Mechanical strengthening and greening of artificial geopolymer aggregates using one-/two-part activation with hybrid sodium metasilicate and sodium carbonate

Artificial geopolymer aggregates (GPA) are produced by alkali-activating aluminosilicate precursors to form a hardened matrix that is subsequently crushed into aggregates. This technology offers a sustainable alternative to natural aggregates (NA) while enabling large-scale utilization of industrial solid wastes. To optimize mechanical performance and environmental benefits, this study systematically investigated the effects of Na 2 CO 3 /Na 2 SiO 3 replacement ratios, Na 2 SiO 3 particle sizes, and mixing methods on the physical and mechanical properties of GPA and the corresponding geopolymer aggregate concrete (GPAC). Compressive, interfacial tensile/shear, and microstructural (microhardness, BSE-EDS) tests revealed that the slow reaction of Na 2 CO 3 provided sustained alkalinity, promoting continued polymerization and enhancing later-age GPA strength and GPA/matrix bonding. Fine Na 2 SiO 3 powders in one-part mixing accelerated heat generation and further strengthened the GPA/matrix interaction, producing GPAC with higher compressive strength and distinctive crushing failure compared with natural aggregate concrete. Finally, the overall assessment demonstrated that GPA produced with 50 % Na 2 SiO 3 -anhydrous powders and 50 % Na 2 CO 3 under one-part mixing exhibited the best mechanical performance, minimal environmental impact, and lowest material cost. It improved compressive strength by 31.9–36.6 %, while simultaneously reducing the embodied carbon and material cost by 41.6 % and 24.6 %, respectively. The research findings provide significant technical support for the future promotion of the low-carbon design and industrialization of GPA.