In situ determination of toughness indices of fibre reinforced concrete

A new method using the pull-out technique has been developed to address the problem of measuring the toughness of fibre reinforced concrete directly on existing structures. It consists of determining the load-displacement curves produced by pulling out pre-inserted bolts and determining the toughness indices expressing the ratio between the energy absorbed up to a given deformation level and the energy resulting in the onset of cracking. For varying fibre proportions, these indices are obtained on the basis of the material's response curves as recorded both from pull-out tests and, as in earlier investigations, from three-point bending tests: the good agreement in the results obtained from the two different types of test substantiates the possibility of using pull-out tests for the in situ determination of toughness parameters. Toughness indices are seen to increase with increasing fibre content, confirming the favourable effects of fibres on the ductility of the composite.