Connection between rheological and microstructural changes during hydration of cement pastes: Fid-Bau Portal

Connection between rheological and microstructural changes during hydration of cement pastes

Blask, O. / Knöfel, D. / Sandor, M. / Pakusch, J.

One of the most important quality requirements to a pasty building material is an easy workability which is described by the rheology. By rheology one understands the motion under operation of a force and/or the result of its interaction with the microstructure of the material. In order to affect the workability purposefully it is important to know exactly about the microstructure and their reaction to outside forces. A characteristic of cementitious building materials is the change of their microstructure by cement hydration. This stiffening is of crucial importance for the working time. A aim of this work was the observation of the stiffening of cement pastes containing chemical admixtures both with rheological and with microscopic methods and from this the development of an improved understanding of the microstructure of cement pastes. For this - with oscillating rheometer measurements - the development of the microstructure was tested and the transition from the liquid state to asolid similar state was observed. With a rotational rheometer the increase of the yield value during the hydration was measured and the influence of mixing on the microstructure of partly hydrated cement pastes was tested. With microscopic methods the appearance of the microstructure was observed. Since the microstructure of soft pastes is easily destroyed, the samples were shock-frozen by liquid nitrogen and the pore solution was removed from the sample by sublimation. The results are SEM micrographs of a hardly changed three-dimensional microstructure.