Bond characteristics of structural polypropylene fibres in concrete with regard to post‐crack strength and durable design

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Abstract
Purpose: Seeks to examine the bond strength of a large range of structural polypropylene fibres, as used in concrete, to determine the most effective fibre capable of transmitting load (N/mm2) between fibre and cement within the concrete matrix.Design/methodology/approach: Following fibre selection characterised by the highest bond strength, determined from a series of pull out tests, BS flexural tests were carried out using high bond strength fibres (40 mm × 0.9 mm diameter used at 6 kg/m3) to determine whether or not structural polypropylene fibres had any effect on the ultimate flexural strength of fibre‐reinforced concrete, when compared with the plain control sample. Fibre orientation, type of rupture failure mode and post‐crack performance were examined.Findings: Even structural fibre dispersion was found to be best achieved with the use of monofilament polypropylene fibres (19 mm × 22 micron used at 0.9 × kg/m3) in addition to the 6 kg/m3 structural fibre dose. Structural polypropylene fibres were found not to provide additional flexural strength however, they did provide post‐crack control, limiting the crack width with subsequent enhanced durability that in turn will provide lower life cycle costs.Practical implications: In addition to increased durability the use of fibre reinforcement negates the need to place steel reinforcement bars.Originality/value: Investigates the ambiguity in literature between claims made by different investigators regarding the effects of polypropylene fibres on compressive and flexural strengths.