What Functions Can Hooked-end Steel Fibers Enhance Concrete

1. Introduction of hooked end steel fiber

The length of hooked end steel fiber refers to the linear distance between the two ends of the fiber, expressed in Lf, and its length can be 15 ~ 60mm. The diameter or equivalent diameter of the fiber cross-section (when the steel fiber has a non-circular cross-section, its cross-sectional area is equivalent to the diameter of the circular cross-sectional area.) is expressed in df, and its length can be 0.3 to 1.2 mm. 

The aspect ratio of the steel fiber refers to the ratio of the length of the steel fiber to the diameter or equivalent diameter, that is, Lf/df, which is usually 30-100. The volume ratio of the hooked end steel fiber refers to the percentage of the fiber concrete volume occupied by the steel fiber, expressed in pf, which indicates how much steel fiber is incorporated in the mixture.

2.Which functions of concrete can be enhanced by the hooked end steel fiber

As the damage of concrete mainly due to the pulling out of the fiber instead of breaking, the steel fiber concrete reinforcement mainly depends on the bonding strength of the steel fiber concrete matrix interface. 

In addition to improving the bonding strength related to the performance of the matrix, as far as the steel fiber itself is concerned, the surface and shape of the fiber should be used to improve its bonding performance with the matrix. In order to improve the bonding strength of the steel fiber, it is often used to: roughen the surface of the hooked end steel fiber, have an irregular cross section, increase the contact area and friction with the matrix; indent or press the fiber surface into a wave shape, increase the mechanical adhesion force; turn the two ends of the fiber into different shapes, and make them into hooks or big head shapes to improve its anchoring force and pull-out resistance. 

The reinforcing effect of the hooked end steel fiber is related to the length, diameter (equivalent diameter) and aspect ratio of the steel fiber. The reinforcing effect of the steel fiber enhances with the increase of the aspect ratio. The length of the steel fiber is too short to have the effect of strengthening while it is too long to finish the construction, which will affect the quality of the mixture. If the diameter is too thin, it will be bent during the mixing process, and if it is too thick, the reinforcement effect will be poor at the same volume rate.