Improvement in Tensile Performance of Ultra-high-performance Alkali-activated Concrete Using Surface-treated Steel Fiber

In this study, the tensile-performance enhancement of ultra-high-performance alkali-activated concrete (UHPAAC) was investigated by applying ethylenediaminetetraacetic acid (EDTA)-treated steel fibers with increased surface roughness. Direct tensile tests and digital image correlation image analyses were conducted to evaluate its crack behavior. When EDTA-treated steel fibers were used in UHPAAC, the tensile strength and maximum tensile strain of the latter improved by approximately 70% and 1.5 times, respectively, compared with those of S13 steel fibers, with a strain energy density increase of approximately 2.8 times. Additionally, EDTA-treated fibers effectively reduced the average and maximum crack widths across all strain levels and facilitated the formation of approximately 1.5 times more microcracks, thus demonstrating excellent crack-width control and strain-hardening behavior. These results confirm that EDTA-treated steel fibers are effective in improving the tensile performance and microcrack behavior of UHPAAC.