Spatial distribution of steel fibres in sprayed and cast concrete

Abstract

Research has investigated the fracture of steel fibre reinforced sprayed concrete under flexural load with the aim of developing a stress-profile model to predict flexural behaviour in the form of a load–deflection response. This paper reports the work associated with establishing the number, distribution and geometry of the fibres bridging a typical cracked section of both sprayed and cast steel fibre reinforced concrete beams. X-ray photographic analysis and manual counting techniques are described. The simple X-ray technique developed is shown to be capable of determining the probability distribution associated with fibre embedment length and fibre orientation occurring across a cracked beam section. The results showed that there was little difference between casting (using table vibration) and spraying (wet process) on the resulting fibre orientation distribution properties. The fibre distribution data obtained can be used, in combination with fibre pull-out data, to model the tensile stress-profile of a beam specimen under flexural load. Hence, these data form a key part of a stress-profile model approach for predicting flexural behaviour – an essential requirement of a much needed design rationale for steel fibre reinforced concrete.