Behaviour of carbon fibre-reinforced polymer-reinforced macro-synthetic fibre-reinforced concrete columns under axial compression

This study experimentally and theoretically analyses the axial compression behaviour of concrete columns reinforced with longitudinal carbon fibre-reinforced polymer (CFRP) bars and steel spirals, incorporating macro-synthetic fibres. Sixteen specimens in four groups (CRPC, CRMSP, SRPC, SRMSP) varied concrete type (plain/macro-synthetic fibre-reinforced concrete (MSFRC)), longitudinal bar material (CFRP/steel) and spiral pitch. Failure modes were consistent across all groups. The axial strength of CFRP-reinforced columns averaged 90.7% of that of equivalent steel-reinforced columns. However, CFRP-reinforced columns exhibited 8.5–12.1% higher ductility. MSFRC columns showed 11–19% greater axial strain at peak load than plain concrete counterparts. Although current codes lack design rules for polymeric compression reinforcement, the proposed theoretical model – accounting for CFRP bar contribution after cover spalling, spiral confinement and concrete type – accurately predicted column performance. The research demonstrates the viable structural performance of CFRP-reinforced MSFRC columns under compression.