Study On Mechanical Properties Of Aligned Steel Fiber Reniforced Geopolymer And Acoustic Emission Characteristics During Bending Failure Process

As a new type of building material,geopolymers have the advantages of high compressive strength,fast hardening,and chemical corrosion resistance.However,they also have defects such as poor toughness and large brittleness,which greatly limit their practical application.Incorporating steel fibers into polymers can improve these shortcomings.In this paper,fly ash and silica fume are used as stimulated materials,the mixture of Na OH solution and sodium silicate is used as activator,sand is used as aggregate.The content of silica fume,volume content of steel fiber and fiber orientation were used as control parameters.Study the influence of control parameters on the mechanical properties of geopolymers.At the same time,the acoustic emission detection technology is used to monitor the whole process of bending failure of the steel fiber reinforced geopolymer beam,and the damage mechanism of the steel fiber reinforced geopolymer beam is systematically analyzed by combining the macro-mechanical effect and the acoustic emission characteristic parameters.The specific research contents and conclusions are as follows:(1)The preparation method of geopolymers was determined,and the preparation of geopolymers with three different matrix strengths(19.36MPa(group A),45.6MPa(group B),65.9MPa(group C))was achieved by changing the content of silica fume.Based on the mixing ratio of group A and group C,steel fiber reinforced geopolymers with different volume content(0.5%,1%,1.5%)were prepared.The cubic compressive strength test results show that when the fiber content is 1%,the compressive strength of the geological polymer reaches its maximum.The fixed fiber content was 1%,and three oriented steel fiber reinforced geopolymers with different matrix strengths were prepared.The results showed that the cubic compressive strength of oriented fiber reinforced geopolymers showed obvious anisotropy characteristics.When the fiber orientation is perpendicular,the compressive strength of the three matrixstrength oriented fiber-reinforced geopolymers is increased by 13%,12%,and 24%,respectively,compared with the blank sample without fiber reinforcement;when the loading direction is parallel to the fiber orientation,the compressive strength Compared with the blank sample without fiber reinforcement,the strength is reduced by 9%,15%,and 16%,respectively.(2)Based on the mixing ratios of the three matrix strengths,fiberreinforced geopolymer beams with different fiber content and orientation were prepared,and the results of the three-point bending test showed.When the steel fiber content is 1%,the flexural strength and fracture energy of the hetero-directional steel fiber reinforced geopolymer reach the maximum,while the flexural strength and fracture energy of the directional steel fiber reinforced geopolymer are 1.5% when the fiber content is 1.5%.When reaching the maximum value.The orientation of the steel fiber can greatly improve the flexural strength of the non-fiber-reinforced geopolymer,and at the same time,there will be obvious zigzag rheology in the descending section of the bending load-deflection curve.(3)A detailed analysis of the acoustic emission characteristic parameters of the directional steel fiber reinforced geopolymer beam with a steel fiber content of 1% during the bending failure process.The results show that the amplitude of acoustic emission is less than 70 d B in the load rising section of sawtooth rheology,and corresponds to low energy rate and wave impact rate,but a small amount of amplitude appears in the falling section of sawtooth rheology.The number of wave strikes higher than 70 d B and energy accounted for more than 90% reveals that the two microscopic damage mechanisms of matrix cracking and fiber slippage are alternately dominant in the sawtooth rheological process.