Investigation Of The Performance Of Extra-short Extra-fine Steel Fiber-reinforced Concrete

In recent years, Steel fiber concrete has been rapidly developed and widely applied. Steel fiber is always partly mixed with concrete in engineering project on account of its improvement of the rupture strength and abrasive resistance. However, as the ordinary steel fiber (Length: 20-40mm, length diameter ratio:40~20) , are of larger size and easy agglomeration,consequently,it will create strength decline out of high-content and uneven distribution. Thence, it generally shouldn't exceed 2% of the content (volume content) that make the strength function of steel fiber a failure for full embodiment.The paper studies about the effect of content and age change of steel fiber on functions of compressive resistance and ruptures resistance and its change rule through test and theory analysis to 2052 units (171sets×12) mortar test block, based on rational mixing proportion. Then it discusses the effect of steel fiber content change on restrained contraction and change rule by test and theory analysis to 18 units mortar test block. In the end, through the test and theory analysis to 288 units (48sets×6) concrete block to make a study of the influence on compressive resistance, ruptures resistance, flexural toughness and other mechanical property and change rule according to the change of steel fiber volume content. The main achievements are as follows:While the content of Steel fiber is less than 3%, the compressive strength and rupture strength of ordinary steel fiber mortar will slightly higher than that of the extra-short extra-fine steel fiber mortar with equal content. But while the content of steel fiber mortar is more than 3%, the compressive strength and rupture strength of extra-short extra-fine steel fiber mortar will obviously higher than the ordinary one with the same content.With the same content of Steel fiber, the extra-short extra-fine steel fiber in mortar is characterized by larger superficial area and more even distribution than the ordinary and its crack area of mortar is far less than the ordinary steel fiber either. While the content exceeds 4%, there is no cracking of mortar.While the Steel fiber content is below 3%, the compressive strength and rupture strength of ordinary steel fiber concrete will lightly higher than that of the extra-short extra-fine steel fiber concrete in terms of the same content. However, while the content of steel fiber is above 3%, the compressive strength and rupture strength of extra-short extra-fine steel fiber concrete is obviously higher than the ordinary with the same content. Under the same volume content, the elasticity modulus of extra-short extra-fine steel fiber concrete is distinctly larger than that of the ordinary and its ductility is also better than the ordinary.Under the fixed volume fraction of steel fiber, the improvement effect of hybrid steel fiber on concrete mechanical property is superior to the single type and the ductility of hybrid steel fiber concrete is also better than the single.The paper makes an analysis on the strengthening mechanism of extra-short extra-fine steel fiber to concrete. Depending on the fundamental characteristics of experimental stress strain curve of extra-short extra-fine steel fiber concrete and staring from the angle of emergence and development of micro crack and micro pore, the damage evolution process is divided into phases of pre-store, crack initiation, stable and unstable expansion of micro crack, by which the paper discusses the strengthening mechanism of extra-short extra-fine steel fiber. Equally, it elaborates the strengthening and toughening mechanism of extra-short extra-fine steel fiber concrete from the standpoints of compound material mechanics, fracture mechanics and interface mechanics.