Development of Ca-rich slag-based ultra-high-performance fiber-reinforced geopolymer concrete (UHP-FRGC): Effect of sand-to-binder ratio

•Ca-rich slag-based UHP-FRGC is successfully developed with sufficient strength and ductility.•Silica fume increases the strength through filler effect and accelerated reactivity of slag.•Highest packing density and compressive strength of 0.78 and 160.7 MPa are achieved at an S/B ratio of 0.8.•Excellent tensile performance with a tensile strength of 10.3 MPa and strain capacity of 0.833 is achieved.•No correlation between the strain-hardening performance and PSH index is observed in UHP-FRGC with steel fibers.