Effect of graphene oxide on interfacial transition zone and strength enhancement of recycled aggregate concrete

This study reports the use of graphene oxide (GO) as an additive for performance enhancement of concrete containing a high volume of recycled aggregates. The current industry practice of incorporating recycled concrete aggregates (RCA) in concrete is limited to ∼30 % replacement of natural coarse aggregates (NCA) in concrete and non-structural applications. The targeted approach of this research is to increase this replacement level to 50 % using GO as a performance enhancer and to investigate the effects of GO on the interfacial transition zones (ITZ). Five concrete mixes were made including 100 % NCA (as a benchmark), 50 % RCA (as a control) and GO admixed recycled aggregate concrete (RAC). The dosage of GO in the mixes were 0.015 %, 0.035 % and 0.065 % by weight of cement. Fresh and hardened properties such as workability, compressive strength, splitting tensile and elastic moduli were evaluated in this study. In addition, the characteristics of the ITZs were examined by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results conclude that the addition of GO at 0.015 %, 0.035 % and 0.065 % enhances the 28-day compressive strength by 4 %, 35 % and 34 % respectively. SEM/EDS evaluations revealed that the widths of three ITZs associated with RCA have improved by the addition of 0.035 % GO. The incorporation of GO has densified the microstructure and reduced the ITZ widths by approximately 40–50 % which agrees well with the mechanical properties. The outcomes of this research provide instrumental scientific evidence that can encourage the industry to replace higher factions of NCA with RCA. • Graphene oxide improves interfacial transition zone of recycled aggregate concrete. • 0.035 % optimum GO dosage increases compressive strength by 35 % over the control mix. • Tensile strength and elastic modulus improve by 27.6 % and 9.6 % with 0.035 % GO. • GO reduces interfacial zone width by up to 40 %, densifying the microstructure. • GO enables 50 % recycled aggregate use without compromising compressive strength.