Synergistic effect of waste steel slag powder and fly ash in sustainable high strength engineered cementitious composites: From microstructure to macro-performance

Engineered Cementitious Composites (ECC), renowned for high ductility, faces sustainability challenges from variability and scarcity of fly ash (FA). This study explores waste steel slag powder (SSP), an industry byproduct, as an FA alternative. Five ECC mixtures with 0∼100 % SSP substitution were mechanically tested and microstructurally analyzed. Results showed that partial SSP substitution (≤50 %) improves compressive strength (79.26 MPa) and tensile strain (6.19 %) through optimized particle packing and interfacial friction. However, more than 50 % substitution of SSP to FA weakens the macro-mechanical properties of ECC. Microstructural analysis elucidated dual role of SSP: enhancing macro-mechanical properties at low replacement ratio via filler effects, while at high replacement ratio, promoting CH dissolution, inhibiting hydration reactions, and increasing porosity, ultimately deteriorating macro-mechanical performance. This study uniquely bridges macro-mechanical effects to microstructural mechanisms of SSP, demonstrating its viability as a sustainable FA alternative, advancing eco-friendly ECC design and promoting industrial waste utilization. • The effect of steel slag powder (SSP) replacement rate on ECC mechanical properties was studied. • In ECC, SSP alters hydration by lowering pore pH and ion levels, suppressing CH and ettringite formation. • Synergistic effects between SSP and FA optimize particle packing and pore refinement.