Abstract: “This paper reports the results of an experimental study of reinforced concrete (RC) beam conducted using irregular-shaped Polyethylene Terephthalate (IPET) as fibre. Three volume fraction of IPET fibre are used namely, 0.5%, 1% and 1.5%. All RC beam specimens are tested under four point loading under flexural capacity behaviour. The results for maximum crack spacing under cracking behaviour are reported. The results than are compared with three models namely, Gilbert model, EC2 1997 and CEB-FIP 1990 to determine the most reliable approach than match with the experimental results. It is found that the addition of IPET fibre improvesthe crack spacing of RC beams proportional to the increment of volume fraction of IPET fibre. None of the models mentioned above considered the fibre factor. Therefore, a modification of the most reliable model arecarried out and proved with the statistical analysis tool to consider IPET fibre factor. At the end of this paper, a modified model is carried out”

Keywords: Irregular-shaped Polyethylene Terephthalate (IPET) fibre, mechanical properties, deflection behaviour, maximum crack spacing, maximum crack spacing model, and reinforced concrete (RC) beam.