How to assess the hydration of slag cement concretes?

Addition of slag modifies the hydration process of cement and the evolution of the mechanical properties of concrete. In this study, the advancement of hydration was monitored for concretes with different blast-furnace slag contents using several techniques such as adiabatic calorimetry, thermogravimetry and analysis by scanning electron microscopy. Results show clearly the slowdown of the hydration for slag cement concretes. A fundamental parameter describing the hydration process and the evolution of the microstructure, named the degree of hydration, is quantified for the slag cement concretes. It appears that the method based on the evolution of the chemically bound water gives the most reliable evolution of the hydration degree. The knowledge of this parameter allows predicting correctly the evolution of compressive strength and Young modulus at early age for concretes with high slag content using an analytical model based on the degree of hydration.