Use of engineered steel fibers as reinforcements in ultra-high-performance concrete considering corrosion effect

Abstract

The feasibility of using steel fibers engineered through a hybrid treatment of ethylenediaminetetraacetic acid (EDTA)-electrolyte solution and nano-SiO2 coating as reinforcements for ultra-high-performance concrete (UHPC) was investigated by considering fiber corrosion effect. For this purpose, two different corrosion degrees of 2% and 5% were intentionally induced, and the interfacial bonding and tensile properties of UHPCs reinforced with plain and surface-reformed (or engineered) steel fibers were evaluated according to the degree of corrosion. The test results indicated that the EDTA-electrolyte solution treatment and nano-SiO2 coating are effective for improving the interfacial bonding of straight steel fibers in UHPC, leading to an 86% increase in the equivalent bond strength (24.7 MPa). The treatments also improved the tensile performance of ultra-high-performance fiber-reinforced concrete (UHPFRC), and more than twice higher energy absorption capacity could be ach-ieved using the hybrid treatment method. In the case of plain steel fibers, the pullout resistance and tensile performance of UHPFRC both increased with fiber corrosion of up to 5%. However, UHPFRCs with surface -reformed steel fibers exhibited performance deterioration beyond a certain degree of corrosion. A longer im-mersion duration in the EDTA-electrolyte solution caused a higher susceptibility to steel fiber corrosion, regardless of the nano-SiO2 coating. Thus, fiber corrosion in UHPFRC must be prevented more strictly when surface-reformed steel fibers are used.