Thermodynamic and kinetic analysis on the effect of CaSO4 on calcination of natural hydraulic lime

Abstract

Natural hydraulic lime (NHL), a mixture of CaO and β-dicalcium silicate (β-C2S), is a traditional binder of mortars in masonry buildings. Though its production conditions are similar with the pure β-C2S, relevant studies on the Ca-rich system are limited. This paper focuses on the influence of S6+ in the form of CaSO4 as an inhibitor on the phase transform between β-C2S and γ-C2S in a thermodynamic and kinetic view. The effect of the dosage of CaSO4 with temperature on the phase transform was analyzed based on the Gibbs free energy criterion of solid solution and γ-C2S, and the critical dosages were calculated. Then, the relationships among cooling process, the dosage of CaSO4, and the conversion rate were discussed and the activation energy of the phase transform was computed.