• An eco-efficient AAUHPC was developed by using GP, WFS, and RSF. • RSM was applied to evaluate and optimize properties of AAUHPC. • WFS and RSF reduced properties; GP enhanced flowability and chloride resistance. • 100% RSF cut CO₂ emissions, embodied energy, and costs by 45.3%, 24.3%, and 69.2%. • Multi-criteria optimization identified five mixes with up to 100% desirability. Alkali-activated ultra-high-performance concrete (AAUHPC) has emerged as a sustainable alternative to cement-based UHPC, providing high engineering performance with substantially lower CO₂ emissions. Despite these benefits, its production still presents economic and environmental challenges that can be mitigated through optimization. In this study, an economical and environmentally friendly AAUHPC was developed by substituting glass powder (GP), waste foundry sand (WFS), and recycled steel fiber (RSF) for ground granulated blast furnace slag (GGBFS), quartz sand (QS), and industrial steel fiber (ISF), respectively, while preserving mechanical and durability performance. The variables were examined at five levels using a response surface methodology (RSM) design. Flowability, compressive, tensile, and flexural strength; beside rapid chloride migration tests were conducted on the AAUHPC mixtures. The results showed that 50% WFS and 100% RSF reduced flowability below 19 cm and lowered 28-day compressive, tensile, and flexural strengths to under 110 MPa, 6 MPa, and 11 MPa, respectively. While GP slightly reduced mechanical performance, it improved flowability and chloride resistance, with a 50% GP addition enhancing flowability by 6% and chloride resistance by 11.8%. These findings were supported by SEM, EDS, and XRD analyses, confirming variations in microstructure and matrix density. Economic and environmental assessments revealed the key role of RSF in reducing impacts, with 100% RSF lowering CO₂ emissions, embodied energy, and production costs by 45.3%, 24.3%, and 69.2%, respectively. Finally, five mix designs with desirability values up to 100% were proposed relative to the initial optimal mix design, allowing selection based on engineering, economic, and environmental priorities.
Sarmast et al. (Fri,) studied this question.