Engineering Properties and Optimal Design of Ultrahigh Performance Alkali-Activated Concrete

The low carbonization of ultrahigh performance concrete (UHPC) and the resource utilization of industrial solid waste have become research hotspots for sustainable development in the construction industry. This study prepared ultrahigh performance alkali-activated concrete (UHP-AAC) using industrial solid waste slag and silica fume as binders. Through experiments on 11 groups of UHP-AAC, the effects of water-to-binder ratio, water-glass modulus, alkali equivalent, and steel fiber content on the fresh and mechanical properties of UHP-AAC were investigated, and the results were compared with those of ordinary portland cement-UHPC (OPC-UHPC) control groups. The results indicate that, in terms of fresh properties, an increase in W/B, water-glass modulus, and alkali equivalent positively influenced the fresh properties of UHP-AAC, while an increase in steel fiber content led to poorer workability. Due to the alkaline environment and the presence of silicates, the flowability and setting time of all UHP-AAC mixtures were lower than those of OPC-UHPC. In terms of mechanical properties, there exists an optimal W/B and alkali equivalent, and an increase in water-glass modulus and steel fiber content enhanced the mechanical properties of UHP-AAC, with all UHP-AAC mixtures exhibiting higher compressive strength than OPC-UHPC. When 1% steel fiber was added, the mechanical properties of UHP-AAC after 7 days of standard curing reached approximately 90% of those at 28 days, demonstrating significant early strength development. Additionally, the tensile stress-strain curves of UHP-AAC under different parameters were analyzed, revealing strain hardening phenomena at steel fiber contents of 2% and 3%. Overall, the optimized mix design significantly improved the mechanical properties of UHP-AAC, with lower carbon emissions and energy consumption, making it a sustainable green building material with broad application prospects.