Mechanical and durability properties of ultra-high performance steel FRC made with discarded materials

Abstract This study investigates the mechanical and durability properties of 12 ultra-high performance fiber reinforced concrete (UHPFRC) mixes manufactured using alternate aggregate sources. Natural gabbro aggregates (GA), steel slag aggregates (SSA), and recycled concrete aggregates (RCA) were employed as coarse aggregates. The volume of the coarse aggregates was limited to 12.5% of the total UHPC volume. Three types of steel fibers were employed: macro hooked-end fibers, micro straight fibers, and a hybrid combination of these two fibers. The fiber volume fractions tested were 0% and 1%. Properties investigated were compressive and flexural tensile strengths, electrical resistivity, porosity, and rapid chloride permeability. Test results revealed that the effect of aggregate type was more pronounced on the flexural strength than compressive strength. UHPFRC with steel micro-fibers or a hybrid combination of both steel macro and micro-fibers had a more noticeable effect on the compressive strength than that with steel macro-fibers, irrespective of aggregate type. Moreover, UHPFRC specimens with steel macro-fibers showed the highest flexural strength, regardless of the aggregate type. The SSA improved all durability properties of UHPFRC, whereas RCA noticeably deteriorated the resistivity and chloride permeability. The incorporation of steel micro-fibers improved the porosity and chloride permeability of all UHPFRC mixes.