Surface refinement of steel fiber using nanosilica and silver and its effect on static and dynamic pullout resistance of reactive powder concrete

This study investigated the effects of steel fibers, surface-reformed by silver and nanosilica coatings, on the static and dynamic pullout behaviors of reactive powder concrete (RPC). To consider the fiber orientation effect, two different inclination angles of 0° and 45° were adopted. The static bond strength of straight steel fiber in RPC significantly increased because of the nanosilica coating but was marginally affected by the silver coating. More than twice the bond strength and pullout energy were achieved by the nanosilica coating compared to the pristine steel fiber. The loading rate sensitivity on the pullout resistance of straight steel fibers from RPC was found regardless of the surface refinement. However, under inclined conditions, the pullout resistances of the silvered and nanosilica-coated steel fibers in RPC were almost insensitive to the loading rate or were even reduced at impact loads. Thus, although the nanosilica-coated steel fiber led to the best pullout resistance from RPC under impact loads, the deposited silver and nanosilica particles negatively affected the rate sensitivity of the pullout resistance of RPC. When the fibers were coated with nanosilica and inclined or impact loads were applied, more scratches and matrix debris were found on the surface of the pulled-out steel fibers, verifying the enhancement of interfacial frictional resistance at the fiber-matrix interface.