Preparation and mechanical properties of super high-strength steel micro-fiber toughened concrete

Super high strength concrete (SHSC) is, due to high brittleness, difficult to be widely employed in civil engineering. The objective of this research is to reduce the brittleness of super high strength concrete by adding steel micro-fibers of length 6 mm and 13 mm. Mechanical properties of the concrete, including the flexural toughness measured by ASTM C1018, were investigated with different aspect ratios and volumes. The test results show that the energy absorption capability of SHSC was enhanced with increase of fiber volume. Compared with control mix, the most effective improvement of the first crack strength, flexural strength and toughness indices were investigated for the case of 1.0% fiber volume. A larger compressive strength of SHSC was measured for the case of 2.0% fiber volume when 6 mm length fibers were added, but an even higher compressive strength was measured for 1.0% fiber volume when 13 mm fibers were added. The results also show that tensile strength and Young's modulus of SHSC were improved by adding steel micro-fibers. It is concluded that a reasonable fiber volume should be applied when steel micro-fibers are used to improve the toughness of SHSC.