Toughness of fiber-Reinforced High-Strength Concrete from Notched Beam Tests

Abstract

The toughness of fiber-reinforced concretes (FRC) is characterized from notched beam tests. The tests are conducted under crack-mouth opening displacement (CMOD) control in a servo-hydraulic machine to determine the stable response of both the unreinforced concrete and the FRC. Several toughness measures are defined in terms of the experimentally obtained load versus CMOD curves. These measures give a better indication of the fundamental behavior of the concrete, avoid the problems associated with the approach based on the deflection of unnotched beams, and are amenable to the incorporation of serviceability considerations. The effect of specimen size on the toughness is found to be significant in both the matrix- and fiber-dominated regimes of the FRC behavior. In general, toughness increases with specimen size and needs to be considered for characterization. The study was performed on beams of a 70 MPa compressive strength silica fume concrete, with and without high-strength hooked steel fibers. Findings indicate that the incorporation of a low volume fraction (1 percent) of steel fibers is sufficient to significantly decrease the brittleness of high strength concretes.