Abstract:

In view of the problems of mechanical properties and durability of recycled sand（RS） partially replacing quartz sand（QS） in the preparation of recycled sand ultra⁃high performance concrete（RS-UHPC），different dosages of graphene oxide（GO） were used as experimental parameters to explore the influence of GO on the working performance，mechanical properties，and chloride ion penetration resistance of UHPC，and to reveal its reinforcement mechanism through TG-DSC and SEM methods.The results showed that the addition of RS could reduce the flowability and mechanical properties of UHPC，as well as its resistance to chloride ion penetration.As the GO content increased，the flowability of RS-UHPC was further decreased，but its mechanical properties and resistance to chloride ion penetration were significantly improved.When the GO content was 0.06%，the 28 d compressive strength and flexural strength of RS-UHPC were increased by 11.8% and 49.6%，respectively.The chloride ion diffusion coefficient was decreased by 31.8%，and the crack toughness was significantly improved.The internal curing effect of RS and the nucleation effect of GO both promoted cement hydration，reduced matrix porosity，improved the interface transition zone between recycled sand and matrix，thereby enhancing the mechanical properties，crack resistance，and chloride ion penetration resistance of RS-UHPC.

Key words: ultra?high performance concrete, graphene oxide, recycled sand, mechanical properties, interface transition zone