Influence of the yield strength of steel fibres on the toughness of fiber reinforced high strength concrete

High strength concrete is known to be a brittle material. To overcome this drawback discontinuous steel fibres are added to convert it into a ductile material and further improve its mechanical properties. However, because of the better bond between steel fibers adn concrete it is possible that at appearance of the first crack the steel fibres which cross the crack, fracture rather than being pulled out slowly. At the Department of Civil Engineering of the K.U.Leuven, toughness of steel fibre reinforced high strength concrete has been investigated by means of the four-point bending test specified in the Belgian Standard NBN B15-238. The investigated parameters were: compressive strength of concrete (50 MPa - 78 MPa - 92 MPa) and yield strength of steel fibre (LC: 1000 MPa - HC: 2000 MPa). From these tests it follows that from a compressive strength equal to 78 MPa, the toughness of concrete is increased considerably by the addition of HC-fibres instead of LC-fibres.