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 achieved 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 immersion 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.