Benefits of chemically treated steel fibers on enhancing the interfacial bond strength from ultra-high-performance concrete. (2nd August 2021)

• Record Type: Journal Article
• Authors: Chun, Booki; Kim, Soonho; Yoo, Doo-Yeol
• Is Part Of: Construction & building materials. Volume 294(2021)
• Publication Date: 2021-08-02
• Subjects: Ultra-high-performance concrete -- Steel fiber -- Pullout behavior -- Chemical treatments -- Surface roughness -- Cleansing effect; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2021.123519
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Surface roughness of steel fiber can be increased by up to 24.9 times through chemical treatments. Roughened fiber surface results in an improvement of average bond strength of steel fiber from UHPC. Nanosilica coating and EDTA electrolyte solution treatment greatly improve an average bond strength. Optimum treatment time of EDTA electrolyte solution is suggested to be less than 6 h. Acetone washing effectively improves both bond strength and pullout energy. Zinc phosphating leads to no significant change in pullout resistance. Abstract: This study investigated the effects of various chemical treatments on the pullout behavior of steel fibers in ultra-high-performance concrete (UHPC). Various methods used in previous studies were adopted and reproduced using macro straight steel fibers. The methods included acetone and acid washing, zinc phosphating, nanosilica coating, and ethylenediaminetetraacetic acid (EDTA) electrolyte solution treatment. The surface conditions and roughness of each treated fiber were analyzed using scanning electron microscopy and atomic force microscopy. The fiber pullout test results indicated that the surface roughness increased between 1.5 and 24.9 times, and that a roughened fiber surface leads to an improvement in the average bond strength. Acetone washing was the most effective in improving the pullout resistance of the fiber due to its cleansing effect. Acid washing resulted in a slip-hardening behavior, which improved the pullout energy significantly. The zinc phosphating treatment exhibited the lowest average bond strength increase rate. Nanosilica coating was found to considerably improve adhesion; however, it caused fractures as inclined. EDTA electrolyte solution treatment significantly improved the average bond strength in proportion to the surface roughness. By considering the energy absorption capacity, the optimum treatment time of EDTA electrolyte solution was proposed to be less than 6 h.