Round Panel Test On Flexural Toughness Of Steel-Polypropylene Hybrid Fiber Shotcrete

The steel polypropylene hybrid fiber reinforced shotcrete refers to a new kind of composite material, which is added steel fiber and polypropylene fiber into the plain concrete mixed with a certain amount. In the steel polypropylene hybrid fiber reinforced shotcrete, high elastic modulus steel fiber and high ductility polypropylene fiber can exploit advantages at different stress stages and structure levels, the new kind of fiber shotcrete will cause hybrid effect that can obviously improve the properties of brittle failure of traditional plain shotcrete, it can enhance the strength and flexural toughness of plain shotcrete at the same time. People used beam bend tests to evaluate the flexural toughness of shotcrete, but the size of beam is too narrow, it can limit the fibers distribute randomly in the concrete, which will show high scatter of test results. Therefore, the traditional beam test can not reflect the real ability for deformation and energy absorption of the support structures. This article uses theoretical analysis and laboratory test, carry out research on the flexural toughness of steel polypropylene hybrid fiber shotcrete. The main research work and achievements are as follows:(1)Carry on the hybrid fiber shotcrete cube compressive strength test, research on steel fiber and polypropylene fiber improvement effect to the shotctete about compressive strength and toughness. The result shows that steel fiber not only can enhance the compressive strength of shotcrete, but also can improve the properties of brittle failure. While the polypropylene fiber can not improve the strength of plain shotcrete obviously.(2)Carry on the hybrid fiber shotcrete square panel test, research on steel fiber volume fraction and polypropylene fiber improvement effect to the shotcrete about flexural strength and toughness. The result shows that the flexural toughness increased with the augment on volume fraction of steel fiber volume fraction, it also shows that adding the steel polypropylene hybrid fiber can increase the residual flexural strength and improve the ability for energy absorption of shotcrete.(3)Carry on the hybrid fiber shotcrete round panel test by an improved electro-hydraulic servo testing machine, research on varieties of fibers and hybrid fibers improvement effect to the shotcrete about flexural toughness. The results show that ultrashort microfilament steel fibers can enhance the ultimate flexural load、the residual flexural load and cumulative energy absorption ability,the enhancement effect is obviously better than multiple anchor steel fibers. The steel polypropylene hybrid fiber has a significantly better improvement in the shotcrete’s flexural toughness effect than the single steel fiber. In addition, study on comparing different kinds of fiber shotcrete’s post cracking energy absorption index, the comparison result shows that the hybrid fiber shotcrete with 1.2% ultrashort microfilament steel and 0.6% polypropylene has the best improvement in the shotcrete’s flexural toughness effect, which is closest to perfect elastoplastic material after initial crack.