Properties of the interfacial transition zone in rubberised concrete – an investigation using nano-indentation and EDS analysis

Abstract

Concrete is the most widely used material in the world after water. Using recycled aggregate derived from waste concrete and end-of-life tyres can significantly reduce the demand for virgin materials and reduce the concrete industry's carbon footprint. Using recycled aggregates may greatly influence concrete's mechanical and other properties. The reduction in strength and stiffness is often attributed to weak bonding between aggregate and cement pastes (weak interfacial transition zone-ITZ). This paper investigates the mechanical and chemical properties of the cement paste and ITZ using statistical nano-indentation technology and X-ray energy dispersive spectroscopy. It is observed that tyre-derived aggregates form weaker bonds with cement paste, and the ITZ has a considerably lower elastic modulus than cement paste. Many nano-pores are found on the tyre-derived aggregate's surface, which may contribute to inferior performance compared to conventional concrete. The study also observes that reducing the water-binder ratio may reduce the number of nano-pores in cement paste and thus improve its mechanical behaviour.