Flexural Behavior Characteristics of UHPC according to Twisted Steel Fiber

This study examines the effects of twisted steel fiber obtained by changing the shape of the fiber in order to improve the toughness of the conventional straight steel fiber. Three types of twisted fiber with different lengths (l) and diameters (d) are considered while maintaining the aspect ratio (l.d) to 100. Flexural tensile test is performed on the K-UHPC paste mixed with 1%, 1.5% and 2% of fiber relative to the volume of the matrix to analyze the flexural tensile performance, deflection capacity and energy absorption performance. The results show that the use of twisted fiber increases significantly the flexural toughness of K-UHPC compared to the use of the traditional straight fiber. Especially, the adoption of a quantity of twisted fiber reduced by 0.5% is seen to secure identical performances. The reduction of this quantity by 1% develops slightly lower flexural strength but provides remarkable deflection capacity. Accordingly, since the adoption of twisted fiber enables to reduce the mix ratio of fiber by 0.5 to 1% according to the intended purpose, such fiber is expected to allow further reduction of the fabrication cost of K-UHPC.