The effects of calcium hydroxide and activator chemistry on alkali-activated metakaolin pastes

• Published in: Cement and concrete research Vol. 145; p. 106453
• Main Authors: Alventosa, Karina M.L., White, Claire E.
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier Ltd 01.07.2021; Elsevier BV
• Subjects: Alkali-activated materials; Aluminosilicates; Aluminum silicates; Amorphous material; Calcium addition; Dissolution; Gel formation; Metakaolin; Pastes; Reaction kinetics; Slaked lime; Sodium hydroxide; Sodium silicates; Metakaolin; Alkali-activated materials; Amorphous material; Calcium addition; Gel formation
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2021.106453

The impact of calcium hydroxide as an additive in sodium hydroxide- and silicate-activated metakaolin pastes is presented with a primary aim to ascertain the specific effects of calcium on the reaction kinetics and phase formation. FTIR and XRD are employed to understand the interaction of calcium hydroxide (10 wt% replacement of metakaolin) in 1, 5 and 10 M NaOH-activated pastes (and equivalent molarity Na2SiO3-activated pastes), with a focus on its impact on the nanoscale properties of the sodium-alumino-silicate-hydrate (N-A-S-(H)) gel. In situ FTIR and ICC are used to assess the impact of calcium hydroxide on the reaction kinetics, including the rate of metakaolin dissolution and associated rate of N-A-S-(H) gel growth. It is found that calcium hydroxide is effective at accelerating the reaction kinetics of 5 M Na2SiO3-activated metakaolin due to the formation of an initial calcium-rich gel that promotes additional metakaolin dissolution and enhances N-A-S-(H) gel formation.