were produced under the sustained load,which provided a channel for the corrosive medium to enter into the resin matrix.And then,the degradation of the mechanical properties and bond properties of FRP bars were caused,and the durability of the beams was degraded. |
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