Investigating environmentally suitable alternatives becomes crucial as demand for Portland cement is expected to increase dramatically over the next several years. Alkaline-activated binders produced by alkali activation of aluminosilicate precursors serve as greener and viable substitutes for PC. However, conventional activators such as sodium silicate (SS) or sodium hydroxide (NaOH) are corrosive, costly, and pose significant environmental concerns. In contrast, sodium carbonate (Na2CO3, NC) and calcium carbonate (CaCO3, CC) are less corrosive, more affordable, and naturally abundant, making them sustainable alkali activators for AAs. To advance the use of sustainable binders, this study investigated the properties of slag activated with a blended activator composed of Na2SiO3/Na2CO3 or Na2SiO3/CaCO3 at room temperature. The findings reveal that using a combined activator of SS and CC reduces compressive strength and delays the setting process, whereas a blend of SS and NC improves strength by 10 to 12% over a curing period of 3–90 days. Additionally, using a blend of 7% SS + 3% NC as an activator reduces total porosity and water absorption and improves the highest bulk density. Under 5% MgSO₄ attack for six months, CC-containing mixes deteriorated severely (strength decreased to 3.1–15.4 MPa), whereas NC-activated mixes retained higher strength (34.4–40.6 MPa). After firing at 300, 600, and 800 °C, M5 retained approximately 70%, 51%, and 39% of its original 28-day strength, respectively, outperforming CC-based systems (32–84% loss). XRD, FTIR, and SEM analyses confirmed denser C–A–S–H and/or N–A–S–H gel formation in SS/NC mixes. The findings demonstrate that Na₂CO₃ is a technically viable, environmentally safer, and economically attractive partial substitute for sodium silicate, delivering enhanced durability and thermal resistance for sustainable structural applications.
Hashem et al. (2026) studied this question.