Influence of the mixture composition of cementitious pastes with optimized packing density on setting and hardening studied by ultrasound investigation

Ultrasonic methods have been developed in the past to study properties of cement based materials in the fresh and hardening period. Especially by combined shear and compressional wave measurements, several possibilities exist for better describing the changing properties of cementitious materials at very early age. Within the paper test results (Vicat and Ultrasound) from different cementitious pastes with optimized packing density (use of inert micro and eco fillers as replacement of Portland cement clinker) are presented and discussed. Dynamic elastic properties at early age like the dynamic shear modulus and the dynamic elastic modulus are calculated from the ultrasound investigations and correlated with standard test methods. Based on the experimental investigations it is discussed that the setting and hardening of cementitious mixes can by strongly influenced by just optimizing packing density. The concept of optimizing packing density results in a decreased water demand and thus reduced water film thickness between the particles that can be calculated analytically. It is shown that the calculated water film thickness is a good indicator not only for initial and final setting, but also for workability and strength development.