Reaction of calcium carbonate minerals in sodium silicate solution and its role in alkali-activated systems

• Published in: Minerals engineering Vol. 165; p. 106849
• Main Authors: Firdous, Rafia, Hirsch, Tamino, Klimm, Detlef, Lothenbach, Barbara, Stephan, Dietmar
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2021
• Subjects: Alkali-activated binder; Calcium carbonate; Mass spectrometry; Thermodynamic calculations; X-ray diffraction; X-ray diffraction; Thermodynamic calculations; Mass spectrometry; Alkali-activated binder; Calcium carbonate
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2021.106849

[Display omitted] •Calcium carbonate in its various polymorphs reacts with sodium silicate solution.•This reaction results in formation of Na-containing C-S-H and sodium carbonates.•Formation of natron and C-S-H are observed at time of second calorimetric peak.•Formation of natron or thermonatrite depends upon the kinetics of reaction.•With higher reaction degree of calcite, formation of gaylussite is predicted. This article investigates the role of calcium carbonate minerals in an alkali-activated system through their reaction with sodium silicate solution. The early reaction kinetics and reaction products are investigated using isothermal conduction calorimetry, in-situ XRD and in-situ FTIR. Later reaction products are identified with thermodynamic modelling and analysis of the paste samples after 8 and 90 d using XRD, TGA, DSC and mass spectrometry. After a few hours of reaction, natron precipitates as the first crystalline carbonate phase, while changes in the connectivity of silicates are observed due to the precipitation of C-S-H, which may contain Na. After 8 and 90 d, C-S-H is observed together with thermonatrite instead of natron. It is shown that calcium carbonate is not just a filler in an alkali-activated system but can provide Ca to form C-S-H and can also enhance the availability of carbonate for the formation of alkali carbonates.