Modification Of Flax Fiber Reinforced Polymer (FFRP) Composites And The Compressive Properties Of The Confined Concrete Columns

Fiber Reinforced Polymer(FRP)has the advantages of lightweight,high strength and corrosion resistance,and has been widely used in medical,automotive,aerospace,civil engineering,etc.The fibers that have been widely applied in FRP are synthetic fibers such as carbon fiber,glass fiber and basalt fiber.The application of natural fiber is a new research direction for the development of composite.Natural fiber has the advantages of environmental friendness,wide source and low price,but it has the drawback in the mechanical properties and durability compared with inorganic fibers.Meanwhile,the application of natural fiber in civil engineering is mainly non-bearing element such as structure decoration,the application for confinement or strengthening is much less.Therefor,it is necessary to study the method to improve the properties of natural fibers,and investigate the application of natural fibers in civil engineering.Flax fiber is the object of this paper,the tensile properties of flax fiber and its renforced polymer(FFRP)composite was improved after treated in alkaline with tension.The structural properties of FFRP were studied with the application of confining concrete columns.The main research contents of this paper are as follows:(1)The modification of flax fiber in alkalization under tension.The study investigated the tensile properties of single flax fiber and fiber bundle treated under tension in alkalization.The effect of tensile stress and speed was investigated and the parameters were optimized.This paper verified that treated in alkaline with tension could greatly improve the fiber tensile strength(such as the optimization of processing conditions of single fiber tensile strength can increase 62%);the fiber tensile yield strain increases.The properties of crystalline and elements on the surface were studied by XRD and XPS.The results showed that the alkalization treatment with tension can improve the flax fibers within the amorphous orientation of cellulose chains,and this is the main reason for the improvement of tensile strength of single fiber after treatment.(2)The study of the tensile properties of flax fiber reinforced polymer composite coupon.The study investigated the mechanical and thermodynamics properties of unidirectional FFRP composites with treated and untreated fibers;the mechanical properties of flax and basalt hybrid fiber reinforced polymer(HFRP)were investigated,and the durability in 98% moisture environment;the study investigated the properties of bidirectional FFRP in different orientations.The results show that the tension in alkaline treatment can effectively improve the tensile properties of unidirectional FFRP,the parameter in treatment was optimaized;the water uptake of FFRP was high,as well as the degraduation of mechanical properties.The mechanical properties and water absorption properties of HFRP were in accordance with the role of mixture.The fitting equation of the tensile modulus of FFRP was given in this paper,and it can be used in HFRP.The tensile properties of flax sheet reinforced polymer composites were different in warp and weft directions.(3)The study of the compressive properties of FFRP confined concrete columns.The monotonic and cyclic compressive properties of concrete filled FFRP tubes were investigated.The effect of hybrid type(i.e.the distribution of flax and basalt fiber)of flax and basalt fiber layer was investigated.The compressive properties of bidirectional FFRP composites was investigated and fitted with design models.The results show that the envelope curve of concrete filled FFRP tubes were under the monotonic axial compressive stress-strain curve in cyclic axial compressive test,which is because the degraduation of elastic modulus of FFRP in cyclic tensile test.The results also show that the hybrid type hardly effect the strength of HFRP confined concrete cylinder,the analysis model can accurately predict the compressive properties of concrete filled HFRP tubes.The design model of compressive properties of flax sheet reinforced polymer composite confined concrete were determined by the tensile strength and modulus of FFRP;the orientation of flax sheet in confinement effected the bearing capacity and maximum deformation of confined concrete.