Experimental study on seawater and sea sand concrete filled GFRP and stainless steel tubular stub columns

• Mix design of geopolymer seawater and sea sand concrete (SWSSC).
• Stub column tests on SWSSC fully filled GFRP and stainless steel tubes.
• Stub column tests on SWSSC filled double skin GFRP and stainless steel tubes.
• Capacity formulae for SWSSC filled GFRP and stainless steel tubes.

This paper presents an experimental investigation on mechanical and associated properties of seawater and sea sand concrete (SWSSC) filled glass fibre reinforced polymer (GFRP) and stainless steel (SS) circular tubes. A proper SWSSC mix was developed to achieve the target strength and desirable workability. A total of 24 stub columns, including hollow sections and SWSSC fully filled tubes or double-skin tubes, were tested under axial compression with the load applied to concrete and tubes simultaneously. The stress-strain curves of the core concrete indicate that concrete strength and ductility is enhanced due to the confinement effect. Discussion focuses on the influence of tube diameter-to-thickness ratio, outer tube types and inner tube types on concrete confinement. Capacity formulae are proposed to estimate the load carrying capacity of SWSSC fully filled SS or GFRP tubes, and that of double skin tubes with four combinations of inner and outer tubes, i.e. SS and SS, SS and GFRP, GFRP and GFRP and GFRP and SS.