Enhanced durability, performance, and sustainability of alkali-activated composites with nano-Fe 2 O 3 and nano-Fe 3 O 4 under hybrid thermal-microwave curing

This study examines alkali-activated composites (AACs) incorporating ground blast furnace slag (GBFS) and waste marble powder, with nano-hematite (n-Fe2O3) and nano-magnetite (n-Fe3O4) as partial GBFS replacements (0%–1.2%). A hybrid curing regime, combining thermal curing at 75 °C with microwave curing, was used to accelerate strength development. Nanoparticle addition reduced flowability (200→177 mm) but enhanced compressive strength, with optimum performance at 0.6% replacement. n-Fe3O4 generally outperformed n-Fe2O3, yielding ∼5%–10% higher strength. Hybrid curing was highly efficient, enabling 79%–89% of the 28-day compressive strength within 3 h. After exposure to 800 °C, all mixtures deteriorated severely (70%–77% strength loss), with the reference mixture showing the greatest residual capacity (29.7%). The 0.6% n-Fe3O4 mixture suffered the highest thermal degradation (76.8%). Durability improved with nanoparticle incorporation, as 1.2% n-Fe3O4 yielded the lowest sulfate-induced deterioration (0.9% strength loss), whereas n-Fe2O3 exhibited slightly better resistance under 50 wetting–drying cycles.