Experimental investigation of rubberised concrete-filled double skin square tubular columns under axial compression

Waste tyres are among the largest and most problematic sources of waste in modern society due to their durability and high rate of dumping in landfills. One possible recycling alternative is to incorporate waste tyre rubber as an aggregate replacement in concrete to promote sustainability and utilise the elastic properties of rubber. Rubberised concrete has not reached its full potential because of the decrease in compressive strength and a lack of research to solve such challenge. Recent research suggests that combining rubberised concrete with confinement increases ductility and energy absorption. Specifically, confined rubberised concrete using single skin or double skin square hollow section tubular columns present higher ductility than those made of normal concrete. This study explored experimentally the use of rubberised concrete filled single skin and double skin steel tubes under concentric axial compression. The experimental investigation included changing the confinement of the outer and inner square hollow sections and explored how confinement affected normal concrete compared to rubberised concrete. Four variations of double skin steel tubes with a total of twelve 300 mm long columns of 0%, 15%, and 30% rubber replacement were created and tested concentrically. Three single skin short columns with 0%, 15%, and 30% rubber content were also tested and compared. The compressive strengths were determined theoretically and compared against those measured experimentally. An interesting spring back phenomenon occurred where the infill rubberised concrete moved upwards after testing due to the large confinement of the core and elasticity of the rubber. This study examined the use of rubberised concrete filled double skin steel tubular columns as a promising construction technique for applications such as columns in buildings located in seismic active zones, security bollards and flexible road side barriers.