Thermodynamic calculation and stability of calcium silicate hydrate system

Abstract

Dissolution of cement clinker minerals involves a number of physical and chemical processes, and the simulation of dissolution processes helps to understand cement hydration conveniently. Dissolution model of cement clinker minerals was set up based on simulation theory of geochemical reaction equilibrium, PHREEQC simulation software provided by United States Geological Survey (USGS) was employed for thermodynamic calculation of C-S-H system. Stability of C-S-H system with low Ca/Si ratio at normal temperature was also explored. The results show that many phase assemblages coexist with the aqueous phase depending on its composition. The most stable product varies with different Ca/Si ratio of C-S-H system. Active SiO₂ will consume excessive CH, so the Ca/Si ratios of C-S-H system decrease, C-S-H with low Ca/Si ratio becomes the most stable product, and this is the thermodynamic driving force of secondary pozzolanic reaction.

Keywords

C-S-H / equilibrium phase / stability / thermodynamic / PHREEQC

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