Low-carbon one-part calcined clay geopolymer binder for sustainable construction: Role of anhydrous sodium metasilicate and water-to-binder ratio

Geopolymer binders offer a low-carbon alternative to Portland cement (PC), but their widespread adoption remains limited by the handling and safety concerns associated with liquid alkali activators. This study developed a one-part geopolymer binder using locally sourced calcined clay as the sole precursor and anhydrous sodium metasilicate as the sole dry activator for ambient-cured construction applications. Calcined clay produced from Saudi white clay calcined at 700 °C was combined with 12%, 14%, and 16% anhydrous sodium metasilicate at water-to-binder (w/b) ratios of 0.25 and 0.30. The fresh, mechanical, durability, microstructural, thermal, and environmental properties of the resulting binders were evaluated. The results show that increasing the w/b ratio improved flowability, while higher sodium metasilicate contents accelerated setting and enhanced geopolymerization. The mixture containing 16% sodium metasilicate and a w/b ratio of 0.30 exhibited the best overall performance, achieving a 28-day compressive strength exceeding 56 MPa, splitting tensile strength of 1.22 MPa, and flexural strength of 5.7 MPa under ambient curing. Microstructural analyses confirmed the formation of a denser matrix and and enhanced geopolymerization at higher activator contents. Although drying shrinkage increased up to 0.28% with 16% sodium metasilicate content, all mixtures exhibited satisfactory performance. Compared with PC, the developed binder reduced CO₂ emissions by 52–60% and energy consumption by 20–25%. These findings demonstrate the feasibility of producing a high-performance, low-carbon one-part geopolymer binder from calcined clay and anhydrous sodium metasilicate, providing a practical and safer alternative for sustainable construction applications.