ABSTRACT
Ultra-high-strength concrete (UHSC) low ductility leads to unfavorable brittle failure. Therefore,
the use of steel fibers in UHSC will extend the possible fields of application. Owing to the very
low water content of UHSC mixes, the incorporation of fibers seems to be impossible. Hence,
modification of the UHSC mix to become a self-compacting mix will enable the inclusion of
steel fibers without sacrificing its workability. In this study, the behavior of eight axially loaded
medium scale columns cast with ultra-high-strength fiber-reinforced self-compacting concrete
(UHS-FR-SCC) is investigated. The parameters included the effect of fiber inclusion, fibers
volume fraction and the transverse steel percentage (i.e. stirrups). Two columns were tested
as control specimen without fiber inclusion; the remaining six columns were tested in 3 groups,
each group consisted of 2 columns. The fiber volume fraction was varied between the three
groups. In each group, the transverse steel percentage was varied. The behavior of the tested
columns was evaluated with respect to ultimate load, strain in concrete, axial reinforcement
and transverse reinforcement, and modes of failure of the tested columns. It was found that the
inclusion of steel fibers increased the deformability (i.e. axial deformation) and load carrying
capacity of the UHSC especially at high fiber volume fractions. At high fiber volume fraction
the high deformability of the concrete activated the confinement exerted by the stirrups.
Keywords: Ultra-high-strength concrete (UHSC), Fiber-reinforced concrete (FRC), Fiber volume fraction, Columns, Strains, Transverse reinforcement.
