Zur Rheologie von polymermodifizierten Bindemittelleimen und Mörtelsystemen

In the context of this doctoral thesis the influence of liquefying additives on the rheology and
the hydration process of cement-based building materials, such as cement pastes, mortars, tile
adhesives and levelling compounds, was examined. For the investigation of the rheology,
measuring procedures for coaxial cylinder rheometers and for the ball measuring system after
Tyrach & Mueller were developed. The measuring procedures were compared on the
example of commercial products and with standardised consistency tests. For the
investigation of the influence of liquefying additives on the hydration process, the
composition of the liquid phase of fresh cement pastes, including pH value and conductivity,
was examined during the corresponding workability-period. Further, the retarding effects of
liquefying additives on the cement hydration was examined by means of heat flow
calorimetry.
The flow behaviour of cement-based building materials depends on many parameters, e.g.
degree of hydration, rheological prehistory and the composition of the building material itself.
Cement-based building materials usually show a pseudoplastic flow behaviour, which can be
described by the two parameters viscosity and “Strukturviskosität”. Most building materials
show also a yield point. The magnitude of the yield point is however strongly dependent on
the testing conditions.
The composition of the liquid phase of the cement pastes is influenced by the different
additives accordingly. All examined plasticizers increase the calcium content of the cement
pastes, which becomes apparent in an extension of the induction-period.