Behaviour of CFRP confined high water-content material under cyclic compression

• A composite FRP tubular columns with the large axial deformation ability (>45% of the overall height) was developed. • The cyclic axial stress-axial strain behaviour of FCCH specimens were first-ever investigated. • The FCCH specimen exhibited a superior energy dissipation ability, which accounts for 90% of the total inputted energy. • The relationship between the macro- mechanical behaviour and micro-structures of infilled material was explored. Composite tubular columns, comprising an external fibre-reinforced polymer (FRP) jacket that confines a high water-content material (HWM) core, exhibit exceptional axial deformability (often >30% of the column height) and are attracting increasing attention for underground applications. However, their cyclic compressive behaviour remains largely unexplored. In this study, 29 FRP-confined HWM (FCCH) tubular specimens were tested to assess the effects of key parameters (FRP jacket thickness, loading rate, and loading scheme) under monotonic and cyclic compression. All FCCH specimens showed pronounced strain-hardening in both regimes, with failure governed by tensile rupture of the FRP jacket. Increasing jacket thickness generally improved energy-dissipation capacity. Microstructural observations suggest that progressive ettringite damage, coupled with the accumulation of plastic deformation, underpins the superior dissipation response. Overall, the results indicate that FCCH columns offer promising performance for underground engineering and other infrastructure requiring large axial deformability, and they point to favourable resistance to explosive/blast-type loading from an energy-dissipation standpoint.