Carbonated fine steel slag (CSS) can be used as supplementary cementitious materials (SCM) to enhance the sustainability of ultra-high performance concrete (UHPC). However, the role of CSS on the mechanical performance of UHPC containing coarse aggregates (UHPC-CA) has not been well understood. Here, the influence of cement substitution by CSS on the hydration products, microstructure, mesoscale fracture characteristics and macroscopic strength of UHPC-CA is investigated. Results reveal that the C-S-H content in UHPC increases with the increase of CSS substitution up to 15%. Replacement of cement by CSS results in a more porous interfacial transition zone (ITZ), consequently, a lower mechanical contribution from CA. Both the compressive and the flexural strength decrease with the increase of CSS substitution, and the negative effect is rather limited till 30% CSS substitution. Moreover, due to a more porous ITZ at a higher cement substitution, the ratio of flexural to compressive strength decreases with the increase of CSS substitution.

碳化细钢渣 (CSS) 可用作辅助胶凝材料 (SCM)，以提高超高性能混凝土 (UHPC) 的可持续性。然而，CSS 对含有粗骨料的 UHPC (UHPC-CA) 机械性能的作用尚未得到很好的理解。在这里，研究了 CSS 替代水泥对 UHPC-CA 的水化产物、微观结构、中尺度断裂特征和宏观强度的影响。结果表明，UHPC 中的 CSH 含量随着 CSS 替代量的增加而增加，最高可达 15%。用 CSS 代替水泥会产生更多孔隙的界面过渡区 (ITZ)，因此，CA 的机械贡献较低。抗压强度和抗弯强度均随着 CSS 替代量的增加而降低，并且负面影响相当有限，直到 30% 的 CSS 替换。此外，由于在较高水泥替代率下更多孔的 ITZ，抗弯强度与抗压强度的比率随着 CSS 替代率的增加而降低。