Title: Reduction of Flexural Crack Widths Using Synthetic Fibres in Reinforced Concrete
Author(s): Bernard, E. S.
Publication: Symposium Paper
Appears on pages(s): 331-340
Keywords: Crack width, fibre reinforced concrete, post-crack performance, flexure, tension stiffening, conventional reinforcement
The use of steel fibres to reduce the width of flexural and tensile cracks in reinforced
concrete members is now well recognised and aspects of this phenomenon have been
incorporated into several codes internationally. Almost all the research work upon which this
has been based has involved hooked-end steel fibres, with very little work undertaken using
other types of fibre. However, the theories underlying how fibres assist in reducing crack
widths are not specific to hooked-end steel fibres, so alternative types of fibre could work in a
similar way to reduce crack widths in flexural and tensile members.
The current paper outlines work recently completed on the effect of several types of
synthetic fibre on flexural crack widths in reinforced concrete members. The fibres have
predominantly been manufactured using polypropylene, but other materials including
aramide, nylon and PVA can also be used for this purpose and have been included in this
investigation. Laboratory testing has demonstrated that synthetic fibres are fully capable of
reducing flexural crack widths, but their efficacy is not consistent across all fibre types and
designs. Testing appears to demonstrate that for a given dosage rate of fibre, the capacity of a
FRC mix to limit flexural crack widths is related to the post-crack residual strength. However,
some fibres can limit crack widths more effectively than is predicted by existing expressions
for design width that are based primarily on post-crack residual strength. This suggests that
post-crack toughness is not the only parameter contributing to crack width reduction in
Reinforced Concrete members.