Comprehensive study on the reactivity and mechanical properties of alkali-activated metakaolin at high H2O/Na2O ratios

• Published in: Applied clay science 2023-01, Vol.231, p.106758, Article 106758
• Main Authors: Souayfan, Faten, Roziere, Emmanuel, Justino, Christophe, Paris, Michaël, Deneele, Dimitri, Loukili, Ahmed
• Format: Article
• Language: English
• Subjects: Condensed Matter; Geopolymer; Materials Science; Mechanical properties; Metakaolin; Physics; Reaction degree; Viscoelastic properties; Water content
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2022.106758

This study focused on the influence of high H2O/Na2O ratios (higher than 20) on the properties of metakaolin-based geopolymers in fresh and hardened states while keeping constant Si/Al and Na/Al atomic ratios. The increase in H2O/Na2O ratio from 21 to 34 resulted in a decrease of 7-day compressive strength from 10 to 0.025 MPa. This can be attributed to the influence of water on the reactivity of the precursor, which was demonstrated by nuclear magnetic resonance (NMR) spectroscopy, and porosity evolution as the water is not chemically bound. Increasing H2O/Na2O ratio did not change the geopolymer structure of reaction products. A correlation was observed between the reaction degree deduced from NMR spectral decomposition and the cumulated released heat obtained using isothermal calorimetry. The maximum loss tangent, obtained using dynamic rheology, was linearly related to strength development. •Activated metakaolin with H2O/Na2O ratio higher than 20 and constant Si/Al and Na/Al atomic ratios•Early stages of structuration evidenced by dynamic rheology and isothermal calorimetry•Reaction degree of metakaolin deduced from quantitative analysis of NMR spectra•H2O/Na2O ratio influenced the reaction degree but not the structure of geopolymer•Loss tangent deduced from rheometry and compressive strength can be correlated