Novel Hybrid Fiber Factor for Hybrid Fiber-Reinforced Concrete

Hybrid use of macro and micro steel fibers offers greater potential for enhanced performance of hybrid fiber-reinforced concrete (HFRC). However, predicting the properties of HFRC has been hindered by inadequate research on a suitable hybrid fiber factor, leading to lots of trial and error in the mix design. To fill such a research gap, an experimental program was launched by producing a total of 18 plain and HFRC mixes using macro and micro steel fibers at a constant total fiber volume of 2.0%. Then, the influences of various hybrid fiber combinations on the fresh and hardened properties of HFRC were investigated and correlated by regression analysis to some suggested hybrid fiber factors to identify the key factor governing each performance attribute. It was found that the hybrid use of macro and micro steel fibers at a constant total fiber volume yielded higher workability and strength, and the traditional fiber factor was not applicable to HFRC. Moreover, in the hybrid fiber factors, the fiber number was more fundamental than the fiber volume. Lastly, design equations for predicting the various performance attributes were derived for HFRC with discussions on the associated mechanism.