Influence of Steel Fibers on Fracture Energy and Shear Behavior of SCC

Abstract

The fracture behavior and the dilatant crack opening in the shear response of self-consolidating concrete (SCC) with discrete steel fiber reinforcement were investigated. The volume fraction of hooked-end steel fibers in concrete was .75%. The fracture behavior of steel fiber reinforced SCC (SFRSCC) was investigated using notched beams tested in flexure. In SFRSCC, there was a significant increase in fracture energy at a small crack opening. The significant postcracking resistance to crack opening provided by fibers in an SCC matrix resulted in a twofold increase in energy up to .1 mm crack opening. In SFRSCC, there was a tenfold increase in energy up to 1. mm crack opening, which was associated with multiple cracking in the matrix. In the second stage of the experimental evaluation, the shear behavior of SCC with and without steel fibers was investigated using a shear beam arrangement. The dilatant behavior of the shear crack was established from in situ full-field displacement measurements from across the primary shear crack, obtained using digital image correlation (DIC). There was a continuous slip between the faces of the shear crack, which produced a continuous increase in the crack opening. Shear crack in SCC beams curves in a direction governed by the applied stress field. Failure in SCC is very brittle and occurs at small crack openings which are less than .1 mm. The sudden loss of internal stress transfer across the primary shear crack produces failure in SCC beams. In SFRSCC, the primary shear crack formed at a load that was nearly double the load at the formation of the shear crack in SCC. The dilatant behavior in SFRSCC was identical to the dilatant behavior obtained from SCC without fibers. In SFRSCC, there was an increase in load-carrying capacity with a continued opening of the shear crack, and load transfer across the primary shear crack was sustained for a larger crack opening. Due to increased contact stress on the crack faces induced by high cohesive crack closing stress produced by fibers, the shear crack at the neutral axis continued to propagate along the initial angle, resulting in a straight crack path without curvature. There was a stress transfer across primary shear crack openings up to 1 mm due to the crack closing stress provided by the fibers. A secondary shear crack in SFRSCC beams led to failure. The improvement in the fracture response of SCC with the addition of fibers results in an increase in shear capacity through better crack control.