Development of low-carbon engineered cementitious composites using pressurized carbonated steel slag aggregates

The high material cost and carbon emission of engineered cementitious composites (ECC) pose significant challenges to their widespread adoption. This study investigates the sustainable potential of utilizing non-carbonated and carbonated steel slag as fine aggregates in developing green ECC under replacement ratios of up to 100%, putting an emphasis on the workability, compressive and direct tensile properties, as well as microstructural evolution. Experimental results demonstrate that carbonation treatment enhances the surface characteristics of steel slag, yielding a 0.3–1.6% improvement in fresh mixture workability relative to non-carbonated steel slag ECC. The nucleation effects and micro-filling capacity of carbonated aggregates increase cubic compressive strength by 2.1–8.4% and elastic modulus by 0.2–2.4% compared to ECC with plain steel slag, while maintaining mechanical superiority over conventional quartz sand systems at full replacement. Moreover, the optimized microstructure of carbonated steel slag ECC elevates fiber bridging peak stress by up to 23.6% but reduces crack opening capacity by less than 36.8% through interfacial densification, as compared with the quartz sand ECC mixture. Although first-crack and peak tensile strengthes progressively improve with substitution rates, the improved fiber-to-matrix bonding reduces ultimate strain while preserving multiple cracking behaviors. Overall, 50% carbonated steel slag substitution can be considered as the optimal mixture, achieving synergistic benefits of tensile strength, strain capacity and waste valorization towards low-carbon ECC design. • The effect of various substitution rates on engineering properties of ECC is investigated. • The saturated strain-hardening behavior of carbonized steel slag ECC is verified. • The micro-mechanism of carbonized steel slag aggregate in ECC systems is revealed. • The optimal replacement rate of carbonized slag is proposed based on tensile properties.