ABSTRACT
The paper will describe an experimental program in which five commercially available steel fibre geometries were investigated in dry-mix shotcrete. The fibres varied in geometry from end hooked to crimped, and their lengths varied between 25 and 30 mm. The intended fiber content was 60 kg/m3. Twelve panels - two without fibres and ten with fibres—were shot. During shooting, appropriate tests were conducted to determine the fibre percent rebound. Once the panels had hardened, beams were sawn and cylinders were cored. While the cylinders were tested in compression, beams were tested in 4-point bending to obtain precise load-deflection curves. These curves were analyzed to obtain suitable toughness characterization parameters. In particular, the ASTM method of calculating “toughness indices” at multiples of first crack deflection and the Japanese Concrete Institute technique of obtaining “flexural toughness factors” from the energy absorbed to a certain midspan deflection, were used. It was noted that the rebound of steel fibres in shotcrete is, on a percent basis, far greater than the other ingredients and strongly dependent upon fibre geometry. Further, fibre percent rebound was found to be closely related to a fibre geometrical parameter called “specific projected area”. In the hardened shotcrete, fibre geometry was found to have a decisive influence on flexural toughness. Both compressive and flexural strengths were found be marginally improved due to fibre presence.
