Thermodynamic modelling of alkali-activated slag cements

• Published in: Applied geochemistry Vol. 61; pp. 233 - 247
• Main Authors: Myers, Rupert J., Lothenbach, Barbara, Bernal, Susan A., Provis, John L.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2015
• Subjects: calcium; cement; chemical composition; geochemistry; physical phases; slags; sodium carbonate; sodium hydroxide; sodium silicate; thermodynamics; zeolites
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2015.06.006

[Display omitted] •A thermodynamic modelling analysis of alkali-activated slag cements is presented.•Thermodynamic database describes zeolites, alkali carbonates, C–(N–)A–S–H gel.•Updated thermodynamic model for Mg–Al layered double hydroxides.•Description of phase assemblages in Na2SiO3- and Na2CO3-activated slag cements.•Phase diagrams for NaOH-activated and Na2SiO3-activated slag cements are simulated. This paper presents a thermodynamic modelling analysis of alkali-activated slag-based cements, which are high performance and potentially low-CO2 binders relative to Portland cement. The thermodynamic database used here contains a calcium (alkali) aluminosilicate hydrate ideal solid solution model (CNASH_ss), alkali carbonate and zeolite phases, and an ideal solid solution model for a hydrotalcite-like Mg–Al layered double hydroxide phase. Simulated phase diagrams for NaOH- and Na2SiO3-activated slag-based cements demonstrate the high stability of zeolites and other solid phases in these materials. Thermodynamic modelling provides a good description of the chemical compositions and types of phases formed in Na2SiO3-activated slag cements over the most relevant bulk chemical composition range for these cements, and the simulated volumetric properties of the cement paste are consistent with previously measured and estimated values. Experimentally determined and simulated solid phase assemblages for Na2CO3-activated slag cements were also found to be in good agreement. These results can be used to design the chemistry of alkali-activated slag-based cements, to further promote the uptake of this technology and valorisation of metallurgical slags.