“Metakaolin‐Slag‐Clinker Blends.” The Role of Na ⁺ or K ⁺ as Alkaline Activators of Theses Ternary Blends

This article reports on research into the use of solid alkalis ( Na 2 CO 3 and K 2 CO 3 ) as activators to obtain hybrid cement (cement whose hydration generates a mix of C–A–S–H and (N,C)–A–S–H gels) from a blend of 20% clínker + 40% blast furnace slag + 40% metakaolin. More specifically, the study aimed to determine the effect of activator dosage (5 and 8 wt%) and type of alkaline cation ( Na + or K + ) on the 2‐ and 28‐d mechanical strength of the end materials. The findings showed that the highest mechanical strength values were obtained with 5% Na 2 CO 3 . According to the XRD , NMR , and SEM / EDX analyses conducted on the reaction products, the alkalinity and solubilized chemical species generated by adding 5% Na 2 CO 3 to the system yielded a mix of (N,C)–A–S–H and C–A–S–H cementitious gels as the main reaction products. The secondary reaction products included metastable (3 CaO · Al 2 O 3 · Ca CO 3 ·11 H 2 O ‐type) carboaluminates that evolved into the calcite or vaterite forms of calcium carbonate. When K 2 CO 3 was used (instead of Na 2 CO 3 ), a (3 CaO · Al 2 O 3 ·0.5 Ca ( OH ) 2 ·0.5 Ca CO 3 ·11 H 2 O ‐type) hemicarboaluminate also formed. The study also revealed that Na + favors coagulation/precipitation more effectively than K + , generating gels with a wider range of Q n species.