Nonlinear flexural behaviour of flax FRP double tube confined coconut fibre reinforced concrete

• Double flax fibre reinforced polymer confined coir concrete composite was studied.
• An additional inner confinement increases lateral load bearing capacity.
• Inner confinement eliminates slippages at polymer–concrete interface.
• Centre concrete void does not adversely affect the composite flexural strength.
• Compared to single confinement double confined composite has higher cracking strength.

The flexural performance of coconut fibre reinforced concrete composites, confined with flax fibre reinforced polymer tubes was investigated. Six 520 mm long cylindrical specimens were tested under four-point bending. Two kinds of specimens were considered. The single tube type consists of coconut fibre reinforced concrete confined by a single, outer, flax fibre reinforced polymer tube, whereas the double tube type involves both the outer polymer tube, and a polymer tube running along the centre line of the concrete cylinder. The ultimate load, flexural deformation, and outer tube strains in the longitudinal and hoop directions were experimentally measured. Additionally, the cracking moments and neutral axis depths of both the double tube and single tube confined specimens, were compared. It was found that the double tube specimens possessed excellent flexural characteristics, particularly in comparison to the single tube specimens.

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