Research On Properties Of Flax/Glass Fiber Hybrid Composites And The Confined Concrete Columns

Hybrid fiber reinforced polymer(HFRP)is the composite composed of two or more kinds of continuous fiber materials to reinforce the same resin matrix,so that they can work together and complement the advantages of each other.Thus,it can acquire the better effect which is the single fiber cannot achieve.At present,the researches of fiber hybrid composites mainly focuses on the hybridization among synthetic fibers,such as carbon fiber and glass fiber hybrid composites,etc.However,no matter what kind of synthetic fiber,it is necessary to consume a great deal of non-renewable resources in the manufacturing process.Simultaneously,there are some shortcomings such as high production costs,non-biodegradable treatment,etc.Currently,the developmental stage of Chinese economy is in the process of high-speed growth to high quality.The renewable green natural fiber is a new direction of composites research field and practical application.Replacing partial synthetic fibers with natural fibers can alleviate the loss of natural resources and damage to ecological environment caused by civil engineering construction.It is of great importance to promote innovative development in civil engineering construction.Therefore,the preparation of flax/glass fiber hybrid reinforced epoxy resin composites and the influence of different stacking sequences on the comprehensive mechanical properties.and hygrothermal durability are investigated in this paper.After that,the axial compressive properties of concrete cylinders with HFRP sheets confining are studied experimentally.It will broaden the application scope of HFRP composite in civil engineering.Moreover,it lays a theoretical and design foundation for the HFRP composite-concrete combination structure.The main contents in this research are as follows:Firstly,the mechanical and thermal properties of flax/glass fiber hybrid composites were tested.And the influence mechanism of different stacking sequences on properties of the composites under the same mixture ratio was revealed through comparing with the properties of pure flax fiber composites.Experimental results show that the tensile and bending properties of HFRP composites represent the positive hybrid effect and there is no obvious difference in tensile properties among various HFRP composites,but the bending properties are significantly different.The storage modulus of hybrid fiber composites is improved distinctly,and the loss factor of the composites is also obviously reduced by adding the high-strength glass fiber.Secondly,the hygrothermal durability of HFRP composites was tested under the environment of distilled water at different temperatures to study the regularity of long-term aging properties.Experimental results show that the water absorption and diffusion law of all the composites immersed in distilled water at different temperatures conforms to the model of Fick water absorption law.In addition,the bending properties show the process of decreasing firstly and then tending to develop smoothly.The deterioration rate of interlaminar shear strength is higher than that of bending strength.Finally,the test of axial compressive properties of HFRP composite confined concrete cylinder specimens was carried out.Experimental results show that the failure modes of HFRP composite confined concrete cylinder members are basically the same.The failure trend of load-displacement curve is essentially in agreement with that of axial stress-circumferential/axial strain curve.The main difference is that the failure process of the second stage depends on the comprehensive mechanical properties of various restrained HFRP composites.