Assessment of the sedimentation stability of fresh concrete (phase 1)

Requirements for fresh and hardened concrete properties (e.g. flowability, high strength, durability) are increasing as construction tasks become more and more complex. These, in turn, are only made possible by the constant further development of concrete technology, among other things in the field of admixtures, and thus increasingly complex concrete compositions that can be precisely matched to the respective construction task. In particular, the increasing use of admixtures such as highly effective PCE superplasticizers, also in combination with other admixtures such as LP formers, have led to a change in concrete technology not only in the field of special concretes (high-strength concretes, SCC, etc.) but also in normal concrete. Thus, due to the dispersing effect of superplasticizer, an increasing trend towards concretes with soft consistency can be observed, as well as the production of concretes with a reduced glue content in the consistency range F2/F3, among others. At the same time, these concretes have become more sensitive to segregation. This is due to an increased sensitivity of the concrete, mainly to variations in water content or in the starting material properties. In addition, it can be observed that as a result of the decreasing qualification level of the construction site personnel, unsuitable concretes are increasingly being used or compaction is not carried out properly. The aim of this research project is therefore to develop and establish a standardized test method for the sedimentation stability of concrete under vibration effects on the basis of existing findings on the sedimentation stability of concrete. For this purpose, the influence of frequency and compaction duration on the sedimentation stability for selected vibrated concretes with and without LP-forming admixtures is to be investigated and the reproducibility and comparability with practice-similar component segments are to be compared in initial tactile tests. Subsequently, first recommendations for the determination of the vibrating action in the test procedure shall be formulated and the need for further research shall be estimated.