Abstract
Abstract
Recycling different solid wastes to manufacture clinker-free cementitious materials has become popular due to their minimal carbon emissions. This study systematically examines the influence of Ca/Si and Al/Si ratios on multi-component alkali-activated materials (MAAM) covering fluidity, early-age strength, setting and hardening processes, gel phase compositions, and microstructure. The results indicate that the optimal initial Ca/Si and Al/Si ratios in the precursor materials are 0.71–0.36 and 0.25–0.39, respectively. The resulting gel phase demonstrate atomic ratios of 0.30–0.50 for Ca/Si and 3.26–1.62 for (Na + K + Ca)/Al, along with a high proportion of highly polymerized Si–O–Si/Al structural units. Consequently, MAAM achieves desired properties, including compressive strengths of 30–48 MPa, fluidity ranging from 24 to 30 cm, setting times of 128–174 min, and fewer volume shrinkage cracks. The decline in the Ca/Si ratio prompts a transformation of the gel phase from C-A-S-H to Ca-rich C-(N)-A-S-H. This transition lowers the Ca/Si and (Na + K + Ca)/Al atomic ratios in the gel phase, along with a diminished proportion of highly polymerized gel structural units. Ultimately, the reaction rate slows down, resulting in a looser microstructure and reduced strength. Conversely, an elevated Al/Si ratio promotes the formation of highly polymerized gel structural units, thereby achieving a denser matrix and increased mechanical properties.