Evaluation Of Fundamental Mechanical Properties Of Thermoplastic FRP Bars For Concrete Structure

Fiber reinforced polymer(FRP)composites,characterized by high strength,light weight and superior corrosion resistance,have been widely used in civil engineering.At present,the application of FRP material mainly uses thermosetting FRP,but because it does not have the secondary processing performance,the shape of the material can not be changed after curing and can not be reprocessed at the construction site.FRP stirrups and crooked bars can only be prefabricated by the factory,at the same time,thermosetting FRP generally has defects such as hard and brittle,poor impact resistance,long curing cycle,difficulty in recycling,and poor environmental adaptability.Aiming at many shortcomings of thermosetting FRP,this paper studied and developed a kind of thermoplastic BFRP bars with thermoplastic epoxy resin as matrix material and new green environmental protection basalt fiber as reinforcement material.The research focuses on the production process,basic mechanical properties,alkali corrosion resistance,bonding properties with concrete,secondary bending theory and technology,and mechanical properties of bent bars for thermoplastic BFRP bars.The specific research content and results are as follows:1.Research on production process of thermoplastic FRP bars.Through the improvement of the traditional thermosetting FRP tensile agent technology,the solution Faraday agent process for the thermoplastic FRP bars was determined;the effect of residual solvents inside the FRP bars on the mechanical properties of the FRP bars was analyzed by making three different impregnated yarns.2.Research on the basic mechanical properties of thermoplastic FRP bars.The tensile properties,interlaminar shear properties,and double shear properties of thermoplastic BFRP bars were tested,and compared with thermosetting BFRP bars and thermoplastic GFRP bars.The results show that the tensile strength and elastic modulus of thermoplastic BFRP tendons are the same as those of thermosetting BFRP bars,but the interlayer shear strength and double shear strength are obviously lower.At the same time,the three mechanical properties of thermoplastic BFRP bars are better than those of GFRP bars.3.Research on alkali corrosion resistance of thermoplastic FRP bars.Accelerated alkali corrosion tests at different temperatures were performed on thermoplastic BFRP bars and compared with thermosetting BFRP bars and thermoplastic GFRP bars.The results show that the alkali corrosion resistance of thermoplastic BFRP bars is better than that of GFRP bars,but the alkali corrosion resistance is obviously worse than that of thermosetting BFRP bars.The SEM observation results show that the thermosetting BFRP bars only have resin-fiber interface at the outer edge of the cross section.The sticking resulted in the complete looseness of the fiber,while the thermoplastic BFRP tendon did not show significant fiber looseness,but there were significant holes and cracks in the entire cross section due to interface debonding.4.Research on the bonding properties between thermoplastic FRP bars and concrete.The uniaxial pull-out test was used to test the bondability between thermoplastic BFRP bars and concrete.The influences of parameters such as the concrete strength grade,rib pattern,and diameter were examined,together with thermosetting BFRP bars and thermoplastic GFRP bars.Rebars and others were compared.The results show that: improving the strength grade of concrete can improve the bond strength;the form of surface ribs has a great influence on the bonding properties of thermoplastic BFRP bars and concrete,and the bonding properties of the integrated deep rib pattern specimens are optimal;thermoplastic BFRP bars and concrete The bond performance is better than that of GFRP bars;compared with the thermoset BFRP bars,the bond properties of the two are comparable to those of concrete.5.Research on bending process and properties of curved thermoplastic FRP rebars.A series of researches on bending process and mechanical properties were carried out on the outstanding characteristics of thermoplastic FRP bars with secondary processing properties.A macro-mechanical model for calculating the bending strength of FRP bending bars was established.A simple bending device for the secondary bending of thermoplastic FRP bars was developed.The tensile mechanical properties of FRP bending bars were tested.The results showed that: the thermoplastic BFRP bending bars The strength retention rate at the bending site is inversely proportional to the diameter d,and is proportional to the bending radius r/d.At the same time,the retention rate of the strength at the bending site of the thermoplastic FRP bars is slightly lower than that of the thermosetting FRP bars.The strength of the bending part is obtained by using the norm empirical formula and the macro mechanical strength model respectively.Theoretical calculations were performed and compared w ith the test results.