Development of Confined Rubberised Concrete for High Ductility Structural Applications

The global environmental and economic implications of the disposal of waste tyres have prompted research exploring valuable outlets for their components. Concrete is an inherently brittle material and can benefit from tyre rubber properties to achieve higher ductility and energy dissipation for special applications in locations of high deformation demands, such as coupling beams. Despite the prospective benefits, the use of rubber as partial mineral aggregate replacement negatively affects concrete workability and strength. Recent research has shown that the external confinement of RuC can benefit from its high lateral expansion and mitigate the drawbacks of RuC, leading to high strength. Nevertheless, the majority of this research is limited to low rubber contents, which restricts the deformability potential of confined rubberised concrete (CRuC). This research aims to advance the understanding on unconfined and FRP-confined RuC, developed with high rubber contents and optimised mix parameters, leading the way for new high-strength high-deformability concrete elements. More than forty RuC mixes were investigated experimentally to develop an understanding of the effect of rubber and various concrete mix parameters on RuC fresh properties and short-term compressive strength. An “optimum” RuC mix with adequate workability and strength at all rubber contents was developed for further study. The influence of rubber (content and type) on the stress-strain behaviour of the optimised RuC mix was investigated in a second parametric study involving more than 60 cylinders. The addition of rubber to concrete led to high lateral strains and premature failure, particularly at high rubber contents, which can be exploited to activate external confinement. The mix with high rubber content (60% total aggregate replacement) was identified as most suitable for study to maximise the deformability in RuC. The use of Aramid or Carbon FRP sheets as external confinement to high rubber contents RuC was examined experimentally under monotonic and cyclic uniaxial compression. This led to the development of constitutive models to accurately predict the performance of confined rubberised concrete (CRuC) subject to monotonic or cyclic loading. CRuC led to unprecedented axial strains (>6%) and compressive strength above 90 MPa, indicating high potential for its use in a variety of structural applications.