A study of toughness indices

Abstract

Synopsis The paper reviews various methods of evaluating the toughness of fibre-reinforced concrete materials by means of toughness indices and discusses in detail the use of various multiples of jirst-crack defection to define toughness indices. A new toughness index is proposed, based on the load–deflection curves obtained up to twice the defection at first cracking. The index is given by the ratio of two areas under the load–deflection curve and is expressed as a percentage which varies from zero for plain concrete, through 67% for an elastic-plastic material, to a theoretical maximum value of 100% for an extremely tough material. Both modulus-of-rupture and notched-beam test specimens were used in the study. Although only one geometry is reported and only Duoform steel fibre was used in the study, the method described is potentially applicable to all geometries and types of fibre. The proposed toughness index is shown to be independent of the notch depths used in the geometry reported and has well defined maximum and minimum values. It also has a large range, which should make it suitable to distinguish between various types and amounts of fibre.