Performance of dove tailed synthetic fibres in concrete

This research investigated the bond strength and toughness of a range of widely used commercially available synthetic Type 2 structural fibres defined within BS EN 14889 [1] and compared these against novel prototype dove tailed (DT) synthetic Type 2 structural fibres. The dove tail shapes are three in number when viewed across the diameter of the circular DT fibre and they run longitudinally, creating an open flute effect. Synthetic fibres tend to be made from low modulus materials when compared to steel crack control products and they suffer a greater diameter reduction and increase in length when compared to steel; for an equal load. Diameter reduction of fibres in concrete causes de-bonding and eventual failure. DT fibres are designed to offer additional bond when a diameter reduction occurs under load. Fibres were cast into concrete cubes to a depth of half their length and pulled out recording load and extension to ultimate failure. The findings showed large degrees of toughness were available when using dove tailed fibre technology, The DT fibres transferred less bond stress at the point of the initial pull out prior to the dove tailed feature of the fibre taking effect. The dovetailed fibre under test provided additional grip through the contraction of the internal faces of the dovetail features when under load. Further work is needed to determine the optimum DT fibre diameter and aspect ratio that may provide increased bond stress whilst retaining large degrees of toughness.