Bond behaviour in rubberised concrete filled circular steel tubes

Rubberised concrete filled steel tube (CFST) is a potential method to utilise the crumb rubber as partial replacement of aggregate, however previous researches show weaker interfacial bond between the rubber and concrete. The aim of this research is to investigate the bond behaviour between the steel tube and the concrete in CFST. Push-out and mechanical tests were conducted on circular specimens, and the variables were: 1) different thicknesses of steel tube; 2) concrete types (normal, rubberised concrete and presence of metakaolin as pozzolan). The results indicated that the use of rubber gives adverse effect on the compressive and splitting tensile strengths, and the modulus of elasticity. However, the use of metakaolin as cement replacement improves its mechanical properties. Based on push-out test, the rubberised concrete shows lower bond strength, and the bond strength increases with increasing section thickness. The presence of metakaolin yielded higher bond strength compared with other mixes.