Experimental Study On Self-recovery And Energy Dissipation Of SMA Fiber Reinforced Cement-based Composite Beams

Concrete is the most commonly used material in construction engineering.but it is easy to crack in the tension zone because of its low tensile strength,affecting the durability and safety of the structure.Therefore,improving the self-recovery ability of concrete structures has become the current research focus.According to the research status of cement-based self-repairing materials at home and abroad.This paper proposed the combination of superelastic shape memory alloy fiber((SE)SMAF)and high ductility cement-based composite(Engineered Cementitious Composites,(ECC)based on the superelasticity of shape memory alloy.The self-recovery and energy dissipation properties of superelastic shape memory alloy fiber reinforced high ductility cement-based composites((SE)SMAF-ECC)were studied.The specific research contents and conclusions of this paper are as follows:(1)The tensile mechanical properties of high ductility cement-based composites were tested.The proportion of high ductility cement-based composites suitable for(SE)SMAF deformation is determined and the mechanical properties of high ductility cement-based composites with this ratio is mastered.(2)The tensile test of superelastic properties of(SE)SMA wire was carried out.The ultimate tensile strength,ultimate strain,starting point,and end point of stress platform of(SE)SMA are analyzed through uniaxial stretching and cyclic stretching.The paper will study on the superelastic properties of(SE)SMA yarn.(3)Experiments on self-recovery and energy dissipation of pre-notched beams are carried out.A crack with 1mm wide and 10 mm deep is prefabricated at the bottom of the span of high ductility cement-based composite beams.(SE)SMAF is embedded in the crack.Through the three-point bending cyclic loading test,the self-recovery and energy dissipation performance of pre-notched beams are studied.Three main influencing factors such as(SE)SMAF volume ratio,diameter,and end form were analyzed.The research shows that the knotted end can provide effective anchoring.With the increase of(SE)SMAF volume ratio and diameter,the deflection self-recovery capacity and energy dissipation capacity of the specimen keep increasing.(4)Experiments on self-recovery and energy dissipation of randomly distributed(SE)SMAF-ECC beams are carried out.The randomly distributed(SE)SMAF-ECC beam specimens are made.The cyclic loading test of three-point bending was carried out.The load-deflection relationship,energy dissipation,and deflection self-recovery performance are analyzed.The results show that the deflection self-recovery and energy dissipation capacity of the specimen increase at first and then decrease with the increase of(SE)SMAF content.Among them,the best self-recovery and energy dissipation performance of the specimen beam is achieved when the volume content of(SE)SMAF is 0.5%.(5)Based on the test,the relationship between single(SE)SMAF stress and beam crack width in pre-notched beam specimen is analyzed,besides,the influence of(SE)SMAF volume content on the bearing capacity,deflection self-recovery rate,and energy dissipation capacity of randomly distributed(SE)SMAF-ECC beams is tested too.The results show that for the knotted end(SE)SMAF,the SMAF stress can be continuously increased to the stress platform when the crack width of the beam is more than 3mm.For randomly distributed(SE)SMAF-ECC beam specimens,when the volume content is between 0.25% and 0.5% and the volume content increases by 0.01%,the ultimate strength of the beam specimen increases by about 0.088 MPa,the residual strength increases by about 0.4258 MPa,the energy dissipation increases by about 0.199,and the deflection self-recovery rate increases by about 1.75%.