Enhancement in strength and toughness of ultra-high performance concrete (UHPC) from micron- and nano-scale

Abstract

The employment of multi-scale materials was considered the most effective and practical way to strengthen and toughen ultra-high performance concrete (UHPC). In this work, three types of enhancement materials at different scales (i.e., steel fibers on millimeter-scale, CaCO3 whiskers on micron-scale, and graphene oxide on nano-scale) were used to prepare a series of steam- and autoclave-cured UHPC. The dynamic elastic modulus, flexural load-deflection response, and compressive stress-strain behavior of the prepared UHPC were investigated, with special attention devoted to the effect of the enhancement materials on the flexural and compressive toughness of UHPC. The test results show that incorporating CaCO3 whiskers could enhance the dynamic elastic modulus of UHPC, but the effect of graphene oxide on the dynamic elastic modulus fluctuated. Under flexural and compressive behaviors, improvements in strength, energy absorption capacity, and toughness index could be found after incorporating CaCO3 whisker or/and graphene oxide. The best improvements of strength and energy absorption capacity were obtained through the hybrid of CaCO3 whisker and graphene oxide. But the hybrid of CaCO3 whiskers and graphene oxide could not necessarily further promote the improvement of the toughness index. Moreover, the hybrid effect for the performance parameters was analyzed, and the strengthening and toughening mechanisms were discussed based on microscopic observation. Overall, this work could provide a valuable reference for UHPC strengthening and toughening at the micron- and nano-scale.