Thermodynamic modelling of temperature effects on the mineralogy of Portland cement systems containing chloride

Thermodynamic equilibrium based modelling was carried out to quantify the influence of temperature on the mineralogy of hydrated ordinary Portland cement. In typical Portland cement system hydrated at 25 degrees C interlayer sites in the AFm phase are occupied by OH, SO4 or CO3 ions. Chloride which can be added as a set accelerating admixture or ingress from the outside environment, has the ability to displace hydroxide, sulfate and carbonate from the AFm structure leading to the formation of Triedel's salt' (Cl-AFm). However temperature variations may cause important compositional changes or even destabilization of Friedel's salt. A description of phase relations and changing balances between AFm and AFt (ettringite) phases is presented in a range of temperatures between 5 and 85 degrees C. With an increasing temperature Friedel's salt is predicted to decompose at the expense of monosulfoaluminate (SO4-AFm) formation. Due to the higher stability of hydroxy- AFm (OH-AFm) at lower temperature the OH substitution in the Friedel's salt is expected to be slightly higher as compared to room temperature.