The dormant period of cement hydration (DCB.6915)

Concrete is the most widely used man-made building material. Nowadays concrete is evolving into a high performance material. Even though high specialized concretes are used the chemical and physical reactions of cement-water system are still not fully understood. This project focuses on the early stage of reaction, i.e. the moment after the initial mixing until the moment that the reaction rapidly accelerates, the so called dormant period. For the building practice this period plays an important roll, because it controls the time in which the concrete is workable and placeable.

The research project aims to explain the origin of this dormant period. Questions that are dealt with are; what are the main influencing factors of the initial reactions, what does slow down the reaction and what makes the reaction to continue after several hours..

In this project emphasize has been on experimental techniques for identifying the initial reactions. Techniques used were calorimetric studies, XRD, pore water analysis, quasi-elastic neutron scattering (Univ. Maryland, USA), high resolution x-ray diffraction (Grenoble) and nuclear resonance reaction analysis (Bochum). A systematic analysis of the experimental data has resulted in more clear ideas about the occurrence of the dormant period. Moreover, the experimental data provides modelers with input and/or validation material for numerical modeling of the reaction process in cement-based systems.