The paper presents results of investigation on the influence of different volume fractions of polyethylene fibre on the toughness and ductility characteristics of normal strength concrete beams. Nine conventionally reinforced concrete beams measuring 150mmÃ—200mmÃ—2500mm containing 0.25%, 0.50% and 1.0% of polyethylene fibres were cast and tested under a two-point symmetrical loading system using an Avery Denison universal testing machine. Three control beams containing only conventional reinforcing steel bars and measuring 150mmÃ—200mmÃ—2500mm were also cast and tested under similar conditions using the same equipment. Throughout the tests, measurements were taken of the loads, mid-span deflections, crack widths and spacings at each load increment until failure. Results of the tests showed that experimental failure loads for the beams averaged 114% of the theoretical failure loads, and failure of the beams was generally governed by the yielding of the tension steel followed by the crushing of concrete in compression. The control specimens possessed a higher energy absorption capacity at toughness indices I5, I10, and I30 compared to the 0.25% and 0.50% fibre concretes. The 1.0% fibre concrete beams however possessed the highest energy absorption capacity averaging 4.79, 11.16, and 51.27 at I5, I10, and I30 respectively. The ultimate deflections exceeded the predicted deflections on the average by approximately 550% with the ratio of maximum deflection at collapse to deflection at first crack ranging from 9.04 to 59.93. The control specimens exhibited little deflection, averaging 31.7mm and therefore very low ductility prior to collapse compared to the fibre reinforced concrete specimen which averaged 40.1mm, 41.5mm, and 46.4mm for 0.25%, 0.50%, and 1.0% fibre reinforced concrete respectively. At failure the fibre reinforced concrete produced more cracks which were closely spaced with visibly smaller crack widths compared to the control beams.
Keywords: Fibre reinforcement; Beam; Toughness; Ductility; Crack width; Crack spacing; Deflection.