Estimation of standard molar entropy of cement hydrates and clinker minerals

It is not straightforward to experimentally measure the standard molar entropy of cement hydrates or clinker minerals. This is further compounded by the controversies surrounding the entropy values reported in established thermodynamic datasets for cements. The purpose of this study is to assess the reliability of standard entropies compiled in those datasets. To this end, a simple but robust method is used in which the standard entropy of an inorganic solid is correlated to its formula unit volume via a linear equation. The results of this analysis show that the standard entropies and/or molar volumes (and in cases solubility products) of the following phases deserve closer scrutiny: meta-ettringite phases; magnesium/aluminium layered double hydroxide solid solutions; almost all iron-bearing monosulfate and hydrogarnet phases; and several calcium silicate hydrate solid solution end-members. In addition, this study reports the provisional estimates for the standard entropies of minerals ternesite and ye'elimite

Kinetic mechanisms and activation energies for hydration of standard and highly reactive forms of β-dicalcium silicate (C2S)

The activation energy for hydration of β–C2S paste was measured as a function of hydration time using a calorimetric method and was found to depend on the surface area and reactivity of the powder as well as on the addition of sodium silicate. For neat paste made with standard β–C2S (similar to that found in portland cement), the activation energy is approximately 32 kJ/mol and is constant with time. For neat paste made with reactive β–C2S (calcined at lower temperature and with high surface area), the activation energy is about 55 kJ/mol and is also constant with time. This large difference in activation energy reflects a difference in the rate-controlling step for hydration. After investigating the effects of sodium silicate and synthetic calcium–silicate–hydrate on the kinetics, we hypothesize that the lower activation energy represents C2S dissolution, while the higher value represents nucleation and growth of hydration product