The main purpose of the thesis, based on the ultrasonic measurements of the formation of the materials with cement binders, is to determine the impact of the mechanical intervention into the structure, in terms of the significant influence on the setting and early development of characteristic strength of material. During our research we mostly pursued changes in mechanical properties: elastic modulus, compressive strength, consistency and setting time.
The issue of the impact (of the mechanical intervention into the structure of the cement paste, mortars and concrete) on the quality and on mechanical properties in relation to time was dealt with from the perspective of the demand for a better built quality as well as with the aim to
provide adequate mechanical properties. As far as the impacts were concerned, we were particularly interested in cases, when material is not built in immediately after its preparation (long transport or any other circumstances which do not allow for immediate placing operation) as well as in the impact of the mechanical intervention into the structure at certain times (revibration, remixing). Setting times, when mechanical intervention into the structure of
the material with binding agent took place, as well as setting time of a particular mixture, were determined by a new ultrasonic method, which is based on the highest ratio of the amplitudes of the two dominant frequencies, which appear in the frequency spectrum of longitudinal waves.
In addition to the ultrasonic method, classical test methods were carried out as well in order to determine compressive strength and static elastic modulus and reach the objective of the thesis. For the purpose of analysis of the dynamic elastic modulus development we used GrindoSonic
device, which is based on the principle of induction of the wave in the sample. Consistency was determined visually.
On the basis of our experimental research, we found out that subsequent mechanical intervention (irrespective of the period at the stage of setting) into the structure of the mixtures, does not affect substantially the final mechanical properties. In some cases setting times are
even shortened in relative terms. However, consistency in practice does not allow us to ensure high quality of placing operation without the use of additives (plastificators).